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Application Note

Step and Touch Voltage Measurements According toVDE 0101/CENELEC HD 637 S1:1999 AND IEEE 80-2000,81-1983 AND 81.2-1991

AuthorsLutz Hulka |[email protected] Ptter |[email protected]

DateJul 15, 2010

Related OMICRON ProductCPC 100

Application AreaGrounding System Analysis

Versionv1.0

Document IDANP_10001_ENU
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]


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OMICRON 2010 Page 2 of 16

Contents

1 Using This Document ............................................................................................................................31.1 Operator Qualifications and Safety Standards ...............................................................................31.2

Safety Measures .............................................................................................................................3

1.3 Conventions and Symbols Used ....................................................................................................31.4 Related Documents ........................................................................................................................4

2 Step and Touch Voltage Measurements .............................................................................................52.1 Introduction to Measurement According to VDE 0101/CENELEC HD 637 S1:1999 .....................52.2 Introduction to Measurement According to IEEE 80-2000, 81-1983 and 81.2-1991 .....................62.3 Connecting the Measurement Setup ..............................................................................................6

2.3.1 Recommended Current Range Settings ........................................................................................... 62.3.2 Estimating the Open-Line Voltage ................................................................... ................................. 72.3.3 Connecting the Measurement Setup to Power Lines ............................................................. ........... 8

2.4 Reduction Factor ......................................................................................................................... 102.5 Performing Measurements .......................................................................................................... 10

2.5.1 Measurement Principles ................................................................................................................. 102.5.2

Measurement Procedure ................................................................................................................ 12

2.6 Interpretation of Measurement Results ....................................................................................... 13

2.6.1 Measurement According to VDE 0101/CENELEC HD 637 S1:1999............................................... 132.6.2 Measurement According to IEEE 80-2000, 81-1983 and 81.2-1991 ............................................... 14

Please use this note only in combination with the related product manual which contains several important safetyinstructions. The user is responsible for every application that makes use of an OMICRON product.

OMICRON electronics GmbH including all international branch offices is henceforth referred to as OMICRON.

OMICRON 2010. All rights reserved. This application note is a publication of OMICRON.

All rights including translation reserved. Reproduction of any kind, for example, photocopying, microfilming, opticalcharacter recognition and/or storage in electronic data processing systems, requires the explicit consent of OMICRON.Reprinting, wholly or in part, is not permitted.

The product information, specifications, and technical data embodied in this application note represent the technicalstatus at the time of writing and are subject to change without prior notice.

We have done our best to ensure that the information given in this application note is useful, accurate and entirelyreliable. However, OMICRON does not assume responsibility for any inaccuracies which may be present.OMICRON translates this application note from the source language English into a number of other languages. Anytranslation of this document is done for local requirements, and in the event of a dispute between the English and a non-English version, the English version of this note shall govern.


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1 Using This Document

This Application Note provides detailed information on how to measure the step and touch voltagesaccording to the VDE 0101/CENELEC HD 637 S1:1999 and IEEE 80-2000, 81-1983 and 81.2-1991international standards safely, properly and efficiently. The AN CP0502 Application Note describesstep and touch voltage measurements using the OMICRON electronics measurement setupconsisting of the CPC 100 test system, the CP CU1 coupling unit, the CP GB1 grounding box andthe CP AL1 FFT voltmeter.Reading the AN CP0502 Application Note alone does not release you from the duty of complyingwith all national and international safety regulations relevant to working with the CPC 100 and theCP CU1. The regulation EN 50191 "The Erection and Operation of Electrical Test Equipment" aswell as all the applicable regulations for accident prevention in the country and at the site ofoperation has to be fulfilled.

1.1 Operator Qualifications and Safety Standards

Working on overhead lines is extremely dangerous. The step and touch voltage measurementsdescribed in this Application Note must be carried out only by qualified, skilled and authorizedpersonnel. Before starting to work, clearly establish the responsibilities. Personnel receiving training,instructions, directions, or education on the measurement setup must be under constant supervisionof an experienced operator while working with the equipment.

The step and touch voltage measurements must comply with the relevant national and internationalsafety standards listed below:

EN 50191 (VDE 0104) "Erection and Operation of Electrical Equipment"

EN 50110-1 (VDE 0105 Part 100) "Operation of Electrical Installations"

IEEE 510 "IEEE Recommended Practices for Safety in High-Voltage and High-Power

Testing"

LAPG 1710.6 NASA "Electrical Safety"

Moreover, additional relevant laws and internal safety standards have to be followed.

1.2 Safety Measures

Before starting a measurement, read the safety rules in the CPC 100 User/Reference Manual andCP CU1 Reference Manual carefully and observe the application specific safety instructions in this

Application Note when performing measurements to protect yourself from high-voltage hazards.

1.3 Conventions and Symbols Used

In this document, the following symbols indicate paragraphs with special safety relevant meaning.

Symbol Description

Equipment damage or loss of data possible.

Personal injury or severe damage to objectspossible.


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1.4 Related Documents

The following documents complete the information covered in this Application Note:

Title Description

CPC 100 User Manual Provides basic information on the CPC 100test system and relevant safety instructions.

CPC 100 Reference Manual Provides detailed hardware and softwareinformation on the CPC 100 test systemincluding relevant safety instructions.

CP CU1 Reference Manual Provides information on the CP CU1 couplingunit and the CP GB1 grounding box includingtypical application examples.

CP AL1 User Manual Provides detailed hardware and softwareinformation on the CP AL1 FFT voltmeter.


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2 Step and Touch Voltage Measurements

In different countries, states and utilities, different rules and regulations apply to step and touchvoltage measurements. For information on whether or not and how the measurement is to beperformed, refer to the relevant standards. The following figure shows the possible scenarios of thetouch voltage hazard.

Figure 1: Touch voltage hazard scenarios

This Application Note describes the step and touch voltage measurements according to the VDE0101/CENELEC HD 637 S1:1999 and IEEE 80-2000, 81-1983 and 81.2-1991 standards.

2.1 Introduction to Measurement According to VDE 0101/CENELEC HD 637S1:1999

Note: This excerpt from the above standard is for reference only. Reading this Application Note doesnot release you from the duty of reading and observing the standard.

For the decision whether step and touch voltage measurements have to be performed, thegrounding current is of major importance. The grounding current is the maximum fault currentthrough the earth for the maximum fault duration assuming the protection works properly. Thegrounding current depends on the neutral-point connection and is to be calculated from the gridsimpedance.

The VDE 0101/CENELEC HD 637 S1:1999 standards specify when the touch voltage measurementis not required. According to the standards, the touch voltage need not be measured if:

The substation is a part of a global grounding system (as defined in the standard).

A set of measures described in Appendix D of the standard is applied, e.g. insulation of metalparts or their protection against touch.

< 2 m 1 m1 m 1 m


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The whole systems grounding voltage is less than two times the allowed touchvoltage for the maximum possible fault current into ground. The systems grounding voltage limitdepends on the fault duration as shown inTable 1: System's grounding voltage vs. fault durationon page6.

Fault Duration tFin Seconds Systems Grounding Voltage Limit in Volts

10 160

1.1 200

0.72 250

0.64 300

0.49 440

0.39 600

0.29 800

0.20 1000

0.14 1200

0.08 1400

0.04 1600

Table 1: System's grounding voltage vs. fault duration

In all other cases, the touch voltage measurement is recommended.

The touch voltage measurement is usually performed on the periphery of a grounding system, i.e. onthe fence of a substation and additional peripheral grounding points such as the first tower of apower line or other grounding systems singularities.

2.2 Introduction to Measurement According to IEEE 80-2000, 81-1983 and 81.2-1991

Note: This excerpt from the above standard is for reference only. Reading this Application Note doesnot release you from the duty of reading and observing the standard.

According to the IEEE 81.2-1991 standard, more extensive measurements including the touchvoltage measurement should be performed if the calculated ground potential rise (GPR) exceeds avalue of 25 kV. Because this limit seems quite high compared with thespecifications in theCENELEC HD 637 S1:1999 standard, OMICRON electronics recommends to evaluate the objectunder test carefully. Particularly, if areas are involved where people are likely to be, it is a good ideato measure the touch voltage if the criterion of the CENELEC HD 637 S1:1999 is met.

According to the IEEE 81-1983 standard, the expected touch voltages can alternatively been readfrom a contour map generated from extensive step voltage measurements in all directions.

2.3 Connecting the Measurement Setup

2.3.1 Recommended Current Range Settings

The highest current range allowed by the open-line voltage (see2.3.3 Connecting the MeasurementSetup to Power Lines on page8)provides the best measurement accuracy. However, depending onthe length of the power line under test, this setting may result in the CPC 100 overload due to lowdriving voltage. As a rule of thumb, the current range required for the power line length is given in


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Table 2: Recommended current range settings on page7.Set the current range switch of the CPCU1 to the value according to the table.

Line Impedance Line Length Range Current Compliance Voltage

01.6

02 km/01.5 miles 100 A 50 V0.88 110 km/0.55 miles 50 A 100 V

4.040 550 km/330 miles 20 A 250 V

> 16 > 20 km/15 miles 10 A 500 V

Table 2: Recommended current range settings

2.3.2 Estimating the Open-Line Voltage

Before connecting the CP CU1 to overhead lines or power cables (further on referred to as powerlines), estimate the open-line voltage as follows. Follow the instructions below exactly andsequentially to protect yourself from high-voltage hazards. In addition to the following safetyinstructions, observe the safety rules in the CPC 100 User/Reference Manual and CP CU1

Reference Manual.

To estimate the open-line voltage:

Caution: Before grounding a power line, make sure that the line is not poweredwith the life-dead-life test as follows: Using a certified voltage tester approved forthe voltage tests, verify on a life system that the tester is operational, on the lineto be unpowered that it is dead and on a life system again that the tester is stillworking. When grounding a power line, observe the five safety rules in the CPCU1 Reference Manual.

1. Switch off, short-circuit and ground the power line on both sides using an installed grounding

switch or, if no grounding switch is available on site, using grounding cables (further on, thegrounding switch or these extra grounding cables are referred to as grounding switch).

2. Make sure that the connection to ground at the far end of the power line is not removed duringthe complete test procedure.

3. In addition to the grounding switch, ground the line at the near end using a grounding setconsisting of three cables rated for the maximum short-circuit current possible on the line.

This connection is called working ground further on.

4. Open the grounding switch at the near end of the power line and measure the current through theworking ground using a clamp-on ammeter on all three phases.

5. Close the grounding switch.

6. Calculate the estimated open-line voltage after removal of the grounding cables as follows:

(1)

or

(2)

where is the estimated open-loop voltage in volts,is the highest measured current in amperes, is the constant of a typical overhead line per wire


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and and is the length of the line in km and miles respectively.

Caution: If the estimated open-line voltage is

> 500 V, stop. The measurement is not possible due to high-voltage hazard.Try to take parallel lines out of service.

250500 V,the measurement is possible only in the 10 A range.

100250 V, the measurement is possible in the 10 A or 20 A range.

50100 V, the measurement is possible in the 10 A, 20 A or 50 A range.

< 50 V, the measurement is possible in all current ranges.

7. If the current range allowed by the estimated open-line-voltage is lower as the current range setaccording toTable 2: Recommended current range settings on page7,set the current rangeswitch of the CP CU1 to the value allowed by the open-line voltage.

Caution: During the grounding switch at the near end of the power line is open,the area around the CP GB1 in the range of 5 m/15 ft and around the CP CU1 inthe range of 2 m/5 ft is a dangerous zone due to high-voltage and mechanicalhazards. Do not enter the dangerous zone. Keep the grounding switch open for atime as short as possible.

Caution: If you see or hear anything uncommon in the test equipment, e.g. noiseof electrical discharge or lightening of surge arrestors, close the groundingswitch before touching the measurement setup.

2.3.3 Connecting the Measurement Setup to Power Lines

If the estimated open-line voltage (see2.3.2 Estimating the Open-Line Voltage on page7)allowsmeasurement in the current range you want to use, connect the measurement setup to an overheadline or a power cable leading from the substation under test as follows:

1. Make sure that the grounding switch at the near end is closed.

2. Connect the CP GB1 to ground using the delivered cable near the place where the connection tothe line is made. Make sure that the grounding stud is in good condition, clean and free ofoxidation.

Caution: Depending on the type of grounding points in the substation, theappropriate connection set and socket clamp have to be used. Connecting socket

clamps of one type to a grounding point of another system is highly dangerouson both the connection of the grounding set to the CP GB1 and the connection ofthe CP GB1 to the grounding point in the substation. The 16 to 20 mm socketclamps are designed and tested for fault currents up to 26.5 kA, the 25 mm (1inch) socket clamp for fault currents up to 30 kA, both for a maximum duration of100 ms. On locations where higher fault currents are possible, the CP CU1 andthe CP GB1 must not be used.

3. Disconnect the grounding cables from the ground (the grounding switch at the near end isclosed!) and connect them to the CP GB1 line studs.

4. Position the CP CU1 at a minimum distance of 5 m/15 ft from the CP GB1.


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5. Position the CPC 100 at a minimum distance of 5 m/15 ft from the CP CU1 and 10 m/30 ft fromthe CP GB1.

6. Ground the CP CU1 using a cable of at least 6 mm2cross-section close to the CPC 100 and the

position of the operator.

7. Connect the CP CU1 with the CP GB1.

8. Ground the CPC 100 using a cable of at least 6 mm2cross-section close to the position of the

operator.9. Connect the CP CU1 with the CPC 100.

10. Mark the area around the CP GB1 in the range of at least 5 m/15 ft and around the CP CU1 inthe range of at least 2 m/5 ft as dangerous zone.

11. Open the grounding switch and read the voltmeter on the CP CU1 front panel from outside of thedangerous zone.

Figure 2: Connecting the measurement setup below shows the measurement setup connected to anoverhead line.

Figure 2: Connecting the measurement setup

Caution: If the voltmeters reading is

> 500 V, stop. The measurement is not possible due to high-voltage hazard.

250500 V, the measurement is possible only in the 10 A range.

100250 V, the measurement is possible in the 10 A or 20 A range.

50100 V, the measurement is possible in the 10 A, 20 A or 50 A range.

< 50 V, the measurement is possible in all current ranges.

12. If the open-line voltage allows measurement in a higher current range as already set on the CPCU1, set the current switch of the CP CU1 to the minimum of the current range set according toTable 2: Recommended current range settings on page7 and the current range allowed by theopen-line voltage. If the open-line voltage allows measurement, proceed as described in2.5Performing Measurements on page10.

Caution: Make sure that the grounding switch is always closed when nomeasurement is performed and especially when the wiring is modified or thecurrent range switch of the CP CU1 is set.

CPC 100 CP CU1

CP GB1


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2.4 Reduction Factor

Due to the inductance of the feed-in line, a considerable part of the current injected into theground does not flow back through the ground but through the ground wire or the line shield. Thiscurrent has to be subtracted from and, consequently, the ground impedance is given by

(3)

This effect is compensated by the reduction factor r as defined in the CENELEC HD 637 S1:1999standard. A field in the XML template allows setting the reduction factor between 0.01 and 1.00 (1.00means no current compensation). However, the IEEE standards do not explicitly recommend usingthe current reduction factor in this way because it can considerably influence the overall results.

For 110 kV overhead lines, the standard gives typical values of r = 0.98 for steel ground wires anddown to 0.60 for steel/aluminum ground wires. For current feeding via power cables, the r factor canbe as low as 0.01. The effect of the current can be eliminated by disconnecting the line shieldor the ground wire of the feed-in line. If the disconnection is not possible, it is recommended tomeasure the current with a clamp-on ammeter and to calculate the reduction factor as

(4)

2.5 Performing Measurements

To measure step and touch voltages, a current is forced to flow into the ground, usually byconnecting one pin of the CP CU1 current output to the ground system and the other pin to a remotegrounding system far away from the system under test typically by using a shut-down overhead lineor power cable. After then, the voltages arising in and around the test object are measured.

2.5.1 Measurement Principles

If an object to be touched is in the range of 2 m around the test object, measure the touch voltagebetween two hand electrodes. If no object to be touched is in this range, measure the touch voltagebetween a hand and a foot electrode placed in a distance of 1 m from the test object (seeFigure 3:Touch voltage Measurement on page11).

There are two ways to perform this measurement. In one approach the voltage measurement isdone with the CPC 100 using the V1 AC input and the "Step & Touch Voltage" template. Accordingto the other method, the CPC 100 and the CP CU1 are used just for current injection and the voltagein and around the substation is measured with the CP AL1 FFT voltmeter. In this case, theCPC 100 and the CP CU1 generate currents with a frequency 20 Hz below and 20 Hz above mains

frequency in an endless loop, requiring no communication between the generating and measuringunits. This method uses the "Step & Touch Voltage with CP AL1" template but you must enter theresults into the Microsoft Excel worksheet manually. The big advantage of the latter method is thatno wired connection between the generating and the measuring unit is needed, which is especially inlarge substations a crucial issue.

Note: When using the CP AL1 for voltage measurement, it is a good idea to start generating currentwith the CPC 100 and the CP CU1 exactly at an even minute because of the following time scheme.During the first 20 seconds current is generated followed by a 100 seconds break to let thetransformers and mains fuse cool down. Consequently, the generating sequence is restarted exactlyat every even minute, which is helpful information on the measurement side.

Note: Connect the electrodes to the CPC 100s V1 AC input using a twistedcable.


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Figure 3: Touch voltage Measurement

Note: The touch electrode shall have a pointed end to safely break through the coat of paint.

According to the CENELEC HD 637 S1:199 standard, the foot electrode shall have a size of 400cm

2. The electrode has to be pressed against ground with a force of at least 500 N (approx. 50 kg).

The foot electrode shall have good contact with ground. On dry soil or concrete, place the footelectrode onto a wet fabric or the like. The OMICRON foot electrodes are water cans equipped witha standard conform electrode. Their empty weight for transportation is only about 6 kg while filledwith water their weight is about 25 kg each.

According to the test probe method defined in the IEEE 81.2-1991 standard, the voltage drop ismeasured close to objects in a distance of 1 m from the object using a 0.30.6 m (12 ft) long testprobe (wholly driven into the soil) of 1216 mm (0.5 inch) diameter. If this voltage divided by ahypothetical human body resistance of 1 k stays under the critical body current limit described in2.6.2 Measurement According to IEEE 80-2000, 81-1983 and 81.2-1991 on page14 no furthermeasurements are required.If the above criterion is not met, a higher resistance could be taken into account; it could bemeasured using the so-called footprint method. However, it seems to be possible to combine the twomeasurements and to directly measure the current over a 1 k resistance simulating the humanbody and two footprint electrodes according to the standard. The two electrodes shall have a surfacearea of 200 cm

2each and a weight of at least 20 kg. They shall be placed 0.5 m from each other and

1 m in front of the test object. The soil under the electrodes shall be soaked with salty water to obtainworst-case conditions. Therefore, the CENELEC methods can be applied accordingly.

For the measurements with a foot electrode, the CENELEC standard recommends to take intoaccount additional resistances as shown inFigure 4: Measurement with foot electrode on page12.The human body is to be represented by a resistance of 1 k switched in parallel to the voltageinput during the measurement. In areas where people usually wear shoes, the shoe resistance canbe simulated by an additional resistance of 1 k switched inseries to the ground electrode. In areassuch as public baths where no shoe wearing is expected, this additional resistance must not beused.

to CPC 100 V1 AC input(use twisted cable)


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Figure 4: Measurement with foot electrode

The adapter for the CP AL1 allows switching in these resistors if applicable.

Alternatively, use a ground rod driven at least 10 cm into the soil connected without additionalresistances to get an overview of the touch potential. If the allowed touch voltage is not exceededusing this method, it can be expected that the footprint method will not yield results above the limits.

For the step voltage measurement, use the foot electrodes of 200 cm2each in a distance of 1 m

from each other and measure the voltage between them.

2.5.2 Measurement Procedure

The measurement procedure is controlled by templates available on the CPC Explorer CD-ROMshipped with the CP CU1 or in the customer area of the OMICRON electronics Web site. Fordetailed information on the templates and instructions how to use them, refer to the CP CU1Reference Manual. Using the CPC 100 Sequencer test card, the test procedure runs without userinteraction.

After wiring the measurement setup to the power line, configure the CPC 100 as described in the CPCU1 Reference Manual for the CP CU1s current range setby the current range switch.

Caution: The configured current range must not exceed the limit by the open-linevoltage.

The further procedure depends on the measurement method (see2.5.1 Measurement Principles onpage10). If you measure the voltage with the CP AL1 FFT voltmeter (recommended), use the"Step & Touch Voltage with CP AL1" templates and proceed as follows:

1. Choose the template for the mains frequency and the optimum current range (e.g. "Step &Touch Voltage with CP AL1 and CU1 20A 50Hz.xmt") and open the template.

2. Start the test exactly at an even minute and check whether the current really flows withoutcausing an overload. Lock the keyboard using the key on the front panel if you leave the deviceuncontrolled and make sure the dangerous zone around the CP CU1 and the CP GB1 isprotected against passerby.

3. Measure the step and touch voltages in around the station using the CP AL1 and write down (ortype directly into the Microsoft Excel worksheet) the results for the frequencies 20 Hz below and20 Hz above the mains frequency. To read out the amplitude, set the cursor of the CP AL1 tothese frequencies manually. It is helpful to know that the generation starts always exactly at aneven minute.

4. Enter the results into the Microsoft Excel template.

When entering the possible ground fault current of the station under test, the possible touchvoltages are calculated.

Rbody

Rshoe

1 k

1 k

Foot electrode1 m


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If you perform the measurement without the CP AL1 FFT voltmeter, use the "Step & Touch Voltage"

templates and proceed as follows:

1. Choose the XML template for the mains frequency (e.g. "Touch Voltage CU1 60Hz.xmt" for the60 Hz mains frequency) and open the template.

2. Select the Enter Location Here card from the template.3. Select Save as Default to reuse this card later on.

4. Place the test probes as described above.

5. Start the test card for the current test point.

6. Rename the test card with the name of the location.

7. Add one Sequencer test card for every test point you want to measure.

8. Proceed with step 6 as long as you want to measure more points.

9. Save the test procedure as a file on the CPC 100.Note: It is recommended to save at most 15 test cards in one file.

10. Download the test file(s) from the CPC 100 to the PC using CPC Explorer.

11. Load the test file(s) into the Microsoft Excel "Touch Voltage" template.

The touch voltage values for the entered fault current are calculated.

Note: If there are more files, load one after another.

2.6 Interpretation of Measurement Results

2.6.1 Measurement According to VDE 0101/CENELEC HD 637 S1:1999

The touch voltage automatically calculated in the template is given by

(5)

where

is the touch voltage in volts is the measured voltage in voltsis the grounding current of a worst case fault in the substation in amperes is the output current of the CP CU1 in amperesis the reduction factor

The touch voltage (depending on the expected fault duration) is assessed as tolerable if thecalculated value is below the limit given inTable 3: Allowed touch voltage vs. fault duration onpage14.The value of the maximum fault duration can be entered under the assumption that theprotection is working properly. If the resulting touch voltage is below the limit given in the table, the

standard is met.


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Fault Duration tFin seconds Allowed Touch Voltage VTpin volts

10 80

1.1 100

0.72 125

0.64 1500.49 220

0.39 300

0.29 400

0.20 500

0.14 600

0.08 700

0.04 800

Table 3: Allowed touch voltage vs. fault duration

2.6.2 Measurement According to IEEE 80-2000, 81-1983 and 81.2-1991

The touch voltage automatically calculated in the template is given by

(6)

where

is the touch voltage in volts is the measured voltage in voltsis the grounding current of a worst case fault in the substation in amperesis the output current of the CP CU1 in amperes

is the reduction factorThe assessment whether a touch voltage is permissible or not is a fairly complicated process. Forrelatively low touch voltages, simple formulas can be used to do the assessment. The equationsbelow use the Dalziels formulasfor the body current. The Biegelmeier's curve is more complex andtherefore not used here. However, when the results approach the limits, it is a good idea to refer tothe IEEE 80-2000 standard for details.

Two formulas for the touch voltage limit depending on the body weight are given below. If thefollowing criteria are met, no further calculations are required.

(7)

for body weight of 50 kg

(8)


and is the touch voltage limit in volts for body weight of 50 kg and 70 kg respectivelyis the maximum fault duration in seconds assuming the protection is operational.


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If one of the above limits is exceeded, the additional resistances of the soil can be taken into accountin two ways. The first method calculates the touch voltage limits using the specific ground resistanceand the factor of the protective surface layer, if applicable. The second method is based on thefootprint resistance measurement.

To calculate the touch voltage limit, the specific ground resistance has either to be measured asdescribed in the CPC 100 Reference Manual or found in the relevant literature. The touch voltagelimit is given by

(9)


(10)


where

and is the touch voltage limit in volts for body weight of 50 kg and 70 kg respectivelyis the coating factoris the resistivity of the surface material in m is the duration of shock current in seconds

For the coating factor , refer to the IEEE 80-2000 standard; is affected by the coating, too. If noprotective surface layer is involved, .

Alternatively, the footprint resistance can be measured as follows. Two electrodes with a diameter of16 cm each weighted with at least 20 kg each shall be used. They shall be placed 0.5 m from eachother and 1 m in front of the test object. The soil under the electrodes shall be soaked with water and

the electrodes shall have a conducting medium between each electrode and ground, such asconductive rubber pad, a sponge fastened to the foot electrode and wetted in a salt solution, or steelwool soldered to the metal disk to obtain worst-case conditions. Then a current is fed into ground(6A AC output using the Quick test card) and voltage, current and impedance Z are measured. Theabsolute value Z in can be used as in the formulas below.

(11)


(12)


where

and is the touch voltage limit in volts for body weight of 50 kg and 70 kg respectivelyis the footprint resistance as measured aboveis the duration of shock current in seconds


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