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By: Engr. Donny N. Salazar

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FUNDAMENTAL QUANTITIES AND UNITS OFELECTRICAL SYSTEM

Flow of Electricity

Electricity is the form of energy created by a flow of tinyparticles called electrons which travels through wires.

This flow is often called electric current (A). Just likewater, which can only flow down a hill, an electric currentcan only flow if there is something to give it a push. Forexample when you plug a socket, the push can comefrom a source like a battery or from the wall socket, which

provides MAINS ELECTRICITY .If the circuit is not complete, then the electrons cannot

move across the gap. There should be a load, wires andthe power source which makes a complete circuit.

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Current Types:

1. Direct Current (DC) is the movement of electrons in one

direction in a conductor.

2. Pulsating direct current is a current in one direction that

varies in intensity at a regular interval of time.

3. Alternating current (AC) is a current that changes in

direction and intensity at a regular interval of time.

VOLTAGE (V)

- An electrical pressure which are necessary to producean electrical current. Examples are: generators, storage

batteries, photoelectric cells and thermocouple.

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RESISTANCE

- The property of a material that causes it to oppose the

movement of electrons. An example of high resistance arecalled non-conductors or insulators.

ELECTRICAL POLARITY

- All DC sources of electrical pressure have two terminals to

which electrical devices are connected. These are positiveand negative terminals. Electrons flow through the devicefrom the negative terminal of the source to the positiveterminal of the source.

OHMS LAW

- States that in any electrical circuit, the current is directlyproportional to the voltage applied to the circuit and isinversely proportional to the resistance in the circuit.

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This can be expressed in the formula as shown below:

I = V/R

Where:

I = intensity of current in amperes.

V = quantity of electrical pressure in volts.

R = amount of resistance in ohms.

ELECTRICAL SYMBOLS

There are various electrical symbols being used in

electrical engineering. You may research other electricalsymbols in the Philippine Electrical Code. For learning

purposes, here are commonly used electrical symbols

when dealing with circuits.

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+

-

Vs

Idealindependent

voltage source

V

i

Vs

Constant

Voltage

is

Ideal

independent

current source

i

V

is

Constant

Current

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+

-

Vs

(a)Ideal

independent

voltage source

is

(b)Ideal

independent

current source

+

-

+

-

Vs =Vx Vs =ix is =Vx is =ix

(c)Ideal dependent

voltage-

controlled

voltage source

(d)Ideal

dependent

current-

controlled

voltage source

(e)Ideal dependent

voltage-

controlled

current source

(f)Ideal

dependent

current-

controlled

current source

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Other electrical symbols like resistor, capacitor and

inductor will be introduced when we tackled RLC

circuit. Other symbols will be introduced when wealso reached the topic about load calculations and

electrical plans.

PASSIVE AND ACTIVE CIRCUITS

- Electric circuit has many elements like resistor,

capacitor, inductor, battery etc. Circuit analysis is the

process by which voltage or current is measuredacross the element. In a complete circuit there are

two types of elements found active elements and

passive elements.

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The active elements generate energy. Batteries,

generators, operational amplifiersetc are active

elements. The passive elements cannot generateenergy, they drop energy. Resistor, capacitor,

inductor etc are passive elements because they

takes energy from circuit.

CONDUCTORS AND ITS PROPERTIES

It is frequently desirable, for the purposes of

comparison and calculation, to know the resistancesof electrical materials in terms of unit dimensions of

length and cross-sectional area. Such resistances

are generally in tables. This is known as resistivity.

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EXAMPLES OF RESISTIVITY CALCULATION

(Note : Solution to be presented during class

discussion)

1. The substation bus bar is made up of 2inches

round copper bars 20 ft long. What is the

resistance of each bar if the resistivity is0.000001724 ohm-cm. (EEF pp6-8)

2. Determine the resistance of a bus bar copper if the

length is 10 meters long and the cross section is 4

x 4 cm. The resistivity is 1.72micro ohm-cm. (EEFpp6-8)

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CHARACTERISTICS OF CONDUCTORS AND

INSULATORS

The energy gap for an insulator is so wide that

hardly any electrons acquire enough energy to

jump into conduction band. The valence bandand the conduction band in a conductor ( such

as copper) overlap so that there are always

many conduction electrons even without

application of external energy. A semiconductorhas an energy gap that is much narrower that in

an insulator.

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TEMPERATURE RESISTANCE RELATIONSHIP

Experiment has, in fact demonstrated that the

resistance of all wires generally used in practice in

electrical systems increases as the temperature is

raised; moreover, within the usual operating rangethe resistance varies linearly with temperature

changes.

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Referring to the graph, note that the results of atemperature resistance test are shown by a heavy

oblique line, and that the extrapolated broken portionof the line is merely inferred for the convenience tobe a continuation of the actual experimental data.Understand that the region indicated by the brokenline is generally below ordinary operatingtemperature and is drawn only because it serves tolocate an arbitrary but convenient inferredabsolutezero for the metal concerned.

Temperature Coefficient of Resistance

It is defined as the ohmic change per degree per ohmat some specified temperature.

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Cont

PROBLEMS:

1. The resistance of a copper wire at 30 degreeCelcius is 50 ohm. If the temperature coefficient of

copper at zero degree is 0.00427, what is the

resistance at 100 degree celcius?

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Cont

2. A coil of copper wire has a resistance of 62 ohms ata room temperature of 24 deg celcius (a) What will

be its resistance at 80 deg celcius (b) at -20 deg

celcius?

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Cont

***You may use this table to solve for this problem.

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3. The moving part of an electrical machine was allowed to

remain at rest sufficiently long to acquire the same

temperature as that of a room i.e. 23 deg celcius; theresistance of the copper winding was then measured and

found to be 0.18 ohm. A second measurement was taken

of the same resistor after the machine had been operated

for a period of time and, because of normal heating, the

resistance rose to 0.206 ohm. Calculate the temperature

and temperature rise of the winding.

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SERIES CIRCUIT

- Is one in which devices are connected so that there isonly one path for current.

- The total voltage applied to a series circuit is distributed

across the various components of the circuit in a series of

voltage drops.

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- The sum of the voltage drops across individual resistors

in a series circuit is equal to the total applied voltage.

E = E1 + E2 + E3 + E4 ++ En- The current in all components are the same.

I = I1 = I2 = I3 = I4 =..=In

- The total resistance of a series circuit is equal to the sum

of resistances of all resistors in a circuit.R= R1+ R2+ R3+ R4 ++Rn

Short Circuitan alternate path of very low resistance in a

circuit.Open Circuitoccurs when some part of a circuit is either

open, such as switch, or malfunctioning such as burned

out fuse etc..

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PARALLEL CIRCUIT

- Has more than one path for a current.- The voltage are the same to all branches of the circuit.

E = E1= E2=E3=E4=.=En

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- The total current in the parallel circuit is equal to the sum

of the currents in the separate components.

I = I1+ I2+ I3+ I4+.+ In- Total resistance for equal resistors is computed as R =

R(value) divide by number of resistors in parallel.

- The total resistance for unequal resistors connected in

parallel is:1/R = 1/R1 + 1/R2+ 1/R3 + 1/R4+.+1/Rn

EXAMPLES: ( copy solution during lecture )

1. Two 10 ohm resistances are connected in parallel. The

two are then connected in series with a 5 ohm resistance.If then connected across a 24 volt battery, find the

voltage across the 5 ohm resistance. Answer: 12 volts

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2. Find the total resistance, total current, and voltage drops

for the circuit shown in the figure.

Answer : R = 12 ohm, I = 20 amps, E1 = 40 volts, E2 = 60volts, E3 = 140 volts.

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3. Referring to the circuit shown in the figure calculate a )

total equivalent resistance b) total current It c) the power

delivered to the 16 ohm load resistor. Answer : 28 ohms,8 amps and 64 watts.

Note: Other lectures were presented during actual classes.Lectures not included are delta to wye and wye to delta

transformation.

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GALVANOMETER

Galvanometer, an instrument used to indicate the

presence, direction, or strength of a small electric current.

The typical galvanometer is a sensitive laboratory

instrument used mainly to detect and compare currents.

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The galvanometer makes use of the fact that an electric current flowingthrough a wire sets up a magnetic field around the wire. In thegalvanometer, the wire is wound into a coil. When current flowsthrough the coil, one end of the coil becomes a north magnetic pole,

the other a south magnetic pole. When a permanent magnet isplaced near the coil, the two fieldsthe one from the coil and theone from the magnetinteract. The like poles will repulse each otherand the unlike poles will attract. The amount of attraction andrepulsion increases as the strength of the current increases.

In the moving-magnet galvanometer, the permanent magnet is a needle(much like a compass needle) mounted on a pivot and surroundedby the coil. In the moving-coil galvanometerthe most commontypethe coil is mounted on pivots or suspended by thin metalstrips. The coil lies between the poles of a permanent magnet insuch a way that it rotates when current flows through it. The directionof the rotation depends on the direction of the current through thecoil, and the amount of rotation depends on the strength of thecurrent. A galvanometer is often used to indicate when the current ina circuit has been reduced to zero, as in the operation of theWheatstone bridge, a device for measuring electrical resistances

precisely.

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A moving-coil mechanism similar to that used in a galvanometeris used in some ammeters. Like the galvanometer, theseinstruments measure the strength of a current but they canhandle a stronger current; unlike the galvanometer, they

cannot indicate the current's direction. A moving-coilmechanism is also used in some voltmeters (which measurethe voltage in a circuit) and ohmmeters (which measure theresistance in a circuit). In some instruments, a selector switchconnects the moving-coil mechanism to different internal

circuits so that a single mechanism can be used in making allthree types of measurements.

The principle upon which the operation of the galvanometer isbased was discovered in 1820 by Hans Christian Oersted

when he observed that a magnetic needle could be deflectedby an electric current. The first galvanometer was made byJohann Schweigger in 1820. In 1882, Jacques ArseneD'Arsonval introduced the moving-coil galvanometer. EdwardWeston made important improvements to the device a fewyears later.

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Ammeter

- Is an electrical measuring device which is used tomeasure electric current through the circuit. It is the

modified form of the galvanometer.SYMBOL:

Conversion of Galvanometer to Ammeter

- Since Galvanometer is a very sensitive instrumenttherefore it cant measure heavy currents. In order toconvert a Galvanometer into an Ammeter, a very lowresistance known as "shunt" resistance is connected inparallel to Galvanometer. Value of shunt is so adjustedthat most of the current passes through the shunt. In thisway a Galvanometer is converted into Ammeter and canmeasure heavy currents without fully deflected.

A

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Value of Shunt Resistance

- Let resistance of galvanometer = Rgand it gives full-scaledeflection when current Igis passed through it. Then,

Vg= IgRg-------(i)

- Let a shunt of resistance (Rs) is connected in parallel to

galvanometer. If total current through the circuit is I.

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Then current through shunt:

Is= (I-Ig)

potential difference across the shunt:Vs= IsRs

Or

Vs= (IIg)Rs-------(ii)

But Vs =Vg(I - Ig)Rs= IgRg

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Voltmeter

- Voltmeter is an electrical measuring device, which is

used to measure potential difference between two points

in a circuit.

SYMBOL:

Conversion of Galvanometer into Voltmeter

- Since Galvanometer is a very sensitive instrument,

therefore it can not measure high potential difference. In

order to convert a Galvanometer into voltmeter, a very

high resistance known as "series resistance" is

connected in series with the galvanometer.

V

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Value of Series Resistance

- Let resistance of galvanometer = Rgand resistance

Rx (high) is connected in series to it. Then ,combinedresistance = (Rg + Rx).

- If potential between the points to be measured = V and if

galvanometer gives full-scale deflection, when current

"Ig" passes through it. Then,

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V = Ig(Rg+ Rx)

V = IgRg + IgRx

VIgRg = IgRx

Rx= (VIgRg)/Ig

Examples: ( Copy Solution during lecture )

1. A galvanometer has a coil resistance of 10 ohms and

deflects full scale with a current of 5 mA.a) Show how this can be used to construct an ammeter

which reads 0 - 1 A.Ans : Rsh = 0.05 ohm

b) Show how this can be used to construct a voltmeter

which reads 25 volts maximum. Ans.: Rs = 4,990 ohms

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2. A shunt is used to extend the range of an ammeter byconnecting it across the ammeter. The ammeter has aresistance of 0.1 ohm and gives a full scale deflection of

2.5 A. Calculate the value of the shunt resistance toextend the range of the ammeter to 50 A.

Ans. : Rs = 5.263 milliohm

3. Calculate the value of the shunt resistance to be used

with the galvanometer having a resistance of 10 ohm ifthe current through the galvanometer is not to exceed 5percent of the total current.

Ans : Rs= 0.526 ohm

4. A galvanometer coil has a resistance of 12 ohm and it

shows full scale deflection at a current of 3 mA. Howwould you convert it into

a. Voltmeter range 0- 18V Ans : Rx = 5998 ohm

b. An ammeter range of 06A Ans : Rs = 6 milliohm

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CLAMP METER

- A clamp meter is an electrical tester that combines a

basic digital multimeter with a current sensor. Clamps

measure current. Probes measure voltage. Having a

hinged clamp jaw integrated into an electrical meter

allows users to simply clamp around wire, cables and

other conductors at any point in the electrical system and

measure its current, without disconnecting it.

What do clamp meters measure?

Any of these: AC current, AC and DC voltage, resistance,

continuity, and, with some models, DC current,capacitance, temperature, frequency and more

Typically measure to the nearest tenth of a unit (rather than

the milli-units you find in a full-function multimeter),

making them perfect for electrical work

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CLAMP METER FIGURE

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Who uses them?

Industrial maintenance technicians

Control technicians

Electriciansin-house and contractors

Facilities, building maintenance and HVAC technicians

Service organizations

What are they used on?

Industrial equipment

Industrial controls

Electrical systems Commercial/industrial HVAC

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What do they use them for?

Service:Repairing existing systems on an as-neededbasis.

Installation: Troubleshooting installation problems,performing final circuit tests and supervising apprenticeelectricians while installing electrical equipment.

Maintenance:Performing scheduled and preventivemaintenance on electro-mechanical systems.

Why use a clamp meter?Industrial situations often call for simultaneousmeasurement as part of troubleshooting, so many of

those users carry two meters: one to measure electricalcurrent and one to measure voltage. For electricians, aclamp meter is a quick and versatile diagnostic tool forfiguring out why an electrical system or piece ofequipment is not operating correctly.

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Whats inrush?Large machinery often requires a big surge of electricity to getstartedelectricians have to make sure the rest of the systemcan support that occasional big surge in demand. That surgeis called inrush and it causes other problems than just overallsupply. Fluke clamps use proprietary technology to filter outelectrical noise and capture the starting current exactly asthe circuit protection sees it.

Whats different about the new clamps?The flexible coil and the extended measurement ranges helpsolve these common issues:

Tight cabinets and bundled wires that make it difficult to use aregular clamp meter.

Large or awkward conductors a regular clamp meter cant getaround to measure.

Needing a co-workers help to get a measurement.

Wanting to measure more than 1,000 amps AC.