Top electrical design_-_questions_&_answers_(ted_-_q&a)_-_3rd_edition_2

Top Electrical Design - Questions & Answers

TED - Q&A

Prepared By: Mahmoud Essam Hezzah

Electrical Design Engineer

Cairo - Egypt TED – Q&A 3rd Edition January 2012

بسم اهللا الرحمن الرحيم

"و قل رب زدنى علما"

الحمد هللا و الصالة و السالم على رسول اهللا صلى اهللا عليه و سلم

اما بعد

تعتبر أعمال التوصيالت والتركيبات الكهربائية فى المبانى من أهم التركيبات فى معظم المشروعات التى يتم تنفيذها فى الوقت الحالى، وقد اتسع مجال استخدامها لتشمل جميع المنشآت العادية وكذلك المنشآت الخاصة فضال عن دورها األساسى فى الحفاظ على سالمة المبانى والمنشآت من أخطار الحريق الناجم عن مخاطر عدم مراعاة

األصول الفنية فى تصميم التركيبات الكهربائية.

وقد صدرت عدة اكواد عالمية و محلية و ايضا العديد من الكتب و الكاتلوجات التى تتكلم فى شأن أسس تصميم وشروط تنفيذ التوصيالت والتركيبات الكهربائية فى المبانى.

و قد فكرت ان اجمع بعضا من هذه المعلومات فى شكل سؤال و جواب لتعظيم االستفادة من هذا المعلومات و لتكون بمثابة ملخص سريع ألسس التصميم الكهربى و يسهل الرجوع اليه.

بالطبع . ولكن ، اعتمدت فى تحضيرى هذه األسئلة على العديد من األكواد و المراجع و بعض الخبرات السابقةهذا ليس كتاب علمى يعتمد عليه ولكنه بمثابة بداية لمساعدة المبتدئين فى هذا المجال.

بعض إلضافة و سيتم عمل اصدارات جديدة بمشيئة اهللا عز و جل لتصحيح اية اخطاء والثالثهذا هو األصدار األسئلة و المعلومات الجديدة.

و ذالك [email protected]فى حالة و جود اى خطأ او استفسار ارجوا مراسلتى على هذا البريد : اسأل اهللا عز و جل ان تنفعنى و تنفعكم هذه المعلومات فى الدنيا و فى األخرة. لتفادى هذه األخطاء الحقا.

رجوا من الجميع اال يبخلوا بنشر هذه المعلومات كى تعم الفائدة على الجميع. و الدال على الخير كفاعله. ا

و السالم عليكم و رحمة اهللا و بركاته.

محمود عصام حزهاخوكم/

mailto:[email protected]



Prepared By: Mahmoud Essam Hezzah Best Wishes Electrical Design Engineer

TED - Q&A 3rd Edition January 2012


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Table of Contents 1. Have you previously done design for electrical work? ............................................................................................................................................................ 11

2. Have you previously done shop drawing (execution) for electrical (high current) work? ....................................................................................................... 11

3. Are you familiar and have used the following computer software’s: ...................................................................................................................................... 11

4. What are the de-rating factors considered in cable installation? .............................................................................................................................................. 12

5. How can you overcome the problems of voltage drop? .......................................................................................................................................................... 12

6. What are the precautions to be taken in mind when selecting an emergency feeder running next to another feeder fed from normal supply? ...................... 12

7. What is the national color code of a three phase circuit?......................................................................................................................................................... 12

8. What is the meaning and the difference between (AF) & (AT) of C.B? ................................................................................................................................. 12

9. What are the types of contracts? State the difference among them? ........................................................................................................................................ 13

10. What is difference between tender drawings, design drawings, shop drawing (Execution) & as built drawings? .................................................................. 16

11. What are the types of tests required for electrical equipment? What are the differences? ....................................................................................................... 16

12. What are the types of circuit breakers? State some applications for each? .............................................................................................................................. 17

13. What is the difference between thermal setting & magnetic setting of C.B? .......................................................................................................................... 17

14. How can you improve the selection of a system earthing arrangement? ................................................................................................................................. 18

15. What is the meant by TVSS or SPD? ...................................................................................................................................................................................... 18

16. What are the types of Discrimination (Selectivity)? State the difference? .............................................................................................................................. 19

17. What is Cascading? ................................................................................................................................................................................................................. 20

18. Estimate the demand load (VA/m2) regarding lighting, sockets, A/C, Equipments...etc for the following type of buildings: Hotels; Residential; Commercial/Offices; Health Care/Hospitals; Educational/Schools ........................................................................................................................................ 20

19. What is meant by: IP54; NEMA 3R ........................................................................................................................................................................................ 21

20. What are codes & standards can be followed in lighting design? ............................................................................................................................................ 21

21. What are the types of earthing systems according to IEC? Explain each & where recommended to be used? Compare among earthing systems. ................ 21

22. Calculate the grounding conductor size & the grounding resistance according to BS 7430:1998 of grid of length 80m width 40m, 12 rods with separation distance of 20m where rod length is 3m, rod diameter is 20mm, soil resistivity is 450 Ω.m, grounding conductor laid 0.8m below ground. 10 earth lattices (600mm x 600mmm) are bonded to the earth loop. Suppose that the symmetrical fault current is 20KA in 1sec duration. Where the grounding conductor is chosen to be copper conductor and the initial temperature of conductor is 30°C & final temperature is °250C. After calculation find out if the grid safe or not safe? .................................................................................................................................................................................................................................. 26

23. What is the Dynamic UPS (No Break Generator)? State some applications? Compare with Static UPS. ............................................................................... 31

24. What are the types of cable trays? State some applications? How can you size a cable tray? What is the difference between cable tray & cable ladder & which is less expensive? State applications for cable ladders? ............................................................................................................................................... 32

25. State some applications for using isolating transformers? What is the advantage of using it? ................................................................................................ 36

26. What are the common types of conduits? State some applications? How can you size a conduit? ......................................................................................... 36

27. What characteristics does a luminaire need to be a good one? ................................................................................................................................................ 37

28. What are the SEC standard specifications for LV distribution panels sizes for transformers 500 kVA, 1000 kVA, 1500 kVA from where: ......................... 37

o Incoming CB. Rating

o Incoming Cables for standalone LV panel

29. What is RGB LED? ................................................................................................................................................................................................................. 38

31. What are the different types of Lighting System Controls?..................................................................................................................................................... 38

32. What is the difference between IP, NEMA, IK, IC & IM? ...................................................................................................................................................... 39




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33. What is the difference between horizontal, vertical illumination & general, task lighting? How can you make calculations for each? State some examples for each? .................................................................................................................................................................................................................................. 43

34. What is color rendering? State the color renderings for sodium lamps, metal halide lamps, fluorescent lamps & halogen lamps? ........................................ 44

35. What is illuminance? State the recommended illumination level for Office, Surgery operating room, Bed room, Class room, Sitting & Corridors ............. 44

36. What is Color Temperature? State some of them .................................................................................................................................................................... 44

37. What is the difference between Fluorescent lamps type T2, T5, T8 & T12? .......................................................................................................................... 45

38. Can we make interconnection bonding among these systems: ................................................................................................................................................ 46

o Grounding System

o Lightning Protection

o Low current & Communication Grounding System

39. Give some types of different lamps showing: type, manufacturers, wattage, lumen output, peak intensity, colour temperature, lamp holder (cap), life time and dimensions? ...................................................................................................................................................................................................................... 47

40. What are the recommended IP and IK code specifications for distribution boards? ............................................................................................................... 53

41. Calculate the number of luminaries required for office (5x6m), height = 3m, consider type fluorescent lighting fixture each have lamps 2x36W. Luminous flux of each lamp 3200 lm, utilization factor is 0.48 and maintenance factor is 0.75. Notice that the required maintained illumination level is 500 lux. ..... 53

42. What is the recommended LV system voltage? Give some examples for the system voltages & frquencies in different countries? ...................................... 54

43. What is LEED & how can you improve your design to match the LEED requirements? ....................................................................................................... 60

44. Which one could achieve more lumen output prismatic or opal diffusers considering same lamps? Why? State application. ............................................... 60

45. What are the different types of substations? ............................................................................................................................................................................ 61

46. Insulation systems are rated by standard NEMA classifications according to maximum allowable operating temperatures. Explain. ................................... 65

47. Differentiate between: ............................................................................................................................................................................................................. 65

o Directional & diffuse lighting.

o Symmetric & asymmetric lighting.

o Direct, indirect lighting & Direct-indirect lighting.

48. In case of presence of 2 sockets back to back in two different rooms. Can we put them directly back to back or we should leave a distance between them? ................................................................................................................................................................................................................................................ 66

49. What is the difference between demand factor & diversity factor? ......................................................................................................................................... 67

50. What are the different methods of starting motors? State the difference among them? State Applications? ........................................................................... 67

51. If we have a big room & contain many sockets which will need about 5 branch circuits. Can we feed these circuits from different phases? Why? ............. 67

52. How can you earn LEED certifications for new constructions? What are the LEED ratings? ................................................................................................ 68

53. If you have a refrigerator or A/C or any other motor equipment that works on 50Hz, can you make it work on 60Hz Power Supply? ................................. 68

54. You have a project consists of 960 small villas (dwelling units). The connected load for each villa (dwelling unit) is 60 KVA. Estimate the number of pillars, transformers & distributors required for this project. Considering that only 400A pillars & 1000KVA Transformers ratings are available. System Voltage is 13..8KV/380-220V. Draw schematic single line diagram to what you obtained. .................................................................................................. 69

55. What are the IEC Switchboard Forms for Internal Configuration? State the difference? ........................................................................................................ 72

56. What is distance between down conductors in lightning system design? How can you design the mesh? .............................................................................. 72

o For building less than 15M height

o For building 80M height.




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57. Give a small brief summary for each of these types of lamps ................................................................................................................................................. 73

o Incandescent

o Halogen

o Fluorescent

o Compact Fluorescent Lamps

o LED (Light Emitting Diodes)

o High-Intensity Discharge Lamps

o Low-Pressure Sodium Lamps

58. What is DALI? ........................................................................................................................................................................................................................ 75

59. Estimate the circuit breaker, disconnecting switch and cable size for: ................................................................................................................................... 76

o Lighting load 3000VA single phase. Feeder wire length is 40 m.

o Outdoor A/C load 3000VA single phase. Feeder wire length is 40 m.

o Panel Board with three single phase loads (3000VA, 4000VA, 2000VA). Feeder cable length is 200 m.

o Where; the system voltage is 380/220V; suppose that total cable de-rating factors is 0.8; suppose cable routing in pipes.

o Use the following cable catalogue cuts for sizing cables.

60. When we should use a remote radiator for a diesel engine generator? .................................................................................................................................... 80

61. Calculate capacitor rating required to improve the power factor of a motor P=500KW from P.F1= 0.8 to P.F2= 0.9? .......................................................... 80

62. What is EIB? ........................................................................................................................................................................................................................... 81

63. Calculate the three phase short circuit current at secondary side of a 1 MVA transformer 13.8KV - 480/227V, 60 Hz; impedance is 6 percent and assuming sustained primary voltage during fault? .................................................................................................................................................................................. 82

64. What are the basic factors would you take into consideration while making lighting design? ................................................................................................ 83

65. Calculate the voltage drop of cable with load 32KW - three phase, cu cable C.S.A= 16mm2, Ra.c= 1.38 ohm/km, X= 0.1068 ohm/km, CosØ = 0.8, cable length =120m, system voltage is 380/220V. ........................................................................................................................................................................... 83

66. What does GFCI & AFCI stands for? What is the difference? State some applications? ........................................................................................................ 83

67. What are LPD specified in ANSI/ASHRAE/IESNA Standard 90.1? Can you state the methods used for computing LPD & give some examples? Does the LPD values specified in ASHRAE accepted by LEED? ......................................................................................................................................................... 84

68. What is power factor? What are the equipments that create poor power factor? How can you improve power factor of your system? ................................. 87

69. Choose the correct answers if any. What is the purpose of discrimination? ............................................................................................................................ 89

o To ensure continuity of service

o To only trip the device just above the faulty feeder

o To increase servicing time for trouble-shooting

o To increase productivity

70. Compare between magnetic ballast & electronic ballast. ........................................................................................................................................................ 89

71. What are the trade sizes of conduits? ...................................................................................................................................................................................... 89

72. In an installation, circuit breaker CB1 is placed upstream from circuit breaker CB2. A short-circuit current occurs downstream from CB2. CB2 opens and CB1 stays closed. This is a case of: ........................................................................................................................................................................................ 89

73. For each of the faults A, B, C in the diagram, say whether or not the protection device opens: ............................................................................................. 90

74. The fault current downstream from circuit breaker CB5 is 400 A. With total discrimination, which circuit breakers will open? .......................................... 90




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75. State which statement is true and which is false: Standard IEC 60364: Section-3-32 & 4-48 on premises with a risk of fire ................................................ 90

o Imposes use of a 500mA RCD device.

o Recommends use of a TT or IT system for the electrical installation on such premises.

o Prohibits use of a TN-C system.

o In TT, IT and TN-S systems, a 300mA RCD eliminates the risk of fire.

76. What are The Main Functions of Earthing/Grounding Systems? ............................................................................................................................................ 90

77. What is the difference between (Ics) & (Icu) of C.B? Which one is considered in design? .................................................................................................... 91

78. State the functions of circuit breaker. ...................................................................................................................................................................................... 91

79. What is more danger on the human body AC current or DC current & why? What is the effect of AC current on the human body? .................................... 91

80. In order to select the right circuit breaker. What are the Criteria’s of choice that should be followed? .................................................................................. 92

81. Compare between earthing systems from the point of: ........................................................................................................................................................... 92

o Protection of people.

o Protection against fire.

o Ease of implementation

o Continuity of service

o Upgradable installation.

o Cost saving

82. What are the Benefits of improving Power Factor?................................................................................................................................................................. 93

83. How the penalty on power factor is calculated? ...................................................................................................................................................................... 93

84. What are the different types of armoured cables which are more expensive, which one can withstand more mechanical load, is the 2 types are accepted by BS & IEC? .............................................................................................................................................................................................................................. 93

85. State the Cable Insulation Temperature Limits (Continuous Operating Temperature, Emergency Temperature & Short Circuit Temperature) for XLPE & PVC ........................................................................................................................................................................................................................................ 93

86. What does mean by day lighting? ........................................................................................................................................................................................... 93

87. Transformers are classified into various categories, according to their: Use, Cooling method, Insulating medium. State & explain each classification. Which is better & why? ...................................................................................................................................................................................................................... 94

88. What are the important factors required for selecting a suitable cable to transport electrical energy from the power station to the consumer? ..................... 95

89. What is the difference between Rapid-Start and Instant-Start of fluorescent lamp? ............................................................................................................... 95

90. What is tap changer? ............................................................................................................................................................................................................... 96

91. What is the difference between beam angle & cut-off angle of a luminaire? What are the different beam classifications & State the difference between them?....................................................................................................................................................................................................................................... 96

92. What are the levels of protection (Coordination of protective devices) for the motor starter? ................................................................................................ 97

93. Calculate maintained illumination level for clinic (4x6m) - height = 3m, consider 4 fluorescent lighting fixture each have lamps 4x36W. Luminous flux of each lamp 3000 lm, utilization factor is 0.50 and maintenance factor is 0.70. ........................................................................................................................ 98

94. What is difference between low smoke halogen free cables & fire resistant cables & fire alarm cables? ............................................................................... 98

95. What is the distance between sockets that should be followed in design? ............................................................................................................................... 98

96. Wrong positioning of desks relative to luminaries could cause reflected glare. ...................................................................................................................... 99

o Define glare.

o Which position of luminaire is right to avoid glare?

97. When many cables are laid on cable tray, what are the factors that determine the final ampacity of each cable? ................................................................... 99

98. What is the difference between Normal load, Emergency load & Critical load? State an example for each. ........................................................................ 100

99. State the Types of static UPS ................................................................................................................................................................................................ 101




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100. If the power factor of a certain electrical installation is low how can the power factor to be improved / corrected? ............................................................ 102

101. What are the devices to be used for earth leakage protection / ground fault protection? ....................................................................................................... 103

102. What is Voltage Drop? What are the factors that determine the Voltage drop of a cable/wire? Write down the V.D equation for single phase cable & 2 phase for 3 phase cable ......................................................................................................................................................................................................... 103

103. What are the C.T. & P.T? When do we use each one and why? ............................................................................................................................................ 104

104. What does these abbreviations stands for: PVC, XLPE & LSF? ........................................................................................................................................... 104

105. Define the Grouping Factor? When does it considered in cable size calculations? Is it applicable for multi core or single core cables? ............................. 104

106. A branch panel board with total connected load 25 KW & P.F. = 0.8. Calculate Main Feeder Cable and Main C.B? ......................................................... 104

107. Mention the different types of conduits used in electrical systems routing inside high rise buildings? What is the common usage for each? ..................... 104

108. Mention the different types of conduits used in electrical systems routing inside high rise buildings? What is the common usage for each? ..................... 105

109. What is the difference between, molded Case Circuit Breaker and miniature circuit breakers? ........................................................................................... 105

110. Suppose you are buying a transformer. You have two options: TR1is 11/0.4KV & Z = 4 %, TR2: is 11/0.4KV & Z = 6 %. Which one you choose & why? Taking into consideration, you need 380V on the secondary at full load. ............................................................................................................................. 105

111. Compare between the following types of lamps according to their Power Range, Efficacy, Lumens, Life Time, Color Temp and CRI. ............................ 105

o Incandescent and Halogen

o Fluorescent

o Compact Fluorescent (CFL)

o Mercury Vapor

o Metal Halide

o High Pressure Sodium (HPS)

o Low Pressure Sodium (LPS)

112. There are new specifications created by SASO to prohibit entry of any plugs or sockets not conforming to the specifications and this should be effective on (23/02/2010). What are these specifications & what are the types specified for 127V Plugs/Sockets & 220V Plugs/Sockets? ........................................... 106

113. What is meant by UL Listed product? ................................................................................................................................................................................... 106

114. Does the voltage supply fluctuation affects the lamps? How? .............................................................................................................................................. 106

115. What is the ballast? State its function & types of ballasts. .................................................................................................................................................... 107

116. What is the difference between a kW and a kWh? What is measured by electric utility? .................................................................................................... 107

117. What are the different types of conductors according to NEC code? .................................................................................................................................... 107

118. How can you estimate the electrical consumption per month for residential buildings? ....................................................................................................... 108

119. What is star-delta starting? Why is it used? What are the advantages & disadvantages of using this method? Should we immediately install soft starters on all our existing motors? ......................................................................................................................................................................................................... 110

120. How the Electricity Bill is computed? ................................................................................................................................................................................... 113

121. What are the different standards of sockets? Draw them & state the difference? .................................................................................................................. 114

122. What are the international codes, standards, regulations & specifications? State some of them that can be followed in electrical design? ......................... 115

123. What are the different types of local power cables for low & medium voltages? ................................................................................................................. 116

124. When can we use neutral with C.S.A equal to the C.S.A of the phase & when can we use reduced neutral and with C.S.A less than the C.S.A of the phase? How can we choose the reduced neutral in 3 phase-systems ................................................................................................................................................ 117

125. What are the types of emergency lighting? State the difference? How batteries shall be provided? ..................................................................................... 117

126. State the target areas for Emergency Lighting to be provided? ............................................................................................................................................. 118

127. What are lighting levels & uniformity mentioned in standards for emergency lighting? ...................................................................................................... 119

128. What are the different systems used in central battery system? Compare between them. ..................................................................................................... 120

129. What are the advantages of using Self Contained EM Lighting? .......................................................................................................................................... 122




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130. What are the advantages of using Central Battery System? .................................................................................................................................................. 122

131. How can you calculate the current carrying capacity or the size of busbar? ......................................................................................................................... 122

132. Why you use sine wave for ac power supply why not triangle wave or square wave? .......................................................................................................... 122

133. Do we can put two branch circuits in one conduit? ............................................................................................................................................................... 122

134. Why do 50 Hz transformers cost more than 60 Hz transformers? Does 50 Hz transformer could work on 60 Hz transformers & How? ............................ 123

135. How can you calculate the full load current for different sizes of motors (1-ph, 2-ph & 3-ph)? ........................................................................................... 123

136. State the way of calculating the short circuit at any point within a LV installation according to IEC & Egyptian Code for electrical installation .............. 126

137. Complete ............................................................................................................................................................................................................................... 129

o Illuminance is measured in footcandles (lumens/square foot) or lux (lumens/square meter). Where one footcandle equals -------- lux.

o Luminous intensity is measured in Candela or Lumen (Lu).where one Candela equals -------- Lumen (Lu).

138. Compare between using Central Battery System and Self Contained EM Lighting. ............................................................................................................. 130

139. What is the difference between circular & sectoral sections in cables? ................................................................................................................................. 130

140. How can you size the earthing conductor according to size of phase cable size or according to C.B. size using NEC & IEC?............................................ 131

141. Why CU wires are preferable in indoor distribution while Al cables are preferred in electrical transmission? .................................................................... 132

142. For the following factors. Explain the effect of increasing or decreasing these factors on short circuit. ............................................................................... 133

o Cable length

o Cable CSA

o Conductor Type

o Transformer per unit impedance

o Transformer load.

o System Voltage

o Bus Bars

o Circuit Breakers

143. What are the different types of cables? ................................................................................................................................................................................. 134

144. What are the standards C.S.A’s for power cables for low, medium & high voltage? ............................................................................................................ 135

145. What is the difference between armoured & unarmoured cables? ........................................................................................................................................ 135

146. Screening of MV cables is used in earthing. Right or wrong? .............................................................................................................................................. 135

147. How can you convert American Wire Gauge (AWG) to square mm cross sectional area? ................................................................................................... 136

148. What is the problem of unloading the transformer? .............................................................................................................................................................. 136

149. For replacing an existing Lighting system of fluorescent lamps 110 Volt, 60 Hz by new fluorescent lamps 220 Volt, 60 Hz, which of the following devices should be changed Lamp, Ballast and Starter? ...................................................................................................................................................................... 136

150. How can you convert from NEMA to IEC Enclosure? ......................................................................................................................................................... 137

151. What are the different risks on human that caused by electricity? Explain. .......................................................................................................................... 138

152. What are the different tripping characteristics and rated currents for MCB’s? ..................................................................................................................... 139

153. What is the obstruction lighting? What are their types? How it’s designed? ......................................................................................................................... 140

154. What specifications must be applied in cable insulation?...................................................................................................................................................... 141

155. Determine how many 6mm2 cu single stranded conductors are permitted in a trade size 1¼ rigid metal conduit (RMC)?.................................................. 142

156. Does the way of mounting, positioning and orientation of a lamp (Burning Position) affect the burning? ........................................................................... 142




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157. According to NEC. Determine the minimum size rigid metal conduit (RMC) allowed for the 9 mixed conductor sizes and types described as followed: . 143

o 3 single stranded wires cu of 4mm2 each

o 3 single stranded wires cu of 10mm2 each

o 3 single stranded wires al of 16mm2 each

158. What are the most available sizes for LV HRC fuses? .......................................................................................................................................................... 143

159. A 200-ampere feeder is routed in various wiring methods (EMT) conduit & (RMC) conduit from the main switchboard in one building to a distribution panel board in another building. The circuit consists of muli-core cable 4x70 + 25 mm2 CU - XLPE/PVC unarmoured. Select the proper trade size for the various types of conduit and tubing to be used for the feeder. .............................................................................................................................................. 144

160. What are the capacities of PVC conduits for different cable sizes (single & multi-core)? .................................................................................................... 145

161. What is the relation between C.B & Busbar? ........................................................................................................................................................................ 145

162. How can you find the cable size with regards to C.B Size? .................................................................................................................................................. 146

163. What are the most available sizes for disconnecting switches? ............................................................................................................................................. 146

164. What are the C.B. ratings & short circuit capacities in American & European standard? ..................................................................................................... 147

165. What is the control gear of a luminaire? ................................................................................................................................................................................ 148

166. What are the methods of cooling of transformers? What does ONAN refers to? .................................................................................................................. 149

167. What is the accepted percentage of loading a transformer? Can we increase the percentage of loading the transformer more than 100%? Explain. .......... 149

168. State the advantages of using dry type transformers over oil immersed type? ...................................................................................................................... 150

169. What is the information necessary while selecting the transformer protection system? ........................................................................................................ 150

170. What are the advantages of selecting outdoor distribution transformers kiosks? .................................................................................................................. 150

171. What are the requirements for fire water pump electrical connection as per NFPA 70? ....................................................................................................... 151

172. When shall we use circuit breaker + back-up fuse as switchgear combinations? .................................................................................................................. 153

173. What are the sizing recommendations for fire pump applications including (sizing the generator set, sizing the utility circuit breaker or fuses, sizing the feeder conductors, sizing the automatic transfer switch, sizing the generator circuit breaker) as per NFPA 70?.................................................................. 154

174. What are the main parts of transformer compartment (Kiosk)? ............................................................................................................................................ 156

175. Using given legend. Draw the wiring diagram for: ............................................................................................................................................................... 159

o 1 Way - 1 Gang Switch.

o 1 Way - 2 Gang Switch.

o 2 Way (3 Way) - 1 Gang Switch.

o 2 Way (3 Way) - 2 Gang Switch.

o Intermediate (4 Way) - 1 Gang Switch.

176. Discuss the construction for LV & MV power cables? ......................................................................................................................................................... 160

177. What are the different distribution losses in industrial facilities? .......................................................................................................................................... 162

178. What are the types of insulations that can be used for cables? .............................................................................................................................................. 163

179. What are the main functions of luminaire? ............................................................................................................................................................................ 163

180. How can you calculate the reactive power Capacitor Bank (power factor correction)? How can you choose the capacitor bank according reactive power from standard? How can you calculate the circuit breaker of capacitor bank? What are the available LV Standad Automatic Capacitor Banks? ............... 164

181. What is the difference between AWA and SWA? ................................................................................................................................................................. 165

182. How can you classify lighting according to applications? ..................................................................................................................................................... 165

183. State some demand factors for different loads that are being used in American NEC Standards? ........................................................................................ 166

184. What are the different classifications of luminaries? Give brief discussion for each. ........................................................................................................... 168




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185. State the difference in wiring between: ................................................................................................................................................................................. 170

o 2-Way Switch & 3-Way Switch.

o 4-Way Switch & Intermediate Switch.

186. What is the ATS & what are the main different parts of ATS? ............................................................................................................................................. 171

187. Specify different ratings of ATS? .......................................................................................................................................................................................... 173

188. What are the advantages of using Busbar Trunking System (Bus Duct)? ............................................................................................................................. 173

189. What are the different types of ATS Devices? ...................................................................................................................................................................... 174

190. When should we use Busbar Trunking (Bus Duct) System? ................................................................................................................................................. 175

191. What is the acceptable percentage voltage drop that can be reached in L.V. calculations? ................................................................................................... 176

192. State the application & operation of the contactor and circuit breaker based transfer switches (ATS)?................................................................................ 176

193. State the application & operation of the solid state transfer switches (ATS)? ....................................................................................................................... 178

194. When should we use tap-off boxes Busbar Trunking (Bus Duct) System? ........................................................................................................................... 178

195. What is the minimum requirement for transfer switch (ATS) arrangement that should be followed for essential & critical loads of health care facilities? 179

196. What are the applications of using Busbar Trunking (Bus Duct) System? ............................................................................................................................ 179

197. What is Busbar Trunking (Bus Duct) System? ...................................................................................................................................................................... 180

198. What are the relations among transformers, main C.B’s and Bus Duct Ratings assuming that the system voltage is 380/220V? ........................................ 181

199. What are the different available standard ratings for Bus Duct? ........................................................................................................................................... 181

200. Which is better in power distribution AC system or DC system? Why? ............................................................................................................................... 182

201. Which is the Cable Bus? What are the applications of using it? What are the advantages & disadvantages of using it? What are the type of conductors & configurations used? Compare between ampacities using Cable Bus & other normal cables. .............................................................................................. 182

202. What are the different batteries types - technologies? State the difference? .......................................................................................................................... 189

203. Consider a pillar with a 3 phase load 200A. The cable length feeding the pillar from a transformer is 140 meters. This cable is laid directly in ground and is grouped with another 5 cables in the same trench. Which size of cable below you prefer to use in order not to exceed 2% voltage drop, p.f = 0.8 & why? .............................................................................................................................................................................................................................................. 190

204. What are the expected room sizes (dimensions) for standby generators with these sizes: 80, 100, 125, 175, 200, 350, 400, 500, 600, 750, 900, 1000, 1500KW ................................................................................................................................................................................................................................ 191

205. State some diversity factors of different purposes (ex: lighting, sockets, air conditioning …. etc) for different type of premises (ex: residential, offices, hotels... etc) according to Egyptian Code? ............................................................................................................................................................................ 192

206. Can you estimate the demand load of a building using its type & its gross area according to Egyptian Code? .................................................................... 193

207. Compare between LV & MV generators. .............................................................................................................................................................................. 194

208. Calculate the grounding conductor size & the grounding resistance according to IEEE Std 80-2000 of grid of length 80m width 40m, 12 rods with separation distance of 20m, rod length is 3m, rod diameter is 20mm, soil resistivity is 450 Ω.m, grounding conductor laid 0.8m below ground. Suppose that expected fault symmetrical current is 20KA in 1sec duration. Where the grounding conductor is chosen to be 40% conductivity copper-clad steel conductor .............................................................................................................................................................................................................................................. 195

209. What are the IP references preferred for switchboard assemblies? ....................................................................................................................................... 197

210. What are the main aims of tunnel lighting? What is necessary to know about tunnel lighting? When to light tunnel by day? When to light tunnel by night? How to light tunnel by day? What are the 5 zones of tunnel lighting? Which type of lamps to use? What are the types of tunnel lighting systems? What is the short tunnel & underpass? How to illuminate tunnels for different lengths in day time 25m, 75m and 125m? What are the tunnel lighting arrangements and state advantages & disadvantages of each? .................................................................................................................................................................... 197

211. Select the required automatic capacitor bank for a transformer rating: 1600 kVA, Voltage: 13.8/0.38 kV, Connected Load: 1516 kVA = 1289 KW, Assumed PF/ Target PF: 0.85 / 0.95? What are the minimum & maximum harmonic orders for this capacitor bank? ........................................................ 202

212. What is harmonics? What is the problem of harmonics? What is k- factor? How to calculate K-Factor? What is K-Factor of a transformer? Why we calculate K-Factor of a transformer? What are the advantages of calculating the K-Factor of a transformer? What are the disadvantages of using the derated standard transformers instead of K-Factor? What should be remembered when using a K-Factor Transformer? How K-Factor Transformer could be calculated? ............................................................................................................................................................................................................................ 203




9

213. Consider transformer 1600 KVA feeding an office building with total lighting load 201 KVA, total power load 483 KVA, total HVAC load (AHU’S) 386 KVA and total EWH load 54 KVA. Select the k-factor required for this transformer. ......................................................................................................... 209

214. What is difference between prime generator & standby generator? ...................................................................................................................................... 210

215. What is difference between metal-enclosed switchgear & metal-clad switchgear? ............................................................................................................... 210

216. What do you know about metal-enclosed switchgear, metal-clad switchgear and arc resistant switch gear? ....................................................................... 212

217. Compare between Static Transfer Switches (STS) and Automatic Transfer Switches (ATS). .............................................................................................. 213

218. State the difference between the three types of ballasts Magnetic, Rapid start, HF ballasts. What is the recommended ballast for T12, T8, T5 & CFL? ... 214

219. Can we dim LED Light? How? Is there any flickering while dimming? Are there any Changes in color and efficacy with dimming? ............................... 214

220. According to SEC Distribution Materials Specification. What are the available ratings for transformers Pole mounted & Pad mounted? What are the maximum accepted losses? What are the available tap changer settings? What is the recommended vector group, Impedance Voltage, Temperature Rise, Noise Level, Short Circuit Level, Degree of Protection, Dimensions, LV bushings/terminals? ........................................................................................... 217

221. What’s the reason of grounding or earthing of equipment? ................................................................................................................................................... 219

222. What is difference between power transformers & distribution transformers? ..................................................................................................................... 219

223. What will happen if DC supply connected to 100W bulb?.................................................................................................................................................... 219

224. Can an armoured cable be laid in a PVC conduit for aesthetic purposes? ............................................................................................................................. 220

225. Is it permissible to install PVC/SWA/PVC cable in Zones I and II flammable areas? If so, what is the authoritative document? ....................................... 220

226. Is it permissible to use aluminum twin & earth cables? ........................................................................................................................................................ 220

227. What are the codes of armoured cable glands? What is application for B/W & C/W? .......................................................................................................... 220

228. What are the minimum CSAs for process instrument cables, power cables & control cables? ............................................................................................. 221

229. Is it possible to use armour of a power cable as its earthing conductor? As an example - for 4 x 240mm cable, is it necessary to install separate earthing cable? Or is the armour of the cable enough for earthing? What is required by BS standards? ............................................................................................ 221

230. What is the filling percentage that should be followed for trunking & conduits & cable trays as per British Standard? ...................................................... 221

231. In order to reduce the size of the sub-main cable, we have installed a separate circuit protective conductor (CPC) with calculations satisfying this. Terminations have been completed as standard. However, on installation, the contractor has installed the CPC so it is not clipped to the armoured cable as normal practice, and takes a different route. Is there a standard that requires an armoured cable's CPC to be clipped to the cable? Is there an issue with running earths in a separate route to the armoured cabling, i.e. different lengths etc? .......................................................................................................... 221

232. We have to pull a 3 X 70mm SWA cable through 80m of 100mm ducting. There will be a bend at each end up to the electrical switch room. The cable run between is more or less straight. Can you tell me what a reasonable bend radius would be to allow satisfactory pulling of the cable? ............................... 222

233. What power cables are suitable for direct burial in ground which may be prone to water logging? ..................................................................................... 222

234. Calculate the annual savings and payback for installing an occupancy sensors given that: No. of fixtures = 20 x 2 Lamps; Fixture wattage Draw = 88 watt/Fix; Time length needed = 20 min/hr.; Operating hours = 4000 hrs./year; Electricity cost = 0.15 LE/kWh; Sensors cost = 200 LE ........................... 223

235. For replacing an existing Lighting system of Incandescent lamps by a new fluorescent lamps, calculate the annual savings and payback given that: Existing lighting system . 100 Lamps (200 watt/lamp); 200 watt lamp efficacy 17.5 Lm/watt; Fluorescent lamps 36 watt (44 watt incl. Ballast); Fl. lamps efficacy 70 lm/watt; Fl. lamps cost = LE. 15 (incl. Fixture); Annual operating hours 4000 hrs./year; Electricity cost = 0.15 LE./kWh ................................................. 223

236. A 23,000 square meter high bay facility is presently lit with 800 twin 400 watt mercury vapour fixtures (455 watts per lamp including ballast.) What are the annual savings of replacing the existing lighting system with 800 single 400 watt high pressure sodium fixtures, (465 watts per lamp including ballast) Assume 8000 hours per year, an energy cost of $0.05 per kWh, and a demand cost of $6.00 per kW-month. ..................................................................... 223

237. Choose the correct answer: .................................................................................................................................................................................................... 223

o The efficacy of a light source refers to the Color rendering index of the lamp. A) True B) False

o Increasing the coefficient of utilization of the room cavity will in many instances increase the number of lamps required. A) True B) False




10

224 .................................................................................................................................................. مبنى يحتوى على عدة وحدات سكنية يشتمل على األحمال التالية: .238

تحديد الحمل األقصى لهذا المبنى مع السماح باستخدام معامالت التباين فى حالة:

إذا كان المبنى عمارة سكنية. (أ)

إذا كان المبنى سوق تجارى. (ب)

224 ................................................ حساب الحمل األقصى لهذا المبنى طبقا للكود المصرى. المطلوب: . متر مربع فى منطقة متوسطة اقتصادية ويتكون من ستة طوابق350مبنى سكنى مساحته .239

224 ....................................................................................................................................................................................................إلى كم تنقسم مصاعد الركاب؟. .240

225 ...................................................................................................... طبقا للكود المصرى ، وهى تحتوى على اآلتى: فيال (وحدة سكنية خاصة) مطلوب تحديد الحمل الكهربائى لها .241

ما هى األحمال التقديرية لألجهزة الكهربية المنزلية شائعة االستعمال مثل: محمر الخبز؛ المكواة؛ الفرن الكهربي؛ مجفف الشعر؛ الثالجة؛ جهاز الراديو؛ جهاز التلفزيون؛ مكنسة الكهرباء؛ دفاية الحجرة؛ .242 226 .................................................................................. غسالة كهربائية؛ غسالة كهربائية بالسخان؛ مجفف الغسيل؛ غالية مياه؛ بروجيكتور؛ طابعة ؛ حاسب ألى؛ سخانات الحمام

227 ................ ° مئوية؟30ك.ف.أ، فما هــو أقصى تحميل زائد مسمــوح به لمدة أربعة ساعات، و ذلك في درجــة حــرارة 750 ك.ف.أ، و الحمل المعتاد لهذا المحول هو 1250محول سعته االسمية .243

227 ................................ ك.ف.أ لمدة العشرين ساعة الباقية250 ك.ف.أ لمدة أربع ساعات، وحمل قيمته 450 يتم تحميله بحمل قيمته ONANالمطلوب تحديد سعة محول توزيع بنظام تبريد .244

228 .............................................................................................................................................................................. عبارة عن:2 م600مبنى سكنى تجارى على مساحة .245

229 .......................................................................................................................................................................................................... مما تتكون مصاعد الركاب؟ .246

229 .................................................................................................................................................................................. كيف يعمل المصعد الذي يعمل هيدروليكيا ؟ .247

230 .................................................................................................................................................. ما هى انواع الجر المختلفة فى المصاعد التي تعمل بمحرك كهربائي ؟ .248

231 ................................................................................................................................................................................. كيف يعمل المصعد الذي يعمل بمحرك كهربائي ؟ .249

232 .................................................................................................................................................................................. كيف يتم تحديد القدرة المطلوبة للمصاعد؟ .250

233 .................................................................................................................. كيف يتم حساب معامـل الطلـب للمجموعـة إذا زاد عدد الكبائـن فى المجموعـة داخـل المبنـى؟ .251

234 .................................................. م/ث، احسب اآلتى:3 كجم وتتحرك بسرعة 1750) كبائن حمولة كل منها 5 مكونة من (1 : 1فى مجموعة مصاعد منفذة بأسلوب التعليق بنسبة .252

235 ........................................................................................................................................................................................................ كيف تعمل الساللم المتحركة؟ .253

236 ................................................................................................................................................................................. كيف يتم حساب الحمل الكهربى للساللم المتحركة؟ .254

236 .................................................................................................................. ما هى األحتياطات الواجب مراعتها عند التصميم لتغذية عدة ساللم متحركة داخل مبنى واحد؟ .255

236 .......................................................................................................................................... ما هى قدرات السخانات المستخدمة فى وحدات تدفئة المنازل من النوع الحائطى؟ .256

237 ..................................................................................)؟ و كيف يتم تحديد القدرة الكهربية لها؟Moving walks and rampsكيف تعمل الحصائر والمنحدرات المتحركة ( .257

238 ............................................................................................................................................ ما هى أنواع و أنظمة التكيف المستخدمة ؟ و ما هى القدرات الكهربية لكل منها؟ .258

ما هى القدرة الالزمة ألجهزة التكييف لكل من هذه األماكن: المكاتب الكبيرة؛ ؛ المكاتب الصغيرة؛ غرف تدريس؛ مخازن تجارية؛ غرف مرضى في ؛ المستشفيات؛ غرف الفنادق؛ البنوك؛ الورش .259 243 ............................................................................................................................................ والمصانع؛ المساجد؛ المحالت التجارية؛ سوبر ماركت؛ غرف كمبيوتر؛ مطاعم

243 .................................................................................................................................................................................. كيف تعمل طلمبات الحريق فى المبانى ؟ .260

244 .................................................................................................................................................. هل يجب استخدام طلمبة كهربائية وأخرى تدار بماكينة ديزل فى المبانى ؟ .261

244 .................................................................................................................. كيف يتم قدرة محرك طلمبة رفع المياه أو طلمبة الصرف الصحى أو طلمبة الحريق فى المبانى ؟ .262

245 .................................................................................................................................................................................. كيف تعمل سخانات حمامات السباحة ؟ .263

245 .................................................................................................................. كيف يتم حساب الحمل الكهربى للسخانات المستخدمة فى تسخين المياه فى المنازل الصغيرة ؟ .264

246 .................................................................................................................................................................................. كيف تعمل طلمبات رفع المياه فى المبانى ؟ .265

247 .................................................................................................................................................................................. كيف تعمل طلمبات الصرف الصحى فى المبانى ؟ .266

ما هو التأريض؟ كيف يتم تحديد مخططات التأريض؟ اشرح انواع مخططات التأريض المختلفة؟ ما هو األختيار األمثل لمخططات التأريض؟ ما هو نوع التأريض الذى يفرضه النظام فى المملكة العربية .267 248 ...................................................................................................................................................................................................................... السعودية؟

251 .................................................................................................................. اذكر بعض األحمال الكهربائية و األسالك و القواطع المناسبة لها حسب قدرتها و طرق تغذيتها؟ .268

فاز 3 فولت موضحا رموز األسالك المستخدمة فى شبكة 230/400 فاز. ثم ارسم كيفية توصيل األحمال الخفيفة و الكبيرة على الجهد الدولى 3ارسم رسم توضيحى لتوصيل األسالك من العداد الى لوحة .269 256 ........................................................................................................ فولت.230مع محايد. ثم ارسم رسم توضيحى لشكل المقبس المطابق و كيفية توصيله بالقطب أحادى الطور




11

1. 0BHave you previously done design for electrical work?

o 1BYes

o 2BNo

3BIf yes, the following two items must be answer

i. 4BWhat facilities or buildings you designed?

o 5BCommercial

o 6BResidential

o 7BIndustrial

o 8BMedical/Health Care

o 9BEducational/Schools

o 10BHotels

o 11BPower Plant/Stations

o 12BSports

o 13BExterior Site Work

o 14BOthers: Please specify:

ii. 15BWhat Standards or Norm you used in your design?

o 16BAmerican

o 17BBritish

o 18BIEC

o 19BFrench


2. 21BHave you previously done shop drawing (execution) for electrical (high current) work?

o 22BYes

o 23BNo

3. 24BAre you familiar and have used the following computer software’s:

o 25BMS Word

o 26BMS Excel

o 27BAutoCAD

o 28BRevit

o 29BLighting Calculation Programs: Please specify:

o 30BVoltage Drop Calculation Programs: Please specify:

o 31BShort Circuit Calculation Programs: Please specify:

o 32BEarthing (Grounding) Calculation Programs: Please specify:

o 33BLightning Protection & Risk Assessment Calculation Programs: Please specify:





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4. 35BWhat are the de-rating factors considered in cable installation?

AAnnsswweerr Ground Temperature de-rating factor Air Temperature de-rating factor Burial Depth de-rating factor Soil Thermal Resistivity de-rating factor PVC Rated Temperature de-rating factor Trefoil or Flat Formation de-rating factor for three & single core cables laid direct in ground Trefoil Formation de-rating factors for multi-core cables laid direct in ground Reduction factors for groups of more than one multi-core cable in air to be applied to the current carrying capacity for one

multi-core cable in free air Reduction factors for groups of more than one circuit of single core cables to be applied to the current carrying capacity for

one circuit of single core cables in free air

5. 36BHow can you overcome the problems of voltage drop?

AAnnsswweerr Using higher system voltages (= lower currents and therefore lower volt drop) Using larger cables (= lower resistance and therefore lower volt drop) Using multiple outgoing circuits (= less current per circuit and therefore lower volt drop)

6. 37BWhat are the precautions to be taken in mind when selecting an emergency feeder running

next to another feeder fed from normal supply?

AAnnsswweerr Type of the used designed cable should be taken into consideration regarding its properties & to be of higher fire resistance.

7. 38BWhat is the national color code of a three phase circuit?

AAnnsswweerr Red for phase (A) Yellow for phase (B) Blue for phase (C) Black for neutral (N) Yellow with green strip for protective earth (PE)

8. 39BWhat is the meaning and the difference between (AF) & (AT) of C.B?

AAnnsswweerr

Abbreviation Stands for Function

AF Ampere Frame, Maximum rated current for the C.B.

AT Ampere Trip. Adjusted rated current for the circuit breaker. (Less than or equal AF).




13

9. 40BWhat are the types of contracts? State the difference among them?

AAnnsswweerr Some common types of contracts are used in the engineering and construction industry

1. Lump Sum Contract or Fixed Price Contract: With this kind of contract the engineer and/or contractor agrees to do the a described and specified project for a fixed

price. You and the contractor agree to a set price, and you pay that price no matter how much the project ends up costing A Fixed Fee or Lump Sum Contract is suitable if the scope and schedule of the project are sufficiently defined to allow

the consulting engineer to estimate project costs. Contractor free to use any means and methods to complete work. Contractor responsible for proper work performance. Work must be very well defined at bid time. Fully developed plans and specifications required. Owner’s financial risk low and fixed at outset. Contractor has greater ability for profit.

Requirements:

– Good project definition. – Stable project conditions. – Effective competition essential when bidding. – Much longer time to bid and award this type of project, – Minimum scope changes due to higher mark-ups than occurred at bidding.

Advantages:

– Low financial risk to Owner. – High financial risk to Contractor. – Know cost at outset. – Minimum Owner supervision related to quality and schedule. – Contractor should assign best personnel due to maximum financial motivation to achieve early completion and

superior performance. – Contractor selection is relatively easy.

Disadvantages:

– Changes difficult and costly. – Early project start not possible due to need to complete design prior to bidding. – Contractor free to choose lowest cost means, methods, and materials consistent with the specifications. Only

minimum specifications will be provided. – Hard to build relationship. Each project is unique. – Bidding expensive and lengthy. – Contractor may include high contingency within each Schedule of Value item.

Example:

– You hire a contractor to build your home for $300,000. If it ends up costing $215,000 to build, the contractor keeps the $85,000 difference as additional profit. However, if the project costs $345,000, then the contractor suffers a $45,000 loss; you still pay the agreed-upon $300,000.




14

2. Unit Price Contract

This kind of contract is based on estimated quantities of items included in the project and their unit prices. The final

price of the project is dependent on the quantities needed to carry out the work. In general this contract is only suitable for construction and supplier projects where the different types of items, but not

their numbers, can be accurately identified in the contract documents. It is not unusual to combine a Unit Price Contract for parts of the project with a Lump Sum Contract or other types of

contracts. Large quantity changes (>15-25%) can lead to increase or decrease in unit prices. Time and Cost Risk are Shared:

– Owner at risk for total quantities – Contractor at risk for fixed unit price

Requirements:

– Adequate breakdown and definition of work units – Good quantity surveying and reporting system – Sufficient design definition to estimate quantities of units – Experience in developing bills of quantities – Payment terms properly tied to measured work completion – Owner-furnished drawings and materials must arrive on time – Quantity sensitive analysis of unit prices to evaluate total bid price for potential quantity variations

Advantages:

– Complete design definition not required – Typical drawings can be used for bidding – Suitable for competitive bidding – Easy for contractor selection – Early project start possible – Flexibility - “ Scope and quantities easily adjustable “

Disadvantages:

– Final cost not known at outset since bills of quantities at bit time are only estimates – Additional site staff needed to measure, control, and report on units completed – Unit price contracts tend to draw unbalanced bidding

Example:

– You hire a contractor to build a home for $70 per square foot. You want 2,000 square feet, so you will pay $140,000 total. Alternatively, you might agree to pay $4 per square foot for framing, $3 per square foot for electrical and plumbing, and $2 per square foot for painting and finish work.

3. Incentive Contracts Compensation is based on the engineering and/or contracting performance according an agreed target - budget, schedule

and/or quality. The two basic categories of incentive contracts are:

– Fixed Price Incentive Contracts

Fixed Price Incentive Contracts are preferred when contract costs and performance requirements are reasonably certain.

– Cost Reimbursement Incentive Contracts

Cost Reimbursement Contract provides the initially negotiated fee to be adjusted later by a formula based on the relationship of total allowable costs to total target costs. This type of contract specifies a target cost, a target fee, minimum and maximum fees, and a fee adjustment formula. After project performance, the fee payable to the contractor is determined in accordance with the formula.




15

4. Cost Plus Contract

A contract agreement wherein the purchaser agrees to pay the cost of all labor and materials plus an amount for

contractor overhead and profit (usually as a percentage of the labor and material cost). The contracts may be specified as:

– Cost + Fixed Percentage Contract

Compensation is based on a percentage of the cost

– Cost + Fixed Fee Contract Compensation is based on a fixed sum independent the final project cost. The customer agrees to reimburse the contractor's actual costs, regardless of amount, and in addition pay a negotiated fee independent of the amount of the actual costs

– Cost + Fixed Fee with Guaranteed Maximum Price Contract Compensation is based on a fixed sum of money. The total project cost will not exceed an agreed upper limit

– Cost + Fixed Fee with Bonus Contract Compensation is based on a fixed sum of money. A bonus is given if the project finishes below budget, ahead of schedule etc.

– Cost + Fixed Fee with Guaranteed Maximum Price and Bonus Contract

Compensation is based on a fixed sum of money. The total project cost will not exceed an agreed upper limit and a bonus is given if the project is finished below budget, ahead of schedule etc.

– Cost + Fixed Fee with Agreement for Sharing Any Cost Savings Contract

Compensation is based on a fixed sum of money. Any cost savings are shared with the buyer and the contractor.

These types of contracts are favored where the scope of the work is indeterminate or highly uncertain and the kinds of

labor, material and equipment needed are also uncertain. Under this arrangement complete records of all time and materials spent by the contractor on the work must be maintained. Example:

– You hire a contractor to build a home for the actual cost, and you also agree to pay the contractor an amount equal to 10 percent of that actual cost. If your home costs $300,000 to build, you would pay the contractor another $30,000, making your total price $330,000. Alternatively, you could agree to pay actual costs plus a specified, flat fee for the contractor. For example, if your home costs $300,000 to build and you agreed to pay the contractor a $20,000 fee, total costs to you would be $320,000.

5. Percentage of Construction Fee Contracts Common for engineering contracts. Compensation is based on a percentage of the construction costs.




16

10. 41BWhat is difference between tender drawings, design drawings, shop drawing (Execution) &

as built drawings?

AAnnsswweerr Tender:

– Studying the nature of project and the client requirements for the level of work. – Make Concept Design, Check List for all Systems to be used and Contract Type. – Make preliminary estimated BOQ and specifications.

Design:

– Study the nature of project and the client requirements for the level of work. – Put solution for the project with regard to electrical spaces that optimize the distribution of electrical power and routing

taking into account the voltage drop. – Study lighting for different areas with respect to type of ceiling and illumination levels (Lux) required for different areas

according to their functions. Design should be according to local regulations and international standards and codes. – Make drawings to show distribution and number of (lighting fixtures, fire alarm detectors, socket outlets …….etc.) as

well as wiring method and circuits references for each circuit. – Make specifications & exact BOQ for the contractor and suppliers to follow according to the design.

Shop Drawing (Execution):

– All detailed drawings including ( installation details & sections, exact dimensions, pull & junction boxes, complete path to the pull box, hatch & sizes of wires & cables, cable Tray sections & levels, exact routing …etc)

– Make coordination among different systems & different trades, Details showing relation and spacing between different systems (electrical, hvac, plumbing, fire fighting ….etc.).

– Show detail of routing cables inside cable trays or trenches with manholes or without. – Mention and show section show cable distribution inside raceways and capacity inside each one as stated in spare

regulations and standards. Make check of all calculations & drawings. – Make details for every item and specifications for the material and fixation method. – Final BOQ and Specification.

As Built:

– Correct all shop drawings in order to match the existing installations that already done – Survey for all existing installations, Collecting data, catalogues, operating manuals & maintenance guides for all existing

installed equipments.

11. 42BWhat are the types of tests required for electrical equipment? What are the differences?

AAnnsswweerr

Type of Test Location & Time of Test Reports & Certificates

Type Tests Done one time at the beginning of manufacturing the equipment for one sample in international laboratories and must pass all tests according to IEC.

Report & certificate must be given for that.

Routine Tests Done each time for all equipments at the factory. Client deputy should be present in these tests

Report & certificate must be given for that.

Site Tests Done in site in order to ensure that the equipment arrived to site in good condition and working well. Site engineer & client deputy should be present in these tests

Report must be given for that.




17

12. 43BWhat are the types of circuit breakers? State some applications for each?

AAnnsswweerr

C.B. Type Applications Ratings & Settings Max. S.C. Limits MCB: Miniature Circuit Breaker

Used for small appliances & small branch circuits. Ratings up to 125A Up to 25 KA

MCCB: Molded Case Circuit Breaker

Usually used as main circuit breaker where we need more reliability, more rated current & short circuit level.

Ratings from 100A up to 3200A Up to 200 KA

RCCB: Residual Current Circuit Breaker (Earth Leakage Circuit Breaker)

Used to protect people against indirect contact, to provide protection against fire hazards due to a persistent earth fault current, without the operation of the over-current protective device.

Settings from 30mA to 1A

ACB: Air Circuit Breaker

Usually used for transformer protection due to its high capacity ratings & more reliability than molded case (micro-logic can be installed).

Ratings from 400 up to 6300A

SF6 CB: Sulfur Hexa Flouride Circuit Breaker

Usually used for medium & high voltage, smaller than ACB

Used from low voltage system and up to 1300 kV (rating 45 GVA).

Vacuum CB:

Usually Used for medium & high voltage Very small damage to contacts (life up to 30 years). Small mechanical energy required for tripping.

Wide Range

13. 44BWhat is the difference between thermal setting & magnetic setting of C.B?

AAnnsswweerr

Type of Setting Type of Trip Type of Protection Thermal Setting Inverse Time Trip. For Overload Protection. Magnetic Setting Instantaneous Trip. For Short Circuit Protection.




18

14. 45BHow can you improve the selection of a system earthing arrangement?

AAnnsswweerr Six Selection Criteria:

– Protection of persons – Protection of equipment – Continuity of the power supply – Effects of disturbances – Easy implementation – Economic analysis

15. 46BWhat is the meant by TVSS or SPD?

AAnnsswweerr SPD: Surge Protection Device TVSS: Transient Voltage Surge Suppressor TVSS or SPD is a device that interrupt and divert electrical transient surge events to ground. Surge events can be caused by

electrical storms or bank switching on electrical distribution lines. These events are responsible for over 2 billion dollars of damage annually in the USA and can effect sensitive electrical equipment, telephone networks, and computer networks.




19

16. 47BWhat are the types of Discrimination (Selectivity)? State the difference?

AAnnsswweerr Current Discrimination:

– Total Discrimination: if for all fault current values, from overloads up to the non-resistive short circuit current, circuit breaker D2 opens and D1 remains closed.

– Partial Discrimination: if the above condition is not respected up to the full short circuit current, but only to a lesser value termed the selectivity limit currents.

– No Discrimination: in the event of fault, both circuit breakers D1 and D2 open.

Time Discrimination:




20

17. 48BWhat is Cascading?

AAnnsswweerr Cascading:

– Is the use of the current limiting capacity of circuit breakers at a given point to permit installation of lower rated and therefore lower cost circuit breakers downstream. Also, the upstream compact C.B acts as a barrier against short circuit currents. In this way, downstream C.B’s with lower breaking capacities than the prospective short circuit (at their point of installation) operates under their normal breaking conditions.

– For example: if the calculated SC current at a point is 30KA so in case of not using cascading we should choose C.B with 35KA SC current. While in case of using the main C.B with cascading technology so we can use C.B of 20KA above this point.

Cascading Advantages:- – Reduce C.B cost. – Reduce mechanical effect (Bus bars). – Reduce thermal effects (Cables). – Reduce electromagnetic effect (Measuring devices).

Conclusion

– Cascading = Reduction of the installation cost

18. 49BEstimate the demand load (VA/m2) regarding lighting, sockets, A/C, Equipments...etc for the

following type of buildings:

o 50BHotels

o 51BResidential

o 52BCommercial/Offices

o 53BHealth Care/Hospitals

o 54BEducational/Schools

AAnnsswweerr

Type of Buildings Demand loads as per type of loads (VA/m2)

Lighting Sockets A/C Equipments Others Hotels 25 20 120 30 25 Residential 30 20 100 25 0 Commercial/Offices 40 40 120 20 10 Health Care/Hospitals 30 30 120 30 50 Educational/Schools 30 20 110 20 20




21

19. 55BWhat is meant by:

o 56BIP54

o 57BNEMA 3R

AAnnsswweerr IP54: Protected against dust limited ingress (no harmful deposit).

Protection against water sprayed from all directions, limited ingress permitted. NEMA-3R: Rain tight, Sleet Resistant – Outdoor - undamaged by the formation of ice on the enclosure

20. 58BWhat are codes & standards can be followed in lighting design?

AAnnsswweerr IESNA: Illuminating Engineering Society of North America. CIBSE: Chartered Institution of Building Services Engineers Lighting Code UK norms. DIN German norms: Deutsches Institut fur Normung

21. 59BWhat are the types of earthing systems according to IEC? Explain each & where

recommended to be used? Compare among earthing systems.

AAnnsswweerr Types of Earthing Systems According to IEC:

– TT System: – IT System – TN System

TN-C System TN-S System TN-C-S System

Neutral & exposed conductive part connections:

– First letter – Relationship of the power system to earth:

T: Direct connection of neutral to earth; I: Neutral isolated from earth, or one connected to earth through impedance.

– Second letter – Relationship of the exposed-conductive-parts of the installation to earth:

T: Direct electrical connection of exposed-conductive-parts to earth. N: Direct electrical connection of the exposed-conductive-parts to neutral.

Arrangement of N & PE conductors:

– Subsequent letter(s) (if any) – Arrangement of neutral and protective conductors:

S: Neutral and protective conductor separate (N & PE). C: Neutral and protective conductor combined (PEN conductor). C-S: TN-C near the source, TN-S near the loads.




22

TT system

– A system having one point of the source of energy directly earthed, the exposed conductive parts of the installation being connected to earth electrodes electrically independent of the earth electrodes of the source.

– In the case of isolation fault, the potential of the exposed conductive parts will suddenly increase causing a dangerous situation of electric shock. This can be avoided with the use of RCD’s with the proper sensitivity in function of touch voltage.

– To ensure safety conditions in the installation, the earth values shall comply with: RA x I∆n ≤ 50V

– RA = Earth resistance value of the installation. – I∆n = Residual operating current value of the RCD.

IT system

– A system having no direct connection between live parts and earth, the exposed conductive parts of the electrical installation connected to an earth electrode.

– The source is either connected to earth through deliberately introduced earthing impedance or is isolated from earth. – In case of insulation fault the value of the current is not high enough to generate dangerous voltages. – Nevertheless protection against indirect contact must be provided by means of an insulation monitoring device which

shall provide visual and sonorous alarm when the first fault occurs. The service interruption by means of breakers must be done in case of a second fault according to the following tripping conditions:

– To ensure safety conditions in the installation, it shall comply with: RA x Id≤ 50V

– RA = Earth resistance value of the installation.`1`q – Id = Fault current value of the first fault.




23

TN system – A system having one or more points of the source of energy directly earthed, the exposed conductive part of the

installation being connected to that point by protective conductors. In case of an insulation fault a short circuit (phase – neutral) is caused in the installation.

– There are three types of TN systems: TN-C, TN-S and TN-C- TN-C system

• A system in which neutral and protective functions are combined in a single conductor throughout the system.

TN-S system • A system having separate neutral and protective conductors throughout the system.




24

TN-C-S system • Part of the system uses a combined PEN conductor, which is at some point split up into separate PE and N lines.

IEC60364-3 Electrical installations in buildings part 3 assessment of general characteristics defines the code used to specify the earthing of low voltage distribution systems. The code consists of 2 letters and subsequent letter(s) if they are required. The definitions given hereafter refer to typical industrial applications.

There is no requirement in IEC Standards to implement earth fault protection on the incoming circuit breaker to eliminate resistive earth faults. According to the above mentioned IEC standard, earth faults can be eliminated by means of phase protection or sensitive earth fault protection. Should earth fault protection to provide on the incoming circuit breaker and phase protection be used on outgoing feeders, protection coordination is often not possible. This results in tripping the incoming circuit breaker for earth faults on outgoing feeders which is normally unacceptable for industrial and commercial applications. If the application requires that earth fault protection be provided on incoming circuit breakers, sensitive earth fault protection should also be provided on outgoing feeders to ensure selective tripping.

The system earthing arrangement must be properly selected to ensure the safety of life and property. The behavior of the

different systems with respect to EMC considerations must be taken into account. European standards (see EN 50174-2 § 6.4 and EN 50310 § 6.3) recommend the TN-S system which causes the fewest EMC

problems for installations comprising information-technology equipment (including telecom equipment).

When an installation includes high-power equipment (motors, air-conditioning, lifts, power electronics, etc.), it is advised to install one or more transformers specifically for these systems. Electrical distribution must be organised in a star system and all outgoing circuits must exit the main low-voltage switchboard (MLVS).

Electronic systems (control/monitoring, regulation, measurement instruments, etc.) must be supplied by a dedicated transformer in a TN-S system.




25

Point of Comparison

Main Characteristics of System Earthing TT IT TN-S TN-C

Safety of persons Good • RCD mandatory

Good • Continuity of the PE conductor must be ensured throughout the installation

Safety against Short circuit currents

Good • Medium fault current

(< a few dozen amperes) • Small values of short-circuit

currents to earth: typically 10 to 100 A

Good • Low current for first fault (< a

few dozen mA), but high for second fault

• Small values of short circuit currents to earth (1st fault), typically 1 to 10 A (0.1A/km cable);

• Medium-high values of short circuit currents to earth (2nd fault)

Poor • High fault current (around 1 kA) • Medium-high values of short circuit currents to earth

Availability of energy Good Excellent Good Good

EMC (Electromagnetic Compatibility) behavior

Good • Risk of overvoltages • Equipotential Problems • Need to manage devices with

high leakage currents

Poor (to be avoided) • Risk of overvoltages • Common-mode filters and surge

arrestors must handle the phase- to-phase voltages

• RCDs subject to nuisance tripping if common-mode capacitors are present

• Equivalent to TN system for second fault

Excellent • Few equipotential

problems • Need to manage devices

with high leakage currents • High fault currents

transient disturbances)

Poor (should never be used) • Neutral and PE are the same • Circulation of disturbed currents in

exposed conductive parts (high magnetic-field radiation)

• High fault currents (transient disturbances)

Contact-voltage typical values 0.7 to 1.0 * U0 very low at the 1st fault, 0.5 * Un

at the 2nd fault 0.5 * U0

Typical applications

• Domestic and small industrial installations fed by the utilities directly from the low-voltage network (Italy and Spain)

• Industrial or utilities installations (especially chemical, petrochemical & telecommunications) for which a very high level of service continuity is required

• Installations for IT apparatuses fed by UPS

• Industrial, utilities or building installations fed from the M.V. network

• Industrial, utilities or building installations fed from the M.V. network

• TN-C (Germany,GB and Scandinavian countries) and TN-C-S systems (France) are normally used for domestic and small industrial installations fed by the utilities directly from the low-voltage network

Protection against earth-faults

• Required the installation of earth-leakage circuit breaker

• 1st fault: normally no circuit interruption is required; voltage or insulation monitoring relays generate an alarm; earth-leakage relays may be employed for a fast location and removal of the fault

• 2nd fault: protection assured by circuit breaker with only overcurrent releases or by fuses

• Breakers with only overcurrent releases or by fuses; circuit breaker with earth-leakage or ground-fault releases (G function) are required in case of loads fed by very long cables (TN-S systems only)

• Breakers with only overcurrent releases or by fuses

Neutral Conductor

• It is strongly recommended not to distribute the N-conductor

• N-conductor may be interrupted at the same time as the phase-conductors

• PEN-conductor cannot be interrupted

Advantages The Simplest • To study : little or no calculation • To run: easy to spot the faulty

part. • To modify: no special checking

of maximum cable lengths • To install: RCD’s are easy to

install & set.

The most efficient • No obligation to trip on first fault • Low fault current (less risk)

The cheapest • Less copper or aluminium: 4-wires instead of 5, 3-poles instead of 4. • Use of existing protections against overcurrent for protection of people

Drawback & Disadvantages

No continuity of service • Not very: cheap: 5-wires and 4

poles if distributed neutral – extensive use of RCD’s

• Difficult in some cases to ensure vertical discrimination of RCD’s

More complex • Imperative need for a reliable

and well-trained maintenance team

• Sensitivity to voltage surges from the MV side

• Necessity to permanently monitor network insulation

• Protection of all poles including neutral, equipment needed for fault tracking.

No continuity of service • Imperative calculations making study more difficult and modification

more delicate • High value of fault current: a simple insulation fault is a short circuit:

not studied to sensitive load • Necessity to seal the settings of the magnetic unit if adjustable




26

22. 60BCalculate the grounding conductor size & the grounding resistance according to BS

7430:1998 of grid of length 80m width 40m, 12 rods with separation distance of 20m where

rod length is 3m, rod diameter is 20mm, soil resistivity is 450 Ω.m, grounding conductor

laid 0.8m below ground. 10 earth lattices (600mm x 600mmm) are bonded to the earth loop.

Suppose that the symmetrical fault current is 20KA in 1sec duration. Where the grounding

conductor is chosen to be copper conductor and the initial temperature of conductor is 30°C

& final temperature is °250C. After calculation find out if the grid safe or not safe?

AAnnsswweerr

– Selection of Grounding Conductor & Connection to an Electrode “Method Based on BS 7430:1998”

S =I√tk

=(20x1000)√1

171.16= 116.85 mm2 ≅ 𝟏𝟏𝟏𝟏𝟏𝟏 𝐦𝐦𝐦𝐦𝟏𝟏

𝐤𝐤 = 𝐊𝐊 𝐥𝐥𝐥𝐥𝐥𝐥𝐞𝐞𝐓𝐓𝟏𝟏+𝛃𝛃𝐓𝐓𝟏𝟏+𝛃𝛃

= 𝟏𝟏𝟏𝟏𝟐𝟐 𝐥𝐥𝐥𝐥𝐥𝐥𝐞𝐞𝟏𝟏𝟐𝟐𝟏𝟏+𝟏𝟏𝟐𝟐𝟐𝟐𝟑𝟑𝟏𝟏+𝟏𝟏𝟐𝟐𝟐𝟐

= 𝟏𝟏𝟏𝟏𝟏𝟏.𝟏𝟏𝟐𝟐 𝐀𝐀/𝐦𝐦𝐦𝐦𝟏𝟏

Where I is the average fault current, in A r.m.s. S is the conductor cross-sectional area, in mm2; k is the r.m.s. current density, in A/mm2 T1 is the initial temperature, in °C; T2 is the final temperature, in °C; K, β have the values given in Table 13.




27

Grounding Resistance Calculations “Method Based on BS 7430:1998”

1. Rods or Pipes Resistance Calculation:

Rrods = R1rod ( 1 + λα ) = 145.46 ( 1 + 5.48x0.0246 ) = 41.27 Ω n 4

R1rod = ρ [ln 8L - 1] = 450 [ln 8x3 -1] = 145.46 Ω 2πL d 2x3.14x2.4 0.02

α = ρ = 450 = 0.0246 2πR1rodS 2x3.14x145.46x20

Note: Since; electrodes are equally spaced around a hollow square Therefore; we can use table 3 Since; no. of rods per side is approximately 5 (n’ = 5) Therefore; λ = 5.48, n = (n’/4 + 1) = (12/4 + 1) = 4

Surface Area of Vertical Rods = No. of rods x Surface Area of Vertical Rod [2πrL] = 12 x [2x3.14x(0.02/2)x3] = 2.26 m2

2. Lattice Resistance Calculation:

Rlattices = R1lattice ( 1 + λα ) = 81 ( 1 + 3.81x0.02316 ) = 8.81 Ω n 10

α = ρ = 450 = 0.02316 2πR1latticeS 2x3.14x129x24

Note: For simplified solution we can use table 2 for rods to get total R for lattice; Therefore; we can use table 2 Taking; number of lattices 10 (n = 10) Therefore; λ = 3.81

Since the Lattice is considered 3 groups connected in parallel then

= + +

1

= 1

+ 1

+ 1

= 1

+ 1

+ 1

R1lattice Relbow Rstar Relbow 243.6 214.2 243.6

R1lattice = 81 Ω

Relbow = ρ [ ln ( 2l² ) + Q ] = 450 [ ln ( 2x0.62 ) + 0.5 ] = 243.6 Ω Pπl wh 4x3.14x0.6 0.025x0.8

Rstar = ρ [ ln ( 2l² ) + Q ] = 450 [ ln ( 2x0.62 ) + 3.6 ] = 214.2 Ω Pπl wh 8x3.14x0.6 0.025x0.8

Surface Area of Lattices = No. of Lattices x Surface of Lattice [8x2πrL] = 10 x [8x2x3.14x(0.025/2)x0.6] = 3.77 m2




28

3. Rectangle Buried Bare Wire Resistance Calculation:

1 = 1 + 1 = 1 + 1 Rbare wires Rbare wire-1 Rbare wire-2 6.79 11.43

Rbare wires = 4.26 Ω

Rbare wire-1 = F1 Rbare wire-1// = 0.596 x 11.39 = 6.79 Ω

Rbare wire-2 = F2 Rbare wire-2// = 0.563 x 20.31 = 11.43 Ω

Rbare wire-1// = ρ [ ln ( 2L’² ) + Q ] = 450 [ ln ( 2x802 ) - 1.3 ] = 11.39 Ω PπL’ wh 2x3.14x80 0.013x0.8

F1 = 0.5 + 0.078 ( S’ )-0.307 = 0.5 + 0.078 ( 40 )-0.307 = 0.596 L’ 80 (i.e. in this case L’ = L’= 80m & S’ = S’ = 40m)

Rbare wire-2// = ρ [ ln ( 2L’² ) + Q ] = 450 [ ln ( 2x402 ) - 1.3 ] = 20.31 Ω PπL’ wh 2x3.14x40 0.013x0.8

F2 = 0.5 + 0.078 ( S’ )-0.307 = 0.5 + 0.078 ( 80 )-0.307 = 0.563 L’ 40 (i.e. in this case L’ = S’= 40m & S’ = L’ = 80m)

Where cable size is 120mm2 of diameter 13mm

From Table 5 For single length round conductor: P=2 & Q = -1.3 F has the following value:

• for two lengths, F = 0.5 + 0.078(S’/L’) –0.307 • for three lengths, F = 0.33 + 0.071(S’/L’) –0.408 • for four lengths, F = 0.25 + 0.067(S’/L’)–0.451

Provided that 0.02 ≤ (S’/L’) ≤ 0.3.

Surface Area of Horizontal Conductors = 2πr (2L+2S) = 2x3.14x(0.013/2)x(2x80+2x40) = 9.78 m2




29

Where

Rbare wire: is the combined resistance of rectangle bare wire of ground loop where two or more straight lengths, each of length (L’) in (m) and of separation (s’) in (m), are laid parallel to each other and connected together, in (Ω);

Rbare wire-n: is the resistance of one straight conductor in isolation calculated from the equation and coefficients given in table 5, in (Ω);

R1rod: is the resistance to earth of one rod or pipe electrode in isolation, in ( Ω);

Rground: is the grounding resistance, in (Ω);

L: is the length of the electrode, in (m);

d: is the diameter of the electrode, in (m);

ρ: is the resistivity of the soil, in (Ω ·m) (assumed uniform);

Rrods: is the combined total resistance of rod electrodes in parallel, in (Ω);

λ: is a factor for electrodes given in Table 2 or Table 3;

S: is the distance between adjacent rods, in (m);

n: is the number of electrodes (as given in Table 2 and Table 3);

n’: is the total number of electrodes along each side of the square.

l: is the length of the strip or conductor, in (m);

h: is the depth of electrode, in (m);

w: is the width of strip or diameter of conductor, in (m);

P, Q: are coefficients for different arrangements of electrode given in Table 5.

L’ or S’: is the length of straight bare wire, in (m);

S’ or L’: is the separation distance between two or more adjacent straight lengths conductors or strips laid parallel to each other and connected together, in (m);

J: is the maximum permissible current density (A/m2);




30

Important Note: If the rods are equally spaced in a straight line an appropriate value of λ may be taken from Table 2. In this

case [n = n’]. If electrodes are equally spaced around a hollow square, e.g. around the perimeter of a building, value of λ

may be taken from Table 3. In this case [n = (n’/4) + 1)].

4. Total Grounding Resistance Calculation: 1 = 1 + 1 + 1 = 1 + 1 + 1

Rground Rrods Rlattices Rbare wires 41.27 8.81 4.26

Rground = 2.68Ω < 5 Ω OKAY

𝐽𝐽 = 103(57.7𝜌𝜌 𝑡𝑡

) = 103( 57.7(450)(1)

) = 358.08 A/m2

Surface Area of Vertical Rods, Horizontal Conductors & Lattices = 2.26 + 9.78 + 3.77 = 15.81 m2 Short Circuit Ground Grid Withstand = 358.08x 15.81 = 5.66 kA < (Fault Current 20 kA) Therefore; the grid is not safe.




31

23. 61BWhat is the Dynamic UPS (No Break Generator)? State some applications? Compare with

Static UPS.

AAnnsswweerr

– At normal conditions the fly wheel is fed from the main electric source and continues rotating. – When loss electricity, the flying wheel continue rotates due to inertia helping the generator to feed critical loads.

Applications – Satellite communication (Internet data centers (IDC)) – Aviation and Airports (Air traffic control towers,

Runway lighting, Reservation centers) – Hi-tech industry (Semiconductor, TFT-LCD flat screens,

Mobile phones) – Hospitals – Industry (Process industry, Pharmaceutical industry, Car

industry) – Defence (Radar, Intelligence centers) – Finance/Banking/Stock Exchange (Data centers) – Telecom/Internet (Telecom centers)

Advantages of Dynamic UPS

– One system powering critical and non-critical loads. – Lower initial investment. – Lower installation and building construction costs. – Reduced floor space. – Lower maintenance costs. – Provides additional protection for the critical loads by

means of the choke coil.

Disadvantages Chemical Batteries – Connected in strings; in case one cell fails, one complete

string fails. – Special fire code regulations. – Increasing installation and insurance costs. – Air-conditioning requirements. – Short real life-time. – Large floor space requirements. – High maintenance. – Increasing disposal costs. – Limited short circuit acceptance.

Conditioning Mode Independent Mode

Static UPS Room Layout

Dynamic UPS Room Layout




32

24. 62BWhat are the types of cable trays? State some applications? How can you size a cable tray?

What is the difference between cable tray & cable ladder & which is less expensive? State

applications for cable ladders?

AAnnsswweerr Types of Cable Trays

– Cable Tray hot deep galvanized before perforation – Cable Tray hot deep galvanized after perforation – Cable Tray hot deep galvanized after perforation with cover – Steel Wire Cable Tray. – Cable Ladders.

Comparison & Applications

– Cable Ladder is less expensive than cable tray. – Cable ladders are more reliable to be used for cables with large CSA (ex. Medium voltage cables). – Cable Tray hot deep galvanized before perforation usually used in dry areas. – Cable Tray hot deep galvanized after perforation usually used in wet areas & technical rooms. – Cable Tray hot deep galvanized after perforation with cover usually used at roof (outdoor).

Steel Wire Cable Tray Cable Ladder

Perforated Cable Tray Perforated Cable Tray with cover




33

Typical Cable Tray Types As per NEMA VE 2-2006




34




35




36

25. 63BState some applications for using isolating transformers? What is the advantage of using

it?

AAnnsswweerr Applications

– Swimming pools. – Surgery operating rooms.

Advantage

– Isolating transformers protect people from electric shock due to its low voltage.

26. 64BWhat are the common types of conduits? State some applications? How can you size a

conduit?

AAnnsswweerr Common types of conduits

PVC: Poly Venyle Chloride Conduit. UPVC: Ultra Venyle Chloride Conduit. RGS: Rigid Galvanized Steel Conduit. EMT: Electrical Metallic Tubing. FMC: Flexible Metal Conduit. IMC: Intermediate Metal Conduit.

Sizing of conduits can be done according to NEC – Tables – Chapter 9




37

27. 65BWhat characteristics does a luminaire need to be a good one?

AAnnsswweerr

To minimize Glare Focus lamp’s light onto the working surface Ensure that the lamp does not overheat

28. 66BWhat are the SEC standard specifications for LV distribution panels sizes for transformers

500 kVA, 1000 kVA, 1500 kVA from where:

o 67BIncoming CB. Rating

o 68BIncoming Cables for standalone LV panel

AAnnsswweerr According to SEC Distribution Materials Specification (31-SDMS-01)

Components Transformer Rating

300 kVA 500 kVA 1000 kVA 1500 kVA 231/133V 400/231V 231/133V 400/231V 231/133V 400/231V 231/133V 400/231V

LV Panel incoming busbar link rating (A) 800 500 1600 800 3000 1600 4000 2500

Incoming C.B. rating (A) 800 500 1600 800 3000 1600 4000 2500

CT Rating on incoming busbars (A) 750/5 750/5 1500/5 750/5 3000/5 1500/5 4000/5 3000/5 Incoming Cables for standalone LV panel

2 / ph 1 / N

2 / ph 1 / N

2 / ph 1 / N

2 / ph 1 / N

4 / ph 2 / N

2 / ph 1 / N

6 / ph 3 / N

4 / ph 2 / N

Number of cables single core

7 x(

1x63

0mm

2) c

u

7 x(

1x63

0mm

2) c

u

7 x(

1x63

0mm

2) c

u

7 x(

1x63

0mm

2) c

u

14 x

(1x6

30m

m2)

cu

7 x(

1x63

0mm

2) c

u

21 x

(1x6

30m

m2)

cu

14x(

1x63

0mm

2) c

u

Detailed number of cables single core

[2 x

3x(

1x63

0mm

2)

–3ph

] +

[1 x

(1x6

30m

m2)

-N]

[2 x

3x(

1x63

0mm

2)

–3ph

] +

[1 x

(1x6

30m

m2)

-N]

[2 x

3x(

1x63

0mm

2)

–3ph

] +

[1 x

(1x6

30m

m2)

-N]

[2 x

3x(

1x63

0mm

2)

–3ph

] +

[1 x

(1x6

30m

m2)

-N]

[4 x

3x(

1x63

0mm

2)

–3ph

] +

[2 x

(1x6

30m

m2)

-N]

[2 x

3x(

1x63

0mm

2)

–3ph

] +

[1 x

(1x6

30m

m2)

-N]

[6 x

3x(

1x63

0mm

2)

–3ph

] +

[3 x

(1x6

30m

m2)

-N]

[4 x

3x(

1x63

0mm

2)

–3ph

] +

[2 x

(1x6

30m

m2)

-N]

For LV panle used in unit package substations Incoming connection shall be through copper busbar links from back of the panel

Number of outgoing MCCB’s 4 2 8 4 12 8 12 10 Minimum Spacing MCCB’s Not less than 10mm Phase Busbars min. cross section (mm2) 10x50 10x50 10x100 10x50 2x10x100 10x100 3x10x100 2x10x100 Phase Busbars min. Raring (A) 800 500 1600 800 3000 1600 4000 2500 Neutral Busbar min. size (mm2) 5x50 5x50 10x50 5x50 10x100 10x50 2x10x100 10x100 Neutral Busbars min. Raring (A) 400 250 800 400 1600 1000 2500 1600 Ammeter Scale 0-1000 0-750 0-1800 0-1000 0-3000 0-1800 0-4000 0-3000 Symmetrical short circuit rating for 2 sec. (RMS). kA 25 25 25 25 40 25 65 40




38

29. 69BWhat is RGB LED?

AAnnsswweerr RGB LED = Red Green Blue Light Emitting Diode.

– It’s the abbreviation of Red, Green, and Blue. The three colours of light which can be mixed to produce any other colour. In fact it’s an additive colour model in which red, green and blue light is combined to create colours, combining full intensities of all three colours makes white.

30. 70BCan we dim Fluorescent or Metal Halide lamps?

AAnnsswweerr Fluorescent lamps

– Dimming of fluorescent using a simple wall potentiometer. – 0V to 10V Dimming of fluorescent.

Metal Halide lamps

– Most HID lamps can be dimmed using Step-level dimming. – Savings of 50% or more might be obtained where available daylight is used with photo sensor and dimming control

system. – HID lamps should be started at full power and the dimming delayed until the lamp is fully warmed up. – HID lamps respond to changes in dimmer settings much more slowly than incandescent or fluorescent sources: delay

between minimum and maximum light output varies 3 to 10 min. – Instantaneous dimming is available over a limited range for some lamps. – Clear metal halide lamps can experience a shift in color temperature of over 1000 K and a drop of 35% in CRI when

dimmed to 50% of rated output. Convenience and simplicity.

31. 71BWhat are the different types of Lighting System Controls?

AAnnsswweerr Manual Control

– Normal on/off switches – Manual Dimmers

Manual / Automatic control (On by user/Off Automatic)

– Timer Switches – Infra Red sensor / Ultrasonic Switches

Automatic Controls

– Time of Day [ Sensor : Timer] – Dimming [ Sensor : Photocell ] – Occupancy Detectors




39

32. 72BWhat is the difference between IP, NEMA, IK, IC & IM?

AAnnsswweerr IP: Ingress Protection (or Index of Protection) --- According to IEC 60529. NEMA: National Electrical Manufacturers Association Protection --- According to NEC. IK: Mechanical Impact Protection. --- According to IEC 62262. IC: International Cooling --- According to IEC 60034-6. IM: International Mounting Arrangements --- According to IEC 60034-7.

NEMA




40




41

IK Code

Standard IEC 62262 defines an IK code that characterises the aptitude of equipment to resist mechanical impacts on all sides.

IC Code




42

IM Code




43

33. 73BWhat is the difference between horizontal, vertical illumination & general, task lighting?

How can you make calculations for each? State some examples for each?

AAnnsswweerr Horizontal illuminance:

– The average luminance values produced at 90°. – For example, the illumination on floor of a room.

Vertical illuminance: – The average luminance values produced at 0°. – For example, the illumination on the switchgear

& breakers must be vertical.

General lighting: – Lighting designed to provide a substantially uniform level of

illuminance throughout an area, exclusive of any provision for special local requirements.

Task lighting: – Lighting directed to a specific surface or area that provides illumination for visual tasks.

For example a typical office, the general lighting often is designed to provide an illuminance of 75 fc (750 lux) at desk height, the middle value from category “E.” In partitioned workspaces, it is difficult for general lighting to deliver this illuminance to the desk surfaces, because shadows from shelves, cabinets, partitions, and the worker’s own body can block light from the ceiling mounted luminaires. Therefore, in an office that requires 75fc (750 lux), a fluorescent under-shelf task light can provide 40 fc (400 lux), which allows the general lighting to be reduced to 35 fc (350lux). Even greater energy savings can be achieved if the task lights are switched off when not in use.

Note: – Calculations can be done for each using point by point calculation or using lighting program (calculation surfaces).




44

34. 74BWhat is color rendering? State the color renderings for sodium lamps, metal halide lamps,

fluorescent lamps & halogen lamps?

AAnnsswweerr Color Rendering Index (CRI):

– A method for describing the effect of a light source on the color appearance of objects being illuminated, with a CRI of 100 representing the reference condition (and thus the maximum CRI possible). In general, a lower CRI indicates that some colors may appear unnatural when illuminated by the lamp.

Type of Lamp Color Rendering (%) Metal Halide 90-93% Fluorescent 75-85% Halogen 95-100% Sodium 20-25%

35. 75BWhat is illuminance? State the recommended illumination level for Office, Surgery operating

room, Bed room, Class room, Sitting & Corridors

AAnnsswweerr Illuminance:

– The amount of light that reaches a surface. Illuminance is measured in footcandles (lumens/square foot) or lux (lumens/square meter). One footcandle equals 10.76 lux, although for convenience the IESNA uses 10 lux as the equivalent.

Application Recommended Illumination level (Lux) Office From 300 lux (General) to 750 lux (Task) Surgery operating room From 2000 lux (General) to 20000 lux (Task) Bed room From 200 lux (General) to 500 lux (Reading) Class room From 500 lux (General) to 1000 lux (Task) Sitting 200-300 lux Corridors 100-200 lux

36. 76BWhat is Color Temperature? State some of them

AAnnsswweerr Correlated Color Temperature (CCT):

– A description of the color appearance of a light source in terms of its warmth or coolness. The CCT relates the color appearance of the light emitted by a lamp to the color appearance of a reference material heated to a high temperature (measured on the Kelvin scale, abbreviated K). As the temperature rises, the color appearance shifts from yellow to blue. Thus, lamps with a low CCT (3000 K or less) have a yellow-white color appearance and are described as “warm”; lamps with a high CCT (4000 K and higher) have a blue-white color appearance and are described as “cool.”

Color Appearance Color Temperature (k) Yellow 2000K Warm White 3000K White 3500K Cool White 4200K Daylight 6500K




45

37. 77BWhat is the difference between Fluorescent lamps type T2, T5, T8 & T12?

AAnnsswweerr

Lamp Type Diameter Type of Gas Efficacy Type of Ballast Life Time (hours) Today Usage T 12 ≡ T38 ≡ TL 38mm Mercury + Argon Less Efficacy Work with magnetic

ballast Almost Disappeared

T 8 ≡ T26 ≡ TL-D 26mm Mercury + Krypton More Efficacy

than T12

Work with magnetic ballast, rapid-start & electronic ballast

Magnetic = 8000 hr Rapid Start = 11000 hr Electronic = 16000 hr

Most Popular

T 5 ≡ T16 ≡ TL5 16mm Mercury + Krypton More Efficacy

than T8 Work with electronic ballast only 20000 hr Fast Growing

T2 7mm Mercury + Krypton More Efficacy than T5

Work with electronic ballast only

Rare

T 12 ≡ T38 ≡ TL T 8 ≡ T26 ≡ TL-D T 5 ≡ T16 ≡ TL5 T2

Watt lm mm Watt lm mm Watt lm mm Watt lm mm 6 330 220 8 540 320 10 650 470 11 750 422 13 930 525 14 1200 550 15 950 440 16 1250 720 18 1350 590

20 1200 590 21 1900 850 23 1900 970 24 1950 550 28 2400 1150 30 2400 900 35 3300 1150 36 3350 1200 38 3300 1050 39 3400 850

40 3000 1200 49 4300 1150 54 4600 1150 58 5200 1500

65 4800 1500 80 6450 1150

115 6850 1200




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T-12 Fluorescent Lamps:

– Until the National Energy Policy Act of 1992 (EPACT), the most commonly applied fluorescent lamp was the T-12, 40-

W, 4-ft (1.22-m), rapid-start lamp with a cool white or warm white phosphor. EPACT banned the production of these type lamps after 1995. EPACT also impacted the T-12, 8-ft (2.44 m) lamps. As with 4-ft lamps, only reduced wattage or improved color rendition lamps are currently produced for U.S. consumption. For many new installations, the more efficient T-8 lamps are often specified.

T-8 Fluorescent Lamps: – T-8 fluorescent lamps are a family of 1-in.-diameter (25.4 mm) straight tube lamps manufactured in some of the same

lengths as T-12 lamps. The 4-ft version of the lamp is designed to consume approximately 32 W. It is also available in 2-, 3-, 5- and 8-ft. (0.16-, 0.91-, 1.52-, and 2.44-m) lengths. The smaller diameter makes it economical to use the more efficient and more expensive rare-earth phosphors. Although the T-8 and T-12 lamps are physically interchangeable, they cannot operate on the same ballast. T-8 lamps are designed to operate on line-frequency rapid-start ballasting systems at approximately 265 mA, or on high-frequency electronic ballasts at slightly less current. Due to the higher efficacies that can be reached with T-8 systems, they have replaced the conventional T-12 lamps in many applications.

T-5 Fluorescent Lamps: – T-5 fluorescent lamps are a family of smaller diameter straight tube lamps employing triphosphor technology. Available

only in metric lengths and mini bipin bases, the T-5 lamps provide higher source brightness than T-8 lamps and better optical control. The lamps provide optimum light output at an ambient temperature of 35°C (95°F) rather than the more typical 25°C (77°F), allowing for the design of more compact luminaires. Also available are high-output versions providing approximately twice the lumens at the same length as the standard versions. T-5 lamps are designed to operate solely on electronic ballasts. Their unique lengths, special lamp holder, and ballast requirements make them unsuitable for most retrofit applications. These lamps are used in shallower luminaries than the T-8 lamps, which are more efficient overall than luminaries for T-8 lamps

38. 78BCan we make interconnection bonding among these systems:

o 79BGrounding System

o 80BLightning Protection

o 81BLow current & Communication Grounding System

AAnnsswweerr According to NEC Article 250.94:

– The Code requires that separate systems be bonded together to reduce the differences of potential between them due to

lightning or accidental contact with power lines. Lightning protection systems, communications, radio and TV, and CATV systems must be bonded together to minimize the potential differences between the systems.

– Lack of interconnection can result in a severe shock and fire hazard.

According to NEC Article 250.106:

– The lightning protection system ground terminals shall be bonded to the building or structure grounding electrode system.

According to NEC Article 930.100:

– A bonding jumper not smaller than 6 AWG copper or equivalent shall be connected between the network-powered broadband communications system grounding electrode and the power grounding electrode system at the building or structure served where separate electrodes are used.




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39. 82BGive some types of different lamps showing: type, manufacturers, wattage, lumen output,

peak intensity, colour temperature, lamp holder (cap), life time and dimensions?

AAnnsswweerr




48




49




50




51




52




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40. 83BWhat are the recommended IP and IK code specifications for distribution boards?

AAnnsswweerr The degrees of protection IP and IK of an enclosure must be specified as a function of the different external

influences defined by standard IEC 60364-5-51, in particular: – Presence of solid bodies (code AE) – Presence of water (code AD) – Mechanical stresses (no code) – Capability of persons (code BA)

Unless the rules, standards and regulations of a specific country stipulate otherwise, Schneider Electric recommends

the following IP and IK values.

Schneider Electric IP Recommendations for distribution boards

Schneider Electric IK Recommendations for distribution boards

41. 84BCalculate the number of luminaries required for office (5x6m), height = 3m, consider type

fluorescent lighting fixture each have lamps 2x36W. Luminous flux of each lamp 3200 lm,

utilization factor is 0.48 and maintenance factor is 0.75. Notice that the required

maintained illumination level is 500 lux.

AAnnsswweerr

N = (E x A) / (Ø x n x U.F x M.F) = (500*30) / (3200*2*0.48*0.75) = 6.71 ≈ 8 Luminaries

Where: E= Average maintained illumination level (lux) A= Room area (m2) Ø= Lamp luminous flux (lm) N= number of lighting fixtures (luminaries) n= number of lamps in each luminaire U.F= Utilization factor M.F= Maintenance factor




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42. 85BWhat is the recommended LV system voltage? Give some examples for the system voltages &

frquencies in different countries?

AAnnsswweerr An international voltage standard for 3-phase 4-wire LV systems is recommended by the IEC 60038 to be 230/400 V.

Voltage of local LV network and their associated circuit diagrams




55




56




57




58




59




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43. 86BWhat is LEED & how can you improve your design to match the LEED requirements?

AAnnsswweerr LEED: Leadership in Energy and Environmental Design

– LEED is the brainchild of the U.S. Green Building Council (USGBC). The Leasership in Energy and Environmental Design (LEED) Green Building Rating System is the accepted benchmark for the design, construction and operation of high performance Green Building.

– Although there is other rating systems available, LEED is the most used worldwide because it is not too difficult to understand and apply.

– When asked to design a “Sustainable development” the first question is what sustainability is and what constitutes a Green Building.

– We can use day lighting controls, lighting controls, occupancy sensors, EIB, BMS foe HVAC…. etc.

44. 87BWhich one could achieve more lumen output prismatic or opal diffusers considering same

lamps? Why? State application.

AAnnsswweerr Prismatic:

– An optical component of a luminaire that is used to distribute the emitted light. It is usually a sheet of plastic with a pattern of pyramid-shaped refracting prisms on one side. Most ceiling-mounted luminaires in commercial buildings use prismatic lenses.




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45. 88BWhat are the different types of substations?

AAnnsswweerr Substations may be classified according to metering arrangements (MV or LV) and type of supply (overhead line or

underground cable). The substations may be installed:

– Either indoors in room specially built for the purpose, within a building, or – An outdoor installation which could be :

Installed in a dedicated enclosure prefabricated or not, with indoor equipment (switchgear and transformers) Ground mounted with outdoor equipment (switchgear and transformers) Pole mounted & with dedicated outdoor equipment (switchgear and transformers)

i.e: Prefabricated substations provide a particularly simple, rapid and competitive choice.

1. Indoor substation 1.1. Conception

– Figure B32 shows a typical equipment layout recommended for a LV metering substation. – Remark: the use of a cast-resin dry-type transformer does not use a fireprotection oil sump. However, periodic cleaning

is needed.




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1.2. Service connections and equipment interconnections

1.2.1. At high voltage – Connections to the MV system are made by, and are the responsibility of the utility – Connections between the MV switchgear and the transformers may be:

By short copper bars where the transformer is housed in a panel forming part of the MV switchboard By single-core screened cables with synthetic insulation, with possible use of plugin type terminals at the

transformer

1.2.2. At low voltage

– Connections between the LV terminals of the transformer and the LV switchgear may be: Single-core cables Solid copper bars (circular or rectangular section) with heat-shrinkable insulation

1.2.3. Metering (see Fig. B33)

– Metering current transformers are generally installed in the protective cover of the power transformer LV terminals, the

cover being sealed by the supply utility – Alternatively, the current transformers are installed in a sealed compartment within the main LV distribution cabinet – The meters are mounted on a panel which is completely free from vibrations – Placed as close to the current transformers as possible, and – Are accessible only to the utility.

1.2.4. Earthing circuits

– The substation must include an earth electrode for all exposed conductive parts of electrical equipment in the substation and exposed extraneous metal including: Protective metal screens veinforcing rods in the concrete base of the substation

1.2.5. Substation lighting

– Supply to the lighting circuits can be taken from a point upstream or downstream of the main incoming LV circuit-

breaker. In either case, appropriate overcurrent protection must be provided. A separate automatic circuit (or circuits) is (are) recommended for emergency lighting purposes.

– Operating switches, pushbuttons, etc. are normally located immediately adjacent to entrances. – Lighting fittings are arranged such that:

Switchgear operating handles and position indication markings are adequately illuminated All metering dials and instruction plaques and so on, can be easily read




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1.2.6. Materials for operation and safety

– According to local safety rules, generally, the substation is provided with: Materials for assuring safe exploitation of the equipment including:

• Insulating stool and/or an insulating mat (rubber or synthetic) • A pair of insulated gloves stored in an envelope provided for the purpose • A voltage-detecting device for use on the MV equipment • Earthing attachments (according to type of switchgear)

Fire-extinguishing devices of the powder or CO2 type Warning signs, notices and safety alarms:

• On the external face of all access doors, a DANGER warning plaque and prohibition of entry notice, together with instructions for first-aid care for victims of electrical accidents.

2. Outdoor substations

2.1. Outdoor substation with prefabricated enclosures

– A prefabricated MV/LV substation complying with IEC 62271-202 standard includes :

Equipment in accordance with IEC standards

A type tested enclosure, which means during its design; it has undergone a battery of tests (see Fig. B37):

• Degree of protection • Functional tests • Temperature class • Non-flammable materials • Mechanical resistance of the

enclosure • Sound level • Insulation level • Internal arc withstand • Earthing circuit test • Oil retention, …

Main benefits are :

• Safety: • For public and operators thanks to a high reproducible quality level • Cost effective: • Manufactured, equipped and tested in the factory • Delivery time • Delivered ready to be connected.




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2.2. Outdoor substations without enclosures (see Fig. B39) – These kinds of outdoor substation are common in some countries,

based on weatherproof equipment exposed to the elements. – These substations comprise a fenced area in which three or more

concrete plinths are installed for: A ring-main unit, or one or more switch-fuse or circuit-

breaker unit(s) One or more transformer(s), and One or more LV distribution panel(s).

2.3. Pole mounted substation

2.3.1. Field of application

– These substations are mainly used to supply isolated rural consumers from MV overhead line distribution systems.

2.3.2. Constitution

– In this type of substation, most often, the MV transformer protection is provided by fuses. – Lightning arresters are provided, however, to protect the transformer and consumers as shown in Figure B40.

2.3.3. General arrangement of equipment

– As previously noted the location of the substation must allow easy access, not only for personnel but for equipment

handling (raising the transformer, for example) and the maneuvering of heavy vehicles.




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46. 89BInsulation systems are rated by standard NEMA classifications according to maximum

allowable operating temperatures. Explain.

AAnnsswweerr Insulation systems are rated by standard NEMA (National Electrical Manufacturers Association) classifications

according to maximum allowable operating temperatures as follows:

Temperature Tolerance Class

Maximum Operation Temperature Allowed

Allowable Temperature Rise at full load - 1.0 service factor motor 1)

Allowable Temperature Rise - 1.15 service factor motor 1)

oC oF oC oC A 105 221 60 70 B 130 266 80 90 F 155 311 105 115 H 180 356 125 -

– T(oF) = [T(oC)](9/5) + 32 – 1) Allowable temperature rises are based upon a reference ambient temperature of 40oC. Operation temperature is reference temperature + allowable temperature rise + allowance for "hot

spot" winding. Example Temperature Tolerance Class F: 40oC + 105oC + 10oC = 155oC. – In general a motor should not operate on temperatures above the maximums. Each 10oC rise above the ratings may reduce the motor's lifetime by one half. – Temperature Tolerance Class B is the most common insulation class used on most 60 cycle US motors. Temperature Tolerance Class F is the most common for international and 50 cycle

motors

47. 90BDifferentiate between:

o 91BDirectional & diffuse lighting.

o 92BSymmetric & asymmetric lighting.

o 93BDirect, indirect lighting & Direct-indirect lighting.

AAnnsswweerr Directional lighting:

– Lighting provided on the work plane or on an object that is predominantly from a preferred direction.

Diffused lighting: – Lighting provided on the work plane or on an object that is not incident predominantly from any particular direction

Symmetric & asymmetric lighting:

Direct lighting:

– Lighting involving luminaries that distribute 90 to 100% of the emitted light in the general direction of the surface to be illuminated. The term usually refers to light emitted in a downward direction

Indirect lighting: – Lighting involving luminaries that distribute 90 to 100% of the emitted light upward.




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Direct-indirect lighting: – A variant of general diffuse lighting in which the luminaires emit little or no light at angles near the horizontal. – For example -a room of dimensions: Length: 4.0 m, Width: 6.2 m, Height: 3.0 m and Reflection factor: 70% / 50% /20%

Direct Lighting Indirect Lighting Direct-indirect Lighting

Luminaries Type used: Luminaries Type used: Luminaries Type used: Matt louver 2/35, T16 Uplight 3/55, TC-L ID matt louver 2/35, T16

48. 94BIn case of presence of 2 sockets back to back in two different rooms. Can we put them

directly back to back or we should leave a distance between them?

AAnnsswweerr There should be a horizontal distance not less than 150 mm between the 2 sockets placed back to back in 2 different rooms

in order to ensure that no sound will transfer between the 2 rooms through them.




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49. 95BWhat is the difference between demand factor & diversity factor?

AAnnsswweerr Demand factor:

– Is the ratio of the maximum demand of a system, or part of a system, to the total connected load on the system, or part of the system, under consideration. This factor is always less than unity.

Diversity factor: – Is the ratio of the sum of the individual maximum demands of the various subdivisions of a system, or part of a system,

to the maximum demand of the whole system, or part of the system, under consideration. This factor generally varies between 1.00 and 2.00.

50. 96BWhat are the different methods of starting motors? State the difference among them? State

Applications?

AAnnsswweerr

Direct Online (DOL) Star- Delta Auto Transformer Soft Starter Horse Power <= 20hp > 20hp & <= 80hp > 20hp & <= 100hp > 50hp Line Voltage 100% 33% 40/65/80% Adjustable, 25 to 75% Starting Current Istarting = 5 to 6 In Istarting = 2.5 to 6 In Istarting = 2In Istarting = 1.5 In Peak Starting Torque as % of DOL equivalent

100% 33% 40/65/80% Adjustable 10 to 70%

Peak Starting Torque 0.6 to 1.5 Tn 0.2 to 0.5 Tn 0.4 to 0.85 Tn Adjustable, 0.1 to 0.7 Tn

Advantages

- Simple Starter - Low Cost - High Starting Torque

-Simple Economic Starter

-Good Starting Torque/current performance

- Good starting torque/current performance

- Possibility of adjusting starting parameters

- No break in supply to motor during starting

- Parameters are fully adjustable during ommissioning

- Compact - Solid State (Electronic) - Easily adapted to the application

Applications

- Small machines may often be started on full load

- Machines starting on no load

- Good starting (small centrifugal pumps, fans etc)

- High Inertia machines where a reduction of starting current/torque is required

- Machines requiring very smooth starting (centrifugal pumps & fans, conveyors, etc)

51. 97BIf we have a big room & contain many sockets which will need about 5 branch circuits.

Can we feed these circuits from different phases? Why?

AAnnsswweerr For any room with area 50 m2 or less. All branch circuits for sockets must be fed from the same phase in order not to obtain

380V between two sockets in case of touching to different phases. In case of room more than 50 m2 and it is necessary to use different phases. So we can, but in this case we should divide the

rooms into areas and each phase will feed separate area in order to decrease the probability of obtaining 380V.




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52. 98BHow can you earn LEED certifications for new constructions? What are the LEED ratings?

AAnnsswweerr To earn LEED for New Construction certification, the applicant project must satisfy all of the prerequisites and a minimum

number of points to attain the established LEED for New Construction project ratings as listed below. Having satisfied the basic prerequisites of the program, applicant projects are then rated according to their degree of

compliance within the rating system. All projects will need to comply with the version of LEED for New Construction that is current at the time of project registration.

LEED for New Constructions Ratings:

– Certified 26-32 points – Silver 33-38 points – Gold 39-51 points – Platinum 52-69 points

53. 99BIf you have a refrigerator or A/C or any other motor equipment that works on 50Hz, can

you make it work on 60Hz Power Supply?

AAnnsswweerr Effect of Change in Supply Frequency on Torque and Speed

– The change in supply frequency hardly occurs in large distribution systems used on land. If there are some major

disturbances or very heavy load fluctuating continuously, then there might be a minimal frequency variation. But large frequency variations are possible on electrical systems used on board ships and emergency supply systems for factories and hospitals. Such large frequency variations are possible on low power systems where diesel engines and gas turbines are used as prime movers.

– The relation between the speed of the motor and its frequency is given by the expression N = 120f/P. – From this expression, it is evident that the speed of the motor is directly proportional to the supply frequency. Thus any

decrease or increase in frequency will affect the speed of the motor. Let us now analyze what exactly happens when a motor of 50Hz made to run with 60Hz supply and vice-versa.

Analysis 1: When a 50 Hz motor is made to run on 60 Hz supply:

– It is general practice in several countries to have all house-hold items and equipments rated for 50 Hz supply. So when such small domestic devices are connected to a 60 Hz supply, they cause a severe problem. For better understanding, let us visualize this small calculation:

– [(60Hz – 50 Hz)/ 50 Hz] * 100 = 20 %. – Thus all such equipments run 20 % faster than their normal rated speed. This is not safe for the equipment as the

insulations may be rated for lesser capacity and windings may burn-out. To run safely, we either require a reduction gear or an expensive 50 Hz source.

– Also this 50 Hz motor will operate perfectly on a 60 Hz supply provided its supply voltage is stepped-up.

60 Hz/ 50 Hz = 6/5 * 100 = 120 %.

Analysis 2: When a 60 Hz motor is made to run on 50 Hz supply: – It is same as the above, but instead of stepping-up the supply voltage, it is necessary to step-down the supply voltage.

50Hz/ 60 Hz = 5/6 * 100 = 80 %

http://www.brighthub.com/engineering/electrical/articles/46495.aspx




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54. 100BYou have a project consists of 960 small villas (dwelling units). The connected load for each

villa (dwelling unit) is 60 KVA. Estimate the number of pillars, transformers &

distributors required for this project. Considering that only 400A pillars & 1000KVA

Transformers ratings are available. System Voltage is 13..8KV/380-220V. Draw schematic

single line diagram to what you obtained.

AAnnsswweerr 1. Using SCECO Method:

According to SEC Distribution Materials Specification “DPS”

Demand Factor “D.F. “ = 0.5 (For Residential Customers). Therefore; Demand load for each villa (dwelling unit) = Connected load of one villa x 0.5 = 60 x 0.5 = 30 KVA.

Consider 4 customers to be fed by one pillar Therefore; Connected load for one pillar = 4 x 60 = 240 KVA. For check: 240 x 1000 / (380 x √3) = 365A < 400A (OKAY). Therefore; Total number of pillars required = 960 / 4 = 240 Pillar.

According to SEC Distribution Materials Specification “DPS” Diversity Factor “DvF “ = 1.25 / (0.67 + (0.33/ (√ N)).

Consider 48 customers in the group on one transformer Therefore; Diversity Factor “DvF “ = 1.25 / (0.67 + (0.33/ (√ 48)) = 1.74 Total Demand load on transformer = (number of villas x demand load for one villa) / DvF = (48 x 30) / 1.74 = 825KVA (82.5% of 1000KVA Transformer) (OKAY) Therefore; Total number of transformers required = 960 / 48 = 20 Transformer. Therefore; Total number of pillars per transformer required = 240 / 20 = 12 Pillar.

Consider 10 Transformers per loop Therefore; Total number of loops required = 20 / 10 = 2 Loops. Therefore; Only one-four loop distributor (i.e: with 2 spare loops) is required. Consists of 12 cubicles: 2 incoming. 8 outgoings (4 C.B’s for the 2 loops & 4 C.B’s for 2 spare loops for other loads). 1 bus-riser. 1 bus-coupler.

SEC Distribution Materials Specification “DPS”




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2. Using NEC Method:

According to NEC demand factors for different loads Demand Factor “D.F. “ = 0.5 Therefore; Demand load for each villa (dwelling unit) = Connected load of one villa x 0.5 = 60 x 0.5 = 30 KVA.

Consider 4 customers to be fed by one pillar Therefore; Connected load for one pillar = 4 x 60 = 240 KVA. For check: 240 x 1000 / (380 x √3) = 365A < 400A (OKAY). Therefore; Total number of pillars required = 960 / 4 = 240 Pillar.

Consider 48 customers in the group on one transformer According to NEC Table 220.32

Therefore; Demand factor for 48 dwelling unit is 26% Total Demand load on transformer = Total Connected load for 48 villas x DF = (48 x 60) x 0.26 = 748KVA (74.8% of 1000KVA Transformer) (OKAY) Therefore; Total number of transformers required = 960 / 48 = 20 Transformer. Therefore; Total number of pillars per transformer required = 240 / 20 = 12 Pillar.

Consider 10 Transformers per loop Therefore; Total number of loops required = 20 / 10 = 2 Loops. Therefore; Only one-four loop distributor (i.e: with 2 spare loops) is required. Consists of 12 cubicles: 2 incoming. 8 outgoings (4 C.B’s for the 2 loops & 4 C.B’s for 2 spare loops for other loads). 1 bus-riser. 1 bus-coupler.




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Pillars (Typical to 240 nos.):

Package Substation – Ring Main Unit (Typical to 20 nos.):

Distributor Loops:




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55. 101BWhat are the IEC Switchboard Forms for Internal Configuration? State the difference?

AAnnsswweerr Separation of functional units within the assembly is provided by forms that are specified for different types of operation. The various forms are numbered from 1 to 4 with variations labeled “a” or “b”. Each step up (from 1 to 4) is cumulative,

i.e. a form with a higher number includes the characteristics of forms with lower numbers. The standard distinguishes: Form 1, Form 2a, Form 2b, Form 3a, Form 3b, Form 4a, Form 4b

– Form 1: No separation – Form 2: Separation of bus-bars from the functional units – Form 3: Separation of bus-bars from the functional units and separation of all functional units, one from another, except

at their output terminals – Form 4: As for Form 3, but including separation of the outgoing terminals of all functional units, one from another

56. 102BWhat is distance between down conductors in lightning system design? How can you design

the mesh?

o 103BFor building less than 15M height

o 104BFor building 80M height.

AAnnsswweerr As per BS 6651 (Protection of structures against lightning):

– A mesh of 10m x 20m is considered sufficient, giving a maximum

distance from any part of the roof to the nearest conductor of 5m. – On high risk structures such as explosive factories, no part of the

roof should be more than 2.5m from an air termination conductor. This is generally achieved by applying a 5m x 10m mesh to the roof.

– There should be one down conductor for every 20m of the building perimeter at roof or ground level.

– If the building is above 20m in height or of an abnormal risk this distance should be reduced to 10m.




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57. 105BGive a small brief summary for each of these types of lamps

o 106BIncandescent

o 107BHalogen

o 108BFluorescent

o 109BCompact Fluorescent Lamps

o 110BLED (Light Emitting Diodes)

o 111BHigh-Intensity Discharge Lamps

o 112BLow-Pressure Sodium Lamps

AAnnsswweerr Incandescent:

– These are the standard bulbs that most people are familiar with. Incandescent bulbs work by

using electricity to heat a tungsten filament in the bulb until it glows. The filament is either in a vacuum or in a mixture of argon/nitrogen gas. Most of the energy consumed by the bulb is given off as heat, causing its Lumens per Watt performance to be low. Because of the filament's high temperature, the tungsten tends to evaporate and collect on the sides of the bulb. The inherent imperfections in the filament causes it to become thinner unevenly. When a bulb is turned on, the sudden surge of energy can cause the thin areas to heat up much faster than the rest of the filament, which in turn causes the filament to break and the bulb to burn out.

– Incandescent bulbs produce a steady warm, light that is good for most household applications. A standard incandescent bulb can last for 700-1000 hours, and can be used with a dimmer. Soft white bulbs use a special coating inside the glass bulb to better diffuse the light; but the light color is not changed.

Halogen:

– Halogen bulbs are a variation of incandescent bulb technology. These bulbs work by passing electricity through a tungsten filament, which is enclosed in a tube containing halogen gas. This halogen gas causes a chemical reaction to take place which removes the tungsten from the wall of the glass and deposits it back onto the filament. This extends the life of the bulb. In order for the chemical reaction to take place, the filament needs to be hotter than what is needed for incandescent bulbs. The good news is that a hotter filament produces a brilliant white light and is more efficient (more lumens per watt).

– The bad news is that a hotter filament means that the tungsten is evaporating that much faster. Therefore a denser, more expensive fill gas (krypton), and a higher pressure, are used to slow down the evaporation. This means that a thicker, but smaller glass bulb (envelope) is needed, which translates to a higher cost. Due to the smaller glass envelope (bulb), the halogen bulb gets much hotter than other bulbs. A 300 watt bulb can reach over 300 degrees C. Therefore attention must be paid to where halogen bulbs are used, so that they don't accidentally come in contact with flammable materials, or burn those passing by.

– Care must be taken not to touch the glass part of the bulb with our fingers. The oils from our fingers will weaken the glass and shorten the bulb’s life. Many times this causes the bulb to burst when the filament finally burns out.

– To summarize, the halogen has the advantage of being more efficient (although not by much) and having longer life than the incandescent bulb. They are relatively small in size and are dimmable. The disadvantages are that they are more expensive, and burn at a much higher temperature, which could possibly be a fire hazard in certain areas.

Traditional

Incandescent Bulbs

Various types of halogen

bulbs




74

Fluorescent:

– These bulbs work by passing a current through a tube filled with argon gas and mercury. This produces ultraviolet radiation that bombards the phosphorous coating causing it to emit light (see: “How Fluorescents Work”). Bulb life is very long - 10,000 to 20,000 hours. Fluorescent bulbs are also very efficient, producing very little heat. A common misconception is that all fluorescent lamps are neutral or cool in color appearance and do not have very good color-rendering ability. This is largely due to the fact that historically the "cool white" fluorescent lamp was the industry standard. It had a very cool color appearance (4200K) and poor CRI rating (62). This is simply no longer the case. Regarding color, a wide variety of fluorescent lamps (T12, T8, T5, etc.), using rare-earth tri-phosphor technology, offer superior color rendition (as high as 95) and a wide range of color temperature choices (from 2700K to 5000K and higher). Fluorescent bulbs are ideal for lighting large areas where little detail work will be done (e.g. basements, storage lockers, etc.). With the new type bulbs, and style of fixtures coming out, fluorescents can be used in most places around the home. Most fluorescent bulb cannot be used with dimmers.

– Note that fluorescent bulbs need components called ballasts to provide the right amount of voltage. There are primarily two types - magnetic and electronic. Electronic ballasts solve some of the flickering and humming problems associated with magnetic ballast, and are more efficient, but cost more to purchase. Some ballasts need a “starter” to work along with it. Starters are sort of small mechanical timers, needed to cause a stream of electrons to flow across the tube and ionize the mercury vapor

– On tube type fluorescent bulbs, the letter T designates that the bulb is tubular in shape. The number after it expresses the diameter of the bulb in eighths of an inch.

Compact Fluorescent Lamps:

– Compact Fluorescent Lamps (CFLs) are a modern type of light bulbs, that work like fluorescent bulbs, but in a much smaller package. Similar to regular fluorescent bulbs, they produce little heat and are very efficient. They are available to fit screw type base fittings and pin type (snap-in). Most CFLs either consist of a number of short glass sticks, or two or three small tubular loops. Sometimes, they are enclosed in a glass bowl, made to look similar to a regular incandescent bulb. Most CFLs cannot be used with dimmers. They normally last up to 10,000 hours.

Approximate Equivalents to Incandescent Bulbs CFL Incandescent

7–10 Watts 40 Watts 15-18 Watts 60 Watts

20 Watts 75 Watts 20-25 Watts 100 Watts

32 Watts 150 Watts

LED (Light Emitting Diodes):

– Light Emitting Diodes (LED) are bulbs without a filament, that are low in power consumption

and have a long life span. LEDs are just starting to rival conventional lighting, but unfortunately they just don't have the output (lumen) needed to completely replace incandescent, and other type, bulbs just yet. Never the less, technology is advancing everyday, and it will not be long until the LED bulb will be the bulb of choice for most applications in the home and work place.

Fluorescent tube

bulbs

Compact Fluorescent (CFL)

PL type bulb (CFL)

Light Emitting Diodes




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High-Intensity Discharge Lamps:

– High Pressure Sodium (HPS), Metal Halide, Mercury Vapor and Self-Ballasted Mercury Lamps are all high intensity discharge lamps (HID). With the exception of self-ballasted lamps, auxiliary equipment such as ballasts and starters must be provided for proper starting and operation of each type bulb. Compared to fluorescent and incandescent lamps, HID lamps produce a large quantity of light from a relatively small bulb.

– HID lamps produce light by striking an electrical arc across tungsten electrodes housed inside a specially designed inner glass tube. This tube is filled with both gas and metals. The gas aids in the starting of the lamps. Then, the metals produce the light once they are heated to a point of evaporation.

– Standard high-pressure sodium lamps have the highest efficacy of all HID lamps, but they produce a yellowish light. High-pressure sodium lamps that produce a whiter light are now available, but efficiency is somewhat sacrificed. Metal halide lamps are less efficient but produce a whiter, more natural light. Colored metal halide lamps are also available. HID lamps are typically used not only when energy efficiency and/or long life are desired, but also when high levels of light are required over large areas. Such areas include gymnasiums, large public areas, outdoor activity areas, roadways, pathways, and parking lots. Lately, metal halide is successfully being used in residential environments.

Low-Pressure Sodium Lamps: – Low-pressure sodium lamps have the highest efficacy of all commercially available lighting sources. Even though they

emit a yellow light, a low-pressure sodium lamp shouldn't be confused with a standard high-pressure sodium lamp. Low-pressure sodium lamps operate much like a fluorescent lamp and require a ballast. There is a brief warm-up period for the lamp to reach full brightness.

– With a CRI of 0, low-pressure sodium lamps are used where color rendition is not important but energy efficiency is. They're commonly used for outdoor, roadway, parking lot, and pathway lighting

58. 113BWhat is DALI?

AAnnsswweerr DALI stands for “Digital Addressable Lighting Interface”.

– DALI is an industrial standard for the digital control of

dimmable electronic ballasts, LV Halogen transformers and other technical lighting components.

– Up to 64 ballasts or luminaires can be individually controlled via a two-wire line/DALI line.

– DALI can provide Flexible Lighting management. – DALI is fully compatible with building management systems. – DALI is standardised digital interface for dimmable luminaires.

Mercury Bulb

Metal Halide Bulb




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59. 114BEstimate the circuit breaker, disconnecting switch and cable size for:

o 115BLighting load 3000VA single phase. Feeder wire length is 40 m.

o 116BOutdoor A/C load 3000VA single phase. Feeder wire length is 40 m.

o 117BPanel Board with three single phase loads (3000VA, 4000VA, 2000VA). Feeder cable

length is 200 m.

o 118BWhere; the system voltage is 380/220V; suppose that total cable de-rating factors is

0.8; suppose cable routing in pipes.

o 119BUse the following cable catalogue cuts for sizing cables.

120B




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78




79

AAnnsswweerr 1. Lighting load 3000VA single phase. Feeder wire length is 40 m.

In = Active Power / Voltage = 3000 / 220 = 13.6 Amp.

As per NEC Article 210.20: Conductors - Minimum Ampacity & Size

Wire Ampacity = 13.6 x 1.25 = 17 Amp. Wire Ampacity with de-rating factors = 17 / 0.8 = 21.25Amp. Therefore, from cable catalogue.

The required wire size is 4 mm2 CU single core cable – PVC insulated. Check: VD% = Load Current (Amp) x Wire Length (Meter) x V.D (mv/Amp/Meter) /

Single phase service voltage x1000 /100 VD% = 13.6 x 40 x 7.83 / 220 x 1000 / 100 = 1.93% (Accepted).

As per NEC Article 215.3: Over-current Protection Circuit breaker size = 13.6 x 1.25 = 17 Amp. Therefore, from C.B & switches catalogues

The Required C.B size is 20A (single phase). 20A normal single pole switch can be used for this lighting load.

2. Outdoor A/C load 3000VA single phase. Feeder wire length is 40 m.

In = Active Power / Voltage = 3000 / 220 = 13.6 Amp.

As per NEC Article 440.32 Single Motor-Compressor Wire Ampacity = 13.6 x 1.25 = 17 Amp. Wire Ampacity with de-rating factors = 17 / 0.8 = 21.25Amp. Therefore, from cable catalogue.

The required wire size is 4 mm2 CU single core cable – PVC insulated. VD% = Load Current (Amp) x Wire Length (Meter) x V.D (mv/Amp/Meter) /

Single phase service voltage x1000 /100 VD% = 13.6 x 40 x 7.83 / 220 x 1000 / 100 = 1.93% (Accepted)

As per NEC Article 440.22(A) Rating or Setting for Individual Motor-Compressor Circuit breaker size = 13.6 x 1.75 = 23.8 Amp. Therefore, from C.B catalogue

The required C.B size is 25A (single phase).

As per NEC Article 430.110: Ampere Rating and Interrupting Capacity Disconnecting switch size = 13.6 x 1.15 = 15.64 Amp. Therefore, from D.S catalogue.

The required fusible D.S size is 30A, (2 Pole), [NEMA-3R]. (i.e. smallest size for fusible D.S)




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3. Panel Board with three single phase loads (3000VA, 4000VA, 2000VA). Feeder cable length is 200 m. In = Active Power / Voltage = (3000 + 4000 + 2000) / √3 x 380 = 13.6 Amp.

As per NEC Article 210.20: Conductors - Minimum Ampacity & Size Cable Ampacity = 13.6 x 1.25 = 17 Amp. Cable Ampacity with de-rating factors = 17 / 0.8 = 21.25Amp. Therefore, from cable catalogue.

The required cable size is 4x4 mm2 CU multi core cable – PVC/PVC insulated. Check: VD% = Load Current (Amp) x Wire Length (Meter) x V.D (mv/Amp/Meter) /

Three phase service voltage x1000 /100 VD% = 13.6 x 200 x 7.741 / 380 x 1000 / 100 = 5.54% (Not Accepted). Using 4x6 mm2 CU multi core cable – PVC/PVC insulated. VD% = 13.6 x 200 x 5.199 / 380 x 1000 / 100 = 3.72% (Not Accepted). Using 4x10 mm2 CU multi core cable – PVC/PVC insulated. VD% = 13.6 x 200 x 3.101 / 380 x 1000 / 100 = 2.22% (Accepted).

As per NEC Article 215.3: Over-current Protection Circuit breaker size = 13.6 x 1.25 = 17 Amp. Therefore, from C.B catalogue The required C.B size is 20A (3phase).

60. 121BWhen we should use a remote radiator for a diesel engine generator?

AAnnsswweerr When there is no location to put radiator beside generator or no good ventilation. For example: if the generator is located in

a small room at basement floor where no good ventilation exists.

61. 122BCalculate capacitor rating required to improve the power factor of a motor P=500KW from

P.F1= 0.8 to P.F2= 0.9?

AAnnsswweerr

Qc = P (tanØ1- tanØ2) = 500 (tan 36.86 - tan 25.84) = 133 KVAR




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62. 123BWhat is EIB?

AAnnsswweerr

EIBA is the (European Installation Bus Association) merged with two other European organizations to form the Konnex

Association, KNX.

Bus Structure & Topology / Technology: (i-bus® EIB)




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Applications:

– Lighting/Dimming Control - Audio/Video Control - Curtains/Shutters Control - Temperature Control - Security control -

Visualization and display - Door Access.

Utilization Area:

– Stadiums / Leisure parks - Hotels / Resorts - Shopping Malls - Public Buildings / Museums - Industrial Facilities - Banks / Offices - Schools / Universities - Hospitals / Elderly homes - Residential - Buildings/Towers - Villas / Luxury Condominium.

Energy Savings with EIB:

– Longer lamp life - Fewer maintenance costs - Lesser lamp replacements - Lesser heat output to the air-conditioning load - Marketing advantage as a green-energy conservation building.

Operating Costs per Year:

63. 124BCalculate the three phase short circuit current at secondary side of a 1 MVA transformer

13.8KV - 480/227V, 60 Hz; impedance is 6 percent and assuming sustained primary

voltage during fault?

AAnnsswweerr

In a simplified approach, the impedance of the MV system is assumed to be negligibly small, so that: In = P x 103 / √3 Uo = 1000 x 103 / √3 (480) = 1202.8 A Isc = In / Usc = 1202.8 / 0.06 = 20 KA Where:

P: kVA rating of the transformer. Uo: phase-to-phase secondary volts on open circuit. In: nominal current in amps. Isc: short-circuit fault current in amps. Usc: short-circuit impedance voltage of the transformer in %.




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64. 125BWhat are the basic factors would you take into consideration while making lighting design?

AAnnsswweerr Average illumination Uniformity Color rendering Type of control Heat dissipation

65. 126BCalculate the voltage drop of cable with load 32KW - three phase, cu cable C.S.A= 16mm2,

Ra.c= 1.38 ohm/km, X= 0.1068 ohm/km, CosØ = 0.8, cable length =120m, system voltage is

380/220V.

AAnnsswweerr

V = √3* I*L(R cosØ + X sinØ) = 1.732*[(32000/0.8)/380/1.732]* [120/1000]* [(1.38)*0.8 + 0.1068)*0.6] = 14 volt. V.D% = (14/380) * 100 = 3.68%

66. 127BWhat does GFCI & AFCI stands for? What is the difference? State some applications?

AAnnsswweerr GFCI Circuit Breaker

– The ground fault circuit interrupter (GFCI) is required on certain

residential receptacles, such as bathroom receptacles, receptacles located within six feet of a kitchen sink, and outdoor receptacles. The GFCI is designed to interrupt a circuit when a ground fault occurs. Often the GFCI is mounted at the receptacle.

AFCI Circuit Breaker

– GFCI devices are designed to protect a person from getting a shock

when touching an ungrounded appliance. Arc Fault Circuit Interrupters (AFCI), in comparison, protect against a fire being started from an unintended arc. An arc fault occurs when a current-carrying conductor has an arching condition to ground or another conductor. An AFCI device is intended to provide protection from the effects of arc faults by recognizing the characteristics unique to arcing and de-energizing the circuit when an arc fault is detected. The arc generated will cause the AFCI to trip. Arcs normally generated from electric equipment such as a light switch or power drill will not cause the AFCI to trip.

– Arc-Fault Circuit Interrupter protection was first introduced in the 1999 National Electrical Code®. NEC® Article 210.12 and has an effective date of 2002. This requirement applies to all branch circuits that supply 125-volt, single-phase, 15- and 20-amp receptacle outlets installed in dwelling unit bedrooms.




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67. 128BWhat are LPD specified in ANSI/ASHRAE/IESNA Standard 90.1? Can you state the methods

used for computing LPD & give some examples? Does the LPD values specified in ASHRAE

accepted by LEED?

AAnnsswweerr Lighting power density (LPD):

Is the maximum lighting power per unit area of a building classification of space function.

According to LEED reference guide, it recommends LPD values specified in ASHRAE.

According to ANSI/ASHRAE/IESNA Standard 90.1-2007

There are two methods for computing LPD:

1. Lighting Power Densities Using the Building Area Method

The building area method is a simplified approach for demonstrating compliance which shall be used only in the following cases:

a- Projects involving the entire building or b- Projects involving a single, independent, and separate

occupancy in a multi-occupancy building. Use the following steps to determine the interior lighting power allowance by the building area method: I. Determine the appropriate building type from Table

9.5.1 and the allowed lighting power density (watts per unit area) from the building area method column. For building types not listed, selection of a reasonably equivalent type shall be permitted.

II. Determine the gross lighted floor area (square feet) of the building.

III. Multiply the gross lighted floor areas of the building area type(s) times the LPD.

IV. The interior lighting power allowance for the building is the sum of lighting power allowances of all building area types. Trade-offs building area types are permitted provided that the total installed interior lighting power does not exceed the interior lighting power allowance.




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2. Lighting Power Densities Using the Space-by-Space Method Alternative approach that allows greater flexibility. Use the following steps to determine the interior lighting power

allowance by the space by- space method:

I.Determine the appropriate building type from Table 9.3.1.2. For building types not listed, selection of a reasonably equivalent type shall be permitted.

II.For each space enclosed by partitions 80% or greater than ceiling height, determine the gross interior floor area by measuring to the center of the partition wall. Include the floor area of balconies or other projections. Retail spaces do not have to comply with the 80% partition height requirements.

III.Determine the interior lighting power allowance by using the columns designated space-by-space method in Table 9.3.1.2. Multiply the floor area(s) of the space(s) times the allowed lighting power density for the space type that most closely represents the proposed use of the space(s). The product is the lighting power allowance for the space(s). For space types not listed, selection of a reasonable equivalent category shall be permitted.

IV.The interior lighting power allowance is the sum of lighting power allowances of all spaces. Trade-offs among spaces are permitted provided that the total installed interior lighting power does not exceed the interior lighting power allowance.

Additional interior lighting power.

When using the space by space method, an increase in the interior lighting power allowance is allowed for specific lighting functions. Additional power should be allowed only if the specific lighting is installed and automatically controlled separately from the general lighting to be turned off during non business hours. This additional power should be used only for the specified luminaries and shall not be used for any other purpose.

An increase in the interior lighting power allowance is permitted in the following cases:

I.For spaces in which lighting is specified to be installed in addition to the general lighting for the purpose of

decorative appearance such as chandelier type luminaries or sconces or for highlighting are or exhibits provided that the additional lighting power shall not exceed 10.8W/m2 of such spaces.

II.For lighting equipment installed in sales areas and specifically designed and directed to highlight merchandise, calculate the additional lighting power as follows: Additional Interior Lighting Power Allowance = 1000 watts + (Retail Area 1 x 11W/m2) + (Retail Area 2 x 18W/m2)

+ (Retail Area 3 x 28W/m2) + (Retail Area 4 x 45W/m2)

Where

Retail Area 1 = the floor area for all products not listed in Retail Area 2, 3 or 4. Retail Area 2 = the floor area used for the sale of vehicles, sporting goods and small electronics. Retail Area 3 = the floor area used for the sale of furniture, clothing, cosmetics and artwork. Retail Area 4 = the floor area used for the sale of jewelry, crystal and china.




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87

68. 129BWhat is power factor? What are the equipments that create poor power factor? How can you

improve power factor of your system?

AAnnsswweerr Definition of Power Factor:

Power factor is the percentage of electricity that is being used to do useful work. It is defined as the ratio of ‘active or actual power’ used in the circuit measured in watts or kilowatts (W or KW), to the ‘apparent power’ expressed in volt-amperes or kilo volt-amperes (VA or VA).

The apparent power also referred to as total power delivered by utility company has two components.

‘Productive Power’ that powers the equipment and performs the useful work. It is measured in KW (kilowatts) ‘Reactive Power’ that generates magnetic fields to produce flux necessary for the operation of induction

devices (AC motors, transformer, inductive furnaces, ovens etc.). It is measured in KVAR (kilovolt-Ampere-Reactance). Reactive Power produces no productive work.

Equipment Creating Poor Power Factor

Lighting: Incandescent Lamps: The power factor is equal to unity. Fluorescent Lamps: Usually have a low power factor, for example, 50% power factor would not be unusual.

They are sometimes supplied with a compensation device to correct low power factor. Mercury Vapor Lamps: The power factor of the lamp is low; it can vary between 40% to 60%, but the lamps

are often supplied with correction devices.

Distribution Transformer: The power factor varies considerably as a function of the load and the design of the transformer. A completely

unloaded transformer would be very inductive and have a very low power factor.

Electrical Motors: Induction Motors: The power factor varies in accordance with the load. Unloaded or lightly loaded motors

exhibit a low power factor. The variation can be 30% to 90%. Synchronous Motors: Very good power factor when the excitation is properly adjusted. Synchronous motors

can be over excited to exhibit a leading power factor and can be used to compensate a low power system.

Industrial Heating: With resistance, as in ovens or dryers, the power factor is often closed to 100%.

Welding: Electric arc welders generally have a low power factor, around 60%.




88

Other types of machinery or equipment those are likely to have a low power factor include:

Methods of Power Factor Correction: Power factor correction can be made in two ways:

1. Reduce the amount of reactive energy

i. Eliminate unloaded motors and transformers ii. Avoid supplying equipment with voltage in excess of the rated voltage

2. Compensate artificially for the consumption of reactive energy with power factor capacitors. In practice, two type of equipment are available for power factor correction:

i. Rotary Equipment: Phase advancers, synchronous motors and synchronous condensers. Where auto-synchronous motors are employed the power factor correction may be a secondary function.

ii. Capacitors: Power factor correction is achieved by the addition of capacitors in parallel with the connected motor circuits and can be applied at the starter, or applied at the switchboard or distribution panel. Capacitors connected at each starter and controlled by each starter is known as "Static Power Factor Correction" while capacitors connected at a distribution board and controlled independently from the individual starters is known as "Bulk Correction".




89

69. 130BChoose the correct answers if any. What is the purpose of discrimination?

o 131BTo ensure continuity of service

o 132BTo only trip the device just above the faulty feeder

o 133BTo increase servicing time for trouble-shooting

o 134BTo increase productivity

AAnnsswweerr To ensure continuity of service To only trip the device just above the faulty feeder To increase productivity

70. 135BCompare between magnetic ballast & electronic ballast.

AAnnsswweerr

Magnetic Ballast Electronic Ballast Flickering ignition Smooth rapid start Disturbing lamp flicker Flicker free No light regulation Light regulation Annoying humming of the coil Silent Not controlled end of life of lamps Automatic switch-off of lamps at end of life Energy costs relatively high compared to HF Energy savings compared to conventional Low initial cost High initial cost Very high operating cost Low operating cost

71. 136BWhat are the trade sizes of conduits?

AAnnsswweerr

Trade Size (inch) ⅜ ½ ¾ 1 1¼ 1½ 2 2½ 3 3½ 4 5 6 Trade size (mm) 10 16 20 25 32 40 50 63 75 90 110 130 150

72. 137BIn an installation, circuit breaker CB1 is placed upstream from circuit breaker CB2. A

short-circuit current occurs downstream from CB2. CB2 opens and CB1 stays closed. This is

a case of:

AAnnsswweerr Discrimination.




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73. 138BFor each of the faults A, B, C in the diagram, say whether or not the protection device

opens:

139B AAnnsswweerr

74. 140BThe fault current downstream from circuit breaker CB5 is 400 A. With total discrimination,

which circuit breakers will open?

AAnnsswweerr CB5

75. 141BState which statement is true and which is false: Standard IEC 60364: Section-3-32 & 4-

48 on premises with a risk of fire

o 142BImposes use of a 500mA RCD device.

o 143BRecommends use of a TT or IT system for the electrical installation on such premises.

o 144BProhibits use of a TN-C system.

o 145BIn TT, IT and TN-S systems, a 300mA RCD eliminates the risk of fire.

AAnnsswweerr All statements are true.

76. 146BWhat are The Main Functions of Earthing/Grounding Systems?

AAnnsswweerr Protection for human against any leakage current Protection for equipment against any leakage current




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77. 147BWhat is the difference between (Ics) & (Icu) of C.B? Which one is considered in design?

AAnnsswweerr As per IEC 60947-2:

– Icu: rated ultimate short circuit breaking capacity.

The rated breaking capacity (Icu) is the maximum fault-current a circuit breaker can successfully interrupt

safely for only one time. After that C.B should be tested. For MCB’s and MCCB’s the C.B should be replaced. While, for ACB’s only the contacts or damaged parts should be replaced. The probability of such a current occurring is extremely low, and in normal circumstances the fault-currents are

considerably less than the rated breaking capacity (Icu) of the CB. On the other hand it is important that high currents (of low probability) be interrupted under good conditions, so that the CB is immediately available for reclosure, after the faulty circuit has been repaired.

– Ics: rated service short circuit breaking capacity. Ics is expressed as a percentage of Icu, viz: 25, 50, 75, 100% for industrial circuit breakers. It’s the short circuit value that C.B could with stand for three successive times (disconnect 3 minutes among

each). But, after that C.B should be tested. Whenever, Ics percentage of Icu is increased. The ability of C.B to withstand more short circuit values is increased.

– We consider Ics as short circuit capacity in design.

78. 148BState the functions of circuit breaker.

AAnnsswweerr Protect cables against overloads and short circuits Let the nominal current flow without problems. Open and close a circuit under rated current. Protect against insulation faults (with an integrated earth leakage device).

79. 149BWhat is more danger on the human body AC current or DC current & why? What is the

effect of AC current on the human body?

AAnnsswweerr AC current is more danger than AC current because the

human heart is affected more by fluctuation in frequency (i.e sine wave of AC current) rather than DC current which is constant (frequency is zero).




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80. 150BIn order to select the right circuit breaker. What are the Criteria’s of choice that should be

followed?

AAnnsswweerr "Basic" Criteria:

– Rating I, U, F, ... – Breaking capacity – Number of poles (grounding system). – Standards (IEC, UL, JIS, ...) – Type of loads to be protected (cable, bus-bar, generator, motor, direct current devices).

"Dependability" Criteria: – Earth leakage protection – Isolating function – Positive break indication – Front face double insulation – Locking – Interlocking – Limiting technology

"Continuity of Service" Criteria: – Selectivity – Draw-out possibility – Maintainability

"Performing" Criteria: – Cascading – Reverse feeding without de-rating – Field installable auxiliaries

"Comfort" Criteria: – Simple to install, easy to work with – Evolutive network (modular system) – Network monitoring, communication

81. 151BCompare between earthing systems from the point of:

o 152BProtection of people.

o 153BProtection against fire.

o 154BEase of implementation

o 155BContinuity of service

o 156BUpgradable installation.

o 157BCost saving

AAnnsswweerr




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82. 158BWhat are the Benefits of improving Power Factor?

AAnnsswweerr Reduce Utility Cost. Optimize Equipment Utilization. Improve Reliability:

– Avoids the overload of the network. – Decreases Voltage Drops. – Masters polluted networks level of harmonics and avoids resonance cases.

83. 159BHow the penalty on power factor is calculated?

AAnnsswweerr For 0.9 < cos (φ) < 0.92 ------- No penalty No Bonus. For cos (φ) > 0.92 ------- Bonus. (For a maximum of 0.95). For cos (φ) < 0.9 ------- Penalty (The company will be charged for reactive power).

84. 160BWhat are the different types of armoured cables which are more expensive, which one can

withstand more mechanical load, is the 2 types are accepted by BS & IEC?

AAnnsswweerr

Tag Stands for Cost Mechanical Strength Standards

SWA Steel Wire Armoured. More expensive.

Withstand about twice mechanical load of STA.

Accepted by BS (BS5467 and BS6724) & IEC.

STA Steel Tape Armoured. Less expensive.

Withstand less mechanical load than SWA.

Accepted by BS only.

AWA Aluminum Wire Armoured. More expensive.

Withstand about twice mechanical load of STA.

Accepted by BS (BS5467 and BS6724) & IEC.

ATA Aluminum Tape Armoured. Less expensive.

Withstand less mechanical load than SWA.

Accepted by BS only.

85. 161BState the Cable Insulation Temperature Limits (Continuous Operating Temperature,

Emergency Temperature & Short Circuit Temperature) for XLPE & PVC

AAnnsswweerr

Cable Insulation Temperature Limits Type of Insulation PVC XLPE Continuous Operating Temperature (ºC) 70 ºC 90 ºC Emergency Temperature (ºC) 105 ºC 130 ºC Short Circuit Temperature (ºC) 160 ºC 250 ºC

86. 162BWhat does mean by day lighting?

AAnnsswweerr The luminous flux from sun plus sky at a specific location, time, date, and sky condition




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87. 163BTransformers are classified into various categories, according to their: Use, Cooling method,

Insulating medium. State & explain each classification. Which is better & why?

AAnnsswweerr 1. Classification of transformers according to the use

1.1. Distribution Transformers:

– They are used in the distribution networks in order to transmit energy from the medium voltage (MV) network to the low voltage (LV) network of the consumers. Their power is usually ranging from 50 to 2000 kVA.

1.2. Power Transformers: – They are used in the high-power generating stations or voltage step up and in the transmission substations for voltage

step up or step down. Usually their power is bigger than 2 MVA.

2. Classification of transformers according to the cooling method 2.1. For dry type transformers which are air cooled, ANSI/IEEE Standard C57.12.01 provide the following

designations:

2.1.1. Ventilated self-cooled class: Class AA 2.1.2. Ventilated forced-air-cooled class: Class AFA 2.1.3. Ventilated self-cooled / forced-air-cooled class: Class AA/FA 2.1.4. Non-Ventilated self-cooled class: Class ANV 2.1.5. Sealed -self-cooled class: Class GA

2.2. Liquid filled transformers offer a few more options for cooling. ANSI/IEE Standard C57.12.00 defines a 4 digit code

to describe the cooling attributes of the transformer.Where

2.2.1. First Letter: Internal Cooling medium in contact with the winding. O = mineral oil or synthetic insulation fluid with a fire point ≤ 300°C K = insulating fluid with a fire point > 300°C L = insulating liquid with no measurable fire point.

2.2.2. Second Letter: Circulation mechanism for internal cooling medium. N = Natural convection flow through cooling equipment and in windings F = Forced circulation through cooling equipment and natural convention flow in the

windings (also called "directed flow") D = Forced circulation through cooling equipment, directed from the cooling equipment

into at least the main windings 2.2.3. Third Letter: External Cooling medium.

A = Air W = Water

2.2.4. Fourth Letter: Circulation mechanism for external cooling medium. N = Natural convection F = Forced circulation (Fans (air cooling), pumps (water cooling))

2.2.5. Examples

ONAN: Oil Natural Air Natural. ONAF: Oil Natural Air Force KNAF: Insulating fluid with a fire point Natural Air Force OFAN: Oil Forced Air Natural. OFAF: Oil Forced Air Forced. OFWF: Oil Forced Water Forced. Combinations: ONAN/ONAF, ONAN/OFAN or ONAN/OFAF is also applicable.




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3. Classification of transformers according to the insulating medium:

3.1. Oil-Immersed Type Transformers:

– The insulating medium is mineral oil.

3.2. Silicon Liquid Transformers: – This type is used when the technical requirement of plants need oil immersed type

transformers, and in the mean while for the ambient there is the necessity of fire proof and security requirements. Synthetic (silicon) oil or Vegta is new technology.

3.3. Dry Type Transformers: – The cooling is implemented with natural air circulation and the

windings are usually insulated with materials of H or F class. The materials of H class are designed in order to operate, in normal conditions, under temperatures up to 180ºC and the materials of F class under temperatures up to 155ºC.

3.4. Cast Resin Type Transformers: – The resin type transformer is a dry type transformer insulated

with epoxy resin cast under vacuum. Their power is usually ranging from 5 to 2500 kVA.

88. 164BWhat are the important factors required for selecting a suitable cable to transport electrical

energy from the power station to the consumer?

AAnnsswweerr Maximum Operating Voltage Insulation Level Frequency Load to be carried Magnitude & duration of possible overload Magnitude & duration of short circuit current Voltage drop Length of line Type of installation (underground direct or in duct – in air) Chemical & physical properties of soil Maximum & Minimum ambient air temperatures and soil temperature. Specification & requirements to be met

89. 165BWhat is the difference between Rapid-Start and Instant-Start of fluorescent lamp?

AAnnsswweerr Rapid-Start: A method of starting fluorescent lamps in which the ballast supplies voltage to heat the lamp electrodes for 1

to 2 seconds prior to starting and, in most cases, during lamp operation. A rapid-start system starts smoothly, without flashing.

Instant-Start: A method of starting fluorescent lamps in which the voltage that is applied across the electrodes to strike the electric arc is up to twice as high as it is with other starting methods. The higher voltage is necessary because the electrodes are not heated prior to starting. This method starts the lamps without flashing; it is more energy efficient than rapid or preheat starting, but results in greater wear on the electrodes during starting. The life of instant-start lamps that are switched on and off frequently may be reduced by as much as 25 percent relative to rapid-start operation. However, for longer burning cycles (such as 12 hours per start), there may be no difference in lamp life for different starting methods.




96

90. 166BWhat is tap changer?

AAnnsswweerr

– The applying medium voltage to the primary winding of transformer is not stable and depends upon the transformer position in the distribution network. Therefore, taken the primary voltage as granted, the tap changer is used in order to keep the secondary voltage of the transformer as stable as possible.

91. 167BWhat is the difference between beam angle & cut-off angle of a luminaire? What are the

different beam classifications & State the difference between them?

AAnnsswweerr 1. Cut- Off Angle “α”:

1.1. Cut-off angle (lamp)

– Angle above which no direct reflection from the light source is visible in the reflector.

In the case of darklight reflectors the cut-off angle of the lamp is identical to the cut-off angle of the luminaire. In other forms of reflector it may be less, so that reflected glare occurs in the reflector above the cut-off angle.

1.2. Cut-off angle (luminaire)

– The angle taken from the horizontal to the line from the inner edge of the luminaire to the edge of the light source. Together with the cut-off angle (lamp), this angle is used to identify the glare limitation of a luminaire.

2. Beam Angle “β”:

– It is the angle, in a plane which contains the axis of the beam, on which luminous intensity decreases to reach a certain percentage (generally 50% or 10%) of its peak value.

2.1. Narrow Beam:

– Beam that concentrates the light within the cone of a comparatively large solid angle

– Narrow beam: ½ Imax< 20o

2.2. Medium Beam:

– Beam that concentrates the light within the cone of a comparatively large solid angle

– Medium beam: 20o < ½ Imax< 40o

2.3. Wide Beam:

– Beam that concentrates the light within the cone of a comparatively large solid angle – Wide beam: ½ Imax> 40o




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92. 168BWhat are the levels of protection (Coordination of protective devices) for the motor starter?

AAnnsswweerr A circuit supplying a motor may include one, two, three or four switchgear or control gear

devices fulfilling one or more functions. When a number of devices are used, they must be coordinated to ensure optimum operation of

the motor. The starter combination should be able to clear the current fault quickly, without any damage to the installation or risk to personnel.

(UL508E) and an IEC 60947 provide a method to measure the performance of these devices should a short circuit occur. They define two levels of protection (coordination) for the motor starter:

– Type 1 Coordination

It is acceptable that in the case of short-circuit the contactor and the thermal release may be damaged. The starter may still not be able to function and must be inspected; if necessary, the contactor and/or the thermal release must be replaced, and the breaker release reset.

Without risk for the operator. It is the most standard solution used. Before to restarting, the replacement of parts can be necessary. Qualified maintenance service. Low cost of switchgear and control gear. Continuity of service is not imperative or may be ensured by simply replacing the

faulty motor drawer.

– Type 2 Coordination

In the case of short-circuit, the thermal release must not be damaged, while the welding of the contactor contacts is allowed, as they can easily be separated (with a screwdriver, for example), without any significant deformation.

It is the high performance solution. The risk of fusion of contacts is possible. In this case, the contacts must be easier separated. Continuity of service is imperative. Limited maintenance service. Specifications stipulating type 2.

– Without Coordination

The risks are important for the personnel, the physiques and materials damages can be also important.

– Total Coordination (Continuity of service)

It is the higher performance solution. No damage and no risk of fusion. Once the fault has been fixed, the motor starter must be able to restart

immediately.

Type 1 Coordination Type 2 Coordination

Without Coordination Total Coordination

(Continuity of service)




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93. 169BCalculate maintained illumination level for clinic (4x6m) - height = 3m, consider 4

fluorescent lighting fixture each have lamps 4x36W. Luminous flux of each lamp 3000 lm,

utilization factor is 0.50 and maintenance factor is 0.70.

AAnnsswweerr

E = (N x n x Ø x U.F x M.F) / A = (4 x 4 x 3000 x 0.5 x 0.7) / (4 x 6) = 700 lux

Where:

E: Average maintained illumination level (lux) A: Room area (m2) Ø : Lamp luminous flux (lm) N: number of lighting fixtures (luminaries) N: number of lamps in each luminaire U.F: Utilization factor M.F: Maintenance factor

94. 170BWhat is difference between low smoke halogen free cables & fire resistant cables & fire

alarm cables?

AAnnsswweerr Low Smoke Halogen Free Cables

– In a fire accident some people die because of the fire, other die because of the smoke. – Halogen-free cables are increasingly specified for public buildings and areas where large numbers of people may be

present. Such as; Theaters, hotels, hospitals and closed public places. – Halogen-free cables contain no halogens. The insulation and sheath materials of these cables are composed of polymers

of pure hydrocarbons. Burning these materials, produce no corrosive compounds or toxic gases, only water vapor and carbon dioxide gas.

Fire Resistant Cables – These cables are used in fire fighting alarm systems in hazardous area where the safety is highly required during fire

condition. – A cable can be described as fire resistant when it complies with the severe test in IEC 60331 in which the middle portion

of a sample of cable 1200 mm long is supported by two metal rings 300 mm apart and exposed to the flame from a tube type gas burner at 750oC. Simultaneously the rated voltage of the cable is applied continuously throughout the test period. Furthermore, not less than 12 hours after the flame has been extinguished, the cable is reenergized. No electrical failure must occur under these conditions.

– Testing of this property is conducted according to IEC 60331 which requies one meter of cable to be hanged and subjected to flame at 750oC for 90 minutes and also according to BS 6387 which required one meter cable to be hanged and subjected to flame at 750oC for 180 minutes.

Fire Alarm Cables – These cables are used for communication and signaling in fire alarm systems.

95. 171BWhat is the distance between sockets that should be followed in design?

AAnnsswweerr

– The distance between 2 sockets should not exceed 3.65 m and 1.8 m between sockets & vertical wall taking into consideration the furniture requirements.

– No point on the floor is more than 1.8m from an outlet.




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96. 172BWrong positioning of desks relative to luminaries could cause reflected glare.

o 173BDefine glare.

o 174BWhich position of luminaire is right to avoid glare?

AAnnsswweerr Glare:

– When excessive brightness as against the general brightness in the interior appears in the visual field directly or as a

reflection, glare is experienced. The direct glare is a result of brightness from luminaries, windows or bare lamp. The reflection of that brightness or glossy materials, mirrors and VDU monitors is known as reflected glare.

– Separately or simultaneously, direct glare and reflected glare can impair usual performance or cause visual discomfort. – Today, indirect lighting system (floor mounted, wall mounted and pendant mounted) is widely used to minimize the

glare. It has to be, however, properly designed to coordinate with the architecture of the interior. Selection of light controllers is definitely the responsibility of the designer to ensure that desirable cut-off light angle is met.

Right positioning:

Wrong positioning:

97. 175BWhen many cables are laid on cable tray, what are the factors that determine the final

ampacity of each cable?

AAnnsswweerr Load current depends on load wattage. Derating factor - Variation in Air Temperature. Grouping factor.




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98. 176BWhat is the difference between Normal load, Emergency load & Critical load? State an

example for each.

AAnnsswweerr Normal Loads:

– Loads that electricity supplying it could be loosed without big danger. – Example for these loads: normal sockets, normal air conditioning, normal lighting, irrigation pumps …. Etc. – These loads are usually fed from normal electric power utility through transformer.

Emergency Loads:

– Loads that electricity supplying it could not be loosed for long time else big danger could occur. – Example for these loads: some lighting, exhaust & ventilation equipments, fire fighting pumps …. Etc. – These loads are fed from normal electric power utility through transformer + Standby generator (in case of failure of

normal power supply from transformer)

Critical Loads: – Loads that electricity supplying it could not be loosed for any else big danger could occur. – Example for these loads: important computers, fire alarm & CCTV systems, security systems, safety & emergency

lighting, Hospitals surgical equipments & rooms, Air traffic control towers, Runway lighting, Reservation centers …. Etc.

– These loads are fed from normal electric power utility through transformer + Standby generator (in case of failure of normal power supply from transformer) + UPS (in case of failure of normal power supply from transformer + Standby generator still didn’t work)

Normal power supply ON. Normal power supply FAILURE Normal power supply FAILURE.

Normal + Emergency + Critical Loads are fed from electric utility

Normal + Emergency Loads are not fed from electric utility.

Normal Loads are not fed from. electric utility.

Standby generator starts to feed emergency & critical loads (but after some minutes).

Emergency + Critical Loads are fed from standby generator.

Critical Loads are fed instantaneously from UPS.




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99. 177BState the Types of static UPS

AAnnsswweerr 1. UPS operating in passive-standby (off-line) mode:

1.1. Operating principle: – The inverter is connected in parallel with the AC input in a standby.

1.1.1. Normal mode: – The load is supplied by utility power via a filter which eliminates certain

disturbances and provides some degree of voltage regulation. 1.1.2. Battery backup mode: – When the AC input voltage is outside specified tolerances for the UPS or the

utility power fails, the inverter and the battery step in to ensure a continuous supply of power to the load following a very short (<10 ms) transfer time. The UPS continues to operate on battery power until the end of battery backup time or the utility power returns to normal.

1.2. Usage: – It can be used only with low power ratings (< 2 kVA). – It operates without a real static switch, so a certain time is required to transfer

the load to the inverter. This time is acceptable for certain individual applications, but incompatible with the performance required by more sophisticated, sensitive systems (large computer centers, telephone exchanges, etc.)

– The frequency is not regulated and there is no bypass. Note: In normal mode, the power supplying the load does not flow through the inverter, which explains why this type

of UPS is sometimes called “Off-line”. This term is misleading, however, because it also suggests “not supplied by utility power”, when in fact the load is supplied by the utility via the AC input during normal operation. That is why standard IEC 62040 recommends the term “passive standby”.

2. UPS operating in line-interactive mode:

2.1. Operating principle: – The inverter is connected in parallel with the AC input in a standby

configuration, but also charges the battery. It thus interacts (reversible operation) with the AC input source.

2.1.1. Normal mode: – The load is supplied with conditioned power via a parallel connection of the AC

input and the inverter. The inverter operates to provide output-voltage conditioning and/or charge the battery. The output frequency depends on the AC-input frequency.

2.1.2. Battery backup mode: – When the AC input voltage is outside specified tolerances for the UPS or the

utility power fails, the inverter and the battery step in to ensure a continuous supply of power to the load following a transfer without interruption using a static switch which also disconnects the AC input to prevent power from the inverter from flowing upstream. The UPS continues to operate on battery power until the end of battery backup time or the utility power returns to normal, which provokes transfer of the load back to the AC input (normal mode).

2.1.3. Bypass mode: – This type of UPS may be equipped with a bypass. If one of the UPS functions fails, the load can be transferred to the

bypass AC input (supplied with utility or standby power, depending on the installation). 2.2. Usage:

– This configuration is not well suited to regulation of sensitive loads in the medium to high-power range because frequency regulation is not possible. For this reason, it is rarely used other than for low power ratings.




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3. UPS operating in double-conversion (on-line) mode: 3.1. Operating principle :

– The inverter is connected in series between the AC input and the application.

3.1.1. Normal mode: – During normal operation, all the power supplied to the load passes

through the rectifier/charger and inverter which together perform a double conversion (AC-DC-AC),

3.1.2. Battery backup mode: – When the AC input voltage is outside specified tolerances for the

UPS or the utility power fails, the inverter and the battery step in to ensure a continuous supply of power to the load following a transfer without interruption using a static switch. The UPS continues to operate on battery power until the end of battery backup time or utility power returns to normal, which provokes transfer of the load back to the AC input (normal mode).

3.1.3. Bypass mode: – This type of UPS is generally equipped with a static bypass, sometimes referred to as a static switch. – The load can be transferred without interruption to the bypass AC input (supplied with utility or standby power,

depending on the installation), in the event of the following: UPS failure Load-current transients (inrush or fault currents) Load peaks

– However, the presence of a bypass assumes that the input and output frequencies are identical and if the voltage levels are not the same, a bypass transformer is required.

– For certain loads, the UPS must be synchronized with the bypass power to ensure load-supply continuity. What is more, when the UPS is in bypass mode, a disturbance on the AC input source may be transmitted directly to the load because the inverter no longer steps in.

Note: Another bypass line, often called the maintenance bypass, is available for maintenance purposes. It is closed by a manual switch.

3.2. Usage: – In this configuration, the time required to transfer the load to the inverter is negligible due to the static switch. Also, the

output voltage and frequency do not depend on the input voltage and frequency conditions. This means that the UPS, when designed for this purpose, can operate as a frequency converter.

– Practically speaking, this is the main configuration used for medium and high power ratings (from 10 kVA upwards). Note: This type of UPS is often called “on-line”, meaning that the load is continuously supplied by the inverter,

regardless of the conditions on the AC input source. This term is misleading, however, because it also suggests “supplied by utility power”, when in fact the load is supplied by power that has been reconstituted by the double conversion system. That is why standard IEC 62040 recommends the term “double conversion”.

100. 178BIf the power factor of a certain electrical installation is low how can the power factor to be

improved / corrected?

AAnnsswweerr By using Capacitor (or Capacitor Bank if several loads are grouped) which should be calculated according to the value

equal to reactive VARS to be neutralized by the capacitor to reach the desired final power factor.




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101. 179BWhat are the devices to be used for earth leakage protection / ground fault protection?

AAnnsswweerr Earth leakage is protected by using ELCB, RCD, GFCI or E.L. relay. Ground fault is protected by using Fault indicator to detect line /ground fault.

102. 180BWhat is Voltage Drop? What are the factors that determine the Voltage drop of a cable/wire?

Write down the V.D equation for single phase cable & 2 phase for 3 phase cable

AAnnsswweerr V.D. is the reduction of voltage from the supply side till load side due to cable’s resistance. Factors: Ampere, length, and conductor size, type of insulation of the cable /wire.

IB: The full load current in amps L: Length of the cable in kilometres R: Resistance of the cable conductor in Ω/km

Note: R is negligible above a c.s.a. of 500 mm2

X: inductive reactance of a conductor in Ω/km

Note: X is negligible for conductors of c.s.a. less than 50 mm2. In the absence of any other information, take X as being equal to 0.08 Ω/km.

Ф: phase angle between voltage and current in the circuit considered, generally:

Incandescent lighting: cos Ф = 1 Motor power:

• At start-up: cos Ф = 0.35 • In normal service: cos Ф = 0.8

Un: phase-to-phase voltage Vn: phase-to-neutral voltage




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103. 181BWhat are the C.T. & P.T? When do we use each one and why?

AAnnsswweerr C.T.: is Current Transformer to provide current transformation ratio.

– Used for measuring (instrument) like Voltmeters, Ameters. Because the load current is big or large that the measuring instrument can not safely pass it.

P.T.: is Potential (voltage) Transformer to provide voltage transformation ratio. – Used for any usage requires reduction in voltage. Because instrument coil can not be connected to HV or MV.

104. 182BWhat does these abbreviations stands for: PVC, XLPE & LSF?

AAnnsswweerr PVC: Polyvinyl Chloride XLPE: Cross Linked Polyethylene LSF: Low Smoke Fume

105. 183BDefine the Grouping Factor? When does it considered in cable size calculations? Is it

applicable for multi core or single core cables?

AAnnsswweerr Grouping factor is a derating factor for the ampacity of the cable when installed near several cables/wires within defined

distances. It is considered when several cables are used on same routing inside the raceway or cable tray. It is applicable for three single core cables in tree foil/flat formation and for multi-core cables formation if they are used in a

group.

106. 184BA branch panel board with total connected load 25 KW & P.F. = 0.8. Calculate Main Feeder

Cable and Main C.B?

AAnnsswweerr

I = (5 *10³) / (√3 * 380 * 0.8) = 47.50 A

Apply Derating & Correction. Factors I ≈ 56 A Applying factor 125% allowable ampacity. (C. B. 80Amp. MCB) & Cable (4*35) +16 mm² cu.

107. 185BMention the different types of conduits used in electrical systems routing inside high rise

buildings? What is the common usage for each?

AAnnsswweerr PVC: for embedded. R.S.C & I.M.C & EMT: for exposed. Flexible: for connection to motors.... etc.




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108. 186BMention the different types of conduits used in electrical systems routing inside high rise

buildings? What is the common usage for each?

AAnnsswweerr Excess voltage drop can cause the following conditions:

– Low voltage to the equipment being powered, causing improper, erratic, or no operation - and damage to the equipment. – Poor efficiency and wasted energy.

109. 187BWhat is the difference between, molded Case Circuit Breaker and miniature circuit

breakers?

AAnnsswweerr The ratings & short circuit of the MCCB is higher and discrimination could be achieved using the MCCB.

110. 188BSuppose you are buying a transformer. You have two options: TR1is 11/0.4KV & Z = 4 %,

TR2: is 11/0.4KV & Z = 6 %. Which one you choose & why? Taking into consideration, you

need 380V on the secondary at full load.

AAnnsswweerr TR1: at no load →Vn.l = 400V & at full load →Vf.l = 400/1.04 = 384.6 > 380V (Accepted) TR2: at no load →Vn.l = 400V & at full load →Vf.l = 400/1.06 = 377.3 < 380V (Not Accepted)

111. 189BCompare between the following types of lamps according to their Power Range, Efficacy,

Lumens, Life Time, Color Temp and CRI.

o 190BIncandescent and Halogen

o 191BFluorescent

o 192BCompact Fluorescent (CFL)

o 193BMercury Vapor

o 194BMetal Halide

o 195BHigh Pressure Sodium (HPS)

o 196BLow Pressure Sodium (LPS)

AAnnsswweerr




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112. 197BThere are new specifications created by SASO to prohibit entry of any plugs or sockets not

conforming to the specifications and this should be effective on (23/02/2010). What are

these specifications & what are the types specified for 127V Plugs/Sockets & 220V

Plugs/Sockets?

AAnnsswweerr Plug 127V / Socket 127V according to SASO specifications 2204

Plug 220V / Socket 220V according to SASO specifications 2203

113. 198BWhat is meant by UL Listed product?

AAnnsswweerr Underwriters Laboratories Inc. (UL) is an independent product safety certification organization that was established in

1894. Based in Northbrook, Illinois, UL develops standards and test procedures for products, materials, components, assemblies, tools and equipment, chiefly dealing with product safety. UL also evaluates and certifies the efficiency of a company’s business processes through its management system registration programs.

UL does not “approve” products. Rather it evaluates products, components, materials and systems for compliance to specific requirements, and permits acceptable products to carry a UL certification mark, as long as they remain compliant with the standards. UL offers several categories of certification. Products under its listing service are said to be “UL Listed,” identified by the distinctive UL mark. In some cases, a component may be “UL Recognized,” meaning UL has found it acceptable for use in a complete UL Listed product. Other products may be “UL Classified” for specific hazards or properties. UL maintains a directory of more than 3 million products through a publicly available, online database.

A manufacturer of a UL-certified product must demonstrate compliance with the appropriate safety requirements, many of which are developed by UL. A manufacturer must also demonstrate that it has a program in place to ensure that each copy of the product complies with the appropriate requirements.

114. 199BDoes the voltage supply fluctuation affects the lamps? How?

AAnnsswweerr The required voltage supply of a lamp must be maintained in order to achieve the rated lumen output and lamp life. When

fluctuation occurs, say 1 volt, the luminous flux of a light source decreases by about 5 lumens. Likewise, the lamp life is shortened when this is not prevented




107

115. 200BWhat is the ballast? State its function & types of ballasts.

AAnnsswweerr All Discharge lamps requires an external device to regulate power. This device is the Ballast Ballast Function :

– Provide Proper Voltage to establish an Arc – Regulate Electric current flowing through the lamp – Supply proper voltage for lamp operation

Ballasts may be Electromagnetic or Electronic 116. 201BWhat is the difference between a kW and a kWh? What is measured by electric utility?

AAnnsswweerr There is a big difference between a kW and

a kWh – A kW is a measure of power being used – A kWh is a measure of energy being

used A Good Analogy for kW and kWh is the

automobile dash board which provides a nice way to understand the difference between the kW and kWh – A kW is like the speed that is measured

by the speedometer. – A kWh is like the distance that is

measured by the odometer The electric utility does not measure

instantaneous values of the kW a facility uses. Instead, they always average the value of the kW over a short period of time- usually 15, 30 or 60 minutes – 900, 1,800 or 3,600 seconds.

117. 202BWhat are the different types of conductors according to NEC code?

AAnnsswweerr NEC conductor types:

– R : Rubber insulated conductor – T : Thermoplastic (or PVC) insulated conductor. – X : Cross-linked polyethylene insulated conductor. – H : Letter which is used for heat-resistant qualities. – W : Letter which is used for water-retardant qualities. – HH : Cable is recommended for dry locations. – HW : Cable is recommended for both wet & dry locations.

Recommended conductor temperature:

– T & R: 70oC – X : 90oC




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118. 203BHow can you estimate the electrical consumption per month for residential buildings?

AAnnsswweerr 1. We should divide the residential building area into three areas:

– Living areas, Sleeping areas & Service areas. 2. We should classify the residential building loads into four types:

– Home appliances loads, Lighting loads, Air conditioning loads & Hot water loads. 3. We should divide the weak in two categories:

– Weekday, Weekends. 4. We should divide the year into four seasons:

– Summer, Winter, Autumn & Spring. 5. We should divide the day into twenty four hours. 6. We should estimate the occupancy as a percentage per day.

Each one of the previous divisions should be taken as a factor or percentage. Here down is a table for small example for residential building in KSA.




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110

119. 204BWhat is star-delta starting? Why is it used? What are the advantages & disadvantages of

using this method? Should we immediately install soft starters on all our existing motors?

AAnnsswweerr Definition:

– Star Delta starting is when the motor is connected (normally externally from the motor) in STAR during the starting sequence. When the motor has accelerated to close to the normal running speed, the motor is connected in DELTA. Pictures 1 and 2 show the two connections for a series connected three phase motor

– The change of the external connection of the motor from Star to Delta is normally achieved by what is commonly referred to a soft starter or a Star Delta starter. This starter is simply a number of contactors (switches) that connect the different leads together to form the required connection, i.e. Star or Delta.

– These starters are normally set to a specific starting sequence, mostly using a time setting to switch between Star and Delta. There can be extensive protection on these starters, monitoring the starting time, current, Voltage, motor speed etc.

– The cost of the soft starter will depend on the number of starts required per hour, run-up time, Voltage, power rating, and protection devices required.

Usage: – Let’s consider an example motor: 120kW, 4 Pole, 380 Volt, Delta connected, 3 Phase, 50 Hz. – First we will examine the normal running condition, i.e. when the motor is connected in Delta.Then, let’s have a look

what happens when the motor is connected in STAR. – To truly grasp the differences between these two starting methods, we will list the values next to each other in table 3,

and on graphs 5 and 6.




111

– Immediately we notice the primary reasons for using star delta starters on electric motors: The starting power is reduced from 98 kW to 33 kW (by approximately 67%), the starting current is reduced from 1495 A to 500 A (by approximately 67%). Because the motor is not intended to actually run in this connection, the reduction in full load speed, power factor and efficiency is not significant for this discussion.

– One major disadvantage of the star delta starting is the reduction in the starting torque from 1038 Nm to 343 Nm (by approximately 67%). This will be discussed in depth later on.

– The reason for these 67% changes becomes clear when we examine the phase voltage on the motor, we see that the phase voltage when the motor is connected in Delta is 380 Volt. When the motor is however connected in Star, the Phase Voltage will be 219.3 Volt. The relations for star and delta connections are as listed in Table 4:

– Thus, when the motor is started in the star connection, the phase voltage of the motor is reduced by a factor of √3.




112

– The reductions in starting current, starting power, and starting torques for a reduced Voltage can each be calculated by using equation 1 (This ignores other factors like saturation, etc.):

– If we apply this equation for the star delta starting, we see from equation 2 where the 67% reduction comes from:

Advantages: – The most significant advantage of using Star-Delta starting is the huge reduction in the starting current of the motor,

which will result in a significant cost saving on the size of the circuit breakers, the size of the fuses, the size cables, as well as the transformers and switch gear.

– Requiring 67% less starting current can have a tremendous cost saving implication!

Disadvantages: – The most significant disadvantage of using Star-Delta starting is the huge reduction in the starting torque of the motor,

which will result in a significantly increased run-up time, and may even result in a stall condition. Eventually this may lead to serious damage to the motor.

– The red arrow indicates what is called a “Stall” condition. At this point, the motor cannot accelerate, because it does not have sufficient torque to overcome the load requirement!

Does that mean that we should immediately install soft starters on all our existing motors?

– Firstly: No! The cost reductions will only result when a new installation is done! If the transformers, switch gear, cables and protection were initially selected for the high starting currents, there would not be a significant cost saving by installing a soft starter.

– Secondly: Let us first further explore the 67% reduction in the motor’s starting torque.




113

120. 205BHow the Electricity Bill is computed?

AAnnsswweerr In KSA “2009”

ثانيا: تعريفة قراءة و صيانة العداد و إعداد الفاتورة (جدول يوضح انواع

القواطع او العدادات مع قيمة التعريفة الشهرية) اوال: تعريفة استهالك التيار (جدول يوضح شرائح اإلستهالك-فئات الخدمة)

In Egypt “2007 - 2008”




114

121. 206BWhat are the different standards of sockets? Draw them & state the difference?

AAnnsswweerr

Socket Outlets Standards Shapes Socket Outlets

Standards Shapes Socket Outlets Standards Shapes

European - German Standard “SCHUOKO” “With Ground” CEE7/4

Europe - Russian Standard “Without Ground” CEE7/16

Italian Standard “With Ground”

European - French Standard “SCHUOKO” “With Ground”

Japanese Standard “Without Ground” JIS C 8303

Euro - US Standard “With Ground”

Chinese Standard “With Ground”

Spanish Standard “Without Ground”

Euro - US Standard “Without Ground”

UK - British Standard “With Ground” BS-1363 SASO No LIC 203181

UK - British Standard Shaver Socket BS-4573

Switzerland Standard “With Ground” SEV-1011

North America - UL Standard “With Ground” NEMA 5-15 SASO No LIC 203182

Spanish Standard “Without Ground”

South Africa – Indian – British Standard round pin “With Ground” BS-546

North America - UL Standard “Without Ground”

Israel Standard “With Ground” SI 32 (IS 16A–R)

Denmark Standard “With Ground” SRAF 1962/DB

Universal UK - Euro-US Standard “With Ground” BS-5733

Australian - Argentina - South America Standard “With Ground” AS-3112

Spanish Standard “With Ground”

Universal UK - Euro-US Standard “With Ground”

Egypt Standard “Without Ground”

UK - British Standard Shaver Socket “With Insulating Transformer”

Chinese - Euro - US Standard “With Ground”

Italian Standard “With Ground” CEI 23-16




115

122. 207BWhat are the international codes, standards, regulations & specifications? State some of

them that can be followed in electrical design?

AAnnsswweerr Standards

Are guidance documents developed by groups that have (hopefully) studied the area and are making recommendations. Thus, standards are not legal requirements unless something or someone else has made them a requirement.

Legislation & Rregulations Is a law and thus the subject matter covered is required legally. Legislation must be passed by some governmental authority to be a law. Often legislation is somewhat vague and the manifestation or full explanation of the requirements must be written in "codes“.Laws are passed leading to regulations

Codes Are the manifestation (or written legal requirements) of legislation.

Different International Codes, Standards, Regulations & Specifications – CSI: Construction Specifications Institute. – BICSI: Building Industry Consulting Service International. – IEC: International Electro-technical Commission. – BSI + EN: British Standards Institute Electrical Code + European Norm – IEEE: The Institute of Electrical & Electronics Engineers. – NEC (NFPA-70): National Electrical Code. – NFPA-70: National Fire Protection Association. (National Electrical Code). – NFPA-72: National Fire Protection Association. (National Fire Alarm Code). – NFPA-92: National Fire Protection Association. (Recommended Practice for Smoke-Control Systems). – NFPA-101: National Fire Protection Association. (Life Safety Code). – NFPA-110: National Fire Protection Association. (Emergency & Standby Power Systems). – NFPA-780: National Fire Protection Association. (Lightning Protection Systems). – ANSI: American National Standard Institute. – ICC: International Code Council. – EIA: Electronic Industries Alliance. – UL: Underwriters Laboratories Standards. – NEMA: National Electrical Manufacturers Association. – IESNA: Illuminating Engineering Society of North America. – SEC (SCECO): Saudi Consolidated Electric Company Distribution Standard. – SASO: Saudi Arabian Standard Organization. – SBC: Saudi Building Code. – GSBC: General Specifications for Building Construction. – SAES: Saudi Aramco Engineering Standards. – IEE Wiring Regulations: The Institution of Electrical Engineers. – DIN German norms: Deutsches Institut fur Normung. – VDE: German standards. – CIBSE: Chartered Institution of Building Services Engineers Lighting Code UK norms. – QCS: Qatar Construction Specification. – DEWA Regulations: Dubai Electricity & Water Authority. – SEWA Regulations: Sharjah Electricity & Water Authority. – LEED + USGBC: Leadership in Energy and Environmental Design +U.S. Green Building Council. – ASHRAE : American Society of Heating, Refrigerating & Air Conditioning Engineers. – OSHA: Occupational Safety & Health Administration Standard. – ASTM: American Society for Testing and Materials. – KAHRAMAA: Qatar General Electricity & Water Corporation Regulations – Saudi Lighting Code – Egyptian Lighting Code – Egyptian Electrical Codes & Specification




116

123. 208BWhat are the different types of local power cables for low & medium voltages?

AAnnsswweerr

Low Voltage Cables - 450/750 V Cable Type Description Application Photo

Single core cables with solid or stranded copper conductors PVC insulated.

• Soft annealed solid or stranded copper conductors insulated with PVC compound rated 70C or 90C.

• Cables are produced According to IEC 60227 & BS 6004.

• For indoor fixed installations in dry locations, laid in conduits, as well as in steel support brackets.

Single core cables with flexible copper conductors. PVC insulated.

• Soft annealed copper fine wires bunched together in subunits or stranded bunched groups into a main unit, which forms the flexible conductor. Insulated with soft PVC 70C or 90C compound. Cables are produced According to IEC 60227 & BS 6004.

• For indoor fixed installations in dry locations, where particular flexibility is required.

• For electrical panels connection or for electrical apparatus they can laid in groups around steel sheets.

Low Voltage Cables - 0.6/1 (1.2) KV Cable Type Description Application Photo

Single core cables with stranded circular copper conductors. PVC (or XLPE) insulated and PVC sheathed.

• Soft annealed stranded copper or aluminum conductors. Insulated with PVC (or XLPE) compound rated 70 C and covered & sheathed with PVC compound layer to form the overall jacket.

• Cables are produced according to IEC 60502 or BS 6004 (or BS 5467).

• For outdoor & indoor installations in damp & wet locations. They are normally used for power distribution in urban networks, industrial plants, as well as in thermo power and hydropower stations.

Multi-core cables with flexible copper conductors. PVC insulated and PVC sheathed.

• Soft annealed copper fine wires bunched together in subunits or stranded bunched groups into a main unit, which forms the flexible conductor. These conductors are insulated with PVC compound rated 70C and sheathed with PVC compound layer.


• For indoor movable installation in dry location connecting to source power portable electrical appliances operating under unfavorable conditions such as portable lamps, fans, refrigerators, washing machines, vacuum cleaners, TV & house hold heating and ventilating apparatus.

Multi-core cables with stranded copper (or aluminum) conductors. PVC (or XLPE) insulated and PVC sheathed.

• Multi-core cables with stranded copper (or aluminum) conductors are insulated with PVC (or XLPE) compound assembled together, covered with overall jacket of PVC compound.

• Cables are produced According to IEC 60502 & BS 6346 (or BS 5467).

• For outdoor & indoor installations in damp & wet locations.

• They are normally used for power distribution in urban networks, industrial plants, as well as in thermo power and hydropower stations.

Multi-core cables with stranded copper (or aluminum) conductors. PVC (or XLPE) insulated, Steel Tape (or Wire) Armoured and PVC sheathed.

• Multi-core cables with stranded copper (or aluminum) conductors are insulated with PVC (or XLPE) compound assembled together, armoured with steel tape (or Wire) and covered with overall jacket of PVC compound.

• Cables are produced According to IEC 60502 & BS 6346 (or BS 5467).

• For outdoor installations in damp & wet locations, where mechanical damages are expected to occur.

Medium Voltage Cables - 6 /10 (12) KV, 8.7/15 (17.5) KV, 12/20 (24) KV &18/30 (36) KV Cable Type Description Application Photo

Single & three cores copper (or aluminum) conductors XLPE insulated and PVC sheathed.

• Stranded circular compacted copper (or aluminum) conductor, semi conductor layer as conductor screen, XLPE insulated, semi conducting layer as nonmetallic insulation screen copper tape or wire as metallic insulation screen, three cores assembled together with non hygroscopic polypropylene fillers, wrapped with binder tape & PVC sheathed.


• These cables are generally sutibale for direct burial or for installation on trays or in ducts.

Three cores copper (or aluminum) conductors XLPE insulated, Steel Tape (or Wire) Armoured and PVC sheathed.

• Stranded circular compacted copper (or aluminum) conductor, semi conductor layer as conductor screen, XLPE insulated, semi conducting layer as nonmetallic insulation screen copper tape or wire as metallic insulation screen, three cores assembled together with non hygroscopic polypropylene fillers, wrapped with binder tape covered with a layer of PVC compound as bedding, steel tape (or Wire) armoured & PVC sheathed.


• For outdoor installations in damp & wet locations, where mechanical damages are expected to occur.




117

124. 209BWhen can we use neutral with C.S.A equal to the C.S.A of the phase & when can we use

reduced neutral and with C.S.A less than the C.S.A of the phase? How can we choose the

reduced neutral in 3 phase-systems

AAnnsswweerr We use neutral with C.S.A equal to the C.S.A of the phase in case of single phase loads or in case of three phase loads that

have a great probability of occur of big unbalance on the three phase wires due to different P.F’s or due to harmonics. For example: the neutral wire of the main cable of 3 phase panel board, the 3 phase lighting circuit with discharge lamps.

We use neutral with C.S.A less than the C.S.A of the phase in case of three phase loads that have very small probability of occur of big unbalance on the three phase wires.

Choice of the reduced neutral in 3 phase-systems is according to followed: – For cables with 3 phases of CSA 16mm2 or less, the neutral should have CSA as phases. – For cables with 3 phases of CSA 25mm2 or 35mm2, the neutral should have the next lesser CSA than CSA of phases. – For cables with 3 phases of CSA 50mm2 or more, the neutral should have CSA of not less than half CSA of phases.

125. 210BWhat are the types of emergency lighting? State the difference? How batteries shall be

provided?

AAnnsswweerr




118

126. 211BState the target areas for Emergency Lighting to be provided?

AAnnsswweerr According to EN 1838 & NFPA101:

– Emergency escape lighting

Safe exit from any location (All escape corridors, Passages and Stairs) – Open area lighting

Reducing the likelihood of panic and enabeling safe movements towards escape routes. (Lobby, Arrival & Dept‘ Halls, Ball rooms, Retail etc)

– High risk task area lighting Illumination for the safety of people involved in a potentially dangerous process. (Mech‘ Plants, Conveyor, Substations etc)

– Public Safety and Anti-panic Illumination for the safety of people who is visiting the premises (Hotel rooms, Offices & Public Toilets etc.)

Minimum of 10 Lux or 1 Ft Candela at these points: A luminaire to illuminate the area must be installed at these points




119

127. 212BWhat are lighting levels & uniformity mentioned in standards for emergency lighting?

AAnnsswweerr According to NFPA 101

– Emergency illumination shall be provided for not less than 1.5 hours in the event of failure of normal lighting. – Emergency lighting facilities shall be arranged to provide initial illumination that is not less than an average of 1 ft-

candle (10.8 lux) and, at any point, not less than 0.1 ft-candle (1.1 lux) measured along the path of egress at floor level. – Illumination levels shall be permitted to decline to not less than an average of 0.6 ft-candle (6.5 lux) and, at any point ,

not less than 0.06 ft-candle (0.65 lux) at the end of the 1.5 hours. – A maximum to minimum illumination uniformity ratio of 40:1 shall not be exceeded.




120

128. 213BWhat are the different systems used in central battery system? Compare between them.

AAnnsswweerr AC/AC Systems: (Input AC & Output AC)

– A static inverter runs conventional mains luminaires at full brightness during both mains healthy and mains failure

conditions. – However, there is usually a requirement for local switching of the luminaires during mains healthy conditions, with

automatic illumination in the event of mains failure. – Local switching with automatic illumination in the event of mains failure can be easily achieved by use of the ACM1

module, which is purpose-designed for this application.




121

AC/DC Systems: (Input AC & Output DC)

– Maintained AC/DC central battery with conversion luminaires – With this option, the normal mains luminaires are fitted with a conversion module, enabling them to also operate as

emergency luminaires in the event of mains failure. – Each conversion module includes a changeover relay which, under normal circumstances, is energised by a permanent

supply from the unswitched side of the normal lighting circuit. – Whilst energised, it connects the lamp to the conventional mains control gear within the luminaire allowing it to operate

as a standard mains fitting, powered via a switched live connection to the mains ballast. – Should the normal lighting fail, the relay within the conversion module drops out, disconnecting the lamp from the

conventional control gear and connecting it to the inverter within the conversion module. This illuminates the lamp at reduced brightness.

– In multi-lamp luminaires, the conversion module only operates a single lamp in the emergency mode. All other lamps will extinguish upon mains failure.

Comparison

AC/AC Systems AC/DC Systems Usually 110V DC Battery Set 24V to 216V Battery Set Static Inverter converts 110V-230V AC Modular Converters or Switchoverunits 2.5 KVA Inverter Blocks Max. 6A Modules / circuit Communication via additional Data Cable Communication on same power cable Use of Conventional ballast possible Use of Electronic ballast only




122

129. 214BWhat are the advantages of using Self Contained EM Lighting?

AAnnsswweerr High Availability Low installation cost Easy extension No fire protection necessary Decentralised installation, therefore high safety level

130. 215BWhat are the advantages of using Central Battery System?

AAnnsswweerr Higher Battery Life with 10 Years Sealed Lead Acid Battery. Modular system with every Fitting is Individually Addressed. Fully monitored Charger and Electronic circuitry. Higher Light output from light fittings. Solution using wide range of Light fitting. Interfacing Switching, Dimming & Lighting Controls. Integration with BMS and Central Monitoring via Ethernet.

131. 216BHow can you calculate the current carrying capacity or the size of busbar?

AAnnsswweerr A very approximate method of estimating the current carrying capacity of a copper busbar is to assume a current density of

2 A/mm2 (1250 A/in2) in still air. This method should only be used to estimate a likely size of busbar, the final size being chosen after consideration has been given to the calculation methods and experimental results.

J (current density in A/mm²) = I (busbar current rating in Amp) A (busbar c.s.a. in mm² width x thickness)

132. 217BWhy you use sine wave for ac power supply why not triangle wave or square wave?

AAnnsswweerr AC power comes from an electrical generator, which is a set of stationary coils (the stator) around a rotating magnetic field

(the rotor). This configuration produces a sine wave output. We use a sine wave on the power grid because that's the way the electricity is generated, and it is a "natural" thing to do. It's a "pain" to have to convert it to another wave shape.

There is also the fact that some nasty harmonics will appear on the power grid if we try to use triangular or square waves. Particularly with a square wave. The electrical loss will be higher, too. See the generator link below.

Additionally, the sine wave is the 'purest' waveform, being the root of all other period waveforms. 133. 218BDo we can put two branch circuits in one conduit?

AAnnsswweerr We can put two branch circuits in one conduit in case they are of the same phase.




123

134. 219BWhy do 50 Hz transformers cost more than 60 Hz transformers? Does 50 Hz transformer

could work on 60 Hz transformers & How?

AAnnsswweerr According to Steven Ensign of Ensign Power Volt, a producer of transformers and power supplies: Back in high school

physics class we observed the circular patterns, called magnetic flux lines, made by sprinkling iron filings over a magnet. An energized transformer is an electromagnet and therefore creates similar magnetic flux line patterns.

When dealing with flux lines and transformers, two laws of physics are particularly significant:

– Each magnetic material has a limit on how many flux lines it can handle; and – The lower the operating frequency, the more flux lines that are generated. (φ α 1/f)

Operating a transformer at 50 Hz generates 20% more flux lines than at 60 Hz. As the number of flux lines approaches the

magnetic material’s limit, the heat in both the magnetic core and the internal coil wires increases, and under certain circumstances, unpredictably so. This can result in a transformer that exceeds safe temperature levels. Therefore, a transformer designed to run at 50 Hz will simply run cooler at 60 Hz. But one designed only for 60 Hz may overheat at 50 Hz.

In order to accommodate 50Hz operation, the transformer must employ a magnetic core material that can handle the added

flux lines. Such materials are readily available, but they are significantly more costly than the normal core materials. Using high-grade core materials when they are not required results in transformers that are over-designed and not competitively priced.

135. 220BHow can you calculate the full load current for different sizes of motors (1-ph, 2-ph & 3-

ph)?

AAnnsswweerr The full-load current Ia supplied to the motor is given by the following formulae:

3-phase motor: Ia = Pn x 1,000 / (√3 x U x η x cos φ) 1-phase motor: Ia = Pn x 1,000 / (U x η x cos φ) Where:

Ia: current demand (in amps) Pn: nominal power (in kW) U: voltage between phases for 3-phase motors and voltage between the terminals for single-phase

motors (in volts). A single-phase motor may be connected phase-toneutralor phase-to-phase. η: per-unit efficiency, i.e. output kW / input kW cos φ: power factor, i.e. kW input / kVA input

The current supplied to the motor, after power-factor correction, is given by:

I = Ia (cos φ / cos φ’)

Where:

cos φ: is the power factor before compensation cos φ’: is the power factor after compensation, Ia being the original current.




124

Rated operational power and currents (concluded):

– According to NEC:

Table 430.248 Full-Load Currents in Amperes, Single-Phase Alternating-Current Motors

Table 430.249 Full-Load Current, Two-Phase Alternating- Current Motors (4-Wire)

Table 430.250 Full-Load Current, Three-Phase Alternating-Current Motor




125

– According to IEC:




126

136. 221BState the way of calculating the short circuit at any point within a LV installation

according to IEC & Egyptian Code for electrical installation

AAnnsswweerr 3-phase short-circuit current (Isc) at any point within a LV installation according IEC

Where Is.c: Short Circuit Current at any point (in KA). Zt: Total impedance per phase of the installation from upstream supply to the fault location (in Ω). Us: Phase voltage at power supply terminals in case of no load (in volts). Un: Phase voltage at power supply terminals in case of load (in volts).

– Step (1): Upstream Network Power Supply “For Medium Voltage”

• Upstream S.C. (kVA) is the short circuit of the protection devices at the medium voltage side and is specified by the

electric utility. • Zs.c is calculated using down formula. • Xs.c = 0.98 Zs.c. • Rs.c = 0.15 Xs.c (Rs.c is almost negligible value, so it’s neglected)

( )).(.

22005.13).(.

3 22

. kVACSkVACSU

Z scs

×==

Where Zs.c: Impedance of the medium voltage network (in mΩ). S.C.: 3-phase short circuits fault level of the protection devices at the

medium voltage side and is specified by the electric utility (in KVA). Us: Phase voltage at power supply terminals in case of no load (in volts).

For Example:

S.C (K.VA) Us (Volts) Rs.c (mΩ) Xs.c (mΩ) Zs.c (mΩ)

250,000 231 0.095 0.633 0.64 350,000 231 0.0675 0.4515 0.4574 500,000 231 0.047 0.316 0.319

ZtU

ZtUcIs nS 05.1. ==




127

– Step (2): Transformers “For One Transformer or n Transformers in Parallel” • The impedance, resistance & reactance of transformer are usually given by manufacturer. • If not known, we can calculate the impedance Ztr of a transformer, viewed from the LV terminals, is given by the

formula:

( )cscs

sRT U

kVAU

kVAUZ .

2

.

2

.22005.133 ×

==

RTn RIPcu .23 ×=

2

3

. 310

nRT I

PcuR

×=∴

2.

2.. RTRTRT XZX −=∴

Where KVA: Transformer rating (in KVA). Pcu: Transformer Total losses (in watts). Us: Phase voltage at power supply terminals in case of no load (in volts). Us.c: Short-circuit impedance voltage of the transformer (in %). Its value is (0.04, 0.05 or 0.06). In: Nominal full-load current (in amps). Rtr: Resistance of one phase of the transformer (in milli-ohms). (Rtr can be ignored, Rtr≈ 0). Xtr: Reactance of one phase of the transformer (in milli-ohms). (Xtr ≈ Ztr). Zt.r: Transformer equivalent impedance viewed from the LV terminals (in mΩ).

• Resistance, reactance and impedance values for typical distribution 400 V transformers with HV windings ≤ 20 Kv

• Notice that in case of using (n) typical transformers in parallel, so the values of given reactance’s, resistance’s & impedance’s should be divided by (n) to obtain the total equivalent values.




128

– Step (3): Bus Ducts “Between Transformer and MDB or in High Rise Buildings” • For prefabricated bus trunking and similar pre-wired ducting systems, the manufacturer should be consulted. • If not known, so the resistance of bus ducts is generally negligible, so that the impedance is practically all reactive,

and amounts to approximately 0.15 mΩ/metre length per phase for LV bus ducts (doubling the spacing between the bars increases the reactance by about 10% only).

0. ≈

Α=

ρDBR

[ ] [ ])()(15.0.. meterlengthmetermXZ DBDB ×Ω≈≈

Where ρ: Resistivity constant of the bus duct material at 70oC (in mΩ.mm2/m).

⇒ For copper: ρ = 21 mΩ.mm2/m. ⇒ For aluminum: ρ = 33 mΩ.mm2/m.

ℓ: Length of the bus duct (in m). A: c.s.a. of bus duct (in mm2).

– Step (4): Circuit Breakers “For Main C.B & Branch Circuits C.B”

• In LV circuits, the impedance of circuit breakers upstream of the fault location must be taken into account. • Values of resistance & reactance of C.B can be found in catalogues. • If not known, the reactance value conventionally assumed is 0.15 mΩ per CB, while the resistance is neglected.

0. ≈BCR

Ω≈≈ mXZ BCBC 15.0..

– Step (5): Bus Bars “For Final Distribution Boards” • The resistance of bus bars is generally negligible, so that the impedance is practically all reactive, and amounts to

approximately 0.15 mΩ/metre length per phase for LV bus bars (doubling the spacing between the bars increases the reactance by about 10% only).

0. ≈

Α=

ρBBR

[ ] [ ])()(15.0.. meterlengthmetermXZ BBBB ×Ω≈≈ Where ρ: Resistivity constant of the bus duct material at 70oC (in mΩ.mm2/m).

⇒ For copper: ρ = 21 mΩ.mm2/m. ⇒ For aluminum: ρ = 33 mΩ.mm2/m.





129

– Step (6): Cables

• Cable reactance values can be obtained from the manufacturers. For c.s.a. of less than 50 mm2 reactance may be ignored.

• In the absence of other information, For 50 Hz systems

⇒ For Single Core: Xs.c = (0.07 mΩ/metre) x ℓ

⇒ For Multi Core: Xs.c = (0.15 mΩ/metre) x ℓ For 60 Hz systems

⇒ For Single Core: Xs.c = (0.09 mΩ/metre) x ℓ

⇒ For Multi Core: Xs.c = (0.17 mΩ/metre) x ℓ

• The resistance of Cable is given by the formula

Α=

ρLR

[ ] [ ])()(07.0 meterlengthmetermX L ×Ω≈ Where ρ: Resistivity constant of the bus duct material at 70oC (in

mΩ.mm2/m). ⇒ For copper: ρ = 21 mΩ.mm2/m. ⇒ For aluminum: ρ = 33 mΩ.mm2/m.


• In case of using n typical cables in parallel, the equivalent resistance will be the

resistance of one cable divided by n.

At Point Resistances (mΩ) Reactances (mΩ) Impedances

(mΩ) Short Circuit Current (KA)

a Ra=RSC+RTR Xa=XSC+XTR Zt(a)=√(Ra2+Xa

2) ISC(a) = Us/Zt(a) b Rb=RSC+RTR+RBD+RMCB Xb=XSC+XTR+XBD+XMCB Zt(b)=√(Rb

2+Xb2) ISC(b) = Us/Zt(b)

c Rc=RSC+RTR+RBD+RMCB+RBB1+RCB1 Xc=XSC+XTR+XBD+XMCB+XBB1+XCB1 Zt(c)=√(Rc2+Xd

2) ISC(c) = Us/Zt(c) d Rd=RSC+RTR+RBD+RMCB+RBB1+RCB1+RL1+RCB4 Xd=XSC+XTR+XBD+XMCB+XBB1+XCB1+XL1+XCB4 Zt(d)=√(Rc

2+Xd2) ISC(d) = Us/Zt(d)

• Notice That: S.C. @ (a) > S.C. @ (b) > S.C. @ (c) > S.C. @ (d)

137. 222BComplete

o 223BIlluminance is measured in footcandles (lumens/square foot) or lux (lumens/square

meter). Where one footcandle equals -------- lux.

o 224BLuminous intensity is measured in Candela or Lumen (Lu).where one Candela equals -

------- Lumen (Lu).

AAnnsswweerr 1 footcandle = 10.76 lux

1 Candela = 12.6 Lumen (Lu)




130

138. 225BCompare between using Central Battery System and Self Contained EM Lighting.

AAnnsswweerr

Features Central Battery System Self Contained EM Lighting Individual light monitoring Standard No Range and Wattage of fittings Extensive Limited Light Output Up to 100% 15-20% Automatic function Test Yes No Automatic Duration Test Yes No Maintenance Cost Negligible High Data Access/ Control at central location Yes No BMS Interface Yes No Battery Life 10 Years 1.5 to 2.5 years Maximum height of mounting Maximum 16 Meters with CEAG lights Maximum 8 Meters Electronic Log Book Facility 10 Years None Available Environment friendly

Maintenance Free Sealed Lead acid batteries are 99% recyclable. Green Li-

on battery option is available

Ni-Cd batteries stress the environment and safe disposal is

an issue Note: Some features can be incorporated in Self contained system, but costs are comparably higher.

139. 226BWhat is the difference between circular & sectoral sections in cables?

AAnnsswweerr

Circular Sections Sectoral Sections

Shape

Usage LV & MV LV only because of Electrical sharp edge in

MV which causes high electrical strengths. Electrical sharp edge Not present. “Good” Present.

Diameter Larger for same C.S.A. “Bad” Smaller for same C.S.A. “Good” Space of installation More “Bad” Less. “Good”

Cost More “Bad” Less. “Good”




131

140. 227BHow can you size the earthing conductor according to size of phase cable size or according

to C.B. size using NEC & IEC?

AAnnsswweerr According to NEC :

Table 250.66 Size of Alternating-Current Grounding Electrode Conductor

Size of Largest Ungrounded Service-Entrance Conductor or Equivalent Area for Parallel Conductors Size of Grounding Electrode Conductor

Copper Aluminum or Copper-Clad Aluminum Copper Aluminum or Copper-

Clad Aluminum (AWG/kcmil) mm ² (AWG/kcmil) mm ² (AWG/kcmil) mm ² (AWG/kcmil) mm ²

2 or smaller 35 or smaller 1/0 or smaller 70 or smaller 8 10 6 16 1 or 1/0 50 or 70 2/0 or 3/0 70 or 95 6 16 4 25

2/0 or 3/0 70 or 95 4/0 or 250 120 or 150 4 25 2 35 Over 3/0

through 350 Over 95

through 185 Over 250

through 500 Over 150 through

(240- 300) 2 35 1/0 50-70

Over 350 through 600



Over (240- 300) through (400-500) 1/0 50-70 3/0 95




Over (4003500) through (800-1000) 2/0 70 4/0 120

Over 1100 Over 500 Over 1750 Over (800-1000) 3/0 95 250 150

Table 250.122 Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment Rating or Setting of Automatic Overcurrent

Device in Circuit Ahead of Equipment, Conduit, etc., Not Exceeding (Amperes)

Copper Aluminum or Copper-Clad Aluminum

(AWG/kcmil) mm ² (AWG/kcmil) mm ² 15 14 2.5 12 4 20 12 4 10 6 30 10 6 8 10 40 10 6 8 10 60 10 6 8 10

100 8 10 6 16 200 6 16 4 25 300 4 25 2 35 400 3 25-35 1 50 500 2 35 1/0 50-70 600 1 50 2/0 70 800 1/0 50-70 3/0 95 1000 2/0 70 4/0 120 1200 3/0 95 250 120-150 1600 4/0 120 350 185 2000 250 120-150 400 185-240 2500 350 185 600 300 3000 400 185-240 600 300 4000 500 240-300 800 400 5000 700 300-400 1200 630 6000 800 400 1200 630




132

According to IEC:

IEC 60364-5-54. This table provides two methods of determining the appropriate c.s.a. for both PE or PEN conductors

(1) Data valid if the prospective conductor is of the same material as the line conductor. Otherwise, a correction factor must be applied. (2) When the PE conductor is separated from the circuit phase conductors, the following minimum values must be respected:

o 2.5 mm2 if the PE is mechanically protected o 4 mm2 if the PE is not mechanically protected

(3) For mechanical reasons, a PEN conductor, shall have a cross-sectional area not less than 10 mm2 in copper or 16 mm2 in aluminium.

– The two methods are:

Adiabatic (which corresponds with that described in IEC 60724) This method, while being economical and assuring protection of the conductor against overheating, leads to small c.s.a.’s compared to those of the corresponding circuit phase conductors. The result is sometimes incompatible with the ecessity in IT and TN schemes to minimize the impedance of the circuit earth-fault loop, to ensure positive operation by instantaneous overcurrent tripping devices. This method is used in practice, therefore, for TT installations, and for dimensioning an earthing conductor.

Simplified This method is based on PE conductor sizes being related to those of the corresponding circuit phase conductors, assuming that the same conductor material is used in each case.

– Note: When, in a TT scheme, the installation earth electrode is beyond the zone of influence of the source earthing

electrode, the c.s.a. of the PE conductor can be limited to 25 mm2 (for copper) or 35 mm2 (for aluminium). The neutral cannot be used as a PEN conductor unless its c.s.a. is equal to or larger than 10 mm2 (copper) or 16

mm2 (aluminium). Moreover, a PEN conductor is not allowed in a flexible cable. Since a PEN conductor functions also as a

neutral conductor, its c.s.a. cannot, in any case, be less than that necessary for the neutral. This c.s.a. cannot be less than that of the phase conductors unless:

• The kVA rating of single-phase loads is less than 10% of the total kVA load, and • Imax likely to pass through the neutral in normal circumstances, is less than the current permitted for the

selected cable size. Furthermore, protection of the neutral conductor must be assured by the protective devices provided for phase-

conductor protection.

141. 228BWhy CU wires are preferable in indoor distribution while Al cables are preferred in

electrical transmission?

AAnnsswweerr CU wires are preferable in indoor distribution because it is more flexible in bending & branching & smaller c.s.a for the

same current. Al cables are preferred in electrical transmission because it’s cheaper, straight distances (no large bending) & causes no

problem in its large c.s.a




133

ZtUcIs S=.

142. 229BFor the following factors. Explain the effect of increasing or decreasing these factors on

short circuit.

o 230BCable length

o 231BCable CSA

o 232BConductor Type

o 233BTransformer per unit impedance

o 234BTransformer load.

o 235BSystem Voltage

o 236BBus Bars

o 237BCircuit Breakers

AAnnsswweerr Equations required:

1. Cable length If ℓ ↑ → RL ↑ → Zt ↑ → ISC ↓ While If ℓ ↓ → RL ↓ → Zt ↓ → ISC ↑

2. Cable CSA

If A ↑ → RL ↓ → Zt ↓ → ISC ↑ While If A ↓ → RL ↑ → Zt ↑ → ISC ↓

3. Conductor Type

If ρ ↑ → RL ↑ → Zt ↑ → ISC ↓ While If ρ ↓ → RL ↓ → Zt ↓ → ISC ↑

Since ρAL > ρCU Therefore ISC(AL) < ISC(CU)

4. Transformer per unit impedance

If USC ↑ → ZT.R ↑ → Zt ↑ → ISC ↓ While If USC ↓ → ZT.R ↓ → Zt ↓ → ISC ↑

5. Transformer load.

If kVA ↑ → ZT.R ↓ → Zt ↓ → ISC ↑ While If kVA ↓ → ZT.R ↑ → Zt ↑ → ISC ↓

6. System Voltage

If US ↑ → ISC ↑ While If USC ↓ → ISC ↓

7. Bus Bars

Increasing or decreasing the rating of B.B’s has neglected effect on short circuit current.

8. Circuit Breakers

Increasing or decreasing the rating of C.B’s has neglected effect on short circuit current.

22ttt XRZ += Α

=ρ

LR css

RT UkVAUZ .

2

.3

=




134

143. 238BWhat are the different types of cables?

AAnnsswweerr 1. Power Cables: “For Lighting, Sockets, Motors, Distribution Boards, Distribution Networks, Transmission Networks … Etc”

1.1. Indoor Wiring: 300/500V & 450/750V. 1.2. Low Voltage Cables: Up to 1KV. 1.3. Medium Voltage Cables: > 1KV ≤ 36KV. 1.4. High Voltage Cables: > 36KV ≤ 170KV. 1.5. Extra High Voltage Cables: ≥170KV.

2. Telecommunication Cables: “For Telephones & Communications”

3. Special Cables: “For Data & Signals”

3.1. LAN and Telephone Cables:

3.1.1. Data Cable – Cat 5e: “The cable is used for Local Area Computer Networks mainly in office or business environments”

3.1.2. Data Cable – Cat 6: “The cable is used for Local Area Computer Networks where performance greater than that available from category 5 specification is required”

3.1.3. Instrumentation Cables: “These cables are used in the chemical and etrochemical industries for the transmission of analogue and digital signals for measurements and process control purposes”

3.2. Coaxial Cables:

3.2.1. MATV Cables: “ TV patented coaxial cables for satellite and digital installations” 3.2.2. RG Cables: “Cables used for transmitting and receiving high frequency signals in radio frequency devices and

connections” 3.2.3. PVC Insulated Multipairs: “The cable is used for Indoor installation and interconnection of Transmission,

Telephone, Telegraph and Electronic equipment” 3.3. Fire Resistant Cables: “These cables are used in fire fighting alarm systems in hazardous area where the safety is highly

required during fire condition” 3.4. Fire Alarm Cables: “These cables are used for communication and signaling in fire alarm systems” 3.5. Control Cables: “For outdoor and indoor installations in damp and wet locations, connecting signaling and control units

in industry, in railways, in traffic signals, in thermopower and hydropower stations. They are laid in air, in ducts, in trenches, in steel support brackets or direct in ground, when well protected”

3.6. Automotive Wires: “ This wire is used in the manufacture of electrical harnesses for cars and other automotive products” 3.7. Appliance Cables and Cords: “These cables can be used for domestic premises, kitchens, cooking, offices and heating

appliances or light duties for light portable appliances provided that the cable does not come into contact with the heating elements”

3.8. Fiber Optic Cables: “Cables are particularly suitable for placing and pulling into cable conduits and shafts inside

buildings and in the building riser between floor distributors” 3.9. Optical Ground Wire: “These cables suitable for installation as optical ground wire in powerline installations. The cable

acts as a normal ground wire protecting phase wires from lightning strikes and carries earth fault currents. The cable provides also an optic path in powerline installations for telecommunication need”

3.10. Low Smoke Halogen: “Power Cable but Halogen-free cables are increasingly specified for public buildings and areas

where large numbers of people may be present. Such as; Theaters, hotels, hospitals and closed public places” 3.11. Submarine Cables: “Power Cable but water blocked can carry power & data”




135

144. 239BWhat are the standards C.S.A’s for power cables for low, medium & high voltage?

AAnnsswweerr

Low Voltage Cables Medium Voltage Cables High Voltage Cables

Single Core - mm2 Multi Core - mm2 Single Core - mm2 Multi Core - mm2 Only Single Core - mm2 1.5 1.5 2.5 2.5 4 4 6 6 10 10 16 16 25 25 25 25 35 35 35 35 50 50 50 50 70 70 70 70 95 95 95 95

120 120 120 120 150 150 150 150 150 185 185 185 185 185 240 240 240 240 240 300 300 300 300 300 400 400 400 400 500 500 500 500 630 630 630 800 800 800

1000 1000 1000 1200 1600 2000 2500

145. 240BWhat is the difference between armoured & unarmoured cables?

AAnnsswweerr Armoured Cables are used for outdoor installations in damp & wet locations, where mechanical damages are expected to

occur. Armoured Cables costs about (10-15%) more than unarmoured cables.

146. 241BScreening of MV cables is used in earthing. Right or wrong?

AAnnsswweerr Right




136

147. 242BHow can you convert American Wire Gauge (AWG) to square mm cross sectional area?

AAnnsswweerr American Wire Gauge (AWG) is a U.S.

standard set of wire conductor sizes. The "gauge" is related to the diameter of the wire.

The higher the gauge number, the smaller the diameter and the thinner the wire.

Conductors larger than 4/0 AWG are sized in circular mils, beginning with 250,000 circular mils.

Prior to the NEC 1990 edition, a 250,000-circular-mil conductor was labeled 250 MCM. The term MCM was defined as 1000 circular mils (the first M being the Roman numeral designation for 1000). Beginning in the 1990 edition, the notation was changed to 250 kcmil to recognize the accepted convention that k indicates 1000. UL standards and IEEE standards also use the notation kcmil rather than MCM.

148. 243BWhat is the problem of unloading the transformer?

AAnnsswweerr The transformer must not be unloaded for large duration, since the transformer will be exposed to humidity. Under such

conditions the transformer must be loaded, to remove the humidity formed inside the insulating materials. In highly polluted area, the turns and core are completely enclosed inside a sealed tank to protect the transformer.

149. 244BFor replacing an existing Lighting system of fluorescent lamps 110 Volt, 60 Hz by new

fluorescent lamps 220 Volt, 60 Hz, which of the following devices should be changed Lamp,

Ballast and Starter?

AAnnsswweerr Ballast Only

American Wire Gauge Size “AWG”

Equivalent Metric Conductor Size “mm2 ”

# Kcmil Actual Size Equivalent Size 20 - 0.519 0.5-0.75 18 - 0.823 1 16 - 1.31 1.5 14 - 2.08 2.5 12 - 3.31 4 10 - 5.26 6 8 - 8.37 10 6 - 13.3 16 4 - 21.15 25 3 - 26.67 25-35 2 - 33.62 35 1 - 44.21 50

1/0 - 53.49 50-70 2/0 - 67.43 70 3/0 - 85.01 95 4/0 - 107.2 120 - 250 127 120-150 - 300 152 150 - 350 177 185 - 400 203 185-240 - 450 228 240 - 500 253 240-300 - 600 304 300 - 700 354 300-400 - 750 380 400 - 1000 507 500 1250 633 630 1500 760 800 1750 886 800-1000 2000 1013 1000




137

150. 245BHow can you convert from NEMA to IEC Enclosure?

AAnnsswweerr Converting from NEMA enclosure classifications to IEC enclosure classifications

– NEMA enclosure classifications: are developed by NEMA and used in the U.S./American market.

– Ingress Protection (or Index of Protection) - IP - ratings: are developed by the European Committee for Electro

Technical Standardization (CENELEC) (described IEC/EN 60529), and specifies the environmental protection and enclosure provided.

NEMA Enclosure Types IEC Enclosure Classification Designation

1 Indoor - General Purpose IP10 Protected against solid objects up to 50mm, e.g. accidental touch by hands.

2 Indoor -Drip proof (limited amounts of falling water ) IP11 Protected against solid objects up to 50mm, e.g. accidental touch by hands. Protection against vertically falling drops of water e.g. condensation.

3R Outdoor - Rain tight, Sleet Resistant- (undamaged by the formation of ice on the enclosure ) IP14

Protected against solid objects up to 50mm, e.g. accidental touch by hands. Protection against water sprayed from all directions, limited ingress permitted.

3 Outdoor - Dust tight, Rain tight, Sleet tight (Same as 3R plus windblown dust) IP54

Protected against dust limited ingress (no harmful deposit). Protection against water sprayed from all directions, limited ingress permitted.

3S Outdoor - Dust tight, Rain tight, Sleet tight (Same as 3R plus windblown dust; external mechanisms remain operable while ice laden)

IP54 Protected against dust limited ingress (no harmful deposit). Protection against water sprayed from all directions, limited ingress permitted.

4 Indoor & Outdoor - Watertight, Dust tight, Sleet Resistant (splashing water, windblown dust, hose-directed water, undamaged by the formation of ice on the enclosure)

IP56 Protected against dust limited ingress (no harmful deposit).

4X Indoor & Outdoor - Watertight, Dust tight, Corrosion-Resistant (Same as 4 plus resists corrosion) IP56 Protected against dust limited ingress (no harmful deposit).

5 Indoor - Dust tight, Drip-Proof (provide a degree of protection against settling airborne dust, falling dirt, and dripping noncorrosive liquids)

IP52 Protected against dust limited ingress (no harmful deposit). Protection against direct sprays of water up to 15o from the vertical.

6 Indoor & Outdoor - Occasionally Submersible, Watertight, Sleet Resistant (Same as 3R plus entry of water during temporary submersion at a limited depth)

IP67 Totally protected against dust. Protected against the effect of immersion between 15cm and 1m.

6P Indoor & Outdoor - Watertight, Sleet Resistant- Prolonged Submersion (Same as 3R plus entry of water during prolonged submersion at a limited depth)

IP67 Totally protected against dust.

Protected against the effect of immersion between 15cm and 1m.

12 Indoor - Dust tight and Drip tight- Indoor IP52 Protected against dust limited ingress (no harmful deposit). Protection against direct sprays of water up to 15o from the vertical.

12K Indoor - Dust tight and Drip tight, with Knockouts IP52 Protected against dust limited ingress (no harmful deposit). Protection against direct sprays of water up to 15o from the vertical.

13 Indoor - Oil tight and Dust tight IP54 Protected against dust limited ingress (no harmful deposit). Protection against water sprayed from all directions, limited ingress permitted.

– This table can be used to convert from NEMA Enclosure Types to IEC Enclosure Types – Note! NEMA standards meet or exceed IEC standards. The conversion does not work in the opposite direction.

http://www.engineeringtoolbox.com/nema-enclosures-d_919.html

http://www.engineeringtoolbox.com/ip-ingress-protection-d_452.html

http://www.engineeringtoolbox.com/nema-enclosures-d_919.html

http://www.engineeringtoolbox.com/ip-ingress-protection-d_452.html




138

151. 246BWhat are the different risks on human that caused by electricity? Explain.

AAnnsswweerr All electrical installations produce earth leakage currents. Even small values of these leakage currents present man risks

which can cause serious injuries and damages to the human life and property A few milliamps suffice to seriously harm the human body. The risk of the person not letting go, breathing arrest or cardiac

fibrillation increases proportionally to the time the person is exposed to the electric current.

Different Risks that caused by electricity:

– Direct contact: With a live conductor.

– Indirect contact: If the person touches a conductive parts that are normally not live, but

may become live by accident due to failure of insulation of a device or conductor.

– Fire hazard: 40 % of fire accidents in industrial & domestic buildings are the result of an electrical

fault, which happens due to one of two main causes. Deterioration of cable insulation due to ageing or overloading and the presence of

dust and humidity create electrical arcs & arc tracking. Very little energy is sufficient to ignite a fire; an insulation fault current ≥ 300 mA represents a real risk of fire. Incorrectly set protective devices or incorrectly calculated fault loop impedances lead

to excessive temperature rise with overloads or short circuits.

– Destruction of loads: Electrical devices deteriorate over time and may present insulation faults. A minor

insulation fault can rapidly develop and turn into a short circuit causing major damage and even the total destruction of the load.




139

152. 247BWhat are the different tripping characteristics and rated currents for MCB’s?

AAnnsswweerr Tripping characteristics and rated currents

– B-, C- and D-Characteristic:

The new characteristics acc. EN 60 898 are for line protection. They all have the same thermal settings and

differ only in their magnetic tripping values. The higher magnetic settings of the C- or D-characteristics are for applications with start or high inrush-

currents.

Characteristic Thermal Tripping Electromagnetic Tripping B-Characteristic 1.13…..1.45 x In 3…...5 x In C-Characteristic 1.13…..1.45 x In 5…..10 x In D-Characteristic 1.13…..1.45 x In 10…..20 x In

– K-Characteristic:

For cable and appliance protection. Rated currents 0.5 to 63 A. Motor protection can be achieved by the selection of the M.C.B. with the correct

rated current corresponding to the motor data. The electro-magnetic trip is set in such a way that the motor starting current does not lead to tripping. Due to the higher magnetic non tripping current, in circuits with incandescent lamp groups, mains parallel

operated fluorescent lamps or other discharge lamps, the conductor cross-section to be protected can be more economically utilized as compared to a M.C.B. of the same rated current in tripping characteristic B.

– Z-Characteristic:

For protection of semiconductor devices and voltage transformer circuits.




140

153. 248BWhat is the obstruction lighting? What are their types? How it’s designed?

AAnnsswweerr Obstruction Aircraft Warning Lights:

– They are high-intensity lighting devices that are attached to tall structures and used as collision avoidance

measures. Such devices make the structure much more visible to passing aircraft and are usually used at night, although in some countries they are used in the daytime also. These lights need to be of sufficient brightness in order to be visible for miles around the structure

Lamp types:

– In the United Kingdom, there are two types of lights: Red lamps that are either constantly illuminated or turn on and off slowly in a cycle of a few seconds. White xenon discharge flashers. (However new regulations stipulate the use of red lamps at nighttime only.

Xenon flashers are therefore gradually being phased out). – In the United States and Canada, there are several types of lights:

Obstruction lights (that are constantly illuminated) Red Beacons/Red strobes High Intensity White (Strobe) Lights Medium Intensity White (Strobe) Lights

Application for Design:

– Traditionally, red lamps (or beacons) use incandescent filament bulbs. In order to improve the otherwise quite short

lifespan, they are made with a ruggedised design and are run below normal operating power (under-running). A recent development has been the use of arrays of high power red LEDs in place of incandescent bulbs, which has only been possible since the development of LEDs of sufficient brightness. LED based lamps have a significantly longer lifespan than incandescent bulbs, thus reducing maintenance costs and increasing reliability. Several manufacturers have also developed medium intensity white strobes based on LED technology to replace Xenon.

– Xenon flashers, whilst more visually impressive, tend to require frequent replacement and so have become a less favored option. However, with the advent of LEDs, white strobes are still somewhat desired.

– It is common to find structures with white xenon flashers/white strobes during the daytime, and red lights at night. Red lights are commonly found to be used in urban areas, since it is easier for pilots to spot them from above. White strobes (that flash 24/7) may also be used in urban areas. However, it has been recommended that flashing white strobes should not be used in densely populated areas; the lights usually merge with background lighting at nighttime, making it difficult for pilots to spot them and thereby aggravating the hazard. In addition, residents near the lit structure will complain of light trespass.

– In rural areas, red beacons/strobes may also be used during nighttime. However, white strobes are (sometimes) preferred since it reduces maintenance cost (i.e. no maintenance of painting, no red side lights) and there are no background lights that would blend with the strobes.

– For white strobes, there is a medium intensity white strobe and a high intensity white strobe. Medium Intensity White Strobes are usually used on structures that are between 200–500 feet (61-152.4 meters). If a medium white strobe is used on a structure greater than 500 feet (152.4 meters), the structure must be painted.

– The common medium white strobe flashes 40 times in a minute, at an intensity of 20,000 candelas for daytime/twilight, and 2,000 candelas at nighttime.

– A high intensity white strobe light is used on structures that are greater than 500 feet (152.4 meters). These lights provide the highest visibility both day and night. Unlike a medium strobe, a high intensity strobe doesn't provide 360˚ coverage; this requires the use of at least 3 high strobes at each level. On the other hand, it reduces maintenance costs (i.e. no painting). If the structure has an antenna at the top that is greater than 40 feet, a medium intensity white strobe light must be placed above it rather than below.

– The common high white strobe flashes 40 times in a minute, at an intensity of 270,000 candelas for daytime, 20,000 candelas at twilight, and 2,000 candelas at night-time.

http://en.wikipedia.org/wiki/United_Kingdom

http://en.wikipedia.org/wiki/Xenon_flash_lamp

http://en.wikipedia.org/wiki/United_States

http://en.wikipedia.org/wiki/Canada

http://en.wikipedia.org/wiki/Incandescent_light_bulb

http://en.wikipedia.org/wiki/Light-emitting_diode

http://en.wikipedia.org/wiki/Candela




141

– Dual lighting is where a structure is equipped with white strobes for daytime use, and red beacons/strobes for nighttime use. In urban areas, these are commonly preferred since it usually exempts a structure from the requirement of having to be painted. One advantage to the dual system is that when the uppermost red lights fail, the lighting switches onto its Backup lighting system, which uses the white strobes (at its night intensity) for nighttime. In the United States and Canada, red beacons are slowly going out of commission and being replaced with red strobes. In addition, some medium strobes are equipped to flash the white light for daytime and red light for night in a single strobe (unlike the old type which had two different lights).

– For high tension power lines, the white strobes are equipped to flash 60 times per minute, using the same intensities as stated above. Unlike the common white strobes, these strobes are specified not to flash simultaneously. The flash pattern should be middle, top, and bottom to provide "a unique system display

Structure using high intensity white lights and a medium intensity white strobe

Structure using a Red/White strobe

Structure using a white stobe

Antenna Tower 446 feet with its red and white aircraft warning paint clearly visible in the setting sun.

Structure using a red warning beacon Closed up aircraft warning light on top of a high-rise

154. 249BWhat specifications must be applied in cable insulation?

AAnnsswweerr The following specifications must be applied in cable insulation:

– High specific resistance. – High dielectric strength. – It should be tough and flexible. – Capable of standing high temperatures without failure. – It should be non-flammable. – It should not be exposed to acids or alkalis. – It should be capable of withstanding high rupturing voltages.




142

155. 250BDetermine how many 6mm2 cu single stranded conductors are permitted in a trade size 1¼

rigid metal conduit (RMC)?

AAnnsswweerr As per NEC Code Table 1 permits 40 percent fill for over two conductors. From Table 4, 40 percent fill for trade size 11 ⁄4 RMC is 394mm2, and from cables catalogue the diameter of a 6mm2 cu

single stranded conductor is 4.7 mm. therefore cross-sectional area is πr2 = 3.14(4.7/2) 2 = 17.36 mm2 the number of conductors permitted is calculated as follows:

conductors

conductorpermmmm

7.2236.17

3942

2

=−

Based on the maximum allowable fill of 40 percent from Table

1, the number of 6mm2 cu single stranded conductors in trade size 1¼ RMC cannot exceed 22. Table 4

156. 251BDoes the way of mounting, positioning and orientation of a lamp (Burning Position) affect

the burning?

AAnnsswweerr There are light sources which can be operated in any position (Universal Burning). There are those which have specific

limits. This characteristic must be given proper attention to avoid system failure and costly maintenance. The tolerances provided by the manufacturers must not be exceeded. In determining lumiaires mounting position and orientation, this information is taken into account.




143

157. 252BAccording to NEC. Determine the minimum size rigid metal conduit (RMC) allowed for the 9

mixed conductor sizes and types described as followed:

o 253B3 single stranded wires cu of 4mm2 each

o 254B3 single stranded wires cu of 10mm2 each

o 255B3 single stranded wires al of 16mm2 each

AAnnsswweerr

Quantity Wire Type and Size Diameter of each wire from catalogue (mm)

C.S.A. of Each Wire (mm2)

Total C.S.A. of each type (mm2)

3 CU - 4mm2 7 38.5 115.5

3 CU - 10mm2 8.9 62.2 186.6

3 AL - 16mm2 9.9 77 231

Total c.s.a for all types (mm2) 533.1

As per NEC Code The ‘‘Over 2 Wires’’ column in Table 4 indicates that 40 percent of a trade size 1½ RMC is 533 mm2. Therefore, trade size

1½is the minimum size RMC allowed for this combination of 9 conductors.

Table 4

158. 256BWhat are the most available sizes for LV HRC fuses?

AAnnsswweerr

According to IEC 269-2-1 Standards

Rated Current Range “A”

2 4 6 10 16 20 25 32 35 40 50 63 80 100 125 160 200 224 250 315 355 400 500 630

Rated Breaking Capacity “kA”

AC 120KA DC 100KA

Rated Voltage “V”

AC 500V DC 440V




144

159. 257BA 200-ampere feeder is routed in various wiring methods (EMT) conduit & (RMC) conduit

from the main switchboard in one building to a distribution panel board in another

building. The circuit consists of muli-core cable 4x70 + 25 mm2 CU - XLPE/PVC

unarmoured. Select the proper trade size for the various types of conduit and tubing to be

used for the feeder.

AAnnsswweerr All the raceways for this example require conduit fill to be calculated according to Table 1 in Chapter 9 in NEC Code

which permits conduit fill to a maximum of 40 percent where more than two conductors are installed in the conduit or tubing.

Wire Size and Type Overall Diameter (mm) C.S.A. (mm2)

4x70 mm2 CU - XLPE/PVC 31.4 774

25 mm2 CU - XLPE/PVC 11 95

Total c.s.a for all types (mm2) 869

The ‘‘Over 2 Wires’’ column in Table 4 indicates that 40 percent of a trade size 2½ EMT is 1513 mm2. Therefore, trade size 2½is the minimum size EMT allowed for this feeder.

The ‘‘Over 2 Wires’’ column in Table 4 indicates that 40 percent of a trade size 2 RMC is 879 mm2. Therefore, trade size 2 is the minimum size RMC allowed for this feeder.




145

160. 258BWhat are the capacities of PVC conduits for different cable sizes (single & multi-core)?

AAnnsswweerr

Capacity of PVC Conduits Single Core Cables (1C PVC)

Cable Size (mm2)

Conduit Size (mm) 20 25 32 40 50 63 75 90 110

1.5 10 16 28 2.5 6 10 18 4 4 6 12 22 6 3 5 8 16 10 2 3 6 10 15 16 1 2 4 8 12 25 1 1 3 5 8 35 1 1 2 3 6 50 1 1 2 4 6 70 1 1 2 3 5 95 1 1 3 4

120 1 1 2 3 4 150 1 1 3 3 185 1 1 2 3 240 1 1 1 2 4 300 1 1 2 3 5 400 1 1 1 2 4

161. 259BWhat is the relation between C.B & Busbar?

AAnnsswweerr

The Relation Between C.B & Busbar C.B ( AF ) Busbar Cross section (mm2)

6000A 6 6.4*152 5000A 6 6.4*127 4000A 4 6.4*127 3200A 4 6.4*102 2500A 2&4 6.4*1276_ 63.5 2200A 2 6.4*102 2000A 2 6.4*102 1600A 2 6.4*76.2 1500A

For current less than 1600 A busbar rating calculation by 1.55A/mm2

1200A 1000A 800A 630A 400A 250A

Note: All circuit breaker ampere frame according to Schneider Electric & all bus bars cross section according to NEC.

Capacity of PVC Conduits Multi Core Cables (4c-XLPE/PVC)

Cable Size (mm2)

Conduit Size (mm) 20 25 32 40 50 63 75 90 110

2.5 1 1 2 4 6 4 1 1 3 5 6 1 1 2 4 10 1 1 1 3 16 1 1 2 25 1 1 1 35 1 1 1 3 50 1 1 2 70 1 1 1 2 95 1 1 1

120 1 1 1 2 150 1 1 1 185 1 1 1 240 1 1




146

162. 260BHow can you find the cable size with regards to C.B Size?

AAnnsswweerr

The Relation Between C.B & Cables Size C.B ( AT ) ( 3 x L + N ) + E (mm2)

400A ( 3 x 300 + 150 ) + 95 300A ( 3 x 240 + 120 ) + 95 250A ( 3 x 185 + 95 ) + 95 225A ( 3 x 150 + 70 ) + 70 200A ( 3 x 120 + 70 ) + 70 175A ( 3 x 95 + 50 ) + 50 150A ( 3 x 70 + 35 ) + 35 120A ( 3 x 50 + 25 ) + 25 100A ( 3 x 35 + 16 ) + 16 80A ( 3 x 25 + 16 ) + 16 63A ( 3 x 16 + 10 ) + 10 50A ( 3 x 10 + 6 ) + 6 40A ( 3 x 10 + 6 ) + 6 32A ( 3 x 6 + 4 ) + 4 20A ( 4 x 4 ) + 4

163. 261BWhat are the most available sizes for disconnecting switches?

AAnnsswweerr

Disconnecting Switches Safety Switches “Ampere” Fuse Size “Ampere”

30 15, 20, 25, 30 60 35, 40, 45, 50, 60

100 70, 80, 90, 100 200 110, 125, 150, 175, 200 400 225, 250, 300, 350, 400 600 450, 500, 600 800 700, 800

1200 1000, 1200 1600 1600 2000 2000 2500 2500 3000 3000 4000 4000 5000 5000 6000 6000

Standard of Disconnected Switch

5 A 10 A 16 A 16 A 20 A 26 A 26 A 30 A 32 A 40 A 50 A 60 A 63 A 80 A 100 A 125 A 800 A 1000 A

The table refer to Schneider Electric

Standard of Fuses and Fixed-Trip Circuit Breakers 20 A 25 A 30 A 35 A 40 A 45 A 50 A 60 A 70 A 80 A 90 A 100 A 110 A 125 A 150 A 175 A 200 A 225 A

250 A 300 A 350 A 400 A 450 A 500 A 600 A 700 A 800 A 1000 A 1200 A 1600 A 2000 A 2500 A 3000 A 4000 A 5000 A 6000 A

Additional standard ampere ratings for fuses shall be 1, 3, 6, 10, and 601. The use of fuses and inverse time circuit breakers with nonstandard ampere ratings shall be permitted. The table refer to NEC , Schneider Electric




147

164. 262BWhat are the C.B. ratings & short circuit capacities in American & European standard?

AAnnsswweerr

C.B Ratings “Ampere” American (NEC) European (IEC) AT AF AT AF

6 63 10 60 10 63 15 60 16 63

20 60 20 63 25 60 25 63 30 60 32 63

35 60 40 60 40 63 45 60 50 60 50 63 60 60 63 63

70 100 80 100 80 100 90 100

100 100 100 100 110 250 125 250 125 125 150 250 160 250 160 160 175 250 200 250 225 250 250 250 250 250 00 400

400 400 400 400 600 600

630 630 800 800 800 800

1000 1200 1000 1000 1200 1200

1250 1250 1600 1600 1600 1600 2000 2000 2000 2000 2500 2500 2500 2500

3200 3200 4000 4000 4000 4000 5000 6300 5000 6300 6000 6000

6300 6300

Short Circuit Capacities “KA” American (NEC) European (IEC)

5 6 8

10 14 15 16

22 25 30 35 40 50

65 65 70 85

100 100 120 200




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165. 263BWhat is the control gear of a luminaire?

AAnnsswweerr

It is essential to provide suitable to operate discharge lamps. These lamps have electrical requirements to ensure efficient operation, as designed, which are provided by these control gears.

Ballast:

– A major component of a luminaire which control and limit electrical energy necessary to operate discharge lamps is series impedance, known as ballast. Its major function is to: Pre-heat the electrodes of a discharge lamp. Supply controlled surge of high voltage and current necessary to initiate an arc between lamp electrodes and

sustain it. – Fluorescent lamps requiring a starter are operated by normal power factor ballast or choke. To improve the power

factor, a capacitor is connected across the AC Supply. Ballast manufacturers specify the P.F. of the ballast to determine the capacitor’s value enough to attain a 0.85 lagging circuit.

– Other fluorescent lamps are designed to be used with a rapid start ballast whish have a heater winding unit. Thus, eliminating the use of a starter and ensure continuous current to the lamps. The lamp starts immediately reducing flickers. Rapid start ballasts are of High Power Factor (P.F = 0.95) and reliable in starting lamps in cold weather operation (-20F)

– A more efficient, lightweight and wider voltage range Electronic Ballast is widely used today. These ballasts are favored by many because of the advantages which are: Immediate start. No stroboscopic effects (flicker free). Reduced electricity consumption. High power factor. No humming sound. No magnetic fields. Automatically shuts-off defective lamps. Suitable for energy saving lamps. Reduced temperature generation. AC and DC operation.

– To control light output of fluorescent lamps from say 100% down to 30% dimming ballast is used with dimmer switch.

– For HID lamps, the ballast (core and coil) may be of open type or encased and potted depending on the luminaire construction and intended application.

Starters:

– The basic function of a starter is the necessary pre-heating of the electrodes of a fluorescent lamp with a limited

current flow from the fluorescent lamp ballast. The starting switch will open automatically once the electrodes reach the required temperature to emit electrons. With the application of starting high voltage from the ballast, the starting is completed resulting to a fully lighted lamp.

– Today, these starters may be equipped with reset buttons which automatically cut-off failing lamps. Other starters have cold weather operation advantage. Electronic starters are widely used as well.

Ignitors:.

– Voltage pulses which are higher than the mains supply are necessary to start discharge lamps. Ignitors provide

required high voltage pulser until the lamp is ignited. Some high pressure sodium lamps have built-in ignitors which may be operated with high pressure mercury ballast.

– A high pressure mercury lamp need not be assisted by these devices during ignition.




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Emergency Back:

– Luminaires may be equipped with an emergency pack comprising of converter/charger and NICD batteries. The system can be maintained, non- maintained or sustained depending on the requirement. During power failure of the mains supply the system is automatically switch-on to keep the lamp lighted for 1.5 or 3.0 hours. Charging starts once the mains supply is restored.

Capacitor:

– To improve the power factor of the circuit, a P.F capacitor is connected across the AC supply. The value of which

is dependent on the wattage and voltage rating from 8 µF to 25 µF – Another type of capacitor is used to suppress radio interference which is connected across the AC supply and

usually of low capacitance value 0.1 µF to 0.5 µF 166. 264BWhat are the methods of cooling of transformers? What does ONAN refers to?

AAnnsswweerr Methods of cooling are symbol with 4 letters. The first 2 letters refers to the type of fluid used & way of flow in cooling the

transformer internal winding. The other 2 letters refers to the type of fluid used & way of flow in cooling the transformer outer case.

Type of Fluid Way of Flow of the Fluid Letter Description Letter Description

O Oil N Natural A Air L Lubricant B Air Blast G Gas F Forced (using pumps) W Water

Example: ONAN refers to Oil Forced Air Natural (transformer internal wiring is cooled using forced oil by pump & the transformer outer case is naturally cooled by air

167. 265BWhat is the accepted percentage of loading a transformer? Can we increase the percentage of

loading the transformer more than 100%? Explain.

AAnnsswweerr The accepted percentage of loading a transformer is 80% for the 24 hours. We can increase the percentage of loading the transformer more than 100% but not all the time (24 hours). This percentage

loading increase depends on:

– Type of transformer: (dry type can be loaded more than oil type for the same conditions).

– Time of loading: (if the time of loading increase the ability of transformer to withstand more load will decrease & vice versa).

– Percentage of loading: (if the percentage of loading increase the withstand time of transformer will decrease & vice versa).

– Ambient temperature: (if the ambient temperature in the site is less than the ambient temperature that transformer is designed for its rated power so we can increase percentage load for more time & vice versa)

The transformer manufacturer gives data on the percentage of loading increase & time of loading & temperature.




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168. 266BState the advantages of using dry type transformers over oil immersed type?

AAnnsswweerr Advantages of dry type transformers over oil immersed type:

– The cheapest fire proof transformers. – Can be easily installed in buildings with complete security. – Need less maintenance and cyclic testing other than fluid immersed transformers. – Need no accessories, such as valves, breather and measuring devices of fluid immersed transformers. – Light, so can be easily installed on the roof of the building. – Completely secure from the view of fire, environment pollution. – Can with stand an acceptable amount of overload. – High efficiency with good voltage regulation and noiseless. – Large Reliability index, and nowadays used in the form of complete substation inside a metallic enclosure having

cable-connecting box in both the H.V. & L.V. sides. 169. 267BWhat is the information necessary while selecting the transformer protection system?

AAnnsswweerr The following information is necessary while selecting the protection system:

– Particulars of Transformer

KVA. Voltage ratio. Connections of windings. Percentage reactance. Neutral point earthing. Value of system earthing resistance. Whether indoor or outdoor, dry or oil filled. With or without conservator.

– Fault level at Power Transformer Terminals. – Network Diagram-Showing Position of Transformer.

170. 268BWhat are the advantages of selecting outdoor distribution transformers kiosks?

AAnnsswweerr Advantages of outdoor transformer kiosks selection:

– Compact dimensions and low installation space (i.e. it can be easily located close to load centers.). – Trouble free operations with energy supply to the customers without interruption. – Personal safety. – Minimum maintenance. – Simple installation. – Reliability.

So, the location of the kiosk should be selected such that the transportation & installation and maintenance are easily done.




151

171. 269BWhat are the requirements for fire water pump electrical connection as per NFPA 70?

AAnnsswweerr

The Requirements for Fire Water Pump Electrical Connection As Per NFPA 70 ( NEC 695) and NFPA 20 Chapter 6, 7, A6 & A7. 1. The supply conductors point (B) shall directly connect the power source (A) to either a listed fire pump controller or

listed combination fire pump controller and power transfer switch. 2. A single disconnecting means and associated overcurrent protective device shall be permitted to be installed between a

power source and one of the following: a) Listed fire pump controller. b) A listed combination fire pump controller and power transfer switch.

– The overcurrent protective device shall be selected or set to carry indefinitely the sum of the locked rotor current of the fire pump motor and pressure maintenance pump motor and the full load-current of the associated fire pump accessory equipment.

– The disconnecting means shall be lockable in the closed position and be marked " Fire pump disconnecting means" – The disconnecting means shall be supervised in the closed position by central station or remote station signal device

or local signaling service that causes the sounding of an audible signal at a constantly attended point. – A placard shall be placed adjacent to the fire pump controller, stating the location of this disconnecting means and

the location of the key.




152

3. A fire pump shall be permitted to be supplied by a separate service or by a tap located ahead of and not within the same cabinet, enclosure, or vertical switchboard section as the service disconnecting means.

4. A tap ahead of the on-site generator disconnecting means shall not be required. 5. Where reliable power cannot be obtained from a service or on-site electrical power production facility and cannot be

arranged to minimize the possibility of damage by fire from within the premises and exposing hazards, one more of the following shall also be provided:

a) An approved combination of two or more of the power sources. b) One of the approved power sources and an on-site standby generator. c) An approved combination of feeders constituting two or more power sources, but only as permitted to multi

building campus-style complexes. d) An approved combination of one or more feeders in combination with an on-site standby generator, but only as

permitted to multibuilding campus-style complexes. e) A redundant diesel engine-driven fire pump. f) A redundant steam turbine-driven fire pump.

6. The power sources shall be arranged so that a fire at one source will not cause an interruption at the other source. 7. Supply conductors shall be physically routed outside a building and be installed as service entrance conductors. Where

supply conductors cannot be physically routed outside building, they shall be permitted to be routed through building. Fire pump supply conductors on the load side of the final disconnecting means and overcurrent device shall be kept entirely independent of all other wiring. They shall be permitted to be routed through a building using one of the following methods:

a) Be enclosed in a minimum 50mm (2 inch) of concrete. b) Be within on enclosed construction dedicated to the fire pump circuit and have a minimum of a 1-hour fire

resistive rating. c) Be a listed electrical circuit protective system with a minimum 1-hour fire rating.

8. Conductors supplying a fire pump motor, pressure maintenance pump and associated fire pump accessory equipment shall have a rating not less than 125 percent of the sum of the fire pump motor and pressure maintenance motor full load currents and 100 percent of the associated fire pump accessory equipment.

– Power circuits shall not have automatic protection against overloads, shall be protected against short circuit only. – The voltage at the controller line terminals shall not drop than 15 percent below normal (controller-rated voltage)

under motor starting conditions, the voltage at the motor terminals shall not drop than 5 percent below the voltage rating of the motor when the motor is operating at 115 percent of the full-load current rating of the motor.

9. External control circuits that extend outside the fire pump room shall be arranged so that failure of any external circuits (open or short circuit) shall not prevent the operation of a pump from all other internal or external means. Breakage, disconnecting, shorting of the wires, or loss of power to these circuits could cause continuous running of the fire pump but shall not prevent the controller from starting the fire pump due to causes other than these external control circuits.

– No under voltage, phase-loss, frequency – sensitive, or other sensors shall be installed that automatically or manually prohibit actuation of the motor contactor.

– A phase loss sensors shall be permitted only as a part of a listed fire pump controller. – No remote devices shall be installed that will prevent automatic operation of the transfer switch. – Control conductors installed between the fire pump transfer switch and standby generator supplying the fire pump

during normal power loss shall be kept entirely independent of all other wiring. they shall be protected to resist potential damage by fire or structural failure. They shall be permitted to be routed through a building encased in 50mm (2 inch) of concrete or within enclosed construction dedicated to the fire pump circuits and having a minimum 1-hour fire resistance rating or circuit protective system with a minimum of 1-hour fire resistance.

10. The isolating switch shall be a manually operable motor circuit switch or a molded case switch having a horsepower rating equal or greater than the motor horsepower and having an ampere rating not less than 115 percent of the motor rated full-load current and also suitable for interrupting the motor locked rotor current.

– The following warning shall appear on or immediately adjacent to the isolating switch:- DON’T OPEN OR CLOSE SWITCH WHILE THE CIRCUIT BREAKER (DISCONNECT MEANS) IS IN CLOSED POSITION.




153

11. The motor branch circuit shall be protected by a circuit breaker that shall be connected directly to the load side of the isolating switch.

– The circuit breaker shall have the following electrical characteristics:- a) A continuous current rating not less than 115 percent of the rated full-load current of the motor. b) Overcurrent-sensing elements of the non thermal type. c) Instantaneous short-circuit over current protection. d) An adequate interrupting rating of provide the suitability rating of the controller. e) Capability of allowing normal and emergency starting and running of the motor without tripping. f) An instantaneous trip setting of not more than 20 times the full-load current.

– When current limiter are integral parts of the circuit breaker, shall have the following requirements:- a) The breaker shall accept current limiters of one rating. b) The current limiters shall hold 300 percent of full-load motor current for minimum of 30 minutes. c) The current limiters, where installed in the breaker, shall not open at locked rotor current. d) A spare set of current limiters of current rating shall be kept readily available in a compartment or rack within

the controller enclosure. – The only other overcurrent protective device that shall be required and permitted between the isolating switch and

the fire pump motor shall have the following characteristics:- a) Of the time-delay type having a tripping time between 8 seconds and 20 seconds at locked rotor current. b) Calibrated and set at a minimum of 300 percent of motor full-load current. c) It shall be possible to reset the device for operation immediately after tripping with the tripping characteristics

thereafter remaining unchanged. – Where the motor branch circuit is transferred to an alternate source supplied by an on-site generator and is

protected by an overcurrent device at the generator, the locked rotor overcurrent protection within the fire pump controller shall be permitted to be by passed when that motor breaker circuit is so connected.

12. The motor contactor shall be horsepower rated for electrical operation of reduced-voltage controllers, timed automatic acceleration of the motor shall be provided, and the period of motor acceleration shall not exceed 10 seconds.

– For controllers 600 volt or less, the operating coil of the main contactor shall be supplied directly from the main power voltage and not through a transformer.

– No under voltage, phase-loss, frequency-sensitive, or other sensors shall be installed that automatically or manually prohibit actuation of the motor contactor.

– Sensors shall be permitted to prevent a three-phase motor from starting under single-phase condition. 172. 270BWhen shall we use circuit breaker + back-up fuse as switchgear combinations?

AAnnsswweerr The prospective short circuit current level may exceed the rated breaking capacity of the circuit breaker installed, if a back

up fuse is connected on the line side of the breaker. To ensure that the fuses and the circuit breaker will operate together in such a way, that the breaker and its contacts are not damaged during the interruption of large short circuit currents.

The fuses assist the C.B in the interruption of currents which marginally exceeds its breaking capacity. For higher short-

circuit currents, the fuse performs the interruption alone, and the breaker opens under no-load. A careful matching of the properties of the protective elements is required. Figure shows the time current characteristics

curve of the fuses lies a sufficient distance “X” above the tripping curve of thermally delayed overload release. The breaker alone is responsible for overload protection.




154

173. 271BWhat are the sizing recommendations for fire pump applications including (sizing the

generator set, sizing the utility circuit breaker or fuses, sizing the feeder conductors,

sizing the automatic transfer switch, sizing the generator circuit breaker) as per NFPA 70?

AAnnsswweerr The building code includes special requirements for generators and transfer switches supplying fire pumps. Where a generator set supplies power to an electric fire pump there are special sizing considerations outlined in the National

Fire Protection Association (NFPA) and National Electrical Code (NEC) requirements.

The generator feed to a fire pump is typically one of two circuit arrangements.

– One arrangement uses a transfer switch integral to a fire pump controller (not shown).

– The second arrangement uses a listed fire pump transfer switch separate from a fire pump controller (refer to FIGURE 1). For fire pump service, both an automatic transfer switch and a bypass-isolation transfer switch are available from generators suppliers. This sizing recommendation covers sizing the generator set for either arrangement and sizing the transfer switch for the second arrangement, where separate from the fire pump controller.

Sizing the generator set

– Background: NEC 695-7 requires that voltage dip no more than 15% of rated controller voltage at the fire pump controller line terminals (includes cable drop) during normal starting of the fire pump motor. This may translate to oversizing the generator set by a factor of two or three times to provide required motor starting kVA compared to when a 30-35% starting voltage dip is permitted.

– Where the fire pump is the only significant load on the generator set, the starting kVA required will be much greater than the required running kVA. Since there are practical limits to the alternator capacity in a generator set, a larger genset may be required, resulting in a light load running condition for the engine (less than the recommended minimum of 30% of rated kW). To alleviate this, consider adding additional loads with low starting requirements, such as lighting, or the application of supplemental load banks, especially during normal routine system testing.

– All fire pump controllers, whether reduced-voltage or DOL (direct-on-line), full voltage, include an emergency manual mechanical means to start the fire pump under full voltage should the starting circuit or contactor coil malfunction. The exception to NEC 695-7 states that the 15% voltage dip limit does not apply when using manual starting emergency means.

– Caution: it’s recommended that an analysis of generator set voltage and frequency dip performance when using the manual DOL starting. This analysis may indicate a larger generator is required to achieve desired performance during this condition. This may be desirable to get assurance that the fire pump controller does not drop out when automatic reduced voltage transition from start to run occurs prior to when the pump achieves near rated speed or when the pump cannot be accelerated during reduced voltage due to high operating head pressure.

– Note: It is not necessary to size the generator set for locked rotor current continuously.




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Sizing the utility circuit breaker, CB1 (or fuses)

– Size any over current device upstream of the fire pump controller on the utility line side to hold locked rotor current

of the fire pump motor continuously, typically a minimum of 600% of motor FLA (Full Load Amps). – Because the maximum allowable current-limiting fuse for a given size transfer switch is higher than the maximum

allowable molded case circuit breaker, using current-limiting fuses in lieu of a circuit breaker may allow a smaller transfer switch to be used.

Sizing the feeder conductors

– Size the feeder conductors at a minimum of 125% of the motor full load current or next higher ampacity. Feeder conductors run from the circuit breaker at the generator (CB2) to the fire pump controller line terminals, and from the load side of CB1 to the fire pump controller line terminals.

– The voltage drop requirement of NEC 695-7 also applies, so if the motor is large and the run is long, the feeder conductors may require oversizing. The facility designer is responsible for cable drop calculations.

Sizing the automatic transfer switch

– Initially, size the ampere rating of the transfer switch to be equal to or next size greater than the required feeder conductors.

– Verify that the over current device used on the utility line side, CB1, does not exceed the maximum allowable circuit breaker or fuse size allowed for the transfer switch. If it does, increase the transfer switch rating to one that includes CB1 as an allowable upstream breaker.

Sizing the generator circuit breaker, CB2

– The objectives for sizing and selection of this over current device are: Complying with code requirements, Using a standard automatic molded case circuit breaker, Selectively coordinating this breaker with locked rotor protection within the fire pump controller, and Having sufficient available fault current from the generator to clear a faulted fire pump circuit without opening

other ranches of the generator supplied emergency system. – The circuit breaker should be a standard molded case circuit breaker; magnetic-only breakers and non-automatic

molded case switches are not recommended. – A magnetic-only (instantaneous trip) circuit breaker is not recommended. These breakers are UL Component

Recognized, but not UL Listed devices. They are only suitable for use in a UL listed assembly, and are typically included with overloads as part of a UL listed combination motor starter. They are not UL listed for feeder conductor protection.

– A non-automatic molded case switch with integral high instantaneous self-protection is not recommended. If the fire pump circuit is faulted, the generator may have insufficient available fault current to trip the switch. If the fire pump branch is not interrupted during a fault, an upstream device may trip, leaving other emergency branches without power. Size molded case breaker CB2 greater than 125% but less than 250% of the motor full load current. NFPA 20,

6-6.5, requires this breaker to pick up the instantaneous load. NEC 695-6 (d) prohibits overload protection, but requires short circuit protection. With a minimum rating of 125%, by exclusion, the breaker is not providing overload protection according to NEC 430-32. With a maximum rating of 250%, for the breaker, by definition, qualifies as short-circuit protection as shown in Table 430-52 of NEC. Within the range of 125% to 250%, select the smallest over current device that will allow pump motor locked

rotor current to flow longer than the 20 seconds allowed by the fire pump controller integral protection.




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174. 272BWhat are the main parts of transformer compartment (Kiosk)?

AAnnsswweerr General Description:

1. Roof mounted lifting eyes. 2. Double roof with neutral ventilation. 3. Ventilation louvers. 4. MV compartment door. 5. Heavy-duty door hinges. 6. Earth fault indicator. 7. Transformer compartment door. 8. LV compartment door. 9. Opening handle. 10. Base for Kiosk.

– The housing is assembled as an integrated unit from

sheet steel built on heavy channel steel skid frame to withstand the weight of the kiosk with its components.

– To reduce the equipments ambient temperature and prevent heating through the roof due to sun radiation, the roof is made of double layers with foam installation in between, the upper layer is made of a solid Alu-Zinc alloy to give the advantage of corrosion resisting in different climates.

– The MV and LV compartments are arranged at both

sides of the substations with the transformer compartment in between.

– The MV and LV compartments are provided with double doors. All doors are equipped with stainless steel rigid

hinges and rigid locking devices. Also all doors are equipped with rubber gaskets to keep a high degree of protection.

Dimensions in (mm):

Kiosk Description Height (mm) Width (mm) Length (mm) Weight without Transformer Rating up to 500 KVA

Voltage 12 KV 2050 1680 3200 = 2.4 ton

Rating up to 1000 KVA Voltage 12 KV 2370 2000 4110 = 3 ton




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Medium Voltage Compartment

– It comprises a Ring Main Unit (RMU) including up to three cable load

break switches and one automatic fused load break switch for transformer. All circuit arrangement may be provided with earth fault indicators.

Transformer Compartment (Kiosk)

– The transformer compartment is designed for a 3- phase oil immersed

power transformer with power up to 2000 KVA at rated MV 12KV and up to 1000KVA at rated MV 24KV.

– The transformer is connected to the LV distribution board via copper busbars or cables based on the transformer capacity, and to the MV equipment via XLPE screened cables, each of the XLPE cables is equipped with two cable end box for three single phase connection.

– For service purposes, sufficient space is provided to the personnel to go in and work freely, necessary opening are provided for air entry and exhaust, so that the temp. Rise is kept to a minimum.

– In substations up to 500 KVA / 12 KV the transformer could be placed into its compartment either from dismarrtable or from the longitudinal side door. For above rating it is preferable to place the trans. from the roof side.

– Dust-rejecting ventilating louvers, are situated at both ends of the transformer compartment and dimensioned for self - cooling.

– The lower part of this compartment functions as an oil collection pit with a sufficient volume to contain all the transformer oil.

– Two doors in both longitudinal sides of the transformer compartment provide maximum flexibility to inspect and maintain the transformer.

Low Voltage Compartment

– The LV compartment contains the LV distribution board. It is built on a steel

frame mounted on the compartment floor and fixed to the back wall of the compartment.

– The main incoming apparatus is usually moulded case automatic air circuit breaker (open frame type is also available) complete with overload and short circuit protection with rating up to 3200A. The incoming unit is equipped with voltmeter and selector switch, 3 ammeters, 3 signal lamps and space for optional K.W.H meter.




158

– There are 3 basic types available for providing the outgoing feeders of the LV distribution board:

Moulded Case Circuit Breakers As an example for the capacity of the 500 KVA/12KV substations, the number of the outgoing feeders with moulded case circuit breakers (MCCB) may be one of the following:

Nine frame size 250A MCCB. Six frame size 400A MCCB. Four frame size 630A MCCB.

Fused Load Break Switches For the same example of the 500KVA/12KV substation, the number of the outgoing feeders using fused load break switches (SF – Switch Fuse) may be one of the following:

Six (SF) up to 400A. Four (SF) up to 630A.

3PH HRC Fuses For the same example of the 500KVA substation, the number of the outgoing feeders with high rupturing capacity fuses may be one of the following:

Four with H.R.C. fuses up to 630A. Five with H.R.C. fuses up to 250A.

As an example for a substation 1000KVA with MV side 24KV or 2000KVA with MV side 12KV, the outgoing feeders with moulded case circuit breakers may be one of the following:

Six frame size MCCB1250A. Eight frame size MCCB 400A. Twelve frame size MCCB 250A.

– It is available to provide the LV compartment optionally with: K.W.H. & K.V.A.R.H. for incoming feeder. Control equipment for street lighting line. Other specifications for the L.V compartment could be supplied but with special dimensions.




159

175. 273BUsing given legend. Draw the wiring diagram for:

o 274B1 Way - 1 Gang Switch.

o 275B1 Way - 2 Gang Switch.

o 276B2 Way (3 Way) - 1 Gang Switch.

o 277B2 Way (3 Way) - 2 Gang Switch.

o 278BIntermediate (4 Way) - 1 Gang Switch.

AAnnsswweerr




160

176. 279BDiscuss the construction for LV & MV power cables?

AAnnsswweerr The general construction of the LV cables is (0.6/1.2kV):

1. Core (Conductor)

All cables have one central core or a number of solid, stranded or flexible - copper or aluminum conductors having highest conductivity with round or sectoral shaped conductors.

2. Insulation

An extruded layer of different types of insulators used to insulate the conductors are paper, varnished cambric, XLPE or PVC which are applied over the conductor for low voltages. But mostly impregnated paper is used which is an excellent insulating material. PVC insulated cables are suitable for maximum conductor operating temperature of 70ºC or 85 ºC and 90 ºC for XLPE.

3. Metallic Sheath (Assembly)

In case of multicore cables. Cores are assembled together using non hygroscopic filler (if needed) to fill space between cores, wrapped with suitable binder tape toform a round cable. A metallic sheath is provided over the insulation so as to prevent the entry of moisture into the insulating material. The metallic sheath is usually of lead and in case of cables having a copper conductor sometimes aluminum is used for providing metallic sheath. The metallic layer provided must be electrically continuous, thus, the sheath used not only provide water proof protection, but also provides an electrical earth shield the potential of the conductor is referred to this.

4. Bedding

In case of armoured cables over the metallic sheath comes a layer of bedding that consists of PVC or paper tape, the function of providing the bedding is to protect the metallic sheath form mechanical injury from the armouring.

5. Armouring

Armouring is provided to avoid mechanical injury to the cable and it consists of one or two layers of galvanized steel wires or steel tapes which are applied helically.

6. Serving (Sheath)

Over armoring, a layer of fibrous material or PVC is again provided as an outer sheath which is similar to that of the bedding but is called serving or sheath.




161

The general construction of the MV cables is (from 6/10 kV up to 18/30 kV):

1. Conductor

Stranded, round and compacted Copper or Aluminum conductors, according to IEC 60228 class 2.

2. Conductor Screen

An extruded layer of semiconducting material applied over the conductor as voltage stress control layer

3. Insulation

An extruded layer of, XLPE, rated 90 ºC which are applied over the inner semiconductor with thickness as specified in IEC 60502.

4. Insulation Screen (Non−Metallic part)

An extruded layer of semiconductive compound firmly bonded to insulation. Conductor screen, XLPE insulation and insulation screen are applied at the same time using triple head extruder. (Semi conductive compound easily strippable from insulation available on request).

5. Metallic Screen (Metallic Part)

a. Copper Tape: an annealed copper tape is applied helically with a suitable overlap. b. Copper Wire: helically applied and binded with a copper tape to achieve electrical contact.

6. Assembly and Filling

In case of multicore cables. Cores are assembled together with suitable lay length, non hygroscopic filler is applied during assembly to fill spaces between cores then wrapped with suitable binder tape.

7. Bedding

In case of armoured cables an extruded layer of PVC or MDPE or LLDPE is applied as bedding.

8. Armouring

Armouring is provided to avoid mechanical injury to the cable and it consists of one or two layers of galvanized steel wires or steel tapes which are applied helically.

9. Serving (Sheath)

Over armoring, an extruded layer of fibrous material or PVC is applied with thickness as specified in IEC 60502.




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177. 280BWhat are the different distribution losses in industrial facilities?

AAnnsswweerr There is a dramatic difference in an AC power distribution system between the simple DC resistance values of the various

conducting elements, and the actual apparent AC resistance, under heavy current load, of these same elements. Motors, lighting systems, wiring, mechanical terminations, distribution panels, protective devices, transformers, switchgear, and all end of circuit equipment experience a variety of resistance increasing inefficiencies that combine to create an average wattage loss in a typical industrial facility of from 10% to 25% of total demanded power. Identifying and calculating the sum of the individual contributing loss components is a challenging engineering specialty, requiring extensive experience and knowledge of all the factors impacting the operating efficiencies of each of these components.

The following list is a simplified overview of several of the more important loss factors in an industrial facility, including a broad range estimate of reasonable loss values attributable to each stated effect. Note that all of these are current dependent, and can be readily mitigated by any technique that reduces facility current load.

– Hysteresis Losses: Hysteresis loss is a heat loss caused by the magnetic properties of the armature in an AC motor. When an

armature core is in a magnetic field, the magnetic particles of the core tend to line up with the magnetic field. When the armature core is rotating, its magnetic field keeps changing direction. The continuous movement of the magnetic particles, as they try to align themselves with the magnetic field, produces molecular friction. This, in turn, produces heat. This heat is transmitted to the armature windings. The heat causes armature resistances to increase. Typical hysteresis losses as a percentage of building demand: 2% to 5%.

– Skin Effect Losses: The apparent resistance of a conductor is always higher for AC than for DC. The alternating magnetic flux

created by an alternating current interacts with the conductor, generating a back EMF which tends to reduce the current in the conductor. The center portions of the conductor are affected by the greatest number of lines of force, the number of line linkages decreasing as the edges are approached. The electromotive force produced in this way by self-inductance varies both in magnitude and phase through the. Cross-section of the conductor, being larger in the center and smaller towards the outside. The current therefore tends to crowd into those parts of the conductor in which the opposing EMF is a minimum; that is, into the skin of a circular conductor or the edges of a flat strip, producing what is known as 'skin' or 'edge' effect. The resulting non uniform current density has the effect of increasing the apparent resistance of the conductor and gives rise to increased losses. Harmonic loading increases skin effect losses by the square of the increase in frequency above nominal line

frequency, and so is responsible for a substantial lost wattage in any facility with large populations of nonlinear equipment loads, such as DC drives, rectifiers, induction heating or other arcing or switching power supply devices. Typical skin effect losses as a percentage of building demand: 2% to 8%.

– Proximity Effect Losses: Proximity effect is a property existing when conductors are close together, particularly in low voltage

equipment, where a further distortion of current density results from the interaction of the magnetic fields of other conductors. In the same way as an EMF may be induced in a conductor by its own magnetic flux, so may the magnetic flux

of one conductor produce an EMF in any other conductor sufficiently near for the effect to be significant. If two such conductors carry currents in opposite directions, their electromagnetic fields are opposed to one

another and tend to force one another apart. This results in a decrease of flux linkages around the adjacent parts of the conductors and an increase in the more remote parts, which leads to a concentration of current in the adjacent parts where the opposing EMF is a minimum. If the currents in the conductors are in the same direction the action is reversed and they tend to crowd into the more remote parts of the conductors. This effect, known as the 'proximity effect' (or 'shape effect'), increases the apparent AC resistance. If the

conductors are arranged edgewise to one another proximity effect increases. In most cases the proximity effect also tends to increase the stresses set up under short-circuit conditions and this may therefore have to be taken into account. Typical proximity effect losses as a percentage of building demand: 1.5% to 3%.




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– Line Losses:

In addition to I2R losses and dielectric losses, cables have other losses such as skin-affect and proximity-effect developed by magnetic induction. For single conductor cables, however, where conductors are not operating close to each other, proximity effect is negligible. Skin-effect loss is caused by the reversing magnetic field, about the cable, which tends to concentrate the current toward the periphery of the conductor. This affect then reduces the effective carrying capacity of a conductor in its central portions. Proximity-effect loss is caused by the opposing force of magnetic fields set up by neighboring conductors. This displaces the points of maximum reactance to a maximum distance from each other, resulting in maximum current density at the nearest surfaces of the two conductors. Operating together in a typical industrial conduit enclosed distribution system; these various loss factors can sufficiently increase the building wiring's apparent AC resistance to more than an order of magnitude above nominal DC resistance values. Thus, typical I2R wiring losses are often far greater than simple chart-based values. With the above, recall that I2R losses occur in ALL distribution system conducting components, not only the

wire. Typical line losses as a percentage of building demand: 1 % to 3.

– Eddy-Current Losses: With any electrical system component comprising an iron or steel frame and an electrical coil, flux will flow in

the steel as a result of the alternating current in the coil. The flux in the steel will itself induce an EMF in the material following the basic laws of induction. Since the material is essentially an electrical circuit closed on itself, the induced EMF will cause a circulating electrical current called an eddy-current. Its value is dependent on the value of EMF and on the resistivity of the path of current. As in any other electrical circuit the power loss is the product of the square of the current times the resistance. In a similar manner to hysteresis losses, the eddy-current loss manifests itself as heat, contributing to the maximum operating temperature limit of the device. Eddy current losses occur in protective circuit breakers, lighting ballasts, power supply transformers, magnetic

motor starters, voltage reducing or isolation transformers, current overload relays, control contactors and relays, all motor windings, and even building wiring, when the wiring is in circular proximity to steel or iron structures, such as electrical enclosures, distribution panels, or terminal or distribution blocks. Typical eddy current losses as a percentage of building demand: 1.5% to 4%.

178. 281BWhat are the types of insulations that can be used for cables?

AAnnsswweerr The following are the chief types of insulation groups that can be used:

– Rubber. – Cross Linked Polyethylene (XLPE). – Polyvinyl chloride (PVC). – Fibrous material. – Silk, cotton, enamel.

179. 282BWhat are the main functions of luminaire?

AAnnsswweerr The functions to which the design of a luminaire are based are as follows:

– To efficiently control and re-direct the light emitted by a light source. – To protect and provide support for the light source, necessary control gears and other components. – To adequately absorb and dissipate heat emitted from the light source and control gears.

Other requirements considered vital in luminaire design imcludes: – Ease in maintenance – Appearance and finishings. – Cost effectiveness.

Note: A luminaire may have optional features to suit the need of a lighting system. It may be equipped with universal mounting accessories, photocell, through-wiring and other electrical or optical systems.




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180. 283BHow can you calculate the reactive power Capacitor Bank (power factor correction)? How can

you choose the capacitor bank according reactive power from standard? How can you

calculate the circuit breaker of capacitor bank? What are the available LV Standard

Automatic Capacitor Banks?

AAnnsswweerr For example if we modified the power factor from 0.80 to 0.95

S = P + jQ P (const) = xx at pf = 0.80 S (old) = xxx Q (old) = S sin Φ P (const) = xx at pf = 0.95 S (new) = P/0.95 Φ = cos-1 (pf) Q (new) = S (new) sin Φ Q (capacitor bank) = Q (old) - Q (new) = xxxx

Choose the capacitor bank according reactive power from standard. If the standard has not the needed capacitor

bank so we choose the nearest one and calculate the new power factor. P (const) = xx at pf = 0.80 S (old) = xxx Q (old) = S sin Φ Q (capacitor bank) = xxxx Q (new) = Q (old) - Q (capacitor bank) Q (new) = S sin Φ (1) P = S cos Φ (2) Dividing equation 1, 2 Q (new) / P = tan Φ Φ (new) = xxxxx pf (new) = cos Φ (new) S (new) = P/ pf (new)

Calculate the circuit breaker of capacitor bank:

S (capacitor bank) = P – jQ Where (P = 0), so the angle equal (-90°) pure reactance.

Q (capacitor bank) = S sin Φ Q (capacitor bank) = √ 3 VI sin Φ Where Q (capacitor bank) = -ve I = (- Q) / (√ 3 V sin Φ) I = (- Q) / (√ 3 V sin (-90)) I = (- Q) / (- √ 3 V) I = Q / (√ 3 V) So I (CB) = I X 1.25

LV Standard Automatic Capacitor Banks AV400 series 3Ø / 60Hz AV500 series 3Ø / 60Hz AV500 series 3Ø / 60Hz

Steps KVAR Rating Steps KVAR

Rating Steps KVAR Rating

(Qty x KVAR) @ 480 V (Qty x

KVAR) @ 480 V (Qty x KVAR) @ 240 V

2 x 25 50 2 x 25 50 2 x 25 50 1 x25, 1 x50 75 1 x25, 1 x50 75 3 x 25 75 2 x25, 1 x50 100 2 x25, 1 x50 100 4 x 25 100 1 x25, 2 x50 125 1 x25, 2 x50 125 5 x 25 125 2 x25, 2 x50 150 3 x 50 150 6 x 25 150 1 x25, 3 x50 175 1 x25, 3 x50 175 1 x25, 3 x50 175

4 x 50 200 4 x 50 200 2 x25, 3 x50 200 - - 1 x25, 4 x50 225 1 x25, 4 x50 225 - - 5 x 50 250 5 x 25 250 - - 1 x25, 5 x50 275 1 x25, 5 x50 275 - - 6 x 50 300 6 x 50 300 - - 1 x50,3 x100 350 - - - - 2 x50,3 x100 400 - - - - 1 x50,4 x100 450 - - - - 2 x50,4 x100 500 - - - - 1 x50,5 x100 550 - - - - 6 x 100 600 - -

The table refers to Digest - Squared (Schneider Electric) The AV400 and AV500 are suitable for use where harmonic generating loads are less than 15% of the total connected load.




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181. 284BWhat is the difference between AWA and SWA?

AAnnsswweerr

A single core armoured cable will always have a layer of aluminium wire armour (AWA) instead of steel wire armour

(SWA). This is because the steel in SWA has a much lower conductivity – and therefore higher resistance – than aluminium. If it were used in a single core cable the magnetic field generated would induce an electric current in the armour (eddy current) and – combined with the increased resistance – would have a heating effect. AWA is non-magnetic and has a much better conductivity (lower resistance), so can conduct these induced currents to earth more efficiently than steel. SWA is used in multicore armoured cables because the electromagnetic fields from the neighbouring cores effectively cancel each other out, meaning less current is induced into the armour.Armouring by non-magnetic material either aluminum tape or aluminum wire armouring to reduce the magnetic losses. If it’s required for single core cable to be armoured by steel wire armouring the magnetic circuit around the single core cable should be onterrupted by inserting insulating copper wires between the steel wires as shown in the figure below.

Armouring of Single Core LV Cables (0.6/1.2 kV)

Armouring of Single Core MV Cables (from 6/10 kV up to 10/30 kV)

182. 285BHow can you classify lighting according to applications?

AAnnsswweerr Indoor lighting

– Office lighting – Conference halls lighting – Industrial lighting – Hazardous areas lighting – Indoor sports lighting – Hospitals lighting – Merchandise lighting – Hotels lighting

Outdoor lighting – Area Flood lighting – Façade lighting – Landscape and Amenity lighting – Outdoor sport lighting – Road lighting – Tunnel lighting




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183. 286BState some demand factors for different loads that are being used in American NEC

Standards?

AAnnsswweerr

Table 220.42 Lighting Load Demand Factors Demand Factor

(Percent) Portion of Lighting Load to Which

Demand Factor Applies (Volt-Amperes) Type of Occupancy

100 First 3000 or less at Dwelling units 35 From 3001 to 120,000 at

25 Remainder over 120,000 at 40 First 50,000 or less at Hospitals* 20 Remainder over 50,000 at 50 First 20,000 or less at Hotels and motels, including apartment houses without

provision for cooking by tenants* 30 Remainder over 100,000 at 100 First 12,500 or less at Warehouses (storage) 50 Remainder over 12,500 at 100 Total volt-amperes All others

Table 220.44 Demand Factors for Non-dwelling Receptacle Loads

Demand Factor (Percent) Portion of Receptacle Load to Which Demand Factor Applies (Volt-Amperes)

100 First 10 kVA or less at 50 Remainder over 10 kVA at

Table 220.54 Demand Factors for Household Electric Clothes Dryers Demand Factor (Percent) Number of Dryers

100 1 - 4 85 5 75 6 65 7 60 8 55 9 50 10 47 11

% = 47 - ( number of dryers - 11 ) 12 - 22 35 23

% = 35 - 0. 50 ( number of dryers - 23 ) 24 - 42 25 43 And over

The table refer to NEC chapter 2 article 220.11 & 220.12 & 220.13 & 220.18 Demand Loads for Household Electric Ranges, Wall-Mounted Ovens, Counter-Mounted Cooking Units, and Other Household Cooking Appliances over 13/4 kW Rating See article And table no 220.19 Demand Loads for Kitchen Equipment — Other Than Dwelling Unit(s) See article And table no 220.20. Demand Loads for Appliance Load — Dwelling Unit(s). See article no 220.17

Table 220.56 Demand Factors for Kitchen Equipment Other Than Dwelling Unit(s) Demand Factor (Percent) Number of Units of Equipment

100 1 100 2 90 3 80 4 70 5 65 6 and over




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Table 220.55 Demand Factors and Loads for Household Electric Ranges, Wall-Mounted Ovens, Counter-Mounted Cooking Units, and Other Household Cooking Appliances over 13⁄4 kW Rating (Column C to be used in all cases except as otherwise permitted in Note 3.)

Column C Maximum Demand (kW) (See

Notes) (Not over 12 kW Rating)

Demand Factor (Percent) (See Notes) Number of Appliances Column B

(3½ kW to 8¾ kW Rating) Column A

(Less than 3½ kW Rating) 8 80 80 1

11 65 75 2 14 55 70 3 17 50 66 4 20 45 62 5 21 43 59 6 22 40 56 7 23 36 53 8 24 35 51 9 25 34 49 10 26 32 47 11 27 32 45 12 28 32 43 13 29 32 41 14 30 32 40 15 31 28 39 16 32 28 38 17 33 28 37 18 34 28 36 19 35 28 35 20 36 26 34 21 37 26 33 22 38 26 32 23 39 26 31 24 40 26 30 25

15 kW + 1 kW for each range 24 30 26-30 22 30 31-40

25 kW + ¾ kW for each range 20 30 41-50 18 30 51-60 16 30 61 and over

Table 220.88 Optional Method - Permitted Load Calculations for Service and Feeder Conductors for New Restaurants Not All Electric Restaurant Calculated

Loads (kVA) All Electric Restaurant

Calculated Loads (kVA) Total Connected

Load (kVA) 100% 80% 0-200

50% (amount over 200) + 200.0 10% (amount over 200) + 160.0 201-325 45% (amount over 325) + 262.5 50% (amount over 325) + 172.5 326-800 20% (amount over 800) + 476.3 50% (amount over 800) + 410.0 Over 800

Table 220.86 Optional Method - Demand Factors for Feeders and Service-Entrance Conductors for Schools Demand Factor (Percent) Connected Load

100 First 33 VA/m² (3 VA/ft2) at 75 Over 33 to 220 VA/m² (3 to 20 VA/ft2) at 25 Remainder over 220 VA/m² (20 VA/ft2) at




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Table 220.84 Optional Calculations - Demand Factors for Three or More Multifamily Dwelling Units Demand Factor (Percent) Number of Dwelling Units

45 3-5 44 6-7 43 8-10 42 11 41 12-13 40 14-15 39 16-17 38 18-20 37 21 36 22-23 35 24-25 34 26-27 33 28-30 32 31 31 32-33 30 34-36 29 37-38 28 39-42 27 43-45 26 46-50 25 51-55 24 56-61 23 61 and over

184. 287BWhat are the different classifications of luminaries? Give brief discussion for each.

AAnnsswweerr Decorative:

– A general lighting or accent lighting, decorative luminaries are designed to satisfy the aesthetic need of an interior. In most cases the luminaire from as an integral part of the architecture.

– The finishing of this type of luminaries usually matches or blends well with the furnitures or finishing of an interior. The shape of the luminaire is irregular, linear or curved.

– Light sources employed vary from the incandescent candle lamp to linear HID lamp. With the availability of energy saving compact flourcsent lamps, compact HID lamps and efficient optical system decorative luminaries construction are compact and aesthetically pleasing.

Commercial: – These are the most common type of luminaries used in offices, shops, supermarkets, etc., from a simple batten to a

modular, multi-lamp, equipped with reflector and light controller. – The light sources employed are usually tubular fluorescent lamps and energy saving compact fluorescent lamps.

The size of the housing depends on the number of light source to be employed and control the gears. – The light from a bare lamp need to be re-directed and shielded in order to reduce the luminance of the luminaire in

directions where glares probable. A reflector is used to direct the light where needed most. The control of light with a highly polished (mirror) reflector is more effective than a white enameled shell sheet.

– This control of light is further improved by using diffusers and louvers of various kinds. The shielding of the lamps from a direct view reduces the glare to be experienced. With these light controllers a wide range of light distribution will help the lighting designers to select the effect that will satisfy the objective. For example, a mirror double- parabolic louver is preferred in a working interior where VDU screens are present to avoid reflected glare. The light distribution it provides is within the desirable cut-off angle.




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– Commercial luminaries may be mounted in so many different ways. Except for he type intended to be recessed on the suspended ceiling system, most of the types can be suspended (rod, wire or chain), surface mounted and bracket mounted.

– Protection class (IP) of these luminaries is usually, IP20. Some types intended for washrooms, stairways and other areas where dust and water may present, IP23 or IP44.

Industrial: – In industrial lighting applications, the use of fluorescent fixture is still preferred. However, due to the

environmental conditions of the working space, other materials and construction of a lumiaire is needed. – Industrial fluorescent luminaries are usually made of materials that could withstand an environment where dust,

corrosion and fumes may be present. Reflectors are widely used, but in some applications bowl diffusers (gasketed) are proffered. Luminaires protection class varies from IP23 to IP67 depending on area of use.

– Mounting may be on surface, suspended (rod, wire or chain) and brackets. – Applications where fluorescent lamps are no longer practical to use, low and high bay luminaries employing HID

lamps will provide the lighting. For the same illumination level, fewer lighting points will be needed; therefore, cost of installation and maintenance will be less.

– The reflectors and refractors used for these luminaries are designed for specific mounting limits. Most low bay luminaries are recommended for a mounting height up to 6 meters while high bays are used for above 6 meters.

– Where flammable gasses and vapors are present, occasionally or for a long period, the area is classified “hazardous”. Thus, luminaries to be provided must be safe to operate. Similarly, a room with presence of easily ignitable fiber area. In addition to the usual classification requirements of an industrial luminaire, this type designed for hazardous areas has to be tested and certified by testing laboratories.

– Luminaries for hazardous areas as in petrochemical plants, chemical laboratories, oil platforms, etc. are of higher degree of protection compared to other types, usually IP57 or IP67.

– Aside from the high IP class, the luminaire is labeled according to the explosion category, temperature class and area of use (Zone or Class and Division). The electrical components are tested and certified confirming the protection from excessive heat, areas and sparks. The luminaries maximum surface temperature (T class) as marked must be less than the ignition temperature of the gases present where it will be installed.

– Some luminaries are robust and made of cast iron aluminum alloy or heavy gauge steel sheets materials and designed to withstand and suppress internal explosion. The maximum surface temperature of these luminaries is also used as basis of applicability. The cover is usually hard, shock resistant tempered glass and tightly sealed to the corrosion resistant body.

– A wide range of lamp types are used in these luminaries except for low pressure sodium.

Exit and Emergency: – Safety is the primary objective in providing egress lighting especially in public buildings. The occupants will find it

difficult to reach a door or stairway in total darkness. In the absence of normal power supply, temporarily or for a long period, an alternative source must be available. The supply from a control battery or stand by generator is common. Today, however, self contained emergency system is becoming more practical (for short periods).

– In practice, there are three systems which are employed as part of the lighting system, namely; Maintained: “A lamp is operating during normal supply and will be lighted, instantly, in case of power

failure”. Non Maintained: “A lamp is lighted when the normal supply fails”. Sustained: “Two lamps are employed: one is operating during normal supply, the other during power

failure”. – A self contained emergency luminaire has its battery pack (NICD) and charger/inverter units in the luminaire

housing. Usually, the duration of the emergency pack is 1.5 hours or 3 hours. There are requirements, however, for a longer duration.

– Exit and other directional luminaries oftentimes are equipped with these emergency units. These luminaries are installed on the wall or ceiling leading to the exit points or stairways. The texts and symbols are usually bold and in red or green color.




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Flood lights: – The materials and construction of floodlights depend on the light source to be employed. A PAR amp, for example,

will require a lamp holder which is protected from penetration of water. The unit can be installed on the surface or with built-in spike. In some applications, buried floodlights made of stainless steel with heat toughened glass are preferred.

– Floodlights intended for area lighting, security lighting, sports and the like to be equipped with HID lamps are constructed with the housing, usually, die-cast aluminum with the lamp holder, optical assembly covered wit tempered glass and mounting unit. Most types are designed to have an integrated control gear box made of the same materials; others are intended to have separately mounted control gear.

– There are floodlights which are equipped with graduated scale for orientation and aiming purposes especially in sports lighting application. Internal or external glare control assembly is standard accessories for some floodlight.

– The mounting unit is usually, a bracket with mounting holes and slip filter, on some. The windage area and weight of these luminaries are vital data to design the mounting structure. Example: pole and mast.

Road and Tunnel Lighting Luminaires: – The optical assembly and control gears of these road lighting luminaries may be together in one or in separate

housing made of aluminum pressed, die-cast or extruded. A tunnel luminaire is usually in one piece housing. The light sources which are widely used in these luminaries are mercury vapor, metal halide, low pressure sodium and high pressure sodium lamps. For tunnel luminaries, fluorescent lamps are also employed.

– The reflectors are of high purity anodized aluminum to provide a high degree of light control. The materials of commonly used diffusers are borosilicate glass wit prismatic pattern, clear polycarbonate and high thermal and impact resistant lens. Tunnel luminaries equipped with asymmetrical reflector and frosted glass are common as well.

– The mounting on lighting poles of these luminaries could either be top mount or side entry (poles with arm). Relamping and minor trouble shooting can be done on these luminaries mounted on the pole since the covers and diffusers are hinged and secured to the housing.

– A tunnel luminaire may be installed directly on a surface using galvanized bracket or on the mounting rails. There are installations where the luminaries are flush mounted on the concrete.

Bollards, Post Top Mounted and Wall Mounted Luminaires. – The design of these luminaries varies in shape, color and mounting system. The most widely used housing material

is aluminum. As other types, efficient optical system is a major concern in the selection of these luminaries. Reflector and refractor designs vary in shape and finish to achieve the desired light distribution. Intended mounting method is also a factor in the final design of these luminaries.

– Most of these luminaries, today are designed to satisfy architectural considerations. For example, the shape and finish of a bollard head matches the type intended for wall and ceiling mounted luminaries.

– Light sources employed are incandescent, compact fluorescent and HID.

185. 288BState the difference in wiring between:

o 289B2-Way Switch & 3-Way Switch.

o 290B4-Way Switch & Intermediate Switch.

AAnnsswweerr The 3 way & 4 way switches (as per American standards) is same as 2 way & intermediate switches respectively (as per

British standards). On the three way switch, there are three screws. So it is called like this. On the 2 way switch, also there are three screws. But, it’s called 2 way because you can switch on or off from 2 positions. On the four way switch, four are three screws. So it is called like this. On the intermediate switch, also there are four screws. But, it’s called intermediate because you can switch on or off from

many positions. Always the first & the last switch should be (2way/3way switches) … while all the intermediate switches should be

(intermediate/4way switches).




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186. 291BWhat is the ATS & what are the main different parts of ATS?

AAnnsswweerr Summary:

– ATS systems stands for the phrase automatic transfer switch system. The specified system shall be a dual-position

transfer switch designed to automatically and manually switch between two synchronized AC power sources without an interruption of power to the load longer than 6 milliseconds. The input power shall be supplied from two different AC power sources, which are nominally of the same voltage level, phase sequence, and frequency. The primary purpose of the ATS shall be to allow virtually uninterrupted transfer from one source to the other in case of failure of one source or by manual initiation for test or maintenance. The switching action shall switch all phases and neutral conductors of the sources and shall not connect together the two sources of power which would allow back-feeding one source to the other. The ATS shall allow for either source to be designated as the "preferred source" to which the switch will automatically transfer to and remain transferred to until manually initiated to transfer or until the selected source fails, at which time, the ATS shall transfer without interruption greater than 6 milliseconds to the other source. The ATS shall be furnished with an integral isolation and bypass switch which allows uninterrupted manual transfer to and from either source for maintenance or replacement of the ATS electronics module without de-energizing the load equipment.

System Description:




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Modes of Operation:

– The specified system shall be a two, three, or four-pole, double-throw, automatic transfer switch that switches all branch circuit conductors, including phase and neutral conductors, that are supplied from the two AC power sources. One source shall be designated as the preferred source while the other is the alternate source. Selection of which input source is preferred shall be user selectable without de-energizing the load equipment or reconnecting the input power sources. All transfers shall be a fast break-before-make with no overlap in conduction from one source to the other. All transfers, including sense and transfer times, shall have less than a 6 millisecond interruption in power to the load.

Normal Mode:

“In normal operation, the load shall be connected to the preferred source as long as all phases of the preferred source are within the acceptable limits. Upon failure of the preferred source, the load shall be transferred to the alternate source until such time as the preferred source returns to within the acceptable limits. Transfer voltage limits shall be +/- 10% of the nominal input voltage for steady state conditions, with low voltage transfer limits having an inverse time relationship that is within the IEEE Std. 446 computer voltage tolerance envelope. After the preferred source returns to within the acceptable voltage limits for at least the user-adjustable retransfer time delay (1 to 60 seconds, 3 seconds typical) and is in phase with the alternate source within the adjustable phase synchronization window (1 to 15 or 20 degrees, 10 degrees typical), the load shall be retransferred automatically to the preferred source. The automatic retransfer to the preferred source can be disabled if so selected by the user from the service port. When the automatic retransfer is disabled, emergency transfers from the alternate source to the preferred source shall not be disabled upon alternate source failure”.

Load Current Inhibit:

“The system shall sense the load current and, if the load current exceeds an adjustable preset level deemed to represent a load inrush or fault condition, the system shall disable the automatic transfer even if the voltage on the selected source exceeds the transfer limits to keep from transferring the load inrush or fault current between the two input sources. The load current transfer inhibits reset shall be user-selectable from the service port for manual or automatic reset. In the automatic reset mode, the transfer inhibit shall be automatically reset after the current returns to normal to allow for continued protection against a source failure. In the manual reset mode, the transfer inhibit shall require that the unit be transferred to maintenance bypass or the unit powered off to reset the transfer inhibit and restore normal operation”.

Manual Transfer:

“The system shall allow manually initiated transfers between the two sources, provided that the alternate source is within acceptable voltage limits and phase tolerances with the preferred source. Allowable phase differences between the sources for manually initiated transfers shall be user-adjustable from the service port. The user-adjustable phase synchronization window shall be limited to +/- 15 or 20 degrees. If the transfer is manually initiated, the system shall transfer between the two sources without interruption of power to the load greater than 2.5 milliseconds provided that both sources are available and synchronized within the user-adjustable phase synchronization window. For sources where the two frequencies are not exactly the same (as would be the case between a utility and standby generator source), manually initiated transfers shall be delayed by the system until the two sources are within the user-adjustable phase synchronization window”.

Maintenance Bypass:

“The system shall be furnished with key-locked maintenance bypass switch, which allows the system electronics to be bypassed to either input source for maintenance without interruption of power to the load greater than 2.5 milliseconds. The packaging of the system shall have all electronics isolated from the input, output, and bypass connections to allow the electronics module to be removed and replaced while the unit is in maintenance bypass without interruption of power to the load”.




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187. 292BSpecify different ratings of ATS?

AAnnsswweerr

UL – Listed (American Standards) IEC (European Standards) 30

63 70

80 100 125 125

160 200

250 260 320 400 400 600

630 800 800

1000 1000 1200

1250 1600 1600

1800 2000 2000

2500 2600 3000

3200 4000

188. 293BWhat are the advantages of using Busbar Trunking System (Bus Duct)?

AAnnsswweerr Busbar Trunking (Bus Duct) System has several advantages ensured

– Higher capacity of system (5000A at maximum) and excellent insulation of conductor. – Take up smaller space, light, economy and pleasant to eyes. – Lower impedance, voltage drop, interference and energy consumption. (i.e. The sandwich type assembly makes it

possible to obtain lower reactance therefore lower voltage drops). – Convenient, easy and quick for installment. – The excellent properties of system are fire and pest prevention, endurance and safe. – Higher short-circuit rating (up to 100 kA for 1sec). – With reliable plug-in box and safety joint. (Feeder and plug-in types are available and interchangeable without any

adapter or special parts). – Easy to add an additional system and make a branch for the system as well as change the setting. – Easy to make maintenance and check. – Excellent heat dissipation by a direct conduction of the bars to the housing. – Thermal expansion of the Busbar system is accomodated within the joint system. – Integral aluminum housing offers standard earth busbar of full cross section. – Integral design enable flames, gases, smokes,vapour or warm air to pass unobstructive.




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189. 294BWhat are the different types of ATS Devices?

AAnnsswweerr A commonly available transfer switching device on the market is called Automatic Transfer Switch (ATS). An ATS is a

device, which automatically transfers one or more load conductors from the “Normal” power source to an “Emergency” power source and back.

All ATS consist of a Power Switching Assembly (PSA), Control Unit Assembly (CUA) and the enclosure. Three most common types of ATS by the type of the Power Switching Assembly used are: contactor based, circuit breaker

based and solid state.

– Contactor Based ATS

Contactor based ATS is the most common type by the number of units installed. Some of the advantages of the contactor based ATS are low cost and availability. The contactors are known as the devices designed for frequent switching of the load current and commonly used as a part of the motor starters. However many contactor based ATS manufacturers do not use traditional contactors in their PSA. Therefore most contactor based ATS are not rated for the number of switching operations (with or without load) as traditional contactors.

Majority of the contactor based ATS manufacturers design their PSA to meet the requirements of the UL 1008 standard.

Traditional contactor base ATS is neither capable nor intended to interrupt a fault current. Therefore UL 1008 standard specifies the minimum fault currents the switch should be able to withstand without damage for a time period of at least 3 cycles. (50 ms).

Power systems with the contactor based ATS must have a circuit breaker or a fuse upstream from the ATS (for each power source: normal and emergency) for the purpose of short circuit protection.

If the ATS is rated to be able to withstand the available fault current for only 3 cycles, the upstream protective device shall interrupt the fault in less than 3 cycles. This means that there is no practical way of coordinating the upstream short circuit protective device with any of the short circuit protective devices downstream from the ATS. As a result, a short circuit anywhere in the critical circuit fed by the ATS will cause operation of the upstream short circuit protective device with the consequent loss of power all the critical circuits fed by the ATS.

At the same time, if the fault is in one of the critical circuits protected by a feeder circuit breaker with the instantaneous protection, the feeder circuit breaker may clear the fault.

Operation of the short circuit protective device upstream from the ATS will look to the ATS as a loss of the present source and will cause the ATS to transfer the critical load to the alternative power source. If the fault in the critical load circuit was cleared by the down stream feeder circuit breaker, than the remaining critical load circuits will be energized by the alternate power source. . If the fault in the critical load circuit was not cleared by the downstream feeder circuit breaker due to the fault location, tripping time, uncoordinated tripping setpoints or feeder circuit breaker malfunction, transferring of the faulted critical load circuit to the alternate power source will cause further damage to the faulted circuit as well as tripping of the alternate power source upstream from the ATS.




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– Circuit Breaker Based ATS

Circuit breaker based ATS typically uses two interlocked, electrically operated circuit breakers as the heart of its PSA. The circuit breaker types, typically used in the ATS PSA are designed to comply with the UL 489. There are two major types of the circuit breakers, which fall in this category. The industry calls them molded case circuit breakers and insulated case circuit breakers. Molded case circuit breakers are the most basic type of circuit breakers, commonly found in low voltage power systems. The trip units typically include overload protection and short circuit protection (instantaneous setting of approximately 5 to 10 times frame rating). Insulated case circuit breakers are designed with stored energy mechanism and spring charging motor for remote closing, and are commonly available in draw-out construction.

The circuit breakers used in the PSA assembly may be with or without the trip unit. Even when used without the trip unit, most circuit breakers will trip and interrupt the fault, when the level of fault current exceeds the withstand rating of the circuit breaker. This self-protecting feature is one of the advantages of a circuit breaker based PSA over a contactor based PSA.

Generally, a circuit breaker based ATS acts the same as a contactor based ATS. Circuit breaker based ATS can integrate the functions of an ATS and normal and alternate sources short circuit protective devices when supplied with the trip units.

If the time delays to transfer setpoints are short, and under certain power system conditions it is possible that the ATS will try to transfer during a fault. In that case a circuit breaker type ATS will be able to successfully disconnect the faulted load and complete the transfer, since the circuit breakers are rated to interrupt fault current. A contactor based ATS is likely to fail under the same scenario, since the PSA contactors are not rated to interrupt fault.

– Solid State ATS

Solid state ATS PSA is based on the use of the heavy duty Silicon-Controlled Rectifiers (SCR). Use of SCRs

in conjunction with the microprocessor based control unit allows the solid state ATS manufacturers to sense the failure of the normal source and transfer to the alternate source in less than ¼ of a cycle. This transfer time is fast enough to not affect the operation of the common computer equipment.

Due to the solid state nature of the SCR based PSA it is common to see an isolation and bypass circuit breakers on each source side and load side of the ATS. The isolation circuit breakers allow for visible disconnection of the SCR units from each source and load in case of the SCR units failure or need for maintenance. After the SCR unit has been fully disconnected by the isolation circuit breakers, one of the bypass circuit breakers can be closed to directly energize the load by the selected power source.

190. 295BWhen should we use Busbar Trunking (Bus Duct) System?

AAnnsswweerr Paralleled sets of conductors are almost always more expensive than a busway of similar current capacity because of the

high installation cost of multiple conduits. – When it is necessary to carry large amounts current (power). – When it is necessary to tap onto an electrical power conductor at frequent intervals along its length.




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191. 296BWhat is the acceptable percentage voltage drop that can be reached in L.V. calculations?

AAnnsswweerr According to NEC Article 215.2:

– Conductors for feeders as defined in Article 100, sized to prevent a voltage drop exceeding 3 percent at the farthest outlet of power, heating, and lighting loads, or combinations of such loads, and where the maximum total voltage drop on both feeders and branch circuits to the farthest outlet does not exceed 5 percent, will provide reasonable efficiency of operation.

– Reasonable operating efficiency is achieved if the voltage drop of a feeder or the voltage drop of a branch circuit is limited to 3 percent. However, the total voltage drop of a branch circuit plus a feeder can reach 5 percent and still achieve reasonable operating efficiency

According to Saudi Electricity Company - SEC

(Distribution Planning Standard - DPS) - Table-1.3: – For LV Customers. The Utility voltage drop allocations

listed in Table-1.3 shall be used as guideline voltage drops over the power system components supplying a low voltage customer. The additional voltage drop in the customer's wiring shall not exceed the value indicated.

– Distribution Transformers have a built-in voltage boost of 5% by virtue of the transformation ratio. Note that this does not extend the voltage drop to the service point beyond 10% however.

192. 297BState the application & operation of the contactor and circuit breaker based transfer

switches (ATS)?

AAnnsswweerr A. Transfer from normal source to emergency source (Transfer between live & dead sources):

The most common application of the contactor and circuit breaker based transfer switches is when they are used in conjunction with the emergency generator. In this case the utility is connected to the normal side of the ATS; the generator is connected to the alternate (emergency) side of the ATS.

Upon utility failure, the ATS will issue a start signal to the emergency generator set after a typical time delay of 1 to 5 seconds. This time delay is intended to avoid starting of the generator set during very short interruptions of the normal power supply. These short interruptions are typically corrected by the upstream utility source reclosing, within 2 seconds.

Once the generator set receives a start signal from the ATS, it takes approximately 10 seconds for the generator to build up voltage and frequency to become available to energize the load. At this time the transfer from the normal to the emergency source will occur. The load is now energized by the emergency source.

Upon utility return, the ATS will activate the time delay return to normal source. This time delay is typically set anywhere between 5 minutes and 30 minutes. This allows ensuring that the utility source has returned to stay as well as gives the generator set some minimum time to run under load as well as allows some minimum time to recharge the generator set engine cranking batteries in case the utility was to fail again, shortly after the transfer to the normal source. Upon expiration of this time delay the transfer from the emergency source to the normal source will occur.




177

B. Transfer from emergency source back to normal source (Transfer between two live sources): Upon utility return, the ATS will activate the time delay return to normal source. This time delay is typically set anywhere

between 5 minutes and 30 minutes. This allows to ensure that the utility source has returned to stay as well as gives the generator set some minimum time to run under load as well as allows some minimum time to recharge the generator set engine cranking batteries in case the utility was to fail again, shortly after the transfer to the normal source. Upon expiration of this time delay the transfer from the emergency source to the normal source will occur.

Most of the time the transfer between the two live sources will occur when transferring from the emergency source back to the returned normal source, therefore all our discussion bellow will be based on this transition. However the phenomena’s described below apply to any load transfer between the two live sources.

There are two ways to transfer load between the two live sources: 1. Open Transition

– During the open transition transfer from the emergency source back to the returned normal source, the emergency source will be disconnected before the normal source will be connected. This will cause a brief outage to the load.

– We know that when the voltage to the running electric motor suddenly decays, the electric motor begins to act as the generator for a short period of time. The duration of the generator action depends on the type of the motor, inertia of the driven equipment as well as the amount of the passive load on the same circuit. This phenomena causes the engineers to consider motor contribution when they calculate the available fault current. During the open transition load transfer, the independent sources are likely not to be synchronized. Fast open transition motor load transfer, can cause connection of the generating motor to the power source out of synchronism. The consequences of this connection are similar to the closing the generator out of synchronism: high line currents (with possible operation of the overcurrent devices) and mechanical stress to the equipment shafts and gears (with possible mechanical damage). Transformers are also known to cause high line currents during fast open transition load transfers, due to the stored magnetic field.

– There are three most common ways to accomplish open transition transfer: 1.1. Non-Delayed Transition.

o In case of non-delayed transition, the normal source will be connected to the load as soon as the emergency source is disconnected from the load, without any intentional time delay. Advantages:

The duration of the outage is minimized; lowest cost.

Disadvantages: (Motors, transformers….etc.) Problems.

1.2. In-Phase Transition. o In case of in-phase transition, the normal source will be

connected to the load as soon as the emergency source is disconnected from the load, but the transfer will only take place when the two sources are in synchronism. Advantages:

The duration of the outage is minimized. Disadvantages:

Relies on the generator to passively fall into synch with the utility, which is not always possible. In this case the transfer may not occur until the generator runs out of fuel. If the substantial passive load is connected to the motor during the transfer, the motor my fall out of synch faster than the transfer time of the ATS. The time of transfer is not predictable. Does not eliminating inrush during transfer of the heavy transformer loads.

1.3. Time Delayed Transition. o In case of time delayed transition, the normal source will be connected to the load after the emergency

source is disconnected from the load, and after an adjustable time delay. Advantages:

The most reliable and flexible operation suitable for reliable transfer of any loads. Disadvantages:

The duration of the outage during transfer is increased.




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2. Closed Transition

– During the closed transition transfer from the emergency source

back to the returned normal source, the emergency source will be disconnected after the normal source is connected. This will not cause an outage to the load during the transfer. Typically the duration of the connection of the two sources is less than 100 ms. since the incoming and the running power sources connect while in synchronism, any type of load can be reliably transferred in this manner.

– The synchronizing of the sources for the closed transition transfer can be accomplished via active synchronizing and passive synchronizing. In both cases the paralleling of the two sources is supervised by a synchronizing check relay.

– In case of passive synchronizing, the system control relies on the generator to randomly fall in to synchronism with the utility source. In case of passive synchronizing there is no way to be sure that the transfer will occur.

– In case of active synchronizing, the system control monitors the voltage and frequency of both sources and provides a speed correction signal to the prime movers (engine, turbine, etc.) governing system to bring it in to synchronism with the running source (utility).

193. 298BState the application & operation of the solid state transfer switches (ATS)?

AAnnsswweerr The main advantage of the solid state ATS over the contactor or circuit breaker based transfer switch is its ability to detect

the failure of the normal source and transfer to the available alternate source within ¼ of a cycle. At the same time the solid state ATS are much more expensive and generally less reliable as compared to the contactor or circuit breaker based ATS. Since the emergency generator set is, typically not available for the first 10 seconds of the normal source outage, the advantages of the solid state ATS would not be utilized when used with the emergency generator set.

Solid state ATS are typically used in the systems with two constantly available separately derived and synchronized power sources, and where the nature of the load is such that brief power outage is not acceptable.

194. 299BWhen should we use tap-off boxes Busbar Trunking (Bus Duct) System?

AAnnsswweerr When a line has to be fed by cables, feed-in boxes can be installed.




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195. 300BWhat is the minimum requirement for transfer switch (ATS) arrangement that should be

followed for essential & critical loads of health care facilities?

AAnnsswweerr As per NEC - Article 517; Essential electrical systems for hospitals shall be comprised of two separate systems capable of

supplying a limited amount of lighting and power service, which is considered essential for life safety and effective hospital operation during the time the normal electrical service is interrupted for any reason. These two systems shall be:

– Emergency Systems The emergency system shall be limited to circuits essential to life safety and critical patient care. These are designated the life safety branch and the critical branch.

– Equipment System The equipment system shall supply major electrical equipment necessary for patient care and basic hospital operation.

The number of transfer switches to be used shall be based on reliability, design, and load considerations. Each branch of the emergency system and each equipment system shall have one or more transfer switches.

One transfer switch shall be permitted to serve one or more branches or systems in a facility with a maximum demand on the essential electrical system of 150 kVA.

196. 301BWhat are the applications of using Busbar Trunking (Bus Duct) System?

AAnnsswweerr Busbar trunking systems are used to advantage wherever higher currents need to be transmitted. They can be used as

transmission lines between transformers and main switch boxes or as a connection between main switch boxes and subsidiary switch boxes of heavy consumers. They can also be used in factory buildings, electric power stations, power plants, water treatment, airports, commercial installations, hospitals, office Buildings, sewage stations, clinics, food processing industries etc., or as riser in multi-store high-rise buildings.

A typical application of heavy-duty busduct might be a vertical feeder in a high-rise building, connecting the basement switchboard to the penthouse machine room.

The same building might also use heavy-duty plug-in busducts vertical risers with taps feeding individual floors. Typical applications for light-duty plug-in busduct (70 to 100 A) could be any machine shop or workshop.




180

197. 302BWhat is Busbar Trunking (Bus Duct) System?

AAnnsswweerr The bus duct system is one of for effective and efficient supply of electricity borne of valuable resources. Copper or

aluminum is used for the conductor of bus duct that be insulated and enclosed completely for protection against mechanical damage and dust accumulation.

The system comprises feeder bus dust, plug-in bus duct, flatwiseelbow and tee et al; therefore the system is a safe, economic, beautiful, enduring system.

Busduct is a kind of wiring material provided with a small size and a large current capacity compared with power cables. The busduct system consists of insulated flat conductors of aluminum or copper, which are closely arranged and

accommodated in a metal duct. The system enables branching at arbitrary places on the conductor line using a class of connectors called plug-in-hole. Busduct is specified by type, material, number of buses, current capacity, and voltage (e.g., aluminum feeder busduct, 4-

wire, 1000 A, 600 V, or copper plug-in busway, 100A, 3-wire, 600 V). A wide variety of fittings and joints are available for all buswaysto permit easy installation. Designs are available for indoor

and outdoor application.




181

198. 303BWhat are the relations among transformers, main C.B’s and Bus Duct Ratings assuming

that the system voltage is 380/220V?

AAnnsswweerr

Transformer Main C.B. Bus Duct Pn

(kVA) at 380V

Ucc (%) In (A) Icc (kA) Rating (A) Rating (A) Phase Size (mm2) - Thickness (mm) x

Width (mm)

Rated Breaking Capacity (KA) - Peak Value

500 4 722 18 800 1250 5x120 105 630 4 9090 22.7 1250 1250 5x120 105 800 5 1155 23.1 1250 1250 5x120 105

1000 5 1443 28.9 1600 2500 5x250 165 1250 5 1804 36.1 2000 2500 5x250 165 1600 6.25 2309 37 2500 2500 5x250 165 2000 6.25 2887 46.2 3200 3200 5x400 220 2500 6.25 3600 57.7 4000 3600 5x500 220

199. 304BWhat are the different available standard ratings for Bus Duct?

AAnnsswweerr

Standard Nominal Capacity ( Ampere ) for Bus Duct 225 400 600 800 1000 1200 1250 1350 1600 2000 2500 3000 3200 3600 4000 5000




182

200. 305BWhich is better in power distribution AC system or DC system? Why?

AAnnsswweerr AC has at least three advantages over DC in a power distribution grid:

– Large electrical generators happen to generate AC naturally, so conversion to DC would involve an extra step. – Transformers must have alternating current to operate, and we will see that the power distribution grid depends on

transformers. – It is easy to convert AC to DC but expensive to convert DC to AC, so if you were going to pick one or the other AC

would be the better choice. 201. 306BWhich is the Cable Bus? What are the applications of using it? What are the advantages &

disadvantages of using it? What are the type of conductors & configurations used? Compare

between ampacities using Cable Bus & other normal cables.

AAnnsswweerr Cable Bus:

– Cablebus is similar to ventilated busduct except that it uses insulated cables instead of bus-bars. The cables are rigidly mounted in an open space-frame. The advantage of this construction is that it carries the ampacity rating of its cables in free air,which is much higher than the conduit rating, thus giving a high amperes per-dollar first-cost figure.

– Cable Bus utilizes fully-rated power cables instead of the more traditional bus bars to carry current. The cables are housed in a ventilated metal enclosure (normally aluminum) to provide a completely protected bus system.

– Cable Bus is a system for distributing power from one electrical apparatus to another using insulated power cables inside of a protective metal housing.

– Cable Bus is designed to carry large amounts of electrical power for use within power generation and industrial plants for service entrance, main feeders, distribution applications and for retrofits for existing power systems.

– Cable Bus is a competitive alternative to conventional non-segregated phase bar bus, cable tray with armored cable and conduit & wire systems. This is due to Cable Bus having lower cost, higher reliability, greater flexibility, easier installation and longer life expectancy. This makes Cable Bus the obvious choice for your power distribution needs.

– Bus systems have an ampacity range from 400A to 6000A and voltage ratings of 600V, 5kV, 15kV, 25kV and 35kV.

– Each system is custom designed and manufactured to meet your specific job requirements. – Cable Bus systems use a compact metal housing that is 50% ventilated taking full advantage of the free air rating of

the cables. This allows using fewer conductors, saving you installation time and money. – Cables are held securely using Cable Support blocks that are held in place in the housing using our Short Circuit

Brace. The combination of these two elements, the Cable Support Blocks and the Short Circuit Brace, allow the Cable Bus systems to withstand short circuit forces of up to 100KA RMS symmetrical, keeping personnel safe in case a fault occurs.




183




184

Cable Bus Applications:

– Typical applications include connections between transformers and switchgear, tie connections between two

switchgears, between motor control centers and large motors and generator to generator breakers or generator step-up transformers.

– Also, Plant Distribution, Primary & Secondary Feeders, Industrial Plants, Convention Centers, Hospitals, Airports, Shopping Malls, Sports Complexes (Indoors or Outdoors).




185

Advantages of Cable Bus:

– Lowest cost:

Cable Bus systems have proven to be the most cost effective available way to distribute electricity with material and installation costs savings of up to 40% in comparison to conventional non-segregated phase bar bus, cable tray & armored cable or conduit and wire systems, making Cable Bus the obvious choice.

– Reliability:

For over five decades Cable Bus systems have proven to be the most reliable systems for almost 50

years in power generation, mining, petrochemical, paper, heavy industrial and commercial industries ranging from heavy pollution areas and hazardous environments to humid tropical, freezing arctic and blazing desert conditions. With long life expectancy, durability, 24 hours a day, 365 days a year maintenance free operation, Cable Bus systems are installed in areas where downtime is NOT an option.

– Safe:

Totally insulated conductors reduce shock hazard. Ventilated enclosure guards against entry of foreign objects and protects cables from physical damage. Designed to safely handle high short circuit currents. Aluminum enclosure and high pressure splice joints provide excellent ground continuity. No additional

ground wire required for most systems.

– Ease of Installation:

Cable Bus Systems are easy to install compared to other systems. No heavy lifting equipment or special tools are required. Housing sections can be easily lifted into place by two men. Every job is engineered and designed to fit the specific application with all Cable Bus sections, elbows and accessories factory precut to fit your project needs. Long vertical sections are easily installed using our Short Circuit Brace which allows the Cable Support Blocks to be installed without any fasteners until all the cables have been pulled into place. Interleaving or crossing of conductors within the Cable Bus housing is not required with our system.

– Long Span:

Cable Bus systems can be designed for up to 20 foot support spans thereby reducing support costs and

installation labor.

– Enclosure:

Standard enclosure is manufactured from a structural grade aluminum alloy which has excellent corrosion resistance and is far superior to painted steel products in industrial and outdoor environments.

The aluminum enclosure also reduces electrical losses compared to steel enclosures.

– Flexibility:

System is very adaptable in joining or connecting to other equipment or other systems. Bus can be easily routed around obstructions or equipment. High salvage value. System can be dismantled and reused or rerouted.

Disadvantages of Cable Bus:

– Bulkiness:

Its principal disadvantage is bulkiness and difficulty in making tap-offs.




186

Type of Conductors & Configuratuions:

Copper Conductor Systems Aluminum Conductor Systems

Ampacity Comparison Chart:




187

Engineering Informations for Cable Bus:

– Cables

• General: The main consideration in any cable bus system is the proper selection of power conductors. MDF uses

only the highest quality cables, pre-tested and designed for use in cable bus systems for indoor or outdoor environments.

Conductors may be copper or aluminum and are typically supplied with an insulation temperature rating of 90o C.

• Insulation: Cross-linked Polyethylene “XLPE”. This is the most economical type of insulation. XLPE has

excellent resistance to most chemicals, and is very resistant to physical damage. Ethylene-Propylene Rubber “EPR”. EPR is recommended for all systems rated above 2000 volts. This

insulation is superior to XLP in most all categories and results in a more reliable system, particularly in outdoor and wet environments.

• Shielding: Shielding is recommended on all systems over 2400 volts. A grounded shield does several things for the power cable:

Confines the dielectric field within the cable. Provides a uniform stress distribution within the dielectric. Protects the cable from induced potentials. Limits radio interference. Reduces shock hazard. Provides a ground path for leakage and fault currents.

– Voltage Drop & Power Loss MDF Cable Bus Systems have low impedance characteristics, which reduce power consumption and

also minimize the system voltage drop. The actual voltage drop and power loss will of course depend on the specific Cable Bus system.

The typical system will have a 2 to 3 volt (line to line) voltage drop per 100 foot, at rated current. Computer analysis and printouts are supplied with each project detailing this information. If you have specific questions regarding voltage drop or power loss, please consult the factory.

– Parallel Conductors & System Balance Cable Bus systems take advantage of the efficiency of using two or more conductors per phase in larger

rated systems. As cable sizes increase the ampacity per circular mil decreases. This is due primarily to the “skin” effect or current distribution within the cable and the decrease in the heat radiating ability per cross section area as the cable size increases.

The current density is highest at the outer surface of the cable. Two smaller cables will have more surface area than one large cable of equal total conductor material and will, therefore, most often be more efficient.

The efficiency of paralleling conductors is not without certain potential problems. When two or more cables are paralleled per phase one might assume that the total current would automatically divide equally between these paralleled conductors. This is definitely not automatic.

Due to inductive coupling between conductors, the total impedance of each conductor also depends on the physical geometry of the system. The mutual coupling between conductors is dependent on the spacing between conductors and the relationship of the phasing of each conductor in the system. Current division between improperly balanced systems can be as high as a 30 to 70 percent split (in a two conductor system)!

One poor solution commonly offered to this problem is to transpose the cables within the cable bus system. Proper transposition techniques, however, would require five transpositions alone on a 2 cable per phase system.

The proper solution to this problem is to engineer each system to produce balanced conductor impedances through careful phasing and spacing arrangements of each conductor. Balance currents can be obtained for most systems through symmetrical cable arrangements.




188

– Short Circuit Capacity

Cable Bus Systems must withstand the forces created by potential fault currents of power distribution systems. Forces are created as unusually large currents are passed through the system during a fault condition. The forces are a function of the current magnitude of each conductor as well as the distance or spacing between conductors. Cables of opposite phases will be repelled while cables of like phases will attracted. A simplified formula for forces between conductors is given below. Force = K (C1 x C2)/D Where K = constant C1 = Current cable 1 C2 = Current cable 2 D = distance between conductors

Cable Bus systems have been designed to withstand these forces. Conductor support blocks firmly hold cables in place within the cable bus enclosure. Blocks are spaced between 12 and 36 inches on centers depending on the required short circuit rating of the system (All vertical cable bus risers have support blocks spaced no greater than 18 inches on centers). The cable support blocks are completely framed and solidly secured to the enclosure to maximize the strength and capabilities of the system to withstand these forces.

– Cable Support Blocks

Cable support blocks can be supplied in either our standard hard maple wood block or am optional fiberglass block.

Wooden support blocks are manufactured using a high grade maple and treated with a quality wood preservative for long life. The blocks are also primed and painted with a fire retardant paint.

Fiberglass blocks are manufactured from NEMA GPO-3 grade material which is flame resistant as well as arc and track resistant.

– Grounding

As in any electrical system, it is important that Cable Bus Systems be properly grounded per article 250 of the National Electric Code.

Cable Bus Systems have high pressure splice joints between bus sections. These joints eliminate the need for bonding jumpers across bus sections.

– Field Testing

It is mandatory to conduct insulation testing for every Cable Bus System prior to energizing. The cables should be completely installed, secured and terminated (but not yet connected to other equipment). The bus covers should also be in place.

600 Volt systems can be meggered to proof test the insulation. Higher voltage systems must be tested using DC high potential testing per IEEE 400, or other suitable standard.

– Connectors & Terminations

Compression type cable connectors are supplied as standard. Termination kits are supplied for 5KV and 15KV systems. Heat shrink or cold shrink kits are also available.




189

202. 307BWhat are the different batteries types - technologies? State the difference?

AAnnsswweerr




190

203. 308BConsider a pillar with a 3 phase load 200A. The cable length feeding the pillar from a

transformer is 140 meters. This cable is laid directly in ground and is grouped with

another 5 cables in the same trench. Which size of cable below you prefer to use in order

not to exceed 2% voltage drop, p.f = 0.8 & why?

Multi-core Cable CU/SWA-XLPE/PVC (0.6/1) kV

1 x (4 x 300 mm2).

2 x (4 x 120 mm2).

Where; Group De-rating Factor (Spacing = 150mm) for 6 cables direct laid in ground is

0.68. Temperature De-rating Factor (@ 40 Degree) 0.95. Depth De-rating Factor (up to

0.6m) 0.96.

Cable Size (mm2)

Resistance R (Ohm/Km)

Reactance XL (Ohm/Km)

Current Capacity Direct Laid in Ground (A)

Unit Price (S.R/Km)

Overall Diameter (mm)

4 x 120 0.197 0.0948 310 188000 48.4

4 x 300 0.0812 0.0935 494 415000 69.7

AAnnsswweerr Pillar Cable Ampacity @ 125% = 200 x 1.25 = 250 A

– For 1 x ( 4 x 300 mm2 ):

Cable De-rated Ampacity = 494 x 0.68 x 0.95 x 0.96 = 306.4 A ≥ 250 A (OK). %V.D. = √3 x 250 x 140 / 380 x [(0.0812/1000) x 0.8] + [(0.0965/1000) x 0.6] x 100 = 1.93% ≤ 2 % (OK). C.B. Size = 300 A ≤ 306.4 A (OK). Cost = 140 x (415000/1000) = 58,100 S.R. Overall Diameter = 69.7 mm

– For 2 x ( 4 x 120 mm2 ):

Cable De-rated Ampacity = (310 x 2) x (0.68 x 0.95 x 0.96) = 384.5 A ≥ 250 A (OK). %V.D. = √3 x (250/2) x 140 / 380 x [(0.197/1000) x 0.8] + [(0.0948/1000) x 0.6] x 100 = 1.71% ≤ 2 % (OK). C.B. Size = 300 A ≤ 384.5 A (OK). Cost = (140 x 2) x (188000/1000) = 52,280 S.R. Overall Diameter = 2 x 48.4 = 96.8 mm

– Comparison:

Cable Options (mm2) Voltage Drop (%)

Cable De-rated Ampacity (A) Cost (S.R) Overall Diameter

(mm) Total

Evaluation 1 x ( 4 x 300 mm2) 1.93 ↑ (Worst) 306.4 ↓ (Worst) 58,100 ↑ (Worst) 69.7 ↓ (Better) Worst 2 x ( 4 x 120 mm2) 1.71 ↓ (Better) 384.5 ↑ (Better) 52,800 ↓ (Better) 96.8 ↑ (Worst) Better




191

204. 309BWhat are the expected room sizes (dimensions) for standby generators with these sizes:

310B80, 100, 125, 175, 200, 350, 400, 500, 600, 750, 900, 1000, 1500KW

AAnnsswweerr

Generator Size Generator Dimensions Generator Room Size KW KVA Length (mm) Width (mm) Height (mm) Length (mm) Width (mm) Height (mm)

80 - 100 100 - 125 2420 840 1230 5000 3500 3000 125 – 175 160 - 220 2600 890 1410 5250 3500 3000 200 – 350 250 - 440 3610 1270 1630 6250 3750 3400 400 – 500 500 – 625 4070 1530 1970 6750 4300 3750

600 750 4310 1830 2280 7000 5250 4250 750 940 4830 1830 2410 7500 5250 4250 900 1125 4830 1900 2510 7500 5250 4750

1000 - 1500 1250 - 1875 5660 1900 2510 8500 5250 5750




192

205. 311BState some diversity factors of different purposes (ex: lighting, sockets, air conditioning ..

etc) for different type of premises (ex: residential, offices, hotels... etc) according to

Egyptian Code?

AAnnsswweerr

حاالت السماح باستخدام معامالت التباين لتحديد التيارالتصميمى للدوائر فى المبانى طبقا للكود المصرى للكهرباء

عمارات تتكون من عدة وحدات نوع الحمل سكنية

وحدة سكنية أو وحدات سكنية خاصة

فنادق صغيرة أو مباني عامة للنوم والمعيشة

مكاتب ومتاجر ومبان عامة خالف الورش والمصانع

٪ من الحمل الكلي50 اإلنارة ٪ من الحمل الكلي66 ٪ من الحمل الكلي75 ٪ من الحمل الكلي90 المآخذ الكهربائية

(البرايز)

٪ من التيار التصميمي ألكبر 100 مآخذ بالدائرة.

٪ من مجموع التيارات 40+ التصميمية لباقي مآخذ الدائرة

٪ من التيار التصميمي 100 ألكبر مآخذ بالدائرة.

٪ من مجموع التيارات 40+ التصميمية لباقي مآخذ الدائرة.

٪ من التيار التصميمي ألكبر 100 مآخذ بالدائرة.

٪ من التيار التصميمي لباقي 40+ مآخذ الدائرة.

٪ من التيار التصميمي لباقي 75+المآخذ في دوائر األماكن العامة

بالمبني.

٪ من التيار التصميمي ألكبر مآخذ 100 بالدائرة

٪ من مجموع التيارات التصميمية 75+ لباقي مآخذ الدائرة

األجهزة الكهربائية

الثابتة خالف المحركات

والسخانات وأجهزة الطهي

٪ من الحمل الكامل ألكبر 100 جهاز.

٪ من الحمل الكامل للجهاز 50+ األول الذي يلي أكبر جهاز

٪ من الحمل الكامل للجهاز 33+ الثاني الذي يلي أكبر جهاز

٪ من الحمل الكامل لباقي 20+ األجهزة

٪ من إجمالي الحمل 100الكامل لمجموع األجهزة حتى

أمبير10سعة ٪ من الحمل لألجهزة 50+

أمبير10التى حملها يزيد عن

٪ من الحمل الكامل ألكبر جهاز100 ٪ من الحمل الكامل للجهاز 80+

األول الذي يلي أكبر جهاز٪ من الحمل الكامل لباقي 60+

األجهزة

٪ من الحمل الكامل ألكبر جهاز100 ٪ من الحمل الكامل لباقي األجهزة.75+

أجهزة الطهي الثابتة

٪ من الحمل الكامل ألكبر 100 جهاز

٪ من الحمل الكامل للجهاز 50+ األول الذي يلي أكبر جهاز

٪ من الحمل الكامل للجهاز 33 الثاني الذي يلي أكبر جهاز

٪ من الحمل الكامل لباقي 20+ األجهزة

٪ من الحمل الكامل 100 أمبير.10لألجهزة حتى

٪ من الحمل المقنن 30+ أمبير10الزائد على

أمبير إذا كان يوجد 5+ بالجهاز مخرج إضافي.

٪ من الحمل الكامل ألكبر جهاز.10 ٪ من الحمل الكامل للجهاز 80+

األول الذي يلي أكبر جهاز.٪ من الحمل الكامل لباقي 60+

األجهزة

٪ من الحمل الكامل ألكبر جهاز.100 ٪ من الحمل الكامل للجهاز األول 80+

الذي يلي أكبر جهاز.٪ من الحمل الكامل لباقي األجهزة60+

المحركات الكهربائية "خالف محركات المصاعد التي لها اعتبارات

خاصة"

٪ من الحمل الكامل ألكبر 100 محرك

٪ من الحمل لباقي 50+ المحركات

٪ من الحمل الكامل 100 ألكبر محرك

٪ من الحمل لباقي 50+ المحركات

٪ من الحمل الكامل ألكبر 100 محرك

٪ من الحمل الكامل لباقي 50+ المحركات.

٪ من الحمل الكامل ألكبر محرك100 ٪ من الحمل الكامل للمحرك الذي 80+

يلي أكبر محرك.٪ من الحمل الكامل لباقي 60+

المحركات.السخانات

الكهربائية متقطعة التشغيل

٪ من الحمل ألكبر سخان100 ٪ من الحمل الكامل للسخان الذي يلي أكبر سخان100+ ٪ من الحمل الكامل لباقي السخانات.25+

تقدر بمعرفة المختصين تبعا لظروف التشغيل الفعلية المحتملة.

السخانات الكهربائية مستمرة

التشغيل٪ من الحمل الكامل في جميع الحاالت.100




193

206. 312BCan you estimate the demand load of a building using its type & its gross area according

to Egyptian Code?

AAnnsswweerr




194

طبقا للكود المصرى

طابقا15نماذج نمطية للطلب على الحمل بوحدات المباني السكنية التي يزيد ارتفاعها عن طلب الحمل لكل مائة متر مربع (ك.ف.أ)

إدارى سكنى8 – 10 12

طابقا15نماذج نمطية للطلب على الحمل بوحدات المباني السكنية التي يقل ارتفاعها عن

طلب الحمل لكل مائة متر مربع (ك.ف.أ) إدارى سكنى

2 – 1.5 إسكان منخفض التكاليف 6 - 12 4 – 2.5 إسكان متوسط

10 - 6 إسكان فاخر

دورا15السعات النمطية لوحدات المبانى التى يزيد ارتفاعها عن

متر مربع100السعة ك.ف.أ./ المنطقة محالت أو مكاتب مسكن

جميع المواقع بالقاهرة 10 - 8 الكبرى 12

207. 313BCompare between LV & MV generators.

AAnnsswweerr

Description LV MV Notes Maintenance More easy and More popular for

all technicians Few Technicians deal with MV

For 10 Electricians you have only one deal with MV

Availability Short Delivery Long delivery As LV Standard unit Spare parts availability for alternator side

On shelf Customer need to get the recommended spare parts

The supplier sold 1 MV compare to 100 LV so it is difficult to have parts availability For MV as it will become slow moved items.

Transformers Losses

Using oil transformer 20% more capacity will not affect the out put

No need to have transformer

Regarding the transformer Maintenance for oil cooled need only added oil every 4:5Year

Operations Normal electrician

Specialized technician So it is more practical to have LV Generator

Replacement You can replace from stock units

in case of emergency You need at least 9 Month for MV

Installation Easy installation Special tools & Instructions MV need Certified team to install Reference More reference Few reference We can show to you some good

references using LV+ Transformers for prime power applications




195

208. 314BCalculate the grounding conductor size & the grounding resistance according to IEEE Std

80-2000 of grid of length 80m width 40m, 12 rods with separation distance of 20m, rod

length is 3m, rod diameter is 20mm, soil resistivity is 450 Ω.m, grounding conductor laid

0.8m below ground. Suppose that expected fault symmetrical current is 20KA in 1sec

duration. Where the grounding conductor is chosen to be 40% conductivity copper-clad steel

conductor

AAnnsswweerr Selection of Grounding Conductor & Connection to an Electrode “Method Based on IEEE Std 80-2000”

– Symmetrical currents – 11.3.1.2 Formula simplification

Ak𝐜𝐜mil = 𝐈𝐈. Kf𝐭𝐭𝐜𝐜 = (20)10.45√1 = 209 kcmil A = 120mm2

For 40% conductivity copper-clad steel conductor Kf = 10.45

Where Akcmil is the area of conductor in kcmil I is the rms fault current in kA tc is the current duration in s Kf is the constant from Table 2 for the

material at various values of Tm (fusing temperature or limited conductor temperature based on 11.3.3) and using ambient temperature (Ta) of 40°C




196

Grounding Resistance Calculations “Method Based on IEEE Std 80-2000” Schwarz’s equations

Rg =R1 R2 − 𝑅𝑅𝑚𝑚2

R1 + R2 − 2Rm =

(4.91)(10.77)− (3.49)2

(4.91) + (10.77) − (2)(3.49) = 𝟐𝟐.𝟐𝟐𝟔𝟔Ω

R1 =ρπLc

ln 2Lc

a′ +k1. Lc

√A− k2

=450

(3.14)(240) ln

(2)(240)0.102 +

(1.1)(240)√3200

− 4.9

= 𝟐𝟐.𝟗𝟗𝟏𝟏Ω

R2 =ρ

2πnrLr ln

4Lr

b−1 +

2k1. Lr

√Anr − 1

2

=450

(2)(3.14)(12)(3) ln

(4)(3)

(0.022 )

−1

+(2)(1.1)(3)√3200

√12 − 12 = 𝟏𝟏𝟏𝟏.𝟏𝟏𝟏𝟏Ω

Rm =ρπLc

ln 2Lc

Lr+

k1. Lc

√A− k2 + 1

=450

(3.14)(240) ln

(2)(240)3 +

(1.1)(240)√3200

− 4.9 + 1

= 𝟑𝟑.𝟐𝟐𝟗𝟗Ω

Lc = 2(40) + 2(80) = 240 m k1= 1.1, k2= 4.9 [see Figure 25(a) and (b) Curve] A = (40) (80) = 3200 m2 Since; the buried conductor used is 120mm2 (i.e Diameter = 13mm)

𝑎𝑎′ = √𝑎𝑎. 2ℎ = 0.013

2 (2)(0.8) = 0.102 𝑚𝑚

R1 ground resistance of grid conductors in Ω R2 ground resistance of all ground rods in Ω Rm mutual ground resistance between the group of grid conductors, R1, and group of ground rods, R2 in Ω ρ is the soil resistivity in Ω·m Lc is the total length of all connected grid conductors in m 2a is the diameter of conductor in m a' is √𝑎𝑎. 2ℎ for conductors buried at depth h in m, or a' is a for conductor on earth surface in m h is conductors buried depth in m A is the area covered by conductors in m2 k1, k2 are the coefficients [see Figure 25(a) and (b)] Lr is the length of each rod in m 2b is the diameter of rod in m nr number of rods placed in area A




197

209. 315BWhat are the IP references preferred for switchboard assemblies?

AAnnsswweerr

210. 316BWhat are the main aims of tunnel lighting? What is necessary to know about tunnel

lighting? When to light tunnel by day? When to light tunnel by night? How to light tunnel

by day? What are the 5 zones of tunnel lighting? Which type of lamps to use? What are the

types of tunnel lighting systems? What is the short tunnel & underpass? How to illuminate

tunnels for different lengths in day time 25m, 75m and 125m? What are the tunnel

lighting arrangements and state advantages & disadvantages of each?

AAnnsswweerr The aims of tunnel lighting are:

• Firstly, to allow traffic to enter, pass through and exit the enclosed section safely • Secondly, to do so without impeding the through-flow of traffic.

Necessary to know about tunnel lighting: For smooth traffic flow, in bright daylight and total darkness, and in all weather conditions, tunnel lighting should be such that the drivers sense of safety and comfort is not diminished compared with the experience on the open approach road. This means that drivers should have adequate visual information concerning the behaviour of other road users, the course of the road ahead and the presence of any obstacles in the tunnel entrance, to be able to react in time within a safe stopping distance (SSD). Guidelines for tunnel lighting according to CIE 88 can be found below and in the references.

When to light tunnel by day:

This depends on a number of factors including the length of the tunnel, visibility of the exit, penetration of daylight, brightness of the walls, and traffic density. CIE recommends day-time light levels throughout the tunnel of 0 %, 50 % and 100 % of the normal threshold zone lighting levels for long tunnels. See table below.

When to light tunnel by night:

During the night, CIE recommends a minimum light level equal to the light level of the approach roads.

How to light tunnel by day: Good tunnel lighting takes care of good visibility conditions for the road users; this requires lighting levels that are matched with the adaptation level of the users’ eyes. As this adaptation level gradually changes while travelling through the tunnel for lighting purposes the tunnel can be divided lengthwise into five zones: the access, threshold, transition, interior and exit zone. (fig. 1)




198

The 5 zones of tunnel lighting: CIE guidance (CIE 88-1990) states that the amount of light required within a tunnel is dependent on the level of light outside and on the point inside the tunnel at which visual adaptation of the user must occur. When planning the lighting of a tunnel, there are 5 key areas to consider:

– 1) Access zone The access zone is not a part of the tunnel itself, but the approach road immediately before the tunnel entrance, from where drivers need to be able to see and stop in front of obstacles in the tunnel. The length of the access zone is consequently equal to the safe stopping distance (SSD). The maximum light adaptation condition of the drivers’ vision in this zone, determines the luminance in the threshold zone at the beginning of the tunnel. CIE defines the adaptation state as L20, the average luminance in a conical field of view of 2 x 10° centred in the tunnel opening at the safe stopping distance from the entrance. L20 measurements and recordings for the access zone over a long period are the most solid basis for the entrance lighting design (fig. 2).

– 2) Threshold zone

The required luminance level in the first section of the threshold zone, which length is equal to the safe stopping distance, is related to the L20, ‘the outside luminance level’, the stopping distance and the applied optical system as shown in table 1. Daylight screens, louvres and other measures that reduce the L20 will proportionally reduce the amount of light and energy needed in the first zones of the tunnel. In the second half of the threshold zone the luminance level is decreased rapidly to 40 % of the initial level (see fig. 3 for a schematic representation).




199

– 3) Transition zone In the transition zone the lighting level is gradually reduced towards the level as required in the interior zone (fig. 3). The reduction speed is related to the adaptation speed of the eyes and thus time dependent. The reduction steps should not exceed a ratio of 3:1. as they are linked to the capacity of the human eye to adapt to the environment and, thus, time related. The end of the transition zone is reached when the luminance is equal to 3 times the interior level.

– 4) Interior zone In the interior zone, which is often the longest section of the tunnel, the required lighting levels are related to traffic speed and traffic density as shown in the tables below.

– 5) Exit zone The part of the tunnel between interior zone and portal. In this zone, during the day time, the vision of a driver approaching the exit is influenced by brightness outside the tunnel. The human eye can adapt itself almost instantly from low to high light levels, thus the processes mentioned when entering the tunnel are not reversed. However, reinforced lighting may be required in some cases where contrast is needed in front of or behind the driver when the exit is not visible, or when the exit acts as entrance in case of emergency or maintenance works where part of a twin tunnel may be closed. there are other reasons for installing an increased lighting level in the exit zone: (1) to make small cars following behind large lorries visible when the daylight at the exit is glaringly bright, (2) to make following cars visible in the rear-view mirror of a car leaving the tunnel and (3) to convert the exit into an entrance (at reduced speed) in case of an emergency or for maintenance. The length is a maximum 50m and the light level 5 times the interior zone level.

– Emergency lighting Emergency lighting is normally part of the night-time lighting, but is fed from an uninterrupted power supply.

``




200

Type of lamps to use: The entrance of a tunnel needs high lighting levels of SON-T lamps. For other areas needing lower light levels, such as the interior zone or at night, fluorescent and compact fluorescent lamps can be used. In general, luminaire photometry is conducted at 25 °C, but the average operating temperature in a tunnel can be much lower and therefore positively influence the efficacy.

Types of tunnel lighting systems:

– Symmetrical and asymmetrical lighting Used generally for transition and interior zones for long tunnels, and in short tunnels, or low speed tunnels for all zones. Asymmetrical lighting can also be a means of reinforcing the luminance level in one way tunnels.

– Asymmetric counter beam lighting To reinforce the luminance level and at the same time accentuate the negative contrast of potential obstacles. Counter beam lighting is achieved with symmetrical light distribution facing into the traffic flow, both in the direction of the on coming driver and in the run of the road. The beam stops sharply at the vertical plane passing through the luminaire. No light is directed with the flow of traffic. This generates negative contrast and enhances visual adaptation.

– Pro beam lighting In some circumstances, positive contrast must be reinforced, often in the exit zone where the exit is visible. In these cases, asymmetric light distribution is used in the same way as counter beam but with direction of the traffic and is called ‘pro beam’. In dual carriage way tunnels, counter beam at entrance can act as pro beam at exit. This technique is not recommended as the road luminance is very low, creating too big a disparity between the exit zone and the parting zone.




201

The short tunnel:

A short tunnel is a road or rail over bridge and underpass of more than 25 m, for motorized traffic including entrances to multi-storey car parks, for example. The height may vary between 2.5 and 6 m or more and the width from 5 to 20 m. If the tunnel is shorter than 25 m no additional tunnel lighting is required.

The underpass: When the underpass is longer than 25 m a dark frame or a dark hole may appear around the bright exit. Here an obstacle may completely be invisible for an approaching driver at a distance equal to the Safe Stopping Distance (SSD).

Day time lighting of tunnels for different lengths: (CIE-Guide for the lighting of tunnels and underpasses) When lighting a tunnel, its length, geometry and immediate environment must be taken into account as well as traffic densities. Differing light levels are set for each project, according to the governing standards summarized below:

Typical tunnel lighting arrangements:




202

211. 317BSelect the required automatic capacitor bank for a transformer rating: 1600 kVA, Voltage:

13.8/0.38 kV, Connected Load: 1516 kVA = 1289 KW, Assumed PF/ Target PF: 0.85 / 0.95?

What are the minimum & maximum harmonic orders for this capacitor bank?

AAnnsswweerr Txfmr Rating: 1600 kVA Voltage: 13.8/0.38 kV Impedance: 5 % Connected Load: 1516 kVA = 1289 kW Assumed PF/ Target PF: 0.85 / 0.95 Formula for Calculating kVAR: kW ( tan Ø1 - tan Ø 2 ) Ø1: Existing PF & Ø2 : Target PF Calculated kVAR Required: 375 kVAR Adopted kVAR Required: 400 kVAR Steps of Capacitor Bank: 2 X 50 + 3 X 100 Minimum Cap Bank Step: 50 kVAR Maximum Cap Bank Step: 400 kVAR Resonance Frequency Formula: √( kVA / ( kVAR X Impedance) ) Minimum Harmonic Order: 8.9 Maximum Harmonic Order: 25.3 % of Non-linear Load assumed: 20 Type of Capacitor Bank: VARSET Comfort ( Overrated Type ) Feeder CB rating of LV Panel: 1000 Amps Assumptions Made:

– Harmonics Creating Loads is around or less than 20 % of the total connected load. – Impedance of Transformer: 5%

Verification : – Possible Harmonic Orders in the system will not interfere with the calculated min and max harmonic orders.

Solution Conclusion : – 400 kVAR Automatic Capacitor Bank, 380 Volts, 60 Hz, Steps Size ( 2 X 50 ) + ( 3 X 100 ) kVAR

LV Standard Automatic Capacitor Banks

AV400 series 3Ø / 60Hz AV500 series 3Ø / 60Hz AV500 series 3Ø / 60Hz

Steps KVAR Rating Steps KVAR

Rating Steps KVAR Rating

(Qty x KVAR) @ 480 V (Qty x KVAR) @ 480 V (Qty x

KVAR) @ 240 V

2 x 25 50 2 x 25 50 2 x 25 50 1 x25, 1 x50 75 1 x25, 1 x50 75 3 x 25 75 2 x25, 1 x50 100 2 x25, 1 x50 100 4 x 25 100 1 x25, 2 x50 125 1 x25, 2 x50 125 5 x 25 125 2 x25, 2 x50 150 3 x 50 150 6 x 25 150 1 x25, 3 x50 175 1 x25, 3 x50 175 1 x25, 3 x50 175

4 x 50 200 4 x 50 200 2 x25, 3 x50 200 - - 1 x25, 4 x50 225 1 x25, 4 x50 225 - - 5 x 50 250 5 x 25 250 - - 1 x25, 5 x50 275 1 x25, 5 x50 275 - - 6 x 50 300 6 x 50 300 - - 1 x50,3 x100 350 - - - - 2 x50,3 x100 400 - - - - 1 x50,4 x100 450 - - - - 2 x50,4 x100 500 - - - - 1 x50,5 x100 550 - - - - 6 x 100 600 - -

The table refers to Digest - Squared (Schneider Electric) The AV400 and AV500 are suitable for use where harmonic generating loads are less than 15% of the total connected load.




203

212. 318BWhat is harmonics? What is the problem of harmonics? What is k- factor? How to calculate

K-Factor? What is K-Factor of a transformer? Why we calculate K-Factor of a transformer?

What are the advantages of calculating the K-Factor of a transformer? What are the

disadvantages of using the derated standard transformers instead of K-Factor? What should

be remembered when using a K-Factor Transformer? How K-Factor Transformer could be

calculated?

AAnnsswweerr The Problem of harmonics

– In today's industrial workplace, the proliferation of solid state devices (lighting ballasts, motor drives and controls,

communications equipment, and other DC-powered loads) has created a major problem for specifying engineers, contractors and building owners. The non-linear nature of their switched-mode power supplies generate harmonic currents that cause transformers and system neutrals to overheat and destroy themselves.

– The extensive utilization of solid state power conversion technologies has created new problems for the power industry and power engineer designer. This technology, called Switch Mode Power Systems (SMPS), consists of various types of solid state switching elements. These switching elements are solid state devices such as: SCR's, DIAC's, transistors and capacitors. These switching devices are in computers, copy machines, fax machines, telecommunications equipment, solid-state drives and controls, energy-efficient lighting ballasts, and numerous types of DC-Power Loads. These solid state elements continuously switch on and off producing non-linear or non-sinusoidal wave shapes in the current supplied from the energy source.

– While a linear load uses current from the AC source continuously over the sinusoidal cycle, a non-linear load (such as the SMPS) uses current in large pulses from the AC source which creates harmonic distortion. These non-linear current pulses may exceed the nameplate ampere rating of the power source and may cause transformers to run hotter than expected, even when these transformers are supplying less than 50% of their rated nameplate capacity.

– With non-linear loads, overloaded neutrals are also showing up in three-phase panel boards serving single-phase loads. In some cases the neutral conductor carries 180 Hertz currents, rather than 60 Hertz currents. This phenomenon is called triplen harmonics. Triplens are multiples of three, which do not cancel but are additive in the neutral conductor.

Harmonics

– As defined by ANSI/IEEE Std. 519-1981; Harmonic components are represented by a periodic wave having a frequency that is an integral multiple of the fundamental frequency.

– In other words, harmonics are voltages or currents at frequencies that are integer multiples of the fundamental (60 Hz) frequency, e.g. 120 Hz, 180 Hz, 240 Hz, 300 Hz, etc. Harmonics are designated by their harmonic number, or multiple of the fundamental frequency. Thus, a harmonic with a frequency of 180 Hz (three times the 60 Hz fundamental frequency) is called the 3rd harmonic.

– Harmonics superimpose themselves on the fundamental waveform, distorting it and changing its magnitude. For instance, when a sine wave voltage source is applied to a non-linear load connected from phase-to-neutral on a 3-phase, 4-wire wye circuit.

– Triplen harmonic currents are phase currents which flow from each of the phases into the fourth wire neutral and have frequencies in integer multiples of three times the 60 hertz base frequency (180Hz, 360Hz, 540Hz, etc). At each of these third multiple triplen frequencies, these triplen phase currents are in phase with each other and when flowing in the neutral as zero sequence currents, are equal to three times their RMS phase values. See Figure 2.

– In a 3-phase, 4-wire system, single-phase line-to-neutral currents flow in each phase conductor and return in the common neutral. Since the three 60 hertz currents are separated by 120°, when balanced they cancel each other. The measured resultant current is equal to zero. See Figure 2

– Theory also states that for even harmonics, starting with the second order, when balanced the even harmonic will cancel in the common neutral.

– Other odd harmonics add in the common neutral, but their magnitude is considerably less than triplens. The RMS value of the total current is the square root of the RMS value of the individual currents squared. As shown in Equation 2.




204

– At any given instant, the 60 Hertz currents on the three-phase legs have a vector resultant of zero and cancel in the

neutral. But, the third (and other odd triplen harmonics) on the phase legs are in phase and become additive in the neutral.

K–factor & its ratings

– K-Factor is a weighting of the harmonic load currents according to their effects on transformer heating, as derived from ANSI/IEEE C57.110. A K-Factor of 1.0 indicates a linear load (no harmonics). The higher the K-Factor, the greater the harmonic heating effects.

– When a non-linear load is supplied from a transformer, it is sometimes necessary to derate the transformer capacity to avoid overheating and subsequent insulation failure. The reason for this is that the increased eddy currents caused by the harmonics increase transformer losses and thus generate additional heat. Also, the RMS load current could be much higher than the kVA rating of the load would indicate. Hence, a transformer rated for the expected load will have insufficient capacity.

– The K-Factor is used by transformer manufacturers and their customers to adjust the load rating as a function of the harmonic currents caused by the load(s).

– Generally, only substation transformer manufacturers specify K-Factor load de-rating for their products. So, for K-Factors higher than 1, the maximum transformer load is de-rated.

– Some manufacturers, who produce both transformers and products like motors or ballasts, are sensitive to measuring K-Factor since they know that poor K-Factors of ballasts and motors will de-rate the maximum load their transformers can carry. From the customer’s viewpoint, K-Factor must be established in order to calculate the size of the transformer that is needed. In other words, if a company with many offices were to install poor quality electronic ballasts having a poor K-Factor, a larger transformer would be needed than is apparent from the overall power consumption calculation.

– The K-Factor rating assigned to a transformer and marked on the transformer case in accordance with the listing of Underwriters Laboratories, is an index of the transformer's ability to supply harmonic content in its load current while remaining within its operating temperature limits. A specific K-Factor rating indicates that a transformer can supply its rated KVA load output to a load of specified amount of harmonic content. At present, industry literature and commentary refers to a limited number of K-Factor ratings: K-1, K-4, K-9, K-13, K-20, K-30, and K-40. In theory, a transformer could be designed for other K-Factor ratings in-between those values, as well as for higher values.




205

– The commonly referenced ratings calculated according to ANSI/IEEE C57.110-1986 are as follows:

• K-1: This is the rating of any conventional transformer that has been designed to handle only the heating effects of eddy currents and other losses resulting from 60 Hertz, sine-wave current loading on the transformer. Such a unit may or may not be designed to handle the increased heating of harmonics in its load current.

• K-4: A transformer with this rating has been designed to supply rated KVA, without overheating, to a load made-up of 100% of the normal 60 Hertz, sine-wave, fundamental current plus: 16% of the fundamental as 3rd harmonic current; 10% of the fundamental as 5th; 7% of the fundamental as 7th; 5.5% of the fundamental as 9th; and smaller percentages through the 25th harmonic. The "4" indicates its ability to accommodate four times the eddy current losses of a K-1 transformer.

• K-9: A K-9 transformer can accommodate 163% of the harmonic loading of a K-4 rated transformer. • K-13: A K-13 transformer can accommodate 200% of the harmonic loading of a K-4 rated transformer. • K-20, K-30, K-40: The higher number of each of these K-Factor ratings indicates ability to handle

successively larger amounts of harmonic load content without overheating.

– Table 1 Gives example of K-Factor loads

K-Factor Calculation

– The K-Factor is a number derived from a numerical calculation based on the summation of harmonic currents generated by the non-linear load. The higher the K-Factor, the more significant the harmonic current content.

– The algorithm used to compute K-Factor is:

– Details of the calculation method can be found in IEEE Standard 1100-1992.




206

– One problem associated with calculating K-Factor is selecting the range of harmonic frequencies that should be included. Some use up to the 15th harmonic, others the 25th harmonic, and still others include up to the 50th harmonic. For the same load, each of these calculations can yield significantly different K-Factors because even very small current levels associated with the higher harmonics, when multiplied by the harmonic number squared (e.g., 502 = 2500), can add significantly to the K-Factor. Based on the underlying assumptions of C57.110, it seems reasonable to limit the K-Factor calculation to harmonic currents less than the 25th harmonic. Sample calculations are shown in Figure 2.

K-Factor Transformers

– Underwriters laboratory (UL) recognized the potential safety hazards associated with using standard transformers

with nonlinear loads and developed a rating system to indicate the capability of a transformer to handle harmonic loads. The ratings are described in UL1561 and are known as transformer K-Factors.

– K-Factor transformers are designed to reduce the heating effects of harmonic currents created by loads like those in the table.1 above. The K-Factor rating is an index of the transformer's ability to withstand harmonic content while operating within the temperature limits of its insulating system.

– In establishing standard transformer K-Factor ratings, UL chose ratings of 1, 4, 9, 13, 20, 30, 40, and 50. From a practical viewpoint, individual loads with K-Factors greater than 20 are infrequent at best. Office areas with some nonlinear loads and large computer rooms normally have observed K-Factors of 4 to 9. Areas with high concentrations of single-phase computers and terminals have observed K-Factors of 13 to 17.

– When multiple nonlinear loads are powered from the same source, lower total harmonic current levels may be expected due to phase-shifts and cancellations. In one study of commercial buildings, (6) single phase loads with current distortions of 104% THD (total harmonic distortion) resulted in only a 7% THD at the service entrance when added with other loads in the building. Additional studies of typical loads are beginning to provide information which should aid in the development of additional rules-of-thumb to use when direct load measurements are not available.

– K-Factor transformers are designed to be operated fully loaded with any harmonic load having a K-Factor equal to or less than its K-Rating. For example, a K-13 transformer can be fully loaded with any harmonic load having a K-Factor up to K-13. If the load has a K-Factor greater than 13, then the transformer cannot be safely operated at full load and would require derating.




207

– K-Factor transformers differ from standard transformers. They have additional thermal capacity to tolerate the heating effects of the harmonic currents. Beyond that, well-designed K-Factor transformers will also minimize the winding eddy current losses through the use of parallel conductors and other winding techniques. The K-Factor indicates the multiple of the 60 Hz winding eddy current losses that the transformer can safely dissipate: Transformer load losses consist of winding I2R losses plus stray losses. Using UL1561 test methods, stray losses are assumed to be primarily winding eddy current losses for transformers 300 kVA and smaller. For example, a transformer having winding I2R losses of 2000 watts and 60 Hz stray losses of 100 watts would, with a K-20 rating, be required to dissipate the 2000 watts of I2R losses plus 20 times the 60 Hz stray losses of 100 watts for a total load loss of 4000 watts without exceeding the maximum winding temperature rise. The result is a larger, more expensive transformer. For K-Factor transformers, UL also requires that the neutral terminal and connections be sized to accommodate twice the rated phase conductor size (double the minimum neutral capacity) of standard transformers.

– Standard transformers, i.e., those not marked with a K-Factor rating, may have some tolerance to nonlinear loading, but their capability is unknown to the user and is not certified by a third party such as UL. Currently, marking a transformer with a K-Factor rating is not required by UL. Due to a conservative design or application, some unmarked transformers may therefore have enough extra thermal capacity to tolerate additional harmonic load heating. This is particularly true for 80ºC or 115ºC rise transformers built with 220ºC insulation materials which can safely withstand a 150ºC winding temperature rise.

– Additional overcurrent protection should be considered for all transformers supplying nonlinear loads. The National Electrical Code allows primary-only overcurrent protection at 125% of the transformer's primary full load amps. With three-phase transformers, the triplen harmonics are cancelled in the delta winding and do not appear in the input current. The output current and transformer loading is greater than is apparent from the input current. Therefore, the transformer can be overloaded without the primary overcurrent protection ever tripping. Adding transformer secondary overcurrent protection helps, but it still does not protect the transformer from the heating effects of harmonic currents. The use of supplemental protection in the form of winding temperature sensors can be used to provide alarm and/or system shutdown in the event of overload, excessive harmonic current, high ambient temperature, or inadequate cooling.

– Because transformers are the power system component most affected by nonlinear loads, they were the first to receive a harmonics capability rating system. K-Factor ratings are based on the heating effects of harmonics and are not necessarily applicable to other power system components. If harmonic rating systems for other components are needed, they will have to be developed by other methods, e.g., THD, crest factor, or some new and component-specific weighting of harmonic currents.

Advantages of calculating the K-Factor of transformers

– The strategy is to calculate the K-Factor for your load and then specify a transformer with a K-Factor of an equal or higher value. In this way, the transformer can be sized to the load without derating.

– The advantage of using a K-Factor transformer is that it is usually more economical than using a derated, oversized transformer.

Disadvantages of using derated standard transformers instead of K-Factor transformers

– First is the issue of managing the derating when the transformer nameplate indicates greater capacity. Initially, the transformer may be operated at the reduced loading, but in the future, the loading may be increased without considering the intended derating.

– Second, if smaller overcurrent protection is used to intentionally limit the loading, nuisance tripping may occur due to the transformer inrush current. Larger overcurrent protection may be required for the oversized (derated) standard transformer resulting in larger conductor requirements with the associated higher feeder costs.

– Third, transformers designed specifically for nonlinear loads minimize losses due to the harmonic currents. They operate with the nonlinear loads more efficiently and generate less heat that needs to be dissipated.




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What should be remembered when using a K-Factor Transformer

• Harmonic loads do cause premature failure when standard transformers are used. • Average reading RMS meters do not measure harmonic currents. True reading RMS meters should be used. • Insist on a K-Factor transformer that has been 3rd party tested. Accept no verbal claims. The proof must be

on the label. Estimating & Calculating K-Factor Loads

– For the most part, each designer or installer must make his/her own decision regarding what K-Factor to assign to

any load or load category. The following table is intended to assist in that determination by presenting what we believe are realistic, yet conservative, K-Factors for a number of loads and load categories based on their relative harmonic producing capabilities.

• List the KVA value for each load category to be supplied. Next, assign an ILK value that corresponds to the relative level of harmonics drawn by each type of load. See Table 2.

• Multiply the KVA of each load times the ILK rating that corresponds to the assigned K-Factor rating. This result is an indexed KVA-ILK value: KVA x ILK=KVA -ILK

• Tabulate the total connected load KVA for all load categories to be supplied. • Next, add-up the KVA-ILK values for all loads or load categories to be supplied by the transformer. • Divide the grand total KVA-ILK value by the total KVA load to be supplied. - This will give an average ILK

for that combination of loads. - (Total KVA-ILK) + (Total KVA) = average ILK • From Table 3, find the K-Factor rating whose ILK is equal to or greater than the calculated ILK.

Corresponding to this ILK is the K-Factor of the transformer required.




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213. 319BConsider transformer 1600 KVA feeding an office building with total lighting load 201 KVA,

total power load 483 KVA, total HVAC load (AHU’S) 386 KVA and total EWH load 54 KVA.

Select the k-factor required for this transformer.

AAnnsswweerr

Item Load description KVA Ilk-factor (from table 2) Ilk-KVA value

1 Lighting 201 25.82 5183.82 2 Power 483 123.54 59669.82 3 A.H.U 386 0.00 0.00 4 E.W.H 54 0.00 0.00

Total 1124 64853.64

– Average ILK = 64853.64 / 1124 = 57.69

– From table 3 K13 transformer can be used.




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214. 320BWhat is difference between prime generator & standby generator?

AAnnsswweerr Standby:

Applicable for supplying continuous electrical power (at variable load) in the event of a utility power failure. The alternators are peak rated (as defined in ISO8528-3).

Prime: These ratings are applicable for supplying continuous electrical power (at variable load) in lieu of commercially purchased power. There is no limitation to the annual hours of operation and these models can supply 10 percent overload power for 1 hour in 12 hours.

215. 321BWhat is difference between metal-enclosed switchgear & metal-clad switchgear?

AAnnsswweerr Metal-Clad vs. Metal- Enclosed

– You will frequently hear the expression “medium voltage Metal-Clad switchgear.” This means that the structures

(and compartments within each structure) are physically separated from each other by grounded metal barriers. The phrase “metal-clad” might not be said every time when talking about medium voltage switchgear assemblies, but it is assumed. This feature separates medium voltage switchgear assembly from other types of assemblies, such as a Metal-Enclosed assembly. A metal enclosed assembly (often associated with low voltage equipment) encloses the equipment in separate metal vertical structures. However, compartments are not separated from one another with metal barriers. Metal-Clad

Equipment in the assembly is enclosed, and separated by metal barriers into individual compartments. Typically associated with medium voltage equipment.

Metal-Enclosed

Equipment in the assembly is enclosed, but not necessarily separated by barriers. Typically associated with low voltage equipment.

As per IEC/BS EN 60298:

– The general term “metal-enclosed” is used in BS EN 60298 for three different categories depending on the design

of the internal compartmentalization

• Metal-clad switchgear has separate compartments for the main switching device and the two adjacent zones, i.e. in general three compartments (for circuit-breaker, busbar system and cable terminal zone). The compartment walls are metal and are earthed.

• Compartmented switchgear has the same degree of bay subdivision as “metal-clad” switchgear, but the compartment walls are of insulating material.

• Cubicle switchgear is defined as all switchgear whose compartmentalization does not meet the requirements of the two above categories (e.g. only two compartments), but this also includes all switchgear that does not have internal compartmentalization.

– The decision on which of these installation categories is to be used in any specific case is up to the user, with most

attention paid to safety of personnel during maintenance and cable work inside the switchbay. Restricting the effects of faults is important only when the resistance of the compartment walls to arcing has been verified and when the compartmentalization forms a true potential separation.




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Advantages of metal-enclosed over metal-clad

– Lower initial cost per cubical (metal-enclosed = 1/3 metal-clad). – Better protection for cables and transformers. – Significantly lower let-thru currents (mechanical energy). – Significantly lower let-thru I²T (thermal energy) - (breakers take 5 cycles from relay sensing to circuit interruption.

Power fuses require no more than 1 cycle for circuit interruption). – Lower installation cost (simple field assembly). – No auxiliary. Power or VTs (voltage transformers) are needed. – No maintenance required for fuses. – No possibility of reclosing on a fault with fuses. – Single-phase protection: shunt trip of three-phase switch in feeder cubical when a fuse operates.




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216. 322BWhat do you know about metal-enclosed switchgear, metal-clad switchgear and arc resistant

switch gear?

AAnnsswweerr Metal-Enclosed Switchgear Power Systems

– Metal-enclosed switchgear power systems are commonly used in low voltage applications. – Metal-Enclosed Indoor Switchgear Power Systems: This type of switchgear power system is enclosed on all sides,

including the top, with sheet metal. Ventilating opening and inspections windows, however, are not covered. The enclosure contains the power switching or interrupting devices with buses and connections, controls, instrumentation, metering, and other auxiliary devices. Doors and/or removable covers provide access to the interior of the enclosure.

– Outdoor Metal-Enclosed Switchgear Power Systems: This type of enclosure is similar to an indoor switchgear power system except that it is waterproof. A walk-in outdoor enclosed switchgear assembly with an aisle in front of the circuit breaker and instrument sections to protect workers and equipment from weather during maintenance and system operation is often available.

Metal-Clad Switchgear Power Systems

Metal-clad switchgear power systems are most commonly used in medium voltage applications. Metal-clad switchgear power systems differ from metal-enclosed in the following ways:

– The main switching and interrupting device is out of the removable type arranged with a mechanism for moving it physically between connected and disconnected positions. It is also equipped with self-aligning and self-coupling primary disconnecting devices and control wiring connections capable of being disconnected.

– Major parts of the primary circuit (i.e. circuit switching, interrupting devices, etc.) are completely enclosed by grounded metal barriers that have no intentional openings between compartments.

– All live parts are enclosed within grounded metal compartments. – Automatic shutters cover primary circuit elements when the removable element is in the disconnected, test, or

removed position. – Primary bus conductors and connections are covered with insulating material throughout. – Mechanical or electrical interlocks are provided for proper operating sequence under normal operating conditions. – The door through which the circuit-interrupting device is inserted into the housing may serve as an instrument or

relay panel and may also provide access to a secondary or control compartment within the housing.

Arc Resistant Switchgear Power Systems

Conventional medium voltage metal-clad switchgear is not designed to withstand high arc energy faults. Arc resistant switchgear power systems are designed to provide protection against internal arcing faults. The following are safety benefits can be gained by using arc resistant switchgear power systems:

– Each compartment door and barrier plate is designed to withstand pressure surges due to internal arcing. – Hot gases and molten particles escape through a specially designed pressure relieve vent located on the roof of the

enclosure away from the operating personnel. – Closed door racking of circuit breaker provides added safety. – Viewing windows allow personnel to observe the status of the circuit breaker without opening the door. – The low voltage compartment is completely segregated to avoid pressure buildup. – Arc resistant switchgear power system design should contain the faulty compartment, reducing down time

http://ecpowersystems.com/ecp.php?p=switchgear

http://ecpowersystems.com/ecp.php?p=switchgear




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217. 323BCompare between Static Transfer Switches (STS) and Automatic Transfer Switches (ATS).

AAnnsswweerr

– Transfer switches are used in power electronics to provide controlled transfers between two power supplies. In this note, we will always refer to devices that are able to perform switching, both with synchronous and asynchronous supply sources, with a Break Before Make (BBM) operation. This last feature is particularly fundamental in order to avoid a paralleling of the two supplies and to avoid that the neutrals get cross-coupled. The break introduced with BBM has to be sufficiently small in order to avoid too long energy gap to the load.

– The use of transfer switches is used to increase the system Mean Time Between Failures (MTBF) through redundancy of supplies and by separating the loads. This is done in two typical ways.

• In first place, the switch will perform a change on the source used for the supply of the load whenever the

original source is out of tolerance. Secondly, separating the different loads, it is possible to avoid that a problem happening in one load will propagate also to the other loads.

• This latter case takes place during a short circuit, hence the switch supplying this load will not permit a transfer on the other source while all the other switches will change the supply source protecting their loads.

Two technologies for Transfer Switches: STS and ATS

– There are two main technologies used for these devices with different characteristics in terms of switching quality and cost each having its merits and deficiencies: Static Transfer Switches (STS) and Automatic Transfer Switches (ATS).

– STS is based on static electronic components (SCR) therefore allowing for a fast and precise control of the switching between one line and the other. This solution permits to obtain a perfect (BBM) behaviour by never permitting a source overlap. Moreover, it is also capable of very fast switching between the two sources with a max delay of less than 5 msec (typically 4 msec).

– ATS is based on electromechanical components where the (BBM) switching is actually made by controlling the relays on each source line. This kind of technology can still make a perfect (BBM) change of supply sources both in synchronous and asynchronous conditions but it is certainly slower than the static solution.

The right Transfer Switch for each load need

– STS should be used in case of more critical loads where a longer voltage gap in the (BBM) procedure can be

deleterious. – ATS, on the other end, is still a reliable product that should be used to increase the overall reliability of an

installation. Indeed, is a product with a very high (MTBF) value. On the other side, due to its intrinsic lower switching speed, should not be used where the loads are very sensible to longer voltage sags (in the order of 6 msec). Anyway, ATS is certainly a lot more cost effective product respect to an STS one of the same rating.

STS ATS Break Before Make (BBM) feature

Always guaranteed. In CROSS there is a sensor for each SCR on and off state for a true BBM.

Always guaranteed. Similar sensor as per the CROSS but for the relays

Synchronous transfer between sources

Typical less than 4msec (max less than 5 msec)

Typical less than 6 msec

Asynchronous transfer between sources

0-20msec delay to be added to the above delay

0-20msec delay to be added to the above delay

Value Highest quality and higher value Good quality/price ratio Reliability Less Reliable More Reliable




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218. 324BState the difference between the three types of ballasts Magnetic, Rapid start, HF ballasts.

What is the recommended ballast for T12, T8, T5 & CFL?

AAnnsswweerr Magnetic Ballasts:

– Are used as a current limiting device. The Magnetic Ballast consists of a large number of windings of copper wire on a laminated iron core. It modulates electrical current at a relatively low cycle rate, which can cause a noticeable flicker. Magnetic ballasts may also vibrate at a low frequency. This is the source of the audible humming sound people associate with fluorescent lamps.

Rapid Start Ballasts: – Start lamps quickly (0.5 – 1.0 seconds) without flicker by heating the lamp electrodes and simultaneously applying

a starting voltage. This starting voltage of about 500V for 32W systems is sufficient to start a discharge through the lamps when the electrodes have reached an adequate temperature. Electrode heating continues during operation typically consumes two watts per lamp. Lamps operated by Rapid Start ballasts typically operate 15000 to 20000 switch cycles before failure.

Programmed Start Electronic Ballasts: – Also start lamps quickly (1.0 – 1.5 seconds) without flicker. Programmed Start ballasts are designed to provide

maximum lamp life in frequent lamp starting applications such as areas where occupancy sensors controls are used. Programmed Start Electronics Ballasts precisely heat the lamp electrodes, tightly controlling the preheat duration before applying the starting voltage. This enhancement over Rapid Start ballasts minimizes electrode stress and depletion of emitter of emitter material, thereby maximizing lamp life. Lamps operated by Programmed Start ballasts typically operate up to 50000 switch cycles before failure.

– Note that: Rapid Start and Magnetic are old solutions banned in Europe and USA, because they consume lots of energy and are not very efficient. The markets are switching fasts to Electronic ballasts solutions.

– For T12, Either Rapid Start ballasts or Electronics can be used. – For T8, Either Magnetic ballasts or Electronic ballasts can be used. – For T5, Electronic ballasts only can be used. – For CFL, Either Magnetic ballasts or Electronic ballasts can be used.

219. 325BCan we dim LED Light? How? Is there any flickering while dimming? Are there any

Changes in color and efficacy with dimming?

AAnnsswweerr Lack of effective and affordable dimming has hampered the adoption of CFLs in the residential sector. LEDs are in

theory fully dimmable, but are not compatible with all dimmer controls designed for incandescent lamps.

Standard dimming controls

– Typical residential incandescent lamp dimmers are essentially electronic switches that toggle on and off 120 times per second. By delaying the beginning of each half-cycle of AC power (known as “phase control”), they regulate the amount of power to the lamp filament. Because this occurs so quickly, most people do not detect flicker, but see continuous dimming. Although the general operation of such electronic dimmers is the same, the specific electrical characteristics of residential dimmers can vary considerably.

– These variations are immaterial to incandescent lamps, but matter greatly when used with electronic devices such as compact fluorescent lamps (CFLs) and LEDs.




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Dimming CFLs

– Some screw-in (integral) CFLs can be dimmed using line-voltage incandescent dimmers but must be specifically designed to do so. They typically dim only to about 20% of maximum intensity, due to limitations of the low-cost ballast. More sophisticated electronic ballasts providing continuous dimming below 5% are available, but are simply not cost-effective for use in screw-in CFLs. Some fixtures (e.g., torchieres) successfully use pin-based CFLs in combination with on-board dimming controls. Four-pin CFLs using separate dimming ballasts can be dimmed via line voltage or 0-10 volt DC control, with dimming range as low as 1%, but more commonly 5% or 20%.

LED (Light Emitting Diodes) Dimmer Circuit

– LEDs are very sensitive components - exceed their rated current or voltage

and their lifespan can be slashed from 50,000+ hours to a microsecond. LEDs are current-driven * which means that the intensity of the light they generate depends on the amount of electric current flowing them. (* The voltage drop across an LED depends entirely on the current flowing through it and ranges from 2-4 Volts for most LEDs).

– Typically current is controlled using a resistor in series with the LED, or a current regulator circuit. Supplying more current to an LED increases its intensity, and reducing the current decreases its intensity. One way of dimming an LED is to use a variable resistor (potentiometer) to dynamically adjust the current getting to the LED and therefore increasing or decreasing its intensity. This works very well when just one LED bulb is involved.

– Unfortunately, all LEDs are not made equal - even those of nominally identical specifications from the same batch from the same manufacturer. Although this will not be apparent when strings of LEDs are being driven with the recommended forward current (e.g. 25mA for ultrabright LEDs), as the current is reduced some LEDs will turn off before others, and some will be dim when others are still quite bright etc.

– LEDs face a dimming challenge similar to that of CFLs: their electronics are often incompatible with dimmers designed for incandescents.

– An LED driver connected directly to a line-voltage incandescent dimmer may not receive enough power to operate at lower dimming levels or it may be damaged by current spikes. Some LED products can be used with line-voltage incandescent dimmers, but the dimmer and the LED driver electronics must be carefully matched. Because of variability in installed dimmers, it is not possible to guarantee that a given LED fixture will work with all dimmers. Some LED light fixture manufacturers publish lists of specific dimmer products tested and approved for use with their fixtures.

– More sophisticated LED dimmers use low-voltage controls (either variable resistors or 0-10 volt DC control) connected separately to the electronic driver. Full AC power is provided to the driver enabling the electronic controls to operate at all times, thus allowing LEDs to be uniformly dimmed (typically down to 5% or lower). However, they may require additional low-voltage wiring for retrofit applications.

Pulse Width Modulation

– A far superior method of dimming LEDs is to use Pulse

Width Modulation (PWM). With PWM strings of LED bulbs can all be driven with the recommended forward current, with the dimming achieved by turning the LEDs on and off at high frequency - so fast the human eye cannot see the strobing effect. The longer the on periods are relative to the off periods, the brighter the LEDs will appear to the observer.

– Duty Cycle is a percentage measure of the time that the LED is physically on. If, for example, the LED cycles ON for 9/1000 of a second, and then OFF for 1/1000 of a second, the duty cycle is 90%: 90% of the time it is ON, and 10% of the time it is OFF. Therefore, the intensity of the light will be approximately 90% of its undimmed level.

http://www.reuk.co.uk/Resistor-Colour-Codes.htm

http://www.reuk.co.uk/Using-The-LM317T-With-LED-Lighting.htm

http://www.reuk.co.uk/buy-VARIABLE-RESISTORS.htm




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– The easiest way to achieve this high frequency switching is to use a 555 timer integrated circuit (IC) - one of the commonest and most versatile ICs ever created. The circuit shown below (from the following article: Pulse Width Modulator with NE555 Timer Oscillator) is designed to be used as a dimmer for 12V DC light bulbs or a speed controller for a 12V DC motor.

– This circuit can easily be modified for use as dimmer circuit for LED bulbs

powered from a 12V DC supply as shown below:

– This dimmer circuit cannot be used to turn the LEDs all the way off or to full brightness. In fact it operates within a duty cycle range of 5%-95% as the potentiometer (labelled P1) is turned from minimum to maximum. (By using germanium diodes in place of the two IN4148 signal diodes this dimming range can be extended to go from 1%-99%.)

PWM with a Microcontroller

– There are now quite a few different microcontrollers on the market which are very easy to

programme, cheap to buy, and can be built into circuits with only very few external components required.

– The advantage of using a microcontroller rather than building a circuit like the one presented above is that the complexity of the system is in the software (instructions) you put onto the microcontroller. This means that changes can be made without needing to change the circuit design, and prototyping can be very quick.

– We connected one of our 12V LED spotlights to the dimmer circuit and found that some of the 20 LEDs in the unit flashed on and off, others turned off altogether, and others alternated between being very bright and very dim.

Flicker and dimming

– Most LED drivers use pulse width modulation (PWM) to regulate the amount of power to the LEDs. This technique turns the LEDs on and off at high frequency, varying the total on time to achieve perceived dimming. Driver output frequency should be at least 120 Hertz (Hz) to avoid perceptible flicker under typical circumstances.

– LED light fixtures may appear to flicker at the lowest settings, but only when the dimmer control is moved. This is due to the finite “resolution” of the digital electronics. Good-quality electronic drivers feature 12-bit or greater resolution to obtain flicker-free operation throughout their dimming range.

Changes in color and efficacy with dimming

– When an incandescent lamp is dimmed, the filament temperature decreases, causing the emitted light to appear “warmer,” changing from white to yellow to orange/red. The luminous efficacy of the lamp also decreases: a 15 lm/W lamp at full power will be 10 lm/W at 50% dimmed.

– CFL color temperature does not change with dimming as dramatically as with incandescents, running counter to our expectation of significantly warmer color at low light levels. Luminous efficacy of fluorescent sources stays approximately constant with dimming until about 40%-50%; thereafter it decreases, but not as steeply as with incandescent lamps.

– Most “white” LEDs are actually blue LEDs with a phosphor coating that generates warm or cool white light. Their light does not shift to red when dimmed; some may actually appear bluer with dimming. White light can also be made by mixing red, green, and blue (RGB) LEDs, allowing a full range of color mixing and color temperature adjustment. Overall LED luminaire efficacy decreases with dimming due to reduced driver efficiency at low dimming levels.

http://www.uoguelph.ca/~antoon/circ/pwm555.html



http://www.reuk.co.uk/Germanium-Diodes.htm




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220. 326BAccording to SEC Distribution Materials Specification. What are the available ratings for

transformers Pole mounted & Pad mounted? What are the maximum accepted losses? What

are the available tap changer settings? What is the recommended vector group, Impedance

Voltage, Temperature Rise, Noise Level, Short Circuit Level, Degree of Protection, Dimensions,

LV bushings/terminals?

AAnnsswweerr Ratings:

The standard ratings shall be: – Pole mounted: 50, 100, 200, 300 KVA – Pad mounted: 300, 500, 1000, 1500 KVA

Maximum Losses:

– The indicated figures below are the maximum acceptable values. Transformers with losses exceeding these values will be rejected.

Transformer Rating No-Load Losses (Watts) Load Losses (Watts) Up to 100KVA 250 1500

200KVA 380 2200 300KVA 520 3200 500KVA 750 4700

1000KVA 11100 9000 1500KVA 1700 14000

Tap Changer:

– On M.V; Transformer shall be fitted with a lockable 5 positions, manual, off-load Tap Changer having the following taps:

• Tap No. 1 + 5% of rated voltage • Tap No. 2 + 2 ½ % of rated voltage • Tap No. 3 0 % of rated voltage • Tap No. 4 - 2 ½ % of rated voltage • Tap No. 5 - 5 % of rated voltage

Vector Group:

– Unless otherwise specified, the transformer shall be connected delta-star in accordance with vector group reference Dyn11.

Impedance Voltage: – The impedance voltage at normal tap shall be 4% for transformers up to 300KVA, 5% for 500 KVA and 6% for

transformers greater than 500KVA.

Temperature Rise: – At the rated power the transformer shall comply with the following Maximum temperature rises:

• Top oil 45°C Max. • Winding 50°C Max. • Hot Spot 98°C Max. • Avg. temp. due to short circuit 250°C Max.

Noise Level:

– The noise level emitted by a transformer, at full load, shall not exceed 48 dB. Measurements shall be in accordance with IEC Standard 60551.




218

Short Circuit Level: – The short circuit current that transformer should withstand for two seconds is: – 25 times full load current for ratings of 50, 100, 200, 300KVA – 20 times full load current for rating of 500KVA – 17 times full load current for ratings of 1000 & 1500KVA

Degree of Protection:

– Transformer and its cable boxes shall be designed to have adequate protection level suitable for outdoor usage.

Dimensions: – The maximum dimensions of the transformer shall be as follows:

• For pole mounted transformers:

• For pad mounted transformers:

– The above dimensions are not applicable for transformers used in Package/Unit substations. LV bushings/terminals:

• For Pole-mounted transformer:

The LV terminals shall be suitable to connect the following Aluminum cables: Transformer Rating (KVA) Cables to be connected Up to

50 one 4cx185mm² 100 200 two 4cx185mm² 300 (400/231V)

300 (231/133V) two 4cx300mm² • For Pad-mounted transformer:

LV bushings/terminals shall be brought out of the transformer tank inside a cable box on the opposite side of the HV box with cable entry coming vertically from bottom; box shall have removable front and bottom sides. The LV terminals shall be suitable to connect the following Copper cables:

Transformer Rating

(KVA) Cables per phase to be

connected Cables for neutral to be

connected 300 one 1cx630mm²

one 1cx630mm² 500KVA (400/231V) 500KVA (231/133V) two 1cx630mm² 1000KVA (400/231V) 1000KVA (231/133V) four 1cx630mm²/ 1500KVA (400/231V) three 1cx630mm²/ two 1cx630mm² 1500KVA (231/133V) six 1cx630mm²/ three 1cx630mm²/

Rating (KVA) Width (mm) Depth (mm) Height (mm) 50 1350 900 1450 100 1350 900 1450 200 1450 1100 1700 300 1450 1100 1700

Rating (KVA) Width (mm) Depth (mm) Height (mm) 300 & 500 1700 1400 1600

1000 1900 1600 1900 1500 1920 1700 2000




219

221. 327BWhat’s the reason of grounding or earthing of equipment?

AAnnsswweerr

– With a ground path, in case of short circuit the short circuit current goes to the body of the equipment & then to the ground through the ground wire.hence if at the moment of fault if a person touches the equipment body he will not get a shock cause his body resistance (in thousands of ohms) will offer a high resistance path in comparison to the ground wire. Hence the fault current will flow thru the ground wire & not thru human body.

– Providing a ground path helps in clearing the fault. A CT in the ground connection detects the high value fault current hence the relay connected to the CT gives breaker a trip command.

– Grounding helps in avoiding arcing faults. IF there would have been no ground then a fault with the outer body can cause a arcing to the ground by breaking the air. This is dangerous both for the equipment & the human beings.

222. 328BWhat is difference between power transformers & distribution transformers?

AAnnsswweerr

– Distribution Transformers are designed for a maximum efficiency at 50% of load. Whereas power transformers are designed to deliver max efficiency ay 90% and above loads.

– The distributions transformers have low impedance so as to have a better regulation. Power transformers have higher impedance so as to limit the SC current.

– Power transformers are used to step up voltages from 11 kV which is the generating voltage to 132 kV or whatever will be the transmission voltage levels. Power transformers are having DELTA-DELTA connection and are located at power generating stations.

– Distribution transformers are used to step down voltages from transformer levels to 11 kV/415 V. Distribution transformers are having DELTA-STAR connection and are located in substations near load centers.

– The difference between power and distribution transformers refers to size & input voltage. Distribution transformers vary between 25 kVA and 10 MVA, with input voltage between 1 and 36 kV. Power transformers are typically units from 5 to 500 MVA, with input voltage above 36 kV.

– Distribution transformer design to have a max efficiency at a load lower than full load.power transformer design to have a max efficiency at full load.

223. 329BWhat will happen if DC supply connected to 100W bulb?

AAnnsswweerr

– Of course the bulb will glow. – Note that the current in case of AC flowing through the bulb will vary from zero to peak value then to zero again &

then to peak value in the -ve side & then again to 0. Hence the bulb actually flickers with a 50 Hz frequency. Of course your eye is not that quick enough to notice that flickering & hence you see a continuous light coming out of the bulb with AC

– Considering a sine wave AC current, A DC current with value equal to peak AC value divided by sq.rt2, will provide exactly the same power consumption. A 100 watt bulb operating at 220 V AC will draw rms current Irms=P/V=100/230=0.43 Amps. The current hence actually varies from 0 to 0.6 (peak value, = 0.43 * sq.rt2) then to 0 then to 0.6 in the other direction & then again to 0. And of course this happens 50 times a second. Since the power consumption is calculated from the rms value hence we need to keep in mind the rms value of current when going to design a switch (or breaker for larger loads) for such a load.




220

224. 330BCan an armoured cable be laid in a PVC conduit for aesthetic purposes?

AAnnsswweerr

– PVC sheathed armoured cable could be placed in PVC conduit. PVC sheathed armoured cable - such as BS 5467 - could be enclosed in a PVC conduit with few ill-effects.

– However, if the cable is a low smoke halogen free type (e.g., BS 6724), or has specific fire performance (e.g., BS 7846), then the use of a PVC conduit could have deleterious effects on the cable in a fire, and guidance should be sought from the cable manufacturer concerned.

– Other types of conduit may be more suitable.

225. 331BIs it permissible to install PVC/SWA/PVC cable in Zones I and II flammable areas? If so,

what is the authoritative document?

AAnnsswweerr

– Armoured (SWA) cables are usually suitable BUT, are subject to the requirements of BS EN 60079 - and also evaluation by the installation designer!

226. 332BIs it permissible to use aluminum twin & earth cables?

AAnnsswweerr

– Prototype aluminum twin & earth cables were produced in 1971, but were soon abandoned because of concerns with conductor corrosion and 'creep' within terminations.

– It’s recommend that these cables are replaced with copper conductor 6242Y (or 6242B) cables, sized in accordance with BS7671:2008 - 17th Edition IEE Wiring Regulations.

227. 333BWhat are the codes of armoured cable glands? What is application for B/W & C/W?

AAnnsswweerr Armoured cable glands codes - and are as follows:

– A - Unarmoured cable – B - Armoured cable (no sealing) – C - Armoured cable (sealing on outer sheath) – D - Armoured cable (sealing on Inner sheath) – E - Armored cable (sealing on both sheaths) – W- SWA – X- Braided – T – Pliable – Y- Aluminum strip.

B/W is used for indoor & C/W is used for outdoor

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228. 334BWhat are the minimum CSAs for process instrument cables, power cables & control cables?

AAnnsswweerr

– To meet BS 7671:2008, assuming that the circuit supplying the instruments is actually a power circuit and not part of the control system, the minimum size is 1.5mm2.

– For signal and control circuits, it is 0.5mm2 minimum. – If the signal circuit is just an IT signal, it can be 0.1mm2.

229. 335BIs it possible to use armour of a power cable as its earthing conductor? As an example -

for 4 x 240mm cable, is it necessary to install separate earthing cable? Or is the armour

of the cable enough for earthing? What is required by BS standards?

AAnnsswweerr

– If the calculations in accordance with BS 7671:2008 are satisfactory using the circuit protective conductor (CPC), then, yes you may use the SWA of the cable as the CPC.

– In this case, it is not necessary to provide separate CPC.

230. 336BWhat is the filling percentage that should be followed for trunking & conduits & cable trays

as per British Standard?

AAnnsswweerr

– The Wiring Regulations (BS7671: 2008) state the 45% fill rule for trunking and conduit for heat dissipation. – For cable tray, you would normally fill to around 80%, as heat can easily escape because of there being no covers. – Another factor to keep in mind is the recommended support positions (span) to ensure that the combined weight of

the cables, plus the tray, does not exceed the manufacturer's recommendations.

231. 337BIn order to reduce the size of the sub-main cable, we have installed a separate circuit

protective conductor (CPC) with calculations satisfying this. Terminations have been

completed as standard. However, on installation, the contractor has installed the CPC so it

is not clipped to the armoured cable as normal practice, and takes a different route. Is

there a standard that requires an armoured cable's CPC to be clipped to the cable? Is there

an issue with running earths in a separate route to the armoured cabling, i.e. different

lengths etc?

AAnnsswweerr

– If you refer to BS7671:2008, Regulation 543.6.1 states: 'Where overcurrent protective devices are used for fault protection, the protective conductor shall be incorporated in the same wiring system as the live conductors or in their immediate proximity'.

– At that point, it would appear that the said installation may not comply with the requirements of this regulation.

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232. 338BWe have to pull a 3 X 70mm SWA cable through 80m of 100mm ducting. There will be a

bend at each end up to the electrical switch room. The cable run between is more or less

straight. Can you tell me what a reasonable bend radius would be to allow satisfactory

pulling of the cable?

AAnnsswweerr

– Manufacturers recommended installation minimum bend radius for SWA cable with shaped cores is eight times the overall cable diameter. So, for your cable, this is 8 X 34 = 270 mm. This is acceptable for a 600/1000V cable. For higher voltages the recommendation is 12 X the OD. If you can go for a bigger bend, obviously this is always better.

– Also take care...ensure that the pull is even etc. This is referred to in the Wiring Regulations BS7671:2008, and also in the cable standard.

233. 339BWhat power cables are suitable for direct burial in ground which may be prone to water

logging?

AAnnsswweerr

– Armoured power cables with Medium Density Polyethylene (MDPE) sheaths are recommended for burial in water logged conditions.

– Standard armoured power cables (PVC & Low Smoke sheaths) are recommended for 'free draining' soils only.

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223

234. 340BCalculate the annual savings and payback for installing an occupancy sensors given that:

341BNo. of fixtures = 20 x 2 Lamps; Fixture wattage Draw = 88 watt/Fix; Time length needed

= 20 min/hr.; Operating hours = 4000 hrs./year; Electricity cost = 0.15 LE/kWh; Sensors

cost = 200 LE

235. 342BFor replacing an existing Lighting system of Incandescent lamps by a new fluorescent

lamps, calculate the annual savings and payback given that:

343BExisting lighting system 100 Lamps (200 watt/lamp); 200 watt lamp efficacy 17.5

Lm/watt; Fluorescent lamps 36 watt (44 watt incl. Ballast); Fl. lamps efficacy 70 lm/watt;

Fl. lamps cost = LE. 15 (incl. Fixture); Annual operating hours 4000 hrs./year; Electricity

cost = 0.15 LE./kWh

236. 344BA 23,000 square meter high bay facility is presently lit with 800 twin 400 watt mercury

vapour fixtures (455 watts per lamp including ballast.) What are the annual savings of

replacing the existing lighting system with 800 single 400 watt high pressure sodium

fixtures, (465 watts per lamp including ballast) Assume 8000 hours per year, an energy

cost of $0.05 per kWh, and a demand cost of $6.00 per kW-month.

237. 345BChoose the correct answer:

o 346BThe efficacy of a light source refers to the Color rendering index of the lamp. A) True B) False

o 347BIncreasing the coefficient of utilization of the room cavity will in many instances increase the number of lamps required. A) True B) False

o Which HID lamp has the highest efficacy? A) Mercury Vapour B) Metal Halide C) High Pressure Sodium

o A sewing factory. Lights are on 9 hours per day. The ceiling height is about 4 meters. Suggest an appropriate light source. A) Incandescent B) Fluorescent C) Metal halide D) High pressure sodium E) Low pressure sodium

o One disadvantage to metal halide lamps is a pronounced tendency to shift colours as the lamp ages. A) True B) False

o A building presently has the following lighting system: Present: 196 mercury vapour light fixtures

Size: 250 watt/lamp 285 watt/fixture, including ballast You have chosen to replace the existing system with the following: Proposed: 140 high pressure sodium fixtures Size: 150 watt/lamp 185 watt/fixture The facility operates 24 hours/day. Approximate the heating effect if the heating system efficiency is 80%, fuel costs $4.25 per GJ, and there are 200 heating days per year. A) $4,445/year B) $2,754/year C) $6,986/year D) $5,289/year E) $2,754/year




224

238. 348Bالتالية األحمال على يشتمل سكنية وحدات عدة على يحتوى مبنى: o 1 = قدرة ومعامل. و.ك 75 إنارة أحمال . o 30 أمبير2 بسعة منها كل مآخذ ست على دائرة كل تحتوى الكهربية للمآخذ دائرة .o 10 1 = قدرة ومعامل. و.ك 1.5 منها لكل اإلسمى والحمل التشغيل متقطعة كهربية سخانات . o المصرى للكود طبقا المطلوب: 349Bحالة فى التباين معامالت باستخدام السماح مع المبنى لهذا األقصى الحمل تحديد : 350B)سكنية عمارة المبنى كان إذا )أ .

351B)تجارى سوق المبنى كان إذا) ب.

اإلجابةاإلجابة

فى حالة استخدام المبنى كعمارة سكنية مكونة من عدة وحدات سكنية : )‌أ( ك.ف.أ 37.5 ك.وات = 37.5 = 75٪ × 50حمل اإلنارة = )1( أمبير 6 = 5 × 2 × 0.40 + 2حمل دائرة المآخذ الكهربائية باألمبير = )2(

)a( ) = ك.ف.أ 1.32 = 1000) / 220× 6حمل الدائرة الكهربية بالكيلو فولت أمبير )b( = ك.ف.أ 39.6 = 1.32 دائرة × 30الحمل الكلى للمأخذ

ك.ف.أ) 6ك.وات(6)= 1.5×8٪(25+1.5+1.5حمل السخانات الكهربية = )3( ك.ف.أ83.1 = 6 + 39.6 + 37.5الحمل الكلى = )4(

فى حالة استخدام المبنى كسوق تجارى: )‌ب(

ك.ف.أ 67.5 ك.وات = 67.5 = 75٪ × 90حمل اإلنارة = )1( أمبير 9.58 = 5 × 2 × 0.75 + 2حمل دائرة المآخذ الكهربائية باألمبير = )2(

)a( ) = ك.ف.أ 2.108 = 1000) / 220× 9.58حمل الدائرة الكهربية بالكيلو فولت أمبير )b( = ك.ف.أ 63.23 = 2.108 دائرة × 30الحمل الكلى للمأخذ

ك.ف.أ 15 ك.وات = 15 = 1.5 × 10حمل السخانات الكهربية = )3( ك.ف.أ145.73 = 15 + 63.23 + 67.5الحمل الكلى = )4(

239. 352Bالمصرى للكود طبقا المبنى لهذا األقصى الحمل حساب :المطلوب .طوابق ستة من ويتكون اقتصادية متوسطة منطقة فى مربع متر 350 مساحته سكنى مبنى.


طابقا 15جدول الطلب على الحمل بوحدات المباني السكنية التي يقل ارتفاعها عن من

متر100 ك.ف.أ / 4الحمل األقصى على أساس إسكان متوسط = –

100 ك.ف.أ 84 = 4 دور × 6× 350الحمل األقصى =

240. 353Bالركاب؟ مصاعد تنقسم كم إلى.


:تنقسم مصاعد الركاب إلى أربعة أقسام رئيسية

مصاعد لألغراض العامة فى المبانى التجارية. )1( مصاعد المبانى السكنية. )2( مصاعد فى المبانى المؤسسية. )3( مصاعد فى المخازن. )4(




225

241. 354Bاآلتى على تحتوى وهى ، المصرى للكود طبقا لها الكهربائى الحمل تحديد مطلوب) خاصة سكنية وحدة (فيال :o وات 15000 بإجمالى اإلنارة مخارج من عدد o مآخذ ست عدد على تحتوى دائرة كل (دائرة 30 /بعدد أمبير 2 سعة: كهربائية مآخذ .(o كهربائية أجهزة :

o حصان 1.2 بموتور يعمل جراج باب o وات 1400 بقدرة رياضية ألعاب جهاز o تكييف أجهزة 7 / عدد :o وات.ك 2.6 (حصان 3.5 بقدرة 2 / عدد (o وات.ك 1.9 (حصان 2.5 بقدرة 3 / عدد (o وات.ك 1.5 (حصان 2 بقدرة 2 / عدد (

o الطهى أجهزة :o وات 6000 بقدرة كهربائى رئيسى طهى جهاز o وات 2000 قدرة فرعى كهربائى طهى جهاز 2 / عدد o وات 1200 قدرة كهربائى تسخين جهاز 1 / عدد

o كهربائى بموتور تعمل طلمبات :o وات.ك 1.6 بقدرة مياه ضخ طلمبة o وات.ك 2.8 بقدرة حدائق رى طلمبة o وات.ك 0.6 بقدرة بالبدروم كسح طلمبة

o يماثلها وما السخانات :o وات.ك 3 بسعة مستمرا يعمل الذى النوع من سخان 2 / عدد o وات.ك 2 بسعة مستمرا يعمل الذى النوع من سخان 1 / عدد o وات.ك 6 بسعة لحظى سخان 1 / عدد o وات.ك 5 بسعة الجاكوزى لجهاز للتسخين سخان جهاز o وات.ك 4 بسعة الساونا بغرفة للتسخين سخان جهاز


:من جدول معامالت التباين العمود الخاص بوحدة سكنية خاصة

اإلنارة: )1(

٪ من أحمال اإلنارة 66تحسب ك.وات9.9 = ٪15000 × 66

المآخذ: )2(

حمل دائرة المأخذ الكهربائية باألمبير:

100 أمبير 6 = 5 × 2 × 40 + 2 0.85 ك.وات باعتبار معامل قدرة 1.122 = 0.85 × 220 × 6حمل الدائرة الكهربية بالكيلووات = ك.وات33.66 = 30 × 1.122الحمل الكلى للمأخذ = األجهزة الكهربائية: )3(

٪ من الحمل 50قدرة] + معامل0.85 ك.وات) على أساس 1.87 أمبير [(10٪ مــن إجمالى الحمــل الكامــل لمجمــوع األجهـزة حتى سعة 100 أمبير 10لألجهزة التى حملها يزيد عن

) 1.2 × 0.746 + 1.4 + 2 × 1.5 + (50 ] ٪ 2 × 2.6 + 3 × 1.9 [

) =0.9 + 1.4 + 3 + (50

ك.و 10.75=5.3+5.4]=5.2+5.7[100

أجهزة الطهى: )4(معامل قدرة واحد ك.وات على أساس 2.2 أمبير (10٪ من الحمل المقنن الزائد على 30 أمبير + 10٪ من الحمل الكامل لألجهزة حتى 100

حيح). ص ك.وات 7.00) = ٪6 (30) + 1.2 + 2.00 × 2= (




226

المحركات الكهربائية: )5( ك.وات 3.9] = 0.6 + 1.6٪ [ 50] + 2.8٪ [100٪ من الحمــل لباقـى المحركات = 50٪ من الحمــل الكامــل ألكبــر محــرك + 100

السخانات وما ماثلها: )6()a( :السخانات الكهربائية متقطعة التشغيل

٪ من الحمل الكامل لباقى الساخانات 25٪ من الحمل الكامل للسخان الذى يلى أكبر سخان + 100٪ من الحمل الكامل ألكبر سخان + 100 ك.وات 12) = ٪4 (25 + 5 + 6 =

)b( :السخانات الكهربائية مستمرة التشغيل٪ من الحمل الكامل فى جميع الحاالت 100

ك.وات 8 = 2 + 3 × 2 = :اإلجماليات

8+ 12+ 3.9 +7+ 10.75+ 33.66 + 9.9 ك.وات 85.21= ب) 6(أ) 6() 5() 4() 3() 2() 1(

:مالحظة

ك.وات فيكون: 137.722إذا تم جمع جميع األحمال جمعا جبريا نجدها

) = diversity factorمعامل التباين اإلجمالى (85.21

=61.87 ٪137.722

242. 355Bجهاز ؛الراديو جهاز ؛الثالجة ؛الشعر مجفف ؛الكهربي الفرن ؛المكواة ؛الخبز محمر: مثل االستعمال شائعة المنزلية الكهربية لألجهزة التقديرية األحمال هى ما

الحمام سخانات ألى؛ حاسب ؛ طابعة بروجيكتور؛ مياه؛ غالية ؛الغسيل مجفف ؛بالسخان كهربائية غسالة ؛كهربائية غسالة ؛الحجرة دفاية ؛الكهرباء مكنسة ؛التلفزيون


القدرة (وات) الجهاز القدرة (وات) الجهاز 100 غسالة كهربائية 500 محمر الخبز

1000-500 المكواة 1500-700 مجفف الغسيل 3000-1500 الكهربيالفرن 100 غالية مياه

Projector 50-75 500 مجفف الشعر300-200 جهاز التلفزيون Printer- 400 طابعة 2500-150 مكنسة الكهرباء Computer 2000حاسب ألى- سخانات الحمام 300 دفاية الحجرة

3000-2000 لتر15 6300 غسالة كهربائية بالسخان 300-100 الثالجة 6000-4000 لتر60

100-30 جهاز الراديو 6000-4000 لتر80




227

243. 356Bفي ذلك و ساعات، أربعة لمدة به مسمــوح زائد تحميل أقصى هــو فما أ،.ف.ك750 هو المحول لهذا المعتاد الحمل و أ،.ف.ك 1250 االسمية سعته محول

مئوية؟° 30 حــرارة درجــة


) منحنيات التحميل الزائد لمحوالت التوزيع في ) فى الكود المصرى1-4من الشكل :

درجة مئوية30درجة حرارة

191

4601250750

2

1

.

;.

=∴

===

k

htk

:وبذلك يكون أقصي تحميل زائد مسموح به لمدة أربعة ساعات هو

S2 = k2. SN = 1.19 * 1250 = 1487.5 kVA

244. 357Bتبريد بنظام توزيع محول سعة تحديد المطلوب ONAN العشرين لمدة أ.ف.ك 250 قيمته وحمل ساعات، أربع لمدة أ.ف.ك 450 قيمته بحمل تحميله يتم

الباقية ساعة

اإلجابةاإلجابة S2/ S1 = 450 / 250 = 1.8 = k2 / k1 S2= 450 kVA , t2 = 4h S1= 250 kVA , t1 = 20h

وتقاطعه ;ويمر بنقطة األصل = k2 / k1 1.8) برسم الخط 1-4من الشكــل ( htمع المنحنى = k1 تكون على النحو التالى: k1، k2، فإن السعات األسمية =4

0.633 , k2 = 1.14

NSkSوحيث أن: .22 NSkS أو = .11 تكون: =

2

2

1

1

KS

KSSN ==

KVAS N 9.394633.0

25014.1

450===

ك.ف.أ. 400 ولذا فإن المحول المناسب هو محول سعته




228

245. 358Bعن عبارة 2م 600 مساحة على تجارى سكنى مبنى :o وخدمات جراج بدروم دور o تجارى) ميزانين + أرضى (دور 2 / عدد o شقة 5/عدد دور بكل متكرر دور 16 / عدد o وات.ك 15 منهم كل كهربائى مصعد 3 / عدد o احتياطية أحدهما ٪88 وكفاءة حصان 17.5 قدرة مياه رفع طلمبة 3/عدد بها العلوى الخزان إلى المياه لرفــع مياه طلمبــات محطــة .o احتياطية أحدهما ٪87 وكفاءة حصان 6.5 قدرة طلمبة 2/ عدد بها البدروم من مياه كسح طلمبة محطة

المصرى للكود طبقا المبنى لتغذية الالزمة) المحوالت (المحول سعة حساب: المطلوب


طابقا 15يرجع جدول الطلب على الحمل بوحدات المباني السكنية التي يزيد ارتفاعها عن ك.ف.أ 10 – 8 سكنى 2م100طلب الحمل لكل – ك.ف.أ12 تجارى 2م100طلب الحمل لكل –

ك.ف.أ12= ) 2 م100 ك.ف.أ / 2 (× 600 ----- 2 م600 البدروم بمساحة )1( ك.ف.أ144) = 2 م100 ك.ف.أ / 12 (× 1200 ----- 2 م1200 = 2 م600 دور × 2التجارى عدد/ )2( ك.ف.أ960) = 2 م100 ك.ف.أ / 10 (× 9600 ----- 2 م9600 = 2 م600 دور × 16السكنى عدد/ )3( ك.ف.أ 12 = المداخل + الساللم + غرف السطح (يمكن أخذها جميعا مثل البدروم) )4(

وبذلك يكون إجمالى أحمال اإلنارة و البرايز و التكيفات و السخانات و األجهزة : ك.ف.أ 1128 = 12 + 960 + 12 + 144 -----

أحمال القوى األخرى: )5()a( 3 ك.ف.أ53 (معامل القدرة) = 0.85 ك.وات / 15 × 3 ----- مصعد )b( 2ك.ف.أ53= (الكفاءة)0.88 (معامل القدرة) × 0.85 / 0.746 ×17.5 × 2 ----- طلمبة مياه )c( 1ك.ف.أ6.6= (الكفاءة) 0.87(معامل القدرة) × 0.85 / 0.746 حصان × 6.5 ----- طلمبة كسح مياه

وبذلك يكون إجمالى أحمال القوى األخرى: ك.ف.أ 95 ≅ 6.6 + 35 + 53 -----

فإذا ما أضيفت أحمال اإلنارة اإلنارة و البرايز و التكيفات و السخانات و األجهزة كاملة دون تطبيق معامالت تباين عليها إلى أحمال القوى تصبح القيمة

اإلجمالية للطلب ك.ف.أ 1223 = 95 + 1128 =

من السعة80سعة المحول على أساس أن التحميل ٪

ك.ف.أ 1528.75 = 0.8 / 1223=

وتكون سعة المحول المناسبة هى ك.ف.أ2000=

أما إذا سمحت ظروف المكان وشركة توزيع الكهرباء ونسبة اإلشغال بالمبنى بتطبيق معامل تباين فإن تطبيقه يتم فقط على أحمال اإلنارة أما أحمال القوى فال يطبق عليها معامالت تباين.

يكون الحمل المطلوب 68فإذا ما افترض معامل تباين قيمته ٪

ك.ف.أ 862 = ٪95 + 68 × 1128 = من السعة80سعة المحول على أساس أن التحميل ٪

ك.ف.أ 1077 = 0.8 / 862=

وتكون سعة المحول المناسبة هى ك.ف.أ 1500=




229

246. 359Bالركاب؟ مصاعد تتكون مما


تكون مصاعد الركاب إما مجرورة أو تعمل هيدروليكيا

)2-1يتكون المصعد الذي يعمل بمحرك كهربائي من: شكل رقم ( – .الكابينة .كابالت الجر .ماكينات المصعد .معدات التحكم .ثقل الموازنة .دالئل الحركة

)7-1من: شكل رقم ( يتكون المصعد الذي يعمل هيدروليكيا –

مضخة لدفع. )1( خزان الزيت. )2( المكبس الهيدروليكي. )3(

247. 360B؟ هيدروليكيا يعمل الذي المصعد يعمل كيف


يعمل هذا المصعد بمكبس يتحرك هيدروليكيا يكون مثبتا بأسفل الكابينة يرفعها أو يخفضها وبذلك ال يكون هناك احتياج لحبال أو طنابير أو مجموعة

المحرك/مولد كما هو الحال فى مصاعد الركاب العادية وتكون وسائل األمان والتحكم بسيطة وغير معقدة مما يجعل هذا النوع من المصاعد مناسبا جدا مترا) وخاصة إذا كانت حفرة االسطوانات 25م/ث) لمسافات غير مرتفعة (حتى 1واقتصاديا فى حالة تحريك الكابينة بسرعات منخفضة (حتى

الهيدروليكية أسفل الكابينة ال تمثل مشكلة معمارية. من العيوب الرئيسية للمصعد الهيدروليكى تكلفة التشغيل المرتفعة، فبسبب غياب ثقل الموازنة يحتاج هذا المصعد إلى محرك بقدرة كبيرة لتشغيل مضخة

الزيت وتكون كل الطاقة المستخدمة مفقودة حراريا. (ملحوظة: المحرك يعمل فقط فى اتجاه الرفع) بمقارنة قيمة التكلفة الشهرية للمصعد الهيدروليكى بالتكلفة الشهرية للمصعد العادى الذي يعمل بمحرك كهربائي ، يتضح ارتفاع تكلفة التشغيل فى حالة

المصعد الهيدروليكى وتأثير وجود ثقل الموازنة فى المصعد العادي.




230

248. 361B؟ كهربائي بمحرك تعمل التي المصاعد فى المختلفة الجر انواع هى ما


فى حالة ماكينة المصعد مركبة أعلى المبنىأوال :

) (أ) 1-1("شكل ( (Single-wrap traction machine) : نظام مزود بماكينة جر أحادية اللفة النوع األول –

عنــد مــرور الحبــال فــوق الطارة التى تحتوى على مجارى لهذه الحبال، فــإن قــدرة الرفــع تتــم بواسطة الطارة من خالل الحبال فى مجاريها، حيــث ). Traction sheave) "ببكرة الجر" (T) والبكـرة (Deflector sheave) "بكـرة الدليل" (Sتسمى البكـرة (

) (ب) 1-1("شكل ( (Double-wrap traction machine) 1:1: نظام مزود بماكينة جر ثنائية اللفة بنسبة تحميل النوع الثانى –

) الحبال ملفوفة على بكرة الجر قادمة من الكابينة ثم على البكرة الثانويةS) وهى بكرة نقل حركة (Idle sheave) ثم مرة أخرى حول بكرة الجر (Tثم ( ) Double-wrap، ويحقق نظام الماكينة ثنائية اللفة (1:1) ثم إلى ثقل الموازنة، ويطلق على طريقة التعليق المبينة بأنها طريقة بنسبة تحميل Sإلى البكرة (

قوة شد أكبر من الحالة أحادية اللفة، ولذا تستخدم هذه الطريقة فى حالة التركيبات ذات السرعات العالية.

) (ج) 1-1("شكل ( (Double-wrap traction machine) 2:1: نظام مزود بماكينة جر ثنائية اللفة بنسبة تحميل النوع الثالث –

م/ث) وذى القدرة المنخفضة للتحريك وتستخدم فيه ماكينات بدون تروس 3.5 إلى 2.5 الذى يستخدم فى السرعات العالية (من 1 : 2نظام التعليق بنسبة .كما يستخدم أيضا فى المصاعد ذات الحمولة الثقيلة والسرعات المنخفضة

فى حالة ماكينة المصعد مركبة بالبدرومثانيا :

) (د)1-1("شكل ( (Double-wrap traction machine) 1:1: نظام مزود بماكينة جر ثنائية اللفة بنسبة تحميل النوع األول –

ولكن ماكينة وبكرة الجر مركبــتان فى غرفــة ماكينــات بـبـدروم المبنى على العكس من النظام المبين فى (أ ، ب ، ج) حيث 1:1طريقة التعليق بنسبة يكونا فى غرفة السطح.

) (ه)1-1("شكل ( (Double-wrap traction machine) 2:1 : نظام مزود بماكينة جر ثنائية اللفة بنسبة تحميلالنوع الثانى –

طوابق 10 تكون ماكينة وبكرة الجر مركبتان بغرفة بالبدروم وتكون فيه الحبال طويلة نسبيا ويمكن استخدام هذا النظام فى المبانى السكنية واإلدارية ذات كجم.2000م/ث ولحمولة كبائن حتى 2فأكثر وسرعات حتى

فى حالة ماكينة المصعد مركبة فوق الصاعدة مباشرةثالثا : ) (m/c room less

) يوجــد نظام حديث يسمى عديم غرف ماكيناتm/c room less .وال يوجد به غرفة ماكينات وإنما تركب جميع المهمات فوق الصاعدة مباشرة (




231

249. 362B؟ كهربائي بمحرك يعمل الذي المصعد يعمل كيف


اعتمادا على سرعة الكابينة وحمولتها، ويتوزع وزن الكابينة 8 إلى 4تقــوم الماكينـات بجـر الكابينـة عــن طريـق مجموعـة متوازية من الحبال (من بحمولتها بين هذه الحبال بالتساوى).

.تمر الحبال المثبتة بأعلى الكابينة فوق طارة ذات مجارى يتم تدويرها بواسطة ماكينة الجر التى يديرها محرك ثم تمر إلى أسفل حيث ثقل الموازنة

) يتلقى محرك المصعد فى معظم التركيبات التقليدية الطاقة والتى مازالت تستخدم فى مبانى شهيرة فى العالم من مجموعة تتكون من محرك ومولدMotor generator.(

) يمكن االستعاضة حديثا عن مجموعات محرك/مولد لتوليد تيار مستمر متغير القيمة ومعكوس اإلشارة باستخدام مغيرات إستاتيكيةStatic converters.(

) يمكن فى ماكينات الجر ذات التروسGeared machines لفة/د اعتمادا على 1500 و 500) أن يكون المحرك ذو قدرة صغيرة وذو سرعة ما بين سرعة المصعد ونسبة تحويل التروس ويمكن أن يعمل المحرك بتيار متردد أو بتيار مستمر (يستخدم فى مصر التيار المتردد).

م/ث) وتكون ذات سرعة واحدة أو سرعتين، كما 0.75 ، 0.125تستخدم المحركات ذات التيار المتردد فى التطبيقات ذات السرعات المنخفضة (ما بين ) أو ذات جهد وذبذبة متغيرتين Variable voltage) أو ذات جهد متغير (Variable speedيمكن استخدام محركات تيار متردد ذات سرعات صغيرة (

(VVVF) ) Variable voltage, variable frequency ويستخدم هذا النوع فى مصاعد الركاب ومعظم مصاعد البضاعة وبمحركات تتراوح ( ) بيانات عن المصاعد بماكينات ذات تروس وبدون تروس.1-1 ك.و. ويبين جدول (75ك.و. ، 2.2قدرتها بين

توجد فى التركيبات الحديثة معدات الكترونية يسهل معها التحكم فى محرك المصعد والحصول على تركيبات ذات أمان زائد وراحة واضحة فى تشغيل المصعد.

مترا وللحمولة الكبيرة حتى 50يمكن استخدام ماكينات جر بدون تروس تعمل بالتيار المستمر لتغيير سرعات الجر فى المبانى ذات االرتفاعات أكبر من ك.وات.260ك.وات إلى 15 م/ث، وتكون قدرة المحرك من 2 كجم وبسرعة ال تقل عن 5000

) نموذج لماكينة جر مصعد ذات تروس.4-1) نموذج لماكينة جر ذات سرعة عالية عديمة التروس وشكل (3-1يبين شكل (

لفة/الدقيقة مع نظام التحكم ذي المتممات أو الميكروبروسيسور مع ثبات التردد.375/1500تستخدم المحركات التأثيرية ثالثية األطوار ذات السرعتين

لفة/الدقيقة مع نظام مغير التردد والجهد ويستخدم نظام التروس لتحديد سرعة 1500تستخدم المحركات التأثيرية ثالثية األطوار ذات سرعة واحدة المصعد.




232

250. 363Bللمصاعد؟ المطلوبة القدرة تحديد يتم كيف


تتحدد القدرة المطلوبة للمصاعد الرأسية بناء على قدرة ماكينات المصعد (بخالف القدرة الالزمة لتشغيل األبواب وتهوية وإضاءة الكابينة ولمبات بيان األدوار). –تعرف القدرة المطلوبة للمصعد بأنها تلك التى تحقق الجر المطلوب وكذلك التغلب على االحتكاك وتتناسب هذه القدرة المطلوبة مع المعدل الذى يتم عنده الشغل –

المبذول:

× قدرة المحرك المطلوب = ك الشغل المبذول (كجم.متر)

الزمن

.حيث تتناسب قدرة المحرك المطلوب طرديا مع سرعة المجموعة ويكون (ك) هو ثابت معامل األمان والفقد كجم فيكون ثقل الموازنة فى 600 كجم ووزن الكابينة بمشتمالتها 900 كجم شاملة الحمولة الكاملة وكانت الحمولة مثال 1500فمثال الصاعدة التى تزن

٪ فقط من 50 كجم)، وفى هذه الحالة يكون المحرك مصمما على تحميل 1200 مساويا لنصف وزن الصاعدة ونصف حمولتها (1 : 1نظام التعليق ٪ زيادة حمولة. 10الحمولة الكاملة صعودا أو هبوطا مضافا إلى ذلك

م/ث. 1 م/ث تكون أكبر من تلك القدرة الالزمة لرفعها عند سرعة 3.6 كجم عند سرعة 1500لذلك فإن القدرة المطلوبة لرفع صاعدة تزن ) رسم تخطيطي لبيان الفقد التفصيلي لكل ك. وات في نظام المصاعد التي تستخدم محركات بتروس أو بدون تروس.5-1يبين شكل (

:ملحوظة

المحرك المطلوبة لكل كابينة. يقوم المحرك بالتغلب على االحتكاك فى النظام باإلضافة إلى القدرة الالزمة للجر ويبين الشكل قدرة )1( ٪ من قدرته.20يالحظ أن قدرة مجموعة مولد / محرك الالزمة لتغذية محرك الجر أعلى بحوالى )2( نظرا ألن االحتكاك أكبر فى حالة الماكينات ذات التروس عنها فى الماكينات عديمة التروس، فتكون قدرة المحرك فى هذه الحالة أكبر. )3(تكون الطاقة المستهلكة فى تحريك المصعد هى الالزمة للتغلب على االحتكاك فى النظام بما فيه الحرارة المتولدة نتيجة للفرامل مضافا إليها الطاقة )4(

الكهربائية المفقودة فى مجموعة محرك الجر وفى مجموعة المحرك / مولد (إن وجدت). أما الطاقة المستخدمة لرفع الكابينة بركابها فهى ببساطة طاقة ) يتـم إعادتهــا إلى نظــام القــوى أثناء هبوط الكابينـــة بركابهـــا عـن طريق نظام استعادة القدرة الفرملية المتولدة Potential energyوضع (

)System regenerative braking.المستخدم فى معظم نظم المصاعد (

جدول القدرة الالزمة لتشغيل المصاعد الكهربية عدد األفراد الحمولة بالكيلوجرام قدرة المحرك بالحصان*

3-4 240 3 4-5.5 320 4 5-6.5 400 5

5.5-8.5 480 6 8-11 640 8

13 750 10 16 900 12

وات746 الحصان = *




233

251. 364Bالمبنـى؟ داخـل المجموعـة فى الكبائـن عدد زاد إذا للمجموعـة الطلـب معامـل حساب يتم كيف


٪ فقط من الزمن ويكون باقى الوقت واقفا عند األدوار المختلفة، ولذا فإنه إذا زاد عدد الكبائـن فى 50من المعروف أن المصعد الواحد يكون فى حركة حوالى –) Group demand factorالمجموعـة داخـل المبنـى، فـإن احتمـال عملهـا كلهـا آنيـا يصبـح قليــال، كمــا يتضــح مــن قيمـة معامـل الطلـب للمجموعـة (

).6-1المبين قى شكل () العالقة بين السرعة والقدرة المطلوبة عند أوزان صاعدات مختلفة. 6-1كما يبين شكل ( –

مثال: – ) ك.و.36م/ث، فإن كل كابينة تحتاج إلى محرك جر قدرة 3 كجم وتتحرك بسرعة 1750) إذا كان عدد الكبائن خمسة بحمولة 6-1فى شكل وبذلك تكون قدرة الجر اللحظية للمحركات فى المجموعة هى: 0.67من الجدول فإن معامل الطلب للمجموعة هو =5 × 36 × 0.67 = 120.ك.و فإن ما يحتاجه نظام المصاعد فى المبنى هو =80فإذا كانت الكفاءة لمجموعة محرك / مولد هى ٪

0.8 ك.و. 150= 120 = .يجب توافر هذه القدرة فى نظام تغذية المبنى بالقدرة الكهربائية




234

252. 365Bاآلتى احسب ث،/م 3 بسرعة وتتحرك كجم 1750 منها كل حمولة كبائن) 5 (من مكونة 1 : 1 بنسبة التعليق بأسلوب منفذة مصاعد مجموعة فى :o الذروة فترات أثناء الماكينات غرفة فى المتولدة الحرارة .o ساعة. و.ك / جنيها 0.21 بمقدار مزدوجة تعريفة باستخدام شهريا المستهلكة للطاقة التقريبية التكلفة.


٪ الباقية من الوقت، وعلى 50٪ من الزمن وفى حالة الحمل فى 50أثناء أوقات الذروة تعمل مجموعة المحرك / مولد باستمرار وتكون فى حالة الالحمل حوالى –

٪ من الفترات الزمنية هو اختيار أقرب إلى الدقة.70ذلك فإن استخدام رقم تقريبي للعمل عند الحمل الكامل بمقدار ٪ من القيمة الكاملة للحمل، وعلى ذلك فإنه 90 ٪ من الوقت، وباعتبار أن كال المحركين يسحبان 50٪ من الوقت على الحمل وال يعمل 50يعمل محرك الجر –

للكابينة الواحدة: = 80). المثال السابق) وباعتبار كفاءة المحرك 6-1 ك.وات (من شكل (36قدرة محرك الجر ٪

0.8 ك.و.45= ك.و.36 =قدرة محرك مجموعة المحرك / مولد ك.و. 5.67٪ فقد = 20٪ فترة التشغيل × 70٪ من الحمل × 90 ك.و. × 45= الفقد فى مجموعة المحرك / مولد ك.و.ساعة 5.67= تكافئ طاقة ك.و. 3.24٪ فقد = 20٪ فترة التشغيل × 50٪ من الحمل × 90 ك.و. × 36= الفقد فى محرك الجر = ك.و. ساعة 3.24تكافئ طاقة ك.وات/ صاعدة 8.91 = 3.54 + 5.67 = مجموع الطاقة للكابينة ك.و. ساعة 44.55= 8.91×5 صاعدات = 5مجموع الطاقة لعدد يتم انبعاثها حراريا فى داخل غرفة الماكينات وهى طاقة فقد مكافئة لطاقة فرن منزلى كبير بطاقة مما يستدعى تهوية غرفة الماكينات جيدا لطرد

الحرارة خارج الغرفة وفى بعض األحيان قد يستدعى األمر تكييف هواء هذه الغرفة. :ملحوظة

ال يستخدم معامل تباين بين الماكينات هنا، حيث أنها جميعها تعمل وأن الحرارة تراكمية وال يستخدم معامل التباين إال لحساب القيمة اللحظية للحمل فقط. –عند حساب تكلفة الطاقة شهريا للمصاعد فمن المطلوب تقدير االستخدام الكلى للنظام، فعلى سبيل المثال إذا كان النظام فى مبنى مكاتب فإن تفصيلة التشغيل على –

مدار اليوم غالبا ما تكون كالتالى: ساعة 2أقصى استخدام للمصاعد لمدة 70 ساعة 2٪ من أقصى استخدام لمدة 50 ساعة 6٪ من أقصى استخدام لمدة 10 ساعة 14٪ من أقصى استخدام لمدة

يوميا ٪ من أقصى حمولة للمجموعة.وتكون الطاقة المستهلكة لكل ماكينة32.5هذا التشغيل يعطى قيمة متوسطة – ساعة 24٪ × الفقد الكلى × 32.5 = ساعة24) ك.و.×5.67+3.24 × (0.325 = ك.و ساعة / يوم / كابينة 69.5 =

وبذلك تكون التكلفة الشهرية –

جنيها 0.21 يوم تشغيل × 25× ك.و ساعة 69.5 = ك.و. ساعة يوم

جنيها / شهر / كابينة 364.86= جنيها / شهر للمجموعة 1824.323=

عند استخدام تحكم الكترونى لمحرك الجر (ثايريستورات) بدال من مجموعة المحرك / مولد، يتم تخفيض القدرة المفقودة فى المجموعة وكذلك يقل االحتياج إلى –٪ عن حالة استخدام مجموعة المحرك/مولد ويتم الحصول على وفر 25٪ إلى 10التهوية بشكل ملحوظ وعلى ذلك فإن تكلفة الطاقة المستهلكة تنخفض لقيمة من

سنوى مقداره

سنة شهر جنيها 4378.374= شهرا 12 ٪ 20× 1824.323=




235

253. 366Bالمتحركة؟ الساللم تعمل كيف


م/ث وتكون السرعة العالية أثناء فترات الذروة والسرعة المنخفضة فى خالف ذلك وهى 0.6 م/ث و 0.45تصمم هذه الساللم عادة للعمل بسرعتين للحركة – المفضلة عموما حيث تمثل السرعة العالية مشاكل لبعض الركاب.

مترا عند نقطة واحدة وذلك باستخدام محرك واحد يقوم بتدوير كاتينة التحريك الرئيسية التى تتولى تحريك كاتينة 20يتم تحريك السلم فى حاالت االرتفاعات حتى –

).8-1الدرج وتسحبها جميعها مما يؤدى إلى تحريك التجميعة بالكامل وكما يتضح من شكل (

) رسما تخطيطيا للوحدات المتكررة 9-1فى حالة زيادة ارتفاع المسافة التى ينقل بينها السلم، فتكون هناك محركات منتشرة على طول الوحدة ، ويوضح شكل ( –) نظام ميكنة تشغيل السلم ذو الوحدات 10-1وفيها يتم توزيع وحدات التحريك على طول السلم باألعداد المتكررة الضرورية لالرتفاع المطلوب. ويبين شكل (

المتكررة، وتصنيف المحركات الموزعة على طول السلم قوة محركة على طول كاتينة التحريك.




236

254. 367Bالمتحركة؟ للساللم الكهربى الحمل حساب يتم كيف


) فى الكود المصرى قدرات المحركات المطلوبة لالرتفاعات المختلفة وطبقا لعرض السلم. 2-1يبين جدول ( –

): محركات الساللم المتحركة2-1جدول رقم ( 1210 810 عرض السلم (مم)0.6 إلى 0.45من السرعة (م/ث) 0.6 إلى 0.45من

7.5 7.5 قدرة المحرك الواحد (ك.و)أقصى ارتفاع

يخدمه السلم عند استخدام

6.5 10 محرك واحد 13.5 20 محرك2 20 30 محركات3

) قدرات المحركات المستخدمة فى تحريك السلم إلى 3-1 هرتز. ويبين جدول (60 أو 50يتـــم إدارة الساللم بمحــركات كهــربائية حثية ثالثيــة األطوار عند –

مترا. 6.5ارتفاعات ال تزيد عن

): القدرة النموذجية للمحركات المستخدمة مع الساللم المتحركة3-1جدول رقم ( قدرة المحرك (ك.و) االرتفاع (م) السرعة (م/ث) عرض السلم (مم)

0.6 إلى 0.45- من 810 0.6 إلى 0.45- من

4.25 5.2

3.75 5.00

1210 -0.45

-0.45 0.6 إلى 0.45- من

5.20 6.40 7.60

5.00 7.5 11.2

255. 368Bما هى األحتياطات الواجب مراعتها عند التصميم لتغذية عدة ساللم متحركة داخل مبنى واحد؟


).Single electric feeder ساللم من مغذى كهربائى واحد (4من الموصى به عدم تغذية أكثر من – ال ينصح أيضا بتغذية جميع الساللم لمبنى مهما كان عددها من نفس المغذى. – نظرا ألن راكبى الساللم المتحركة لن تعاق حركتهم إذا انقطعت التغذية العمومية، فال يتطلب األمر تغذية الساللم من المصادر االحتياطية للقوى. – ك.و. فتكون الحرارة المفقودة منه فى 7.5 ٪ من القدرة تفقد حراريا، فعلى سبيل المثال إذا كان المحرك بقدرة 40يجب تهوية غرفة المحرك ومراعاة أن حوالى –

المكان: و.ح.ب/ساعة10250 ≈) 3415.2 ك.و. × 7.5×0.4 (

256. 369Bما هى قدرات السخانات المستخدمة فى وحدات تدفئة المنازل من النوع الحائطى؟


) ثى الكود المصرى قدرات السخانات المستخدمة فى وحدات تدفئة المنازل من النوع الحائطى، ويمكن بناء مجموعات منها داخل وحدة 4-1يبين جدول ( –

السخانات الواحدة أو تكرار الوحدات داخل المكان الواحد.

): قدرات وحدات السخانات المستخدمة فى وحدات التدفئة الكهربائية4-1جدول رقم ( (وات) قدرة السخانات (و.ح.ب/ساعة) السعة الحرارية (مم) عرض الوحدة (مم) طول الوحدة )2م (المساحة المخدومة

350 1194 200 355 2 750 2559 200 750 4 – 6

2000 6824 200 1500 12 - 16




237

257. 370B) كيف تعمل الحصائر والمنحدرات المتحركةMoving walks and ramps؟ و كيف يتم تحديد القدرة الكهربية لها؟(


درجة فى حالة 15 درجات فى حالة الحصائر و5ذيتولى هذا النوع من المصاعد النقل إما أفقيا فقط أو أفقيا ورأسيا فى شكل تجميعى (نسبة الميل ال تزيد عن – المنحدرات المتحركة).

– يستخدم هذا النوع فى المطارات لنقل األفراد وعربات األمتعة رأسيا أو نقل األفراد الذين قد ال يمكنهم استخدام الساللم المتحركة، كما يستخدم أيضا فى نقل –

األشياء كبيرة الحجم وتستخدم أيضا فى تجمعات التسوق متعددة الطوابق حيث ال تناسب الساللم المتحركة انتقال األفراد بعربات المشتريات بين المستويات المختلفة أو انتقالهم إلى أماكن انتظار السيارات الموجودة بسطح المبنى.

– م وتدار كل منها بمحرك واحد وتتحرك فى 55م لكل ممشى وبطول 1) حصائر متحركة للمشاه ثنائية الممرات فى أحد المطارات بعرض 11-1يبين شكل ( –

مم 1000 مم لراكب واحد أو بعرض 660) منحدر متحرك ينقل ما بين دورين فى مجمع تجارى ويمكن أن يكون بعرض 12-1اتجاهين متضادين. و يبين شكل ( لراكبين ويكون عادة بزوايا انحدار وسرعات مختلفة.

– ال يمكن هنا تحديد بيانات عن قدرات المحركات المطلوبة لتحريك هذا النوع من وسائل النقل، ويجب الرجوع إلى المصنع فى طلب معرفة القدرة المطلوبة. –




238

258. 371Bما هى أنواع و أنظمة التكيف المستخدمة ؟ و ما هى القدرات الكهربية لكل منها؟


)Window type ACالشباك ( .1

يتم تبريد المنازل الصغيرة بطريقة بسيطة باستخدام وحدة تتكون من ضاغط (كباس) ومكثف ومبخر ودائرة وسط التبريد وباستخدام تبريد الهواء )13-1بالهواء كما هو موضح فى شكل (

) تكييف الهواء من نوع الشباكWindow type AC به عادة ثالثة محركات واحد لمروحة المبخر والثانى لمروحة تبريد المكثف والثالث لضاغط ،( وسط التبريد (الفريون).

"يمكــن عكــس دورة وسط التبريد لتسخين الهواء بالمكان المراد تكييفه شتاء باستخدام نفس الضاغط ويسمى الجهاز فى هذه الحالة "مضخة حرارية)Heat pump.كما يمكن استخدام سخان كهربائي أمام مروحة المبخر مع فصل الضاغط ومروحة المكثف شتاء فى هذه الحالة ،( ) وذلك للوحدات المزودة بسخانات كهربائية للتدفئة5-1تكون وحدات الشباك ذات السخانات الكهربائية عادة بالسعات والقدرات المبينة فى جدول (




239

)Split Unitالوحدة المنفصلة ( .2

يتم وضع المكثف ذى الضوضاء العالية نوعا ما فى مكان بعيد عن المبخر بالنسبة لدائرة التكييف و ذالك للحصول على مكيف أكثر مالئمة وراحة كما). 14-1هو مبين فى شكل (

) 15-1يمكن عكس دورة وسط التبريد ليسخن الهواء بالمكان المراد تكييفه كما يمكن أيضا استخدام سخان كهربائى أمام مروحة المبخر. و يبين شكل ( بعض طرق تركيب الوحدة الداخلية والوحدة الخارجية لوحدات التكييف المنفصلة.

) الوحدات المنفصلة يمكن أن تكون وحــدات حائطيــة أو سقفيــةExposed floor or ceiling unit أو سقفية غاطسة فوق السقف المستعار ()Concealed unit) 15-1) كما هو مبين فى شكل.( ك.و. ومروحة مبخر تكون قدرتها 0.44 ك.و. بمروحة مكثف قدرة 7 كباس قدرة 2 طن تبريد مزودة بعدد 15يمكن بناء وحدات منفصلة حتى سعة

ك.و. 2.25فى حدود ) سعات وقدرات الوحدات المنفصلة.6-1يبين جدول (

ملحوظة: في حالة عمل السخانات الكهربائية فإن الضاغط ال يعمل. و بالتالى يتم اخذ القيمة األكبر اما للضاغط او للسخان. و دائما تكون قيمة قدرة السخان هى

األكبر. اذن يتم اخذ قيمة قدرة حمل السخان فقط.




240

)Package unitsالوحدات القائمة بذاتها ( .3 .يمكن بناء وحدات تكييف هواء قائمة بذاتها للتدفئة والتبريد وتكون الوحدة إما رأسية أو أفقية كما يمكن وضعها إما على السطح أو بالبدروم ) 1يتم عادة نقل الهواء المكيف منها باستخدام شبكة مجارى هواء معزولة لهـواء التغذيــة وهـواء الراجع وكما هو واضح فى األشكال المبينة فى شكل-

16 .(




241

) Central Station Air Conditioningالتكييف المركزي ( .4 يؤدى هذا النوع من التصميم إلى التوفير فى استخدام المعدات واالقتصاد فى الطاقة إلى أقصى درجة، ويتم استخدامه فى المبانى الكبيرة ذات

و ينقسم الى نوعين من األنضمة. اإلشغال العالى مثل الفنادق و المستشفيات والمسارح الكبيرة.

a. ) نظام مولدات الماء المثلجWater Chillers System( ) يتم فى هذا النظـام استخدام مولدات الماء المثلجWater chillers) التى تكون إما ذات كباسات ترددية (Reciprocating أو حلزونية (

)Screw) أو طــاردة مركـزيـة (Centrifugal) مـع وحـدات مناولـة الهـواء (Air handling units والتى تحتوى على قطاعات لمراوح () وقطاع ملف التبريد (الذى يتم تغذيته بالماء المثلج) وقطاع ملف التسخين (قد Supply and return air fansتغذية الهواء وراجع الهواء (

يكون التسخين باستخدام ملف يغذى من ماء ساخن من غالية أو يكون التسخين كهربائيا باستخدام مقاومات) وقطاع ترشيح الهواء وقطاع ضبط درجة الرطوبة النسبية بالهواء المكيف.

طن تبريد وأكبر من ذلك إذا كان يبرد بالماء باستخدام أبراج تبريد350تبنى هذه الوحدات إذا كان مكثفها يبرد بالهواء حتى (Cooling Towers) .

وحـدة تثليـج الميـاه يبـرد مكثفهـا بالهـواء وتحتـاج إلـى قــدرة كهربائيــة للضواغــط ولمراوح تبريد المكثف كما تحتاج إلى قــــدرة) وكذلك طلمبة أو طلمبات المياه المثلجة. Air handling unitsللمعــــدات الملحقــــة بهـــا مثل وحدة أو وحدات مناولة الهواء (

.يتم رفع المياه إلى البرج التبريد باستخدام طلمبات هرتز/ثالثي األطوار ويتم تقويم محرك 50 فولت/380 طن تبريد وقد تعمل بجهد تشغيل 850يمكن أن تصل سعات وحدات تثليج المياه حتى

فولت، وقد تصل قدرة 6600 فولت ، 3300) وتوجد وحدات تعمل بجهود تشغيل Soft startersالضاغط بطريقة ستار/دلتا أو التقويم اللين ( ك.750المحرك فى الوحدات الكبيرة إلى




242

b. ) نظام التبريد باالمتصاصAbsorption Chillers System( طن تبريد، حيث يتم إنتاج ماء مثلج باستخدام بخار أو حتى إشعال نار مباشرة(1000يصل سعاتها حتى Direct fire لتسخين محلول ملحى (

)Lithium bromide فى عملية إعادة توليد الملح بعد نزع بخار الماء من المحلول والحصول على وسط مائى ذو درجة حرارة منخفضة (يقوم بتبريد الماء وتثليجه الستخدامه فى تكييف هواء المبنى .

يتم تبريد مكثفات هذه الوحدات بالماء ويستخدم لهذا الغرض أبراج تبريد ذات مراوح ضخمة ومزودة بطلمبات مياه ضخمة أيضا حسب سعةالوحدة.

تحتاج وحدات التبريد باالمتصاص لمصدر قدرة كهربائية اصغر بشكل ملحوظ لالستغناء عن القدرة الضخمة الالزمة للضواغط مقارنة بحالةالوحدات الكهربائية وتحتاج هذه الوحدة فقط إلى قدرة كهربائية فقط لتغذية الطلمبات وهى طلمبات مياه المبخر وطلمبتى المحلول وطلمبات

ك.و. 40 طن تبريد ال تحتاج إلى قدرة كهربائية أكبر من 330أبراج التبريد. فمثال وحدة تثليج المياه باالمتصاص سعة




243

259. 372B ما هى القدرة الالزمة ألجهزة التكييف لكل من هذه األماكن: المكاتب الكبيرة؛ ؛ المكاتب الصغيرة؛ غرف تدريس؛ مخازن تجارية؛ غرف مرضى في ؛ المستشفيات؛ غرف الفنادق؛ البنوك؛ الورش والمصانع؛ المساجد؛ المحالت التجارية؛ سوبر ماركت؛ غرف كمبيوتر؛ مطاعم


وات لكل متر مربع طن تبريد لكل متر مربع نوع المبنى

75 0.5 المكاتب الكبيرة 55 0.033 المكاتب الصغيرة

75 0.05 غرف تدريس 81 0.054 مخازن تجارية

65 0.043 غرف مرضى في المستشفيات 65 0.043 غرف الفنادق

81 0.054 البنوك 65 0.043 الورش والمصانع

90 0.06 المساجد 90 0.06 المحالت التجارية

65 0.043 سوبر ماركت 108 0.072 غرف كمبيوتر

165 0.11 مطاعم

260. 373Bكيف تعمل طلمبات الحريق فى المبانى ؟


بار وتكون قدرة 10/ساعة عند رفع حوالى 3م40يمكن أن تستخدم طلمبة منفردة لضخ المياه عند حدوث حريق، فعلى على سبيل المثال قد يكون تصرفها حوالى – .380/50/3 لفة/د وجهد 2900 ك.و. عند سرعة 22محركها الكهربائى

يجب أن تحقق نظم اإلطفاء بالماء فى المناطق الكبيرة أو المبانى شاهقة االرتفاع التوازن الهيدروليكى بين أبعد وأقرب نقطة لمحطة الضخ. – يمكن أن يتم إدارة المضخة من المحرك الكهربائى إما مباشرة (بدون استخدام كوبلنج) أو باستخدام كوبلنج. –




244

261. 374Bهل يجب استخدام طلمبة كهربائية وأخرى تدار بماكينة ديزل فى المبانى ؟


فى معظم المبانى يكون فى محطة الضخ طلمبة تدار بمحرك كهربائى وأخرى تدار بواسطة محرك ديزل يقوم تلقائيا عند حدوث حريق وتتولى طلمبة جوكى –)Jockey pump) إيجاد ضغط على مجمع المواسير (Header.الرئيسي يؤدى إلى عمل الطلمبات باستخدام حساس ضغط ولوحة تشغيل (

262. 375Bكيف يتم قدرة محرك طلمبة رفع المياه أو طلمبة الصرف الصحى أو طلمبة الحريق فى المبانى ؟


) من المعادلة التالية: Pمحرك الطلمبة (ويمكن حساب قدرة –

KWHQP 746.075.

×××

=η

ω

حيث:

Q : ث)3معدل التصرف (م/ H : (م) الرافع االستاتيكى η : 80- 75 الكفاءة (حوالى(٪ ω: 3 كجم/م1200 وللفضالت 1000الكثافة = (للمياه(

فولت ثالثي األطوار.380) بار وتعمل عند جهد 10ويوضح الجدول التالي قدرة طلمبات المياه حسب معدل التصرف عند رفع ( –

(ك.وات) قدرة الطلمبة/ساعة) 3(م معدل التصرف18 5.5

21.6 7.5 22.4 7.5

.380/50/3) بار وتعمل عند جهد 10ويوضح الجدول التالي قدرة محرك طلمبات الحريق حسب السرعة عند رفع مانومترى ( –

(ك.وات) قدرة المحرك(لفة/د) السرعةم 1

1500 15

2 20 3 35 4

2900

77 5 102 6 130 7 155 8 175 9 205

بار وتكون قدرة 10/ساعة عند رفع حوالى 3م40يمكن أن تستخدم طلمبة منفردة لضخ المياه عند حدوث حريق، فعلى على سبيل المثال قد يكون تصرفها حوالى –. 380/50/3 لفة/د وجهد 2900 ك.و. عند سرعة 22محركها الكهربائى




245

263. 376Bكيف تعمل سخانات حمامات السباحة ؟


يتم عادة استخدام سخانات الزيت أو سخانات البخار لتسخين الماء المستخدم فى حمامات السباحة وقد يتم أحيانا استخدام الكهرباء فى عملية التسخين. – م (يستثنى من ذلك الحمامات المستخدمة ألغراض 26.5 يجب أن تزود حمامات السباحة بوسائل للتحكم للحد من ارتفاع درجة حرارة الماء حتى ال تزيد عن –

العالج. بالنسبة للحمامات المكشوفة فى األندية والفنادق والقرى السياحية فيتم التحكم فى درجة حرارة الماء بحيث يتوقف التسخين تلقائيا إذا قلت درجة حرارة الهواء –

م (توفيرا للطاقة).16الخارجى عن

264. 377Bكيف يتم حساب الحمل الكهربى للسخانات المستخدمة فى تسخين المياه فى المنازل الصغيرة ؟


) قدرة الدخول للسخانات المستخدمة فى المنازل الصغيرة (عائلة أو عائلتين) باستخدام الكهرباء وتكون هذه السخانات مركزية وتوضع 10-1يبين جدول ( – بالبدروم ويتم التوزيع منها باستخدام شبكة مياه خاصة ويتم فيها استخدام طلمبة تقليب لضمان بقاء الماء ساخن وكذلك طلمبات الرفع إن اقتضت الضرورة.

، 70 ، 50 ، 30 فى المبانى السكنية ذات الشقق تستخدم أحيانا سخانات كهربائية قائمة بذاتهــا (غير مركزية) وتوضــع بالقـرب من دورات المياه بسعات حتى – ك.و.4.5 ك.و. وحتى 1.2 لترا قد تصل قدرة السخانات بها ما بين 100

380/50/3 ك.وات عند جهد 22قد تستخدم سخانات كهربائية فورية (بدون خزانات) تركب على خط المياه الساخن الرئيسى وقد تصل قدرتها الكهربائية حتى – وذلك بالمنازل والفيالت لتسخين مياه حمامات الجاكوزى وكذلك بالمستشفيات التى تحتاج إلى مياه ساخنة فورية.

خاصة بوحدات (سكنية عائلة وعائلتين) ) أقل سعة حرارية لسخانات مياه مركزية10-1جدول رقم (

3 to 32

1 2 to 22

1 1 to 12

1 عدد الحمامات

عدد حجرات النوم 1 2 3 2 3 4 5 3 4 5 6 سعة خزان السخان باللتر 75 115 150 150 190 190 250 140 250 250 300 القدرة بالكيلووات 2.5 3.5 4.5 4.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5

كمية السحب من الخزان فى 115 170 225 220 270 270 330 270 330 380 385 ساعة واحدة باللتر

مياه االستعواض (لتر/ساعة) 3 55 68 68 84 84 84 84 84 84 84




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265. 378Bكيف تعمل طلمبات رفع المياه فى المبانى ؟


بار) 4.8 بار إلى 3.5تكون تغذية المياه للمبانى المنخفضة (ذات الطابقين أو الثالثة طوابق) من مصـدر مـرفق مياه الشرب مباشرة اعتمادا على ضغط الشبكة ( – بار) بعد التغلب على االحتكاك فى المواسير والصنابير.1.35 بار و 0.35وهو ضغط كاف لدفع الماء من الصنابير عند ضغط يتراوح ما بين (

طوابق) ضخ الماء من المصدر الرئيسي مباشرة (أو من خزان أرضى بالبدروم يمأل من الشبكة 10 مترا (حوالى 30يتم فى المبانى متوسطة االرتفاع حتى –العمومية تثاقليا) إلى خزان علوى فوق سطح المبنى (أو فوق شخشيخة السلم)، ويالحظ أن الضغط عند األدوار أسفل الخزان مباشرة يكون منخفضا، وال بد من

) تعمل تلقائيا وذلك لضمان ضغط أعلى Expansion tank ك.و.) مزودة بخزان تمدد (1.5استخدام مضخة صغيرة لرفع الضغط وتركب بالسطح (قدرة حوالى عند هذه األدوار.

Level ك.و. لملئ الخزان وتعمل تلقائيا من مفتاح منسوب (7.5يتولى رفع المياه إلى الخزان العلوى فوق سطح المبنى طلمبة كهربائية تعمل بمحرك فى حدود –switch.ويوجد عادة طلمبتان أحدهما تعمل والثانية احتياطية. ويمكن تحديد قدرات المحركات حسب االرتفاع وكمية المياه من قوانين الهيدروليكا .(

طابقا تم تقسيمه إلى ثالثة مناطق تتولى الرفع لكل منطقة مجموعة من طلمبتين.64) رسما تخطيطيا لنظام تغذية خزان علوى لمبنى مكون من 22-1يبين شكل ( –). يبين شكل Pressure-stat) وحساس للضغط (Expansion tankيمكــن فى المبانــى متوسطــة االرتفـاع استخدام ضغط ثابت عــن طريــق خزان تمــدد ( –

) أ ، ب رسما تخطيطيا للتغذية إلى أعلى عند ضغط ثابت. ويمكن أن تكون هناك مجموعة من ثالثة طلمبات تعمل واحدة منها أو اثنتان أو ثالثة حسب 1-23(االحتياج، كما يمكن أن تكون هذه المضخات مزودة بمحركات متغيرة السرعة وبالتالى يمكن الحصول على عدد كبير من معدالت الضخ ما بين الصفر والقيمة

) عند أقل سرعة ثم يقوم حساس الضغط ولوحة التشغيل Jokey pumpالقصوى، حيث تعمل هذه المضخات طبقا لتتابع معين حيث تعمل أصغر مضخة (والتحكم بتتابع التشغيل بين الطلمبتين الكبيرتين بحيث تعمالن بالتبادل.

نظرا ألن تشغيل المجموعة من ثالثة طلمبات وقت الذروة فى المبنى قد يؤثر على ضغط المياه فى الماسورة الرئيسية بالشارع، فقد تضطر السلطات إلى إجبار –) ب. 23-1المالك ببناء خزان أرضى بالبدروم للسحب منه، وكما هو موضح فى شكل (

) الطلمبات المستخدمة لرفع ضغط المياه وتوصيلها إلى األدوار العليا بالعمارات السكنية متوسطة االرتفاع. وقد توجد وحدات متعددة يمكن أن 24-1يبين شكل ( – مضخات ويمكن استخدام نفس األسلوب فى المبانى السكنية أو التجارية أو فى المبانى العامة أو الفنادق أو المستشفيات. وتصـل القــدرة فى 6يصل عددها إلى

بار. 5/ساعة عند 3م40 وتقوم برفع 380/50/3لفة/د وجهد 2900 ك.و. عند سرعة 2.98 × 6المجموعة إلى




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266. 379Bكيف تعمل طلمبات الصرف الصحى فى المبانى ؟


يتم رفع مياه الصرف مع المخلفات والفضالت من المبانى والتى ال يمكن صرفها تثاقليا ويكون ذلك بواسطة محطة طلمبات خاصة تقوم برفعها إلى خطوط – صرف المجارى العمومية.

تستخدم لهذا الغرض طلمبات غاطسة تعمل كهربائيا بطريقة تلقائية. –) وتتكون من طلمبتين وعوامات التحكم واإلنذار عند ارتفاع Waste water) محطة لرفع مياه صرف (بدون فضالت) والتى يطلق عليها (26-1 يبين شكل ( –

منسوب المياه فى البيارة عن الحد المسموح.) نماذج لطلمبات صرف سوائل بالمخلفات. و تصل قدرة المحركات 28-1) نماذج طلمبات صرف سوائل بدون مخلفات ثقيلة، وشكل (27-1 يبين شكل ( –

ك.و. عند جهد 15 ك.و. وقد تصل فى النماذج المستخدمة فى صرف سوائل بها مواد صلبة إلى 10) إلى 28-1المستخدمة فى النماذج المبينة فى شكل ( وتكون عادة فى مجموعة طلمبتين أو ثالثة.380/50/3

يجب أن تعمل الطلمبات المغمورة بالتبادل تفاديا لتلف تلك التى تظل بداخلها مياه الصرف، إذا بقيت دونما عمل لفترة طويلة. ويكون ذلك باستخدام دائرة انتقاء – تلقائية تقوم بتشغيل الطلمبتين تبادليا بعد كل توقف.




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267. 380B ما هو التأريض؟ كيف يتم تحديد مخططات التأريض؟ اشرح انواع مخططات التأريض المختلفة؟ ما هو األختيار األمثل لمخططات التأريض؟ ما هو نوع التأريض الذى يفرضه النظام فى المملكة العربية السعودية؟


:التأريض

يعمل التأريض فى المبانى عامة و منها المبانى السكنية على منع ظهور جهود كهربائية خطيرة غلى حياة االنسان و األحياء األخرى حيث قد تظهر تلك

الجهود الكهربائية الخطيرة بين اى نقطتين موصلتين يمكن لمسهما او الوصول اليهما فى حالة العمل الطبيعية و بشكل اهم فى حالة االعطال الكهربائية. و يقصد بالنقكتين الموصلتين اى جسم موصل كمعدن هيكل الجهاز الكهربائى او المواسير و الصناديق المعدنية المستخدمة بالتركيبات الكهربائية.

يصطلح حسابيا على ان جهد الرضى يكون مساويا للصفر و هو عمليا يكون أقرب ما يكون للصفر بحيث يمكن من تحقيق غايتنا فى الوقاية من خطرالصدمة ( الصعقة) الكهربائية و يتم ذالك عبر الوصل الجيد مع القطب األرضى لكل النقاط الموصلة لألجهزة و التركيبات و المعدات الكهربائية الممكن

لمسها او الوصول اليها.

:كيفية تحديد مخططات التأريض

تحدد مخططات التأريض من جانبين )a( الجانب األول: منبع التغذية الكهربائية و عالبا فى شبكات التوزيع الكهربائية فى المناطق السكنية يكون محول التوزيع الكهربائى من الجهد

النتوسط للجهد المنخفض و قد يكون اى منبع تغذية كهربائية اخر حسب شبكات التوزيع الكهربائية.)b( الجانب الثانى: التركيبات و الجهزة و المعدات الكهربائية التى تتغذى من منبع التغذية المذكور انفا. و يقصد بجانب التركيبات و الجهزة و

المعدات الكهربائية طريقة تأريض األجزاء الموصلة المكشوفة التى ممكن ان يصل اليهااو يالمسها األنسان او األحياء األخرى. و بالتالى فإن مخططات التأريض وفقا لتوصيل طريقة التأريض من الجانبين المذكورين اعاله تحكم طرق الوقاية من مخاطر التالمس غير المباشر

للتركيبات و الجهزة و المعدات الكهربائية و تصنيف مخططات التأريض بشكل قياسى متعارف عليه دوليا حسب المواصفات القياسية الصادرة عن الهيئة الدولية الكهروتقنية

يرمز للتصنيف القياسى لمخططات التأريض برمزين من األحرف اإلنجليزية يدل األول على طريقة تأريض منبع التغذية بينما يدل الثانى على طريقة تأريض التركيبات و الجهزة و المعدات الكهربائية التى تتغذى من منبع التغذية ذاك.

انواع مخططات التأريض المختلفة

TTمخطط التأريض القياسى –

توصل نقطة المحايد (نقطة النجمة لملفات الجهد المنخفض فى محول التوزيع) عند منبع التغذية مباشرة باألرض بينما توصل كل األجزاء الموصلة

)1المكشوفة بقطب ارض مستقل عند التركيبات و األجهزة او المعدات المتصلة بها. الحظ الشكل (أ-




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TNمخطط التأريض القياسى – ) يؤرض منبع التغذية كما فى المخطط السابقTT:بينما توصل كل األجزاء الموصلة المكشوفة بموصل المحايد و ذالك بطرق مختلفة حسب األتى (

TN-Cمخطط التأريض القياسى •

بحيث يستخدم فيه الموصل المحايد كموصل وقائى اضافة لكونه الموصل المحايد و بذالك يصبح يشار اليه بموصل "األرضى المحايد" و يرمز

).2. الحظ الشكل (أ-2مم10" و ال يسمح باستخدام هذا المخطط للدارات الكهربائية التى تقل مساحة مقطع اسالكها عن PENله بالرمز "

TN-Sمخطط التأريض القياسى •

) و هذا المخطط هو األكثر شيوعا فى المبانى السكنية حيث PE) مستقال عن الموصل الوقائى (Nفى هذا المخطط يكون موصل المحايد ( أطوار (فازات) و محايد و وقائى (أرضى)) الزاميا خاصة للدارات الكهربائية التى تقل مساحة مقطع اسالكها 3يعتبر استخدام الخمس أسالك (

).3 ألسالك األلمونيوم. الحظ الشكل (أ-2مم16 ألسالك النحاس و 2مم10عن

TN-C-Sمخطط التأريض القياسى •

) مع مراعاة عدم TN-C-S) فى نفس شبكة التمديدات الكهربائية بمخطط مركب يرمز له (TN-S) و (TN-Cيمكن استخدام كال المخططين () ذو الخمس اسالك. كما ان ذالك TN-S) ذو األربع اسالك بنفس اتجاه مجرى مخطط التأريض (TN-Cاستخدام استخدام مخطط التأريض (

).4مرتبط بمراعاة مساحات مقاطع األسالك كما ورد سابقا. الحظ الشكل (أ-




250

ITمخطط التأريض القياسى –

و هنا ال تكون نقطة المحايد عند منبع التغذية موصلة بشكل مباشر و بطريقة مقصودة مع األرض بينما توصل كل األجزاء الموصلة المكشوفة بقطي أرض مستقل عند التركيباتاو المعدات المتصلة بها. و يمكن توصيل هذا المخطط كذالك عبر وصل معاوقة بين نقطة المحايد

).5لملفات الجهد المنخفض لمحول التوذيع و األرضى. الحظ الشكل (أ-

األختيار األمثل لمخططات التأريض

) يستفاد من مخططات التأريض المختلفة حسب الخيارات الفنية لطريقة التأريض و ترتيب الموصالت الوقائيةPE و تنسق الوقاية من التالمس غير (المباشر بحيث يستفاد من نتائج ذالك فى الحماية المرجوة من الصدمة الكهربائية او الحماية من الحريق كما يهمنا فى بعض الحاالت استمرارية منبع التغذية

الكهربائية. .فكافة مخططات التأريض توفر حماية من خطر الصدمات الكهربائية و لذا ينصح كل المستخدمين لتطبيق و تنفيذ التأريض فى المبانى حماية لألرواح بينما فى اقل الظروف التى تكون فيها التركيبات و األجهزة و المعدات الكهربائية مراقبة كهربائيا بشكل محدود او يتوقع لتلك التركيبات تعديالت او توسع

) حيث انه ابسط مخطط يمكن تطبيةه.TTفى المبانى فيستخدم مخطط ( ) بينما فى المبانى التى قد يظهر فيها احتمالية حدوث حرائق ذات منشأ كهربائى فال يوصى بأستخدام مخططاتTT) و (IT ألنه يكون عند حدوث خلل او (

التيار الكهلربائى منخفض او حنى منخفض جدا كما هو الحال بالنسبة لتيار حالة حدوث الحلريق من منشأ كهربائى. و لذا يجب استخدام مخطط التأريض )TN-S) و اضافة اجهزة الحماية من التيار المتبقى (RCD لتوفير اكبر حماية ممكنة من خطر الحريقز و هنا يجدر االنتباه إال انه يمنع استخدام (

) فى المبانى او المواقع التى فيها خطر كبير متوقع لنشوب الحرائق و االنفجارات.TN-Cالمخطط( ) و اخيرا من جانب استمرارية منبع التغذية الكهربائية فإن مخطط التأريض األمثل لهذه الحالة هو مخططIT الذى يطبق عند لزوم استمرارية التغذية و (

يعطى افضل ضمان لتوفير التغذية. يالحظ انه فى المبانى او المنشأت المتعددة األغراض يكون اختيار مخططات التأريض معقدا بعض الشىء حيث يجب ان تحلل كل حالة لتركيبات كهربائية

معينة بصورة مستقلة بحيث يكون االختيار النهائى مبنيا على القيود الخاصة لتلك التركيبات الكهربائية او مزودى الخدمة. بحيث نحصل على الحل المناسب لكل تركيبة مما ينتج مخططات تأريض متنوعة فى نفس شبكة التمديديات الكهربائية لنفس المبنى.

نوع التأريض الذى يفرضه النظام فى المملكة العربية السعودية

فى جميع األحوال فإن ابسط المخططات الكهربائية للتأريض الذى يفرضها النظام فى المملكة العربية السعودية على المبانى السكنية الشائعة ذات تيار ال

) و الذى يوفر حماية مقبولة من الصدمات الكهربائية إال ان TN-S امبير و التى تتيع للفسح من قبل البلديات هو مخطط التأريض (400 – 250يزيد عن ) بشكل الزامى للمواقع الرطبة (المطابخ و دورلت RCDكود البناء السعودى فى جزءه من المتطلبات الكهربائية قد اشترط الحماية من التيار المتبقى ( المياه و المسابع و ما يشابهها) مما يجعل الحماية من الصعق الكهربائى كافية بعون اهللا تعالى.




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268. 381Bاذكر بعض األحمال الكهربائية و األسالك و القواطع المناسبة لها حسب قدرتها و طرق تغذيتها؟


فولت:230/400 الجهد لتناسب الكهربائية التمديدات لتعديل اإلرشادي حسب الدليلجدول




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269. 382B فولت موضحا رموز األسالك المستخدمة فى 230/400 فاز. ثم ارسم كيفية توصيل األحمال الخفيفة و الكبيرة على الجهد الدولى 3ارسم رسم توضيحى لتوصيل األسالك من العداد الى لوحة

فولت.230 فاز مع محايد. ثم ارسم رسم توضيحى لشكل المقبس المطابق و كيفية توصيله بالقطب أحادى الطور 3شبكة





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الحمد هللا الذى بنعمته تتم الصالحات

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