checking - site tests - energizing

ELECTRICAL INSTALLATIONSCHECKING - SITE TESTS - ENERGIZING

TEST PROCEDUREMETHOD

That hand book is only reserved for testers.It isn't allowed to diffuse or distribute it either to the customers or to foreign

people of the Society.

SITE TESTS - PROCEEDING METHOD

SUMMARY

1. GENERALITIES P. 5

2. HV EQUIPMENT P. 6 CIRCUIT BREAKER / DISCONNECTING SWITCH P. 6

3. MEASUREMENT TRANSFORMERS P. 7 CURRENT TRANSFORMER P. 7 CHECKING OF WINDING DIRECTION AND CONTINUITY P.8 TEST OF THE RATIO TRANSFORMER P. 9 SECONDARY WIRING INSULATION MEASUREMENT P. 10 MEASURE OF THE SECONDARY WIRING RESISTANCE P. 10 DIELECTRIC TEST P. 10 MAGNETISATION CURVE P. 11 CONSUMPTION TESTING P. 13

VOLTAGE TRANSFORMER P. 14 CHECKING OF WINDING DIRECTION AND CONTINUITY P. 15 CHECKING OF THE RATIO P. 16 COUPLING CAPACITOR VOLTAGE TRANSFORMER (CCVT) - POLARITY TEST P. 17 CHECKING OF PHASES ROTATING SEQUENCE P.19 MEASURE OF WINDINGS INSULATION P.20 SECONDARY WINDING RESISTANCE P. 20 DIELECTRIC P. 20 CONSUMPTION TESTING P. 20

4. POWER TRANSFORMER P. 21

MEASUREMENT OF WINDINGS INSULATION RESISTANCE P. 22 WINDING RESISTANCE MEASUREMENT P. 24 RATIO TESTS P. 26 CHECKING OF THE VECTOR-GROUP P. 29 IMPEDANCE MEASUREMENT P. 32 OIL TESTING P. 37 DIELECTRIC TESTS P. 42 CHECK OF SOUND LEVEL P. 44 MESURE OF CAPACITIES AND TANGENT DELTA P. 45 TEST PROCEDURE ON A WINDING TEMPERATURE INDICATOR (TYPE AKM) P. 47

5. DIRECT CURRENT AUXILIARIES P. 52

BATTERIES P. 52 BATTERY CHARGER P. 53

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SUMMARY

6. CONTROL CIRCUITS P. 54

INSULATION P. 54 DIELECTRIC P. 54

7. PROTECTION RELAYS P. 55

DISTANCE PROTECTION P. 55 DIFFERENTIAL PROTECTION P. 56 CURRENT GENERAL PROTECTION P. 56 VOLTAGE RELAY P. 56 DIRECTIONAL RELAYS P. 57 RESTRICTED EARTH FAULT PROTECTION P. 59 BUSBAR PROTECTION PRIMARY INJECTION TEST P. 60 LONGITUDINAL DIFFERENTIAL PROTECTION P. 62 GENERATOR DIFFERENTIAL PROTECTION P. 64 TRANSFORMER DIFFERENTIAL PROTECTION P. 65 OPERATING TEST BY PRIMARY INJECTION P. 67

8. MEASURING AND METERING EQUIPMENTS P. 68

9. EARTH RESISTANCE MEASUREMENT P. 69

MEASURE OF GROUND INSULATION P. 69 TESTING OF GROUND CONNECTIONS P. 70 MAX. VALUES OF EARTH CONNECTIONS RESISTANCES P. 70

10. DIELECTRIC TEST P. 71

11. INSULATION TESTING P. 75

PRINCIPLE OF INSULATION MEASURE FOR A LV CIRCUIT P. 75 INSULATION VALUES P. 76

12. MAX. RESISTANCE AUTHORISED BETWEEN FRAME AND MAIN EQUIPOTENTIAL EARTH P. 77

13. MEASURE OF STEP AND TOUCH VOLTAGE P. 78

METHOD P. 79 STEP VOLTAGE MEASUREMENT (FOOT TO FOOT CONTACT) P. 80 TOUCH VOLTAGE MEASUREMENT (FOOT TO HAND CONTACT) P. 81 CALCULATION OF POTENTIAL GRADIENT P. 82 CURRENT ALLOWED DURING 1 SECOND P. 83

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SUMMARY

14. SEARCH OF FAULTS P. 85

FAULT ON CABLE P. 85 SHORT-CIRCUIT BETWEEN 2 CABLES P. 87

15. MV 5,5 KV TO 30 KV CIRCUITS CONTINUITY OF MV CIRCUITS P. 88

SCHEMATIC DIAGRAM FOR THE PHASE TO PHASE TEST P. 88

16. MEASURE OF CONTACT RESISTANCES ON BUSBARS P. 89

TESTING DIAGRAM P. 89

17. CABLES CHECKING P. 90

GENERALITIES P. 90 MV CABLES (NOMINAL VOLTAGE 6-30 KV) P. 95 LV CABLES (50 V £ U £ 500 V) P. 97 CONTROL COMMAND CABLES P. 98 INSTRUMENTATION CABLES P. 100

18. ON LOAD TESTS P. 103

EHV, HV, MV, LV FEEDERS P. 103 TRANSFORMER OUTGOING FEEDERS P. 103 MOTOR FEEDERS P. 104 DIESEL ENGINE INCOMING P. 104

19. IEC NORMS P. 105

20. ANNEXS :

ANNEX 1 : DIELECTRIC TEST FOR CABLES ANNEX 2 : DIELECTRIC TEST FOR CABLES AND SWITCHBOARDANNEX 3 : EHV DIELECTRIC TESTANNEX 4 : FEEDBACK PRINCIPLEANNEX 5 : RECOMMANDED SETTINGS

DOUBLE CILCK TO OPEN ANY ANNEX

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TESTS DEFINITIONMETHOD

1. GENERALITIES

Before proceeding to the energization of an electrical installation, it is necessary to :

a) Check that :

- The HV, MV, LV equipment installed is with adequate characteristics,

- All the safety devices are installed :

. tapes, posters,

. gloves, stools,

. poles,

. earthing equipment,

. communication devices,

. consignment sheets,

. fire protection equipment,

- All control and electrical locking circuits are well done (analysis of documents).

b) Carry out all the preliminary checkings described on the test sheets, for each equipment.

c) Ensure that the conformity of cables and wiring has been checked for conformity during erection orat the end of erection.

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2. HV EQUIPMENT

2.1 CIRCUIT BREAKER / DISCONNECTING SWITCH

Point out the characteristics and ensure that they are in accordance with the feeding voltage :

- For circuit breakers check

references,general locking,no leaks of oil circuit,mechanical lockings,condition of the porcelains,earthing,insulation regarding with earth,HV connections, torque test,SF6 pressure,

auxiliaries :. driving motor,. anti-condensing resistance,. panel lighting.

- Test

operation of closing coil,anti-pumping,simultaneity of opening and closing of poles,tripping timeclosing timecontact resistance measurementcabling of interlocksVoltage drop between poles crossed by the nominal current.

- For disconnecting switch

- adjust the controls and carry out the mechanical and electrical tests,

- test the good operating of locking devices,

- check blades penetration,

- contact resistance measurement.

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3. MEASUREMENT TRANSFORMERS

3.1 CURRENT TRANSFORMER

3.1.1 Definition of tests

a) Check

references,earthing of terminal S2 of the LV wiring,wiring direction (polarity),wiring continuity,transformer ratio,LV wiring insulation.

b) Measure

secondary wiring resistance.

c) Carry out

magnetisation curve, ) If specified on designdielectric between LV wiring and earth. )

d) Verify

Consumption of LV circuit ) If specified on design

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3.1.2 Checking of winding direction and continuity

According to hereunder diagram, for each transformer.

Use a voltmeter with central zero scale connected on the current transformer S1 & S2 terminals and a battery of 9 V capacity.

By action on push button, the voltmeter will indicate :

- a positive deviation at the closing- a negative deviation at the opening

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3.1.3 Test of the ratio transformer

Method - according to the hereunder diagram.

Verify by primary injection of In (if possible) :

- the indication of A1,

- the indication of A2.

The ratio is given by the calculated value of A1 / A2.

Then, compare the calculated ratio with the ratio written on the manufacturer's plate of the CT.

A3 will allow to check the presence of a leakage current.

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3.1.4 Secondary wiring insulation measurement

After disconnection of CT earthing, carry out :

a) an insulation measure between each wiring and the others earthed.

b) an insluation measure between separate windings.

Equipment to be used : 500 V megohm meter.

3.1.5 Measure of the secondary wiring resistance

The wiring resistance of the CT can be measured by using an equipment like the wheatstone bridge (low resistance measurement).

Compare with the value measured in factory.

NOTA : S2 earthing checking : after the test, connect the earth cable and check theinterconnection of S2 outputs of the CT.

3.1.6 Dielectric test

According to the standards, this test is not required because the dielectric test at 1000 V during 1 mn is only applied for voltages < 60 V. 500 V magneto test is sufficient.

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3.1.7 Magnetisation curve

a) Schematic diagram

Equipment to be used :

1) Analogie ammeter, class 0,5 or 1

2) Analogie Voltmeter class 0,5 of 1

3) Voltage transformer

4) Variable power supply 0-240 V & 10 A minimum

Initial state : main circuit breaker open, the test will be carried out by a current injection at the secondary of the current transformer.

Remark :It's better to carry out this test with the CT test box from the control room in order to make sure that the cabling from the CT to the relay is correct.

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b) Purpose

1. Check that there is no core out of use,2. Compare the knee voltage with the typical test.

PROCEDURE

The knee point voltage is characterised by the value which increase by 50 % the magnetisation current when the voltage applied at the secondary of the CT is increased by 10 % (all other windings being open).

The excitation curve will be drawn until the point corresponding to an increase by 100 % of the current when the voltage increase by 10 %.

PRECAUTIONS

At the end of the tests, it is absolutely necessary to reduce gradually the voltage before the interruption of the feeding voltage, because an abrupt variation of the flux could produce a sufficent voltage to damage the insulation of the secondary winding.

Type of curve

100

200

300

400

500

50 100 150 200

m A

V

10 %

50 %

Example for 500/1 CTKnee - point at 420 V.

Calculation of Vk

The minimum knee point voltage Vk and maximum current Ie are calculated as follows :

Vk = 2 If (Rs + Rp)Ie = Is - Ir

n

Where :If = equivalent secondary pilot current of maximum fault currentIs = effective fault setting expressed in secondary AmpsIr = relay setting currentRs = CT secondary winding resistanceRp = maxi loop lead resistance between CT's and relayn = number of CT groups forming the protected zone for bus zone differential protectionn = 2 for machine or transformer differential protectionn = 3 for restricted earth fault protection on delta windingsn = 4 for restricted earth fault protection on star windings

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3.1.8 Consumption testing

During the primary injection of the nominal current on the CT, check the voltage on the terminals S1 and S2. Then make the calculation (U x I) and check that this CT consumption is not higher than the value given on the name plate by the manufacturer (in VA).

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3.2 VOLTAGE TRANSFORMER

3.2.1 Definition of tests

a) Check

reference,earthing of S2 LV winding terminal,earthing of P2 HV winding terminal,winding direction (polarity),winding continuity,transformer ratio,insulation between HV & LV windings and between LV windings and earth,phases rotating sequence.

b) Measure

secondary winding resistance

c) Carry out

dielectric between LV winding and earth

d) Test

consumption.

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3.2.2 Checking of winding direction and continuity

a) Schematic diagram

Use a voltmeter with central zero scale connected on VT S1 & S2 teminals, and a battery of 9 V capacity. By action on the Push Button, at the closing the voltmeter will indicate a positive pulse, at the opening, a negative pulse.

Purpose : Check the continuity of primary and secondary windings of the VT and their winding direction. This test also allows the correction of secondary windings until the incoming LV fuses.

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3.2.3 Checking of the ratio

1st method :primary injection by using of a HV generator giving a voltage of 0,5 Un to 1,2 Un. It is possible to check the ratio by injection of a low voltage around 500 V.

2d method : by using a measuring bridge (with potentiometer). See the hereunder scheme of principle.

The measure consist in making both voltages at zero by action on the resistor divider then the galvanometer will indicate "zero".

Results analysis

The standards allow an error margin of ± 0,5 % of the calculated measure. The error in % will be calculated with of the following formula :

Compare the results with the ratio found on factory tests.

Purpose : to detect the following anomalies,- short-circuited winding,- open winding,- bad connections during the assembling.

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E (%) = Measured ratio - calculated ratio 100 X Calculated ratio


3.2.4 Coupling Capacitor Voltage Transformer (CCVT) - Polarity test :

1st testing method

- calculate CCVT ratio U1 / U2 = Xr

- prepare resistor divider (R1 + R2)/R1 = Xr

- connect in parrallel the CCVT and the resistor divider - take care of polarity.

- connect the mVoltmeter and apply an AC voltage.

- the mVoltmeter reading should be near zero, if the CCVT polarities are correct.

Testing diagram :

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2d method

As a principle see the hereunder diagram. The calculation depends on the ratio of the VT.

The voltage transformer is connected in parallel to the capacitive voltage transformer.

The voltage U1 is applied between A and N, NHF both earthed.

U2 (S1 S2) = 220/190,52 = 1,155 voltsU2 (CVT) = 220/KK = ratio of capacitive VT

Correct polarities U of the milivoltmeter is near of zero.

In this case :

U'2 = U2 (CVT)R1 = 100 U2/U2 (CVT) - 100

DIVIDER RATIO K VOLTAGE U2 (CVT) = mV R1 ohms

220 000/V3

100/V3

2200 U2 (1a2 - 1n) = 100

or (2a2 - 2n)

1055

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3.2.5 Checking of phases rotating sequence

After energizing, check :

Phases rotating sequence by means of a field-controller through the 3 phases (see hereunder schematic diagram).

By applying rated three-phased voltage on the primary terminal of the VT with open delta diagram, verify that the resultant voltage is less than 5 V.

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3.2.6 Measure of windings insulation

After disconnection of the earth, carry out :

1) insulation measurement between HV and LV windings,

2) insulation measurement between each LV winding and earth

The measured values will be around several megohms. Equipment to be used : 500 V megohm meter.

3.2.7 Secondary winding resistance

The winding resistance of the VT can be measured by means of an equipment like wheatstone bridge. Compare with the others VT to detect any anomaly.

NOTA : Check of S2 earthing after tests, connect the earth cable and check the interconnections of the S2 terminals of the VT.

3.2.8 Dielectric

- between each LV winding and earth,

- between one LV winding and the others LV windings connected, together and to the earth,

- test : apply 2 000 V during 1 mn.

3.2.9 Consumption testing

Method :

After energizing check the consumption at the measuring point "A" by means of an ammeter in serial successively with each phase :

1) check the correction of phases (balancing),

2) consumption (VA) of each phase by multiplication U x I,

3) compare the result with the value indicated on manufacturer's plate of the VT.

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4. POWER TRANSFORMER

4.1 DEFINITION OF TESTS

Check :

Reference,coupling (horary index),connections tightening,looking of terminals,looking of porcelains,insulation between winding and tank,insulation between auxiliaries and earth, 500 V magneto,connection and earthing of lightning arrester,tank earthing,earthing of HV or MV neutral,cooling device : . rotation direction of motors,

. mechanical looking of fans,

. coupling of radiators.

Verify :

- safety devices operation,

- Buccholz 1st step : alarm by air injection,

- Buccholz 2nd step : tripping discharge,

- Thermostat alarm + tripping,

- tap changer operation,

- limit switch for high position,

- + operation step by step,

- ratio for each position of the tap changer,

- tap changer cubicle heating operation,

- thermal sensors of cooling system and starting of fans, oil circulation.

Measure of insulation

windings resistance with correction of the room temperature for each position of the tap changer.

Carry out

Dielectric value of the oil (spintermeter).

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4.2 MEASUREMENT OF WINDINGS INSULATION RESISTANCE

Principle

The measurements are carried out with the help of a MEGGER delivering voltages of 2500 and 5000 V. Windings are short-circuited. The duration of the measurement is around 1 mn. During the measurement, the windings, which are not supplied, must be earthed.

Measures

With a megohm meter, apply 5000 V between :

- HV an MV windings,

- HV winding and earth + tank connected,

- MV winding and earth + tank connected.

With a megohm meter, apply 2500 V between :

- MV an LV windings,

- MV winding and resistance,

- resistance and earth.

With a meghom meter, apply 1000 or 500 V between :

- LV winding and earth + tank connected,

- LV auxiliary tap changer and earth,

- Tank and blocking rail (in case of tank protection).

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Schematic diagram

1. Between HV windings and earth,

2. Between HV an MV windings,

3. Between MV winding and earth,

Same method if there is a tertiary winding.

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4.3 WINDING RESISTANCE MEASUREMENT

- this measurement is necessary to determine the transformer conductor losses RI 2

- the measurements should be done when the transformer is cold. It should be de-energized for atleast 3 hours.

- the temperature measurements should be done at differents points on the transformer and theaverage Tm should be calculated. The temperature difference between the top and the bottom of the transformer should not exceed 5°C.

Testing schematic diagram

The voltmeter leads should be connected as closely as possible to the terminals of the winding to be measured. It's better to disconnect the voltmeter when switching on and off.

- the current used should not exceed 15 % of the winding nominal current.

- the voltage and current values should be recorded to calculate the resistance after the readings arestabilized.

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Conversion of resistance measurements

To calculate the winding resistance for others temperatures the conversion shall be done by the following formula.

Rs = Rm x Ts + TkTm + Tk

Rs = resistance at desired temperature

Rm = measured resistance

Ts = desired reference temperature

Tm = temperature at which the measurement is done

Tk = 234.5 (copper)

Tk = 225 (aluminum)

Remark :

Measurement by resistor bridge method could be used if the rated current of the transformer winding to be measured is less than 1 Ampere.

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4.4 RATIO TESTS

1st method : Voltmeter method

Two voltmeters shall be used. One to read the voltage injected on the high voltage terminals. The other to measure the voltage on the low voltage terminals.

The two voltmeters shall be read simultaneously.

The test should be repeated four times (4 different values). The average ratio should be taken as the true value (within ± 1%).

For three phases transformers refer to table (here with) concerning voltmeters connections.

2nd method :

Ratio bridge method

- material to be used

- 1 high impedance digital voltmeter

- 2 high accuracy decade resistors.

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Testing diagram

Test procedure

- apply voltage to primary terminals

- adjust R1 and R2 in order to read zero m Volt

Ratio = U1 = R1 + R2U2 R1

compare the calculated ratio with this one given by the manufacturer on the name plate. For three phases transformers refer to table (here with) for connections.

Using this method will allow to check transformer polarity and vector - group.

28


3 phases transformers ratio and vector-group test

TransformerVector - group

Primary voltageApply on terminals

Secondary voltagemeasured on terminals Ratio

D d oA.BA.CB.C

a.ba.cb.c

U1 / U2

D y 5A.BA.CB.C

n.ac.nn.b

U1 / U2 x Ö3

D d 6A.BA.CB.C

b.ac.ac.b

U1 / U2

D y 11A.BA.CB.C

a.nn.cb.n

U1 / U2 x Ö3

Y y oA.NB.NC.N

a.nb.nc.n

U1 / U2

Y d 5B.NA.NC.N

a.bc.ab.c

U1 x Ö3 / U2

Y y 6A.NB.NC.N

n.an.bn.c

U1 / U2

Y d 11A.NB.NC.N

a.cb.ac.b

U1 x Ö3 / U2

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4.5 CHECKING OF THE VECTOR-GROUP

4.5.1 1st method : (by mean of a DC feeder)

Apply at the terminals A & B of the HV winding a DC voltage around 12 V (terminal A connected to the positive pole, terminal B to the negative).

By connecting a voltmeter, with zero central scale, successivily between LV terminals a-b, b-c, c-a, read the direction of voltmeter deviation at the connection of DC feeder on the wiring. Then compare the coupling schedule index with the values obtained in comparison with the table extracted from EDF standard. The indicated polarities are those who appear at the a, b, c, LV terminals when a correct DC voltage is applied between the HV terminals A & B (terminal A connected to the positive pole, terminal B to the negative).

For instance, by locating, on table, the indications read on the galvanometer, successivelyconnected on terminals a-b, b-c, c-a, we find that this transformer has a coupling whose schedule index is of 6.

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4.5.2 2nd method (by three phases voltage injection)

Test procedure

- disconnect the transformer (no earth on neutral point)

- connect the high voltage phase "H1" and the low voltage phase "X1" together.

- apply a three phases voltage to high voltage terminals H1, H2 and H3

- note voltage measurements between the various pairs of terminals (see table here under)plot the vectors on the paper and check transformer vector-group.

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4.5.3 Usual couplings of transformers

a) Three-phase transformers

See hereunder table extracted from the standart UTE 52.100, annex D.from the standart ANSI/IEEE C 57.12.90 - 1980

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4.6 IMPEDANCE MEASUREMENT

4.6.1 Goal

This measure allows to establish a reference value of impedance in ohms per phase. This reference allows to check the variation of impedance with the time, especially in case of faults.

4.6.2 Testing method

The measure is done when the transformer is completely installed :

1) Single phase transformer 2 windings HV, LV.

The equipment is supplied throuhg the HV side, the LV side being short circuited.

We measure the current of the winding supplied, and the voltage at the terminals of the windings.

Z (Ohms) = U / I

2) Three phase transformer, 2 windings HV, LV :

The equipment is supplied in single phase between 2 terminals of the HV side, the LV side being short circuited.

We measure the current, and voltage at the terminals of the windings supplied.

Z (Ohms) = U / I

We measure ZAB, ZBC, ZAC, by circular permutation and we calculate the impedance per

phase.

ZA = 1/2 (ZAB + ZAC - ZBC)

ZB = 1/2 (ZAB + ZBC - ZAC )

ZC = 1/2 (ZAC + ZBC - ZAB)

3) Transformers with more than 2 windings :

The measurement is done for all the pairs of windings (HV / MV, MV / Ground, ...) using the same method like (1) for single phase transformers or (2) for the three phases transformers.

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4.6.3 Diagram to realize

1) Autotransformer :

Remark : Take in to account the transformer ratio in order to define the correct section for the short-circuit.

According to the windings disposition, it's necessary to insulate the winding which is not use during the measure.

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2) Single phase transformer

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4.6.4 Tools to be used

- variac 0-220 V single phase

- digital voltmeter class 0,1

- digital ammeter class 0,1

- current transformer, ratio 5/1 (if necessary)

36


4.6.5 Testing procedure

1. Short circuit the L.V. winding

2. Connect on each HV terminal, 2 wires, 1 for the supply, 1 for the measure

3. Realize the test diagram, in accordance with chapter 4.6.3.

4. Adjust the variac to minimum

5. Connect the variac on the network

6. Increase the supply voltage until you can measure properly the current

7. Read voltage and current simultaneously, repeat the measure two times

8. Decrease the voltage to zero

9. Disconnect the variac

10. If it is a single phase transformer, dismantle the test. If it's a three phase transformer,repeat the same test for the two others pairs of terminals.

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4.7 OIL TESTING

4.7.1 Dielectric strength

Use a spintermeter (UTE 27.101 standard)

It is the most important test because it gives the insulation capacity of the oil and allows to ensure that the transformer can operate without danger.

That test is carried out by measuring the breakdown voltage between 2 metallic electrodes dipped into the oil to be tested (spintermeter). The two main types of spintermeters used have different distances and electrodes :

Curve A - UTE standard spintermeterÆ sphere = 12,5 mm - distance : 2,5 mm

Curve B - VDE standard spintermeterspherical caps : r = 25 mm

Using conditions of these spintermeters are provided by manufacturers, but following precautions are applicable for all equipments :

a) clean the chamber and the electrodes with ether, then wipe carefully these pieces with awash-leather or a non fluffy rag. Finally wash the pieces with a lot of oil coming from the sample bottle.

b) Put the oil to be tested into the chamber, operate very carefully to avoid air-bubble, thenwait 15 mm before each test.

c) Take into account only the voltage corresponding to the striking, excluding the smalldischarge occuring during the voltage rising.

d) Operate in accordance with the operating mode of UTE C 27.101 standard.

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4.7.2 Test

The test consists in application of increasing alternative voltage of 40 to 60 Hz on the terminals of the electrods. The increasing is equal to 2 KV per sec from 0 to breakdown value. The breakdown voltage is the value of the voltage reached at the moment when occurs the first spark between the electrods (fugitive or clear).The test will be carried out 6 times. Take the average value of the 5 last tests.

Results

1) for a treated oil : breakdown voltage > 70 KV

2) for a no-treated oil (1st check) : breakdown voltage > 40 KVA value of dielectric strength < 40 KV indicates that oil is wet. Proceed to a treatment.

Water content in oil (in mg/kg)

For an oil of convenient oxidation the water content factor will be < 20Content of 0.002 % or 20 ppm.

4.7.3 Curves

1 - EDF method

2 - UTE method

3 - VDE method

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40


41


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4.8 DIELECTRIC TESTS

4.8.1 Purpose

By applying voltage this test allow to check the insulation of all the points of windings which are at the same potential :

1) with regard to all the other windings connected to earth,

2) with regard to all the metallic pieces (inside the transformer) connected to the tank and thetank connected to earth.

The test is good if there is no fall of test voltage.As overvoltages can often appear, we also have to check the windings tightness with higher voltage according to the standarts.

Causes of overvoltage :

- Discharge of an alternator,

- Opening of a CB on a long line without load,

- Voltage by resonance,

- Atmospheric voltage (direct lightning or not)

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4.8.2 Method

Apply during the specific time (see standards board chap. ) a single-phase voltage between a short-circuited winding and the earth. The other windings have to be connected to the tank and the earth.

The test voltage at industrial frequency (50 or 60 Hz) must be progressively increased to reach the specified test voltage and maintained 1 mn.

Schematic diagram

44


4.9 CHECK OF SOUND LEVEL

4.9.1 Purpose

Checking of sound level according to specified requirements. The transformer has to be installed in normal operating conditions.

4.9.2 Method

With a sound-meter, measure sound level at different points around the transformer.

1) The transformer being alive without charge at rated frequency and voltage withoutauxiliaries,

2) The transformer being alive without charge at rated frequency and voltage with air-coolingfans in normal operation.

4.9.3 Measurements

1) For transformer the tank of which is < 2.5 m high, measures are carried out at half height onan horizontal plan,

2) For transformer the tank of which is > 2.5 m high, measures are carried out at 1/3 and 2/3 ofheight on an horizontal plan.

4.9.4 Measurements points

1) At 30 cm from radiation area, the points will be distant of 1 m at maximum and equallyspaced.Minimum of 10 points.

2) Check also the sound level at 5 then 10 m from the 4 angles A, B, C, D of the transformer.

45


4.10 MESURE OF CAPACITIES AND TANGENT DELTA

4.10.1 Purpose

This test consists on measuring at the ambient temperature, the capacities, the dielectric losses of the insulation and the insulation quality of the windings, to detect the possible internal faults of the transformer. The important dielectric losses show that the transformer has an degradated insulation by the following factors :

- over voltage- over heating- presence of moisture- mechanical forces.

4.10.2 Method

The measure is done with a portable capacitor bridge under a low single phase voltage, of capacities and tangentes by direct readings ; (capacities in F, tangent in % and then determination by calculation of elementary capacities).

Principle : measurement of a winding (single or three phases) in regard with all others windings connected to the frame and earthed.

Case of a 2 windings transformer :

measure 1 = HV/LV grounded Þ c1 + c2 = ameasure 2 = LV/HV grounded Þ c3 + c2 = bmeasure 3 = HV + LV/ ground Þ c1 + c3 = c

c1 = (a + c - b) / 2

c2 = (a + b - c) / 2

c3 = (b + c - a) / 2 MEASURE HV / LV + Earth

46


Case of a 3 windings transformer :

Measure 1 : HV/MV + LV + ground c1 + c2 + c5 = aMeasure 2 : MV/HV + LV + ground c2 + c3 + c6 = bMeasure 3 : LV/HV + MV + ground c4 + c5 + c6 = cMeasure 4 : HV + MV/LV + ground c1 + c3 + c5 + c6 = dMeasure 5 : HV + LV/MV + ground c1 + c2 + c4 + c6 = eMeasure 6 : MV + LV/HV + ground c2 + c3 + c4 + c5 = fMeasure 7 : HV + MV + LV/ground c1 + c3 + c4 = g

The following deductions can be done :

d + f + e = a + b + c + g

c1 = (a + g - f) / 2 c2 = (a + b - d) / 2

c3 = (b + g - e) / 2 c4 = (e + f - a - b) / 2

c5 = (a + c - e) / 2 c6 = (b + c - f) / 2

47


4.11 TEST PROCEDURE ON A WINDING TEMPERATURE INDICATOR (Type AKM)

4.11.1 Generalities

The temperature indicator for winding serie 35 is erected with a resistance used to simulate the hot spot temperature.

4.11.2 Technical characteristics

The maximum secondary current allowed from the main CT is 1,5 A (max. overload is 90 % = 2,85 A during 2 hours).

The current corresponding to the wished temperature increase is adjustable between 45 to 85 % of the secondary current of the main CT at nominal load.

4.11.3 Example

With a secondary current of 1,5 A at nominal load, the proportionnal current to the wished temperature increase is adjustable between 0,7 and 1,3 A.This gives an increase temperature from 10°C to 35°C for an indicator having a scale between 0 and 150°C (see curve folio TD - 52, 35)

5. Heating resistance

16. Main CT

20. Adaptator resistance

I1. Current from the main CT

I2. Current proportionnal to the wished temperature rise.

48


4.11.4 Instructions for the setting of the adaptator resistance

1) Determine the current I2 to the heating element 5 from the curve TD - 52, 35proportionnal to the temperature increase at nominal load obtained by heating tests.

2) Calculate the current I2 in the heating element being part of the current I1 from the CTat nominal load (I2/I1).

3) Set the resistance between 5-5 with the adaptator resistance 20 at the value found onthe following curve.The adaptator resistance is installed behind the scale in the corner at the top on the left.Unscrew the blocking screw before turning the axis.

49


AKM WINDING TEMPERATURE INDICATOR

GENERAL

AKM WINDING TEMPERATURE INDICAOTR serie 35 is a conventional AKM OILTEMPERATURE INDICATOR serie 34, supplemented with an electrical heating element.The winding temperature indicator measures the temperature of the hottest part of the transformer winding. It is difficult to measure the temperature of the winding directly, therefore an instrument has been developed by means of which a "thermal image" of the temperature can be reproduced indirectly.

CONSTRUCTION AND PRINCIPLES OF OPERATION

The winding temperature indicator (fig. 1) is provided with at sensing bulb (1) placed in an oil filled pocket in the transformer tank cover. The bulb is connected to the instrument housing by means of a flexible capillary tubing (2). The capillary is connected to the measuring bellows of the instrument. The measuring system is filled with a liquid which changes voltume with varying temperature. A compensating bellows acts upon the measuring bellows through a linkage, compensating for variations in ambient temperature.

Inside the instrument is fitted a heating resistance (5), which is fed by a current proportional to the transformer loading current. The heating resistance is connected by the leads to the terminal block. Both the temperature of the heating resistance and the temperature in the oil filled pocket affect the measuring bellows, whose motion is transmitted by a linkage to the pointer and the shaft with the switches. Either two or four switches are supplied and each may be set independently of the others.

The instrument is supplied with a maximum indicating pointer, which moves with the pointer when the temperature rises. The maximum pointer thus indicates the maximum temperature reached. It can be reset by means of a screwdriver from the outside. The bottom of the housing is fitted with two or three cable glands for the incoming cables. The housing is ventilated.

The heating resistance is fed by the current transformer on the loaded winding of the transformer. The temperature increase of the heating resistance is there by proportional to the temperature increase of the winding over the top oil temperature. The bulb of the instrument at the other hand is located in the hottest oil of the transformer and thus senses the top oil temperature. Therefore, the measuring bellows reacts to both the temperature increase of the heating resistance, corresponding to the temperature increase of the winding above the top oil temperature, and the top oil temperature. In this way the instrument indicates the temperature in the hottest part of the winding, i.e. "hot spot temperature".

The thermal time constant for the instrument is of the same magnitude as that of the winding. There by the indicator gives a true "thermal image" of the winding temperature in relation to time.

ADJUSTING

The AKM MATCHING UNIT, available for primary current 2 A or 5 A from the main current transformer at rated load, operates as a shunt and is an adjustable resistance.For primary current 1,5 A a built-in adjustable resistance is available.

When the main current transformer generates a current of max. 2 A at rated load, the current to the winding temperature indicator is adjusted only with the adjustable resistance. An approximative heating current may be obtained from the TD-52 curve as a basis for the final adjustment to give the correct temperature increase above the top oil temperature.

When the main current transformer generates a current of max. 5 A at rated load, the AKM MATCHING UNIT is also equipped with a matching current transformer with a number of secondary taps. The movable leads should be connected to the terminal post that gives a current next over the current obtained from TD-52, whereafter the final adjustment is made with the adjustable resistance.

50


51


--

52


5. DIRECT CURRENT AUXILIARIES

5.1 BATTERIES

- characteristics reading,

- electrolyte filling until intermediate level

5.1.1 Check

temperature during charge (< 45° C),looking (battery cleanness),connections and tightening,electrolyte level (average),cells inter-connections (polarity check),general installation,insulation between + and earth,insulation between - and earth,no leakage on pots.

5.1.2 Charging at constant current

Charge during 20 hours at I = 1/10 of capacity within 10 hoursThen charge during 30 hours at I = 1/20 of capacity within 10 hoursThe battery must receive 3,5 of its capacity within 10 hours

5.1.3 Control

- Density (for lead - acid battery),discharged after filling 1,13 18 - 22 ° C

1,24 28 - 32 ° C

- battery room ventilation,

- charging current,

- voltage at end of charging time a) per cell (2,45 to 2,6 V)b) whole battery,

- under voltage relay,

-safeties - charger fault,- insulation fault,- directionnal current,

- Floating operation

- I & U meters : compare indicated value with measured value by means of acalibrated equipment,

- battery cleanness, leave it dry and clean after charging.

53


5.1.4 Finishing

if necessary, fill the cells with distilled water untill max level.

5.1.5 Precautions

don't let the battery heat over 45° Cdon't let cells short of liquid,never put tools on battery,don't create sparks near cells,fill the cells in a ventilated room,don't approach the cells with a flame or an incandescent part (soldering iron...)

5.2 BATTERY CHARGER

5.2.1 Check

rated power,earth insulation,rating of upstream and downstream side protections,incoming voltage,outgoing voltage,equalizing current

54


6. CONTROL CIRCUITS

6.1 INSULATION

After end-to-end test, carry out an insulation test between each polarity collector and the earth (use a 500 V megger).

6.2 DIELECTRIC

This test consist, after insulation test, to apply an alternative voltage of 2000 V during 1 mm between all the collectors connected together and the earth. The result is good if there is no breakdown. This test must be carried out before automatic devices test or functional relays test.

6.3 CHECK

- conformity with diagrams,- rating of collectors protections,- cables references,- terminals references,- relays and equipment references,- terminals tightening,- earthing of relay-frames (in loop).

6.4 CONTROL

- collectors voltage,- standing up of relays at + 10 % and - 20 % of the nominal power supply,- auxiliary voltage of protection relays,- signalling and alarms,- all functions TL and TPL,- servo systems between polarities distribution- when the relay is in service it's essential to measure the phase angle U/I to make sure the

relay is correctly connected.

55


7. PROTECTION RELAYS

7.1 GENERALITIES

First, check :

- CT characteristics,- equipment reference,- setting ranges, comparison with calculation sheets or selectivity manual,- there is no open circuit on CT.

7.2 CHECKING

- auxiliary voltage,- relay operating at + 10 % and - 20 % of auxiliary voltage,- consumption,- I, U and t operating threshold function of setting (by means of current injection).

7.3 TESTING

- insulation in regard with the earth.

7.4 DIELECTRIC

- carry out a dielectric test between function (polarity, relay output) and earth at 2000 Vduring 1 mm.Test to be carried out before functionnal test of relay.

7.5 DISTANCE PROTECTION

- check cabling from CT to relay,- check the relay by secondary injection according to manufacturer instructions.

56


7.6 DIFFERENTIAL PROTECTION

- transformer differential protection- longitudinnal differential protection- restricted earth fault- busbar differential protection

7.7 CURRENT GENERAL PROTECTION

Max I, Ho, CB failure, reset device.

1) Test with primary injection, at In if possible. Carry out the test phase after phase.

2) Injection on secondary circuit by means of testing box

7.8 VOLTAGE RELAY

Injection of an adjustable voltage from the test box,

- check operating threshold : at 10 % - 20 % - 50 % - 80 % and 100 % of the nominalvoltage (Un).

- check tripping time with a timer.

VOLTAGE RELAYS should be supplied from a variac or a low resistance potentiometer. Check on the voltmeter if the voltage is influenced by the pickup action. If the voltage doesn't correspond to the increase of the variac, the voltage source is not sufficiently strong.

57


7.9 DIRECTIONAL RELAYS

DIRECTIONAL RELAYS have an operating value that must be tested with a certain phase angle between current and voltage. The phase angle should be approximately as large as the characteristic angle of the relay. However, a deviation of ± 20° can be tolerated since the measuring error only will be 6 % (cos 20° = 0.94). If an angle error is compensated, it is possible to tolerate even larger deviations. That means that all types of single phase power directional relays can be tested with a phase power directional relays can be tested with a simple test set without phase shifters.

The phase angle 0° is obtained by connecting the current circuit via a series resistor to the voltage that supplies the voltage circuit. See diagram A. The phase angle 90° is obtained by connecting the current circuit via a capacitor to the voltage that supplies the voltage circuit. See diagram B. Certain other phase angles can be obtained by connecting the current and the voltage circuits in different ways in a symmetrical three-phase system. See diagram C.

Diagram A : Connection to a single-phase circuit to obtain 0° phase shift.

The current is approximately in phase with the voltage (phase angle 0° between current and voltage) if the resistance R is 10 times larger than the impedance of the current coil.

Diagram B : Connection to single-phase circuit to obtain 90° phase shift.

The current leads the voltage with approximately 90° if the reactance

Xc = 106. 1 ohms2 p f C

is 10 times larger than the impedance of the current coil (C = the capacitance in mF)

58


Diagram C : Connection to a three-phase system to obtain diffrent phase angles between current and voltage.

Phase angle With the voltage circuit connected to UST, the current

circuit is connected to

90° capacitive R - N60° capacitive R - T30° capacitive N - T0° S - T30° inductive S - N60° inductive S - R90° inductive N - R

Note 1It is presupposed that the three-phase system is symmetrical even with the load connected. This can be checked by for example measuring the three voltages between lines.

59


7.10 RESTRICTED EARTH FAULT PROTECTION

7.10.1 Stability test diagram

- Test successively the stability between each phase and neutral.

7.10.2 Operating test diagram

While carrying out the operation test it's advisable to measure the voltage across the relay coil and also across stabilizing resistor in order to determine the voltage developed by the main current transformer which will make the relay operating.

60


7.11 BUSBAR PROTECTION PRIMARY INJECTION TEST

7.11.1 Stability test

As all the current transformers are connected in parallel it's essential to have the same ratios on each circuit.The best way to check the stability for busbar protection is to check the ratio and the polarity for one bay and to compare it with all the others bays. Primary injection should be carried out through two current transformers. Secondary circulating and differential currents should be recorded for each phase and each bay. With correct ratios and polarities the differential current should be only a few miliamperes.

Stability test diagram

61


7.11.2 Busbar protection operating test

- Primary injection should be carried out on each CT to make sure that all thecurrent transformers are able to pick-up the differential unit.

- In case of multi zone bus protection the test should be performed for differentdisconnecting switches configurations to make sure that the zone selection is working properly.

Operating test diagram

62


7.12 PRINCIPLE TO TEST LONGITUDINAL DIFFERENTIAL PROTECTION

7.12.1 Preliminary test

- check the CT ratio polarity and magnetization curves, both CT on each phaseshould have the same characteristics.

- check the relay by secondary injection

- check the cabling from CT terminals to relay current test box

- make sure that there is only one earthed point at CT secondary circuit

7.12.2 Stability test by primary injection

- by pass the stator phase A winding

- inject a nominal current through the two windings of phase A current transformers

- check the secondary currents at the CT test box. The differential current shouldbe nearly zero mA

- differential relay should not trip

- repeat the test for phase B and C

Stability test diagram

63


7.12.3 Operation test by primary injection

- inject successivly current through each current transformer

- the differential relay should trip

- record primary and secondary currents tripping values

Operation test diagram

We should find the following results

I1 @ Id

I2 very low (transformer magnetization current)

64


7.13 GENERATOR DIFFERENTIAL PROTECTION

Another method to check operation and stability for generator differential protection is to use the machine itself .

A short circuit should be installed on the busbar and the generator excitation should be increased until full load current for stability test or until differential relay trip for operation test.

7.13.1 Test diagram for operation test

Primary current tripping value should be recorded and compared to secondary injection test value.

7.13.2 Test diagram for stability test

During this test, differential current should be measured on each phase. It should be found negligeable.

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7.14 TRANSFORMER DIFFERENTIAL PROTECTION

- the best way to prove the stability of the protection is to proceed by short circuit test on thetransformer.

7.14.1 Testing diagram for stability test

Example

Voltage applied should be £ Ucc

7.5 MVA Ucc = 10 %33 KV / 11 KV D Yn 11

I1N = 131 Amp

I2N = 393 Amp

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7.14.2 Testing method and calculation

- proceed to CT loop test before short circuit test

- make sure there is no more than one earthing point on the CT at the secondarycircuit

- prepare short-circuit busbar at the secondary side of the transformer make surethe busbar section is big enough to carry the short-circuit current (see diagram n°1)

- prepare a three phases power supply at the primary side of the transformer.

7.14.3 Currents calculation for 400 Volts supply

Ucc = 33000 V x 0.1 = 3300 V

For supply 400 V I1cc = 131 x 400 = 15.87 Amp

3300

I2cc = 393 x 400 = 47.63 Amp

3300

Secondary currents I1 = 15.87 x 5 = 0.53 Amp

150

I2 = 47.63 x 5 x Ö3 * = 0.51 Amp (* = delta connection)

800

7.14.4 Test and measurement

- supply the transformer under 400 V 3 phases

- measure the currents I1, I2 and Id at the current test box

Id = I1 - I2 @ 0.02 Amp

- measure the phase angle between primary and secondary current for eachphase. The phase angle should be 180°

- when it's possible apply a voltage near short-circuit voltage (in this case3300 Volts) in order to reach the nominal current. Check that the differential relay doesn't trip.

67


68


7.15 OPERATING TEST BY PRIMARY INJECTION

- repeat the 3 phases voltage injection test with the short-circuit placed before the CT atthe secondary side of the transformer

measure I1, I2, Id

I2 should be near zero mA

We should have I1 = Id

If the primary voltage value is high enough check the relay operating value.

Testing diagram for operating test

69


70


8. MEASURING AND METERING EQUIPMENTS

8.1 CHECK

- gauge correpondance with measuring transformer ratio,

- scale with equipment characteristics.

8.2 TEST

Before energizing

- operation of wattmeters and meters by current and voltage injections from the test boxes(secondary circuit of CT and VT),

- compare the indicated value with that given by a high accuracy equipment class 0,5 afterseveral measures (in principle 3) :

- bottom of the scale (15%)

- middle of the scale (50%)

- top of the scale (85%)

71


9. EARTH RESISTANCE MEASUREMENT

9.1 MEASURE OF GROUND INSULATION

Test voltage : AC supply

P : 250 mm square metallic plate, thickness : 20 mmT : 270 mm square humid piece of linenV : high internal resistance voltmeter (> 3000 ohms) = Rv

If the neutral of the installation is isolated from earth, then connect temporarily to the earth one of the non used phase for measurements.

In a same room, carry out 4 measurements (maximum 1 m from a conductor).Minimum values : 50.000 ohms if U < 500 V

100.000 ohms if U > 500 V (300 V regard to earth)

Results

Check U1 and U2 Rs = Rv U1 / U2 - 1

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9.2 TESTING OF GROUND CONNECTIONS

- check the ground-grid network continuity,

- check the earth loop connection on bar,

- check the different earth connections :

* Steel structure,* Equipments,* Steel supports,* Cable boxes,* Relaying frame,* Boards,* LV motors,* Screen,* LV apparatus frame,

- check the continuity of the earth along cable trays.

9.3 MAX. VALUES OF EARTH CONNECTIONS RESISTANCES

Substation of 2nd class : 500 V < U < 50000 V (C 13100 french standard)

- installation of a substation said "Connected Earth" : R < 1 ohm

- installation of a substation said "Separated Earth" :

. aerial or mixed network : R < 10 ohms

. underground network : R < 3 ohms

73


10. DIELECTRIC TEST

10.1 GENERALITIES

All HV, MV, LV equipments have to be submitted to a dielectric test at the end of the erection,

1. disconnected from cables links.

2. dielectric tests on cables :This test has to be carried out when cable terminations are finished. Test will be carried out under an alternative voltage of Ö3 Uo or under a DC voltage of 4 Uo during 15 mn (HN 33S22 standard from 6 to 30 kV).

NOTA : a oversheat test can be carried out under 7 kV DC voltage or 2 kV AC voltageduring 1 mn.

Remind : specified voltage Uo/UUo : voltage between core and a reference potential, screen or earth.Test voltage is good if there is no breaking, no flashover.

10.2 SAFETY

During the test, it is necessary to ensure safety of persons, so :

- delimit the area where test has to be carried out,

- tests have to be carried out by qualified people,

- discharge the cables after test.

10.3 TEST EQUIPMENT

Use an AC/DC dielectric test set.

74


10.4 METHOD

1) dielectric strength of all circuits regarding the earth (diagram n°1). All CB or interruptorsclosed, test voltage will be applied between one phase, or all phases connected together and the earth.

2) dielectric strength of opening distance (diagram n°2).All circuits being short-circuited downstream of opened CB or interruptors. Test voltage is applied between the three phases connected together and the earth.

3) dielectric strength between phases (diagram n°3).All CB and interruptors are closed, two phases are short circuited and earthed, the test voltage is applied between the 3rd phase and earth. The test will be carried out again by permutation of phases.

In principle :

for LV : use diagrams 1 & 3

for MV : use diagrams 1,2,3

75


10.5 TABLES OF TEST VOLTAGES TO BE APPLIED

(See tables on Annex 1 - 2 and 3)

a) LV values (from UTE C 15 100 Chap. 621 standard)

Insulation nominal voltageU in Volts

Dielectric test voltagein effective Volts (RMS)

U < 60

60 < U < 300

300 < U < 660

660 < U < 800

800 < U < 1000

1000 < U < 1200

1000

2000

2500

3000

3500

3500 *

* only for DC current

At the beginning, test voltage must not be higher than 50 % of the nominal. Then increase it progressively until the specified value in the above table.

This value will be maintained during 1 mn.

b) HV values (from UTE C10100 Chap. 5 standard or IEC 298)

Insulation nominal voltageof equipment in kV

Industrial frequency test voltageduring 1 mn effectif value in kV

3,6

7,2

12

17,5

24

36

52

72,5

1st list *

10

20

28

38

50

70

95

140

2nd list

12

23

32

45

60

80

110

160

* according to equipment, for example :

1st list : circuit breakers,2nd list : disconnecting switches

On site we apply 80 % of the specified value in above table.

76


c) THT values

Voltage 100 to 245 kV

See table III - Norm IEC 294

Nominal VoltageU

kV (RMS value)

Voltage of lightningKv (peak value)

Nominal Voltage at industriel frequency

kV (RMS value)

100380450

150185

123450550

185230

145550650

230275

170650750

275325

2458509501050

360395460

Nominal Voltage equal or higher than 300 kV.

See table IV - Norm IEC 294

Nominal Voltage

UVoltage

kV (RMS value)Breaker in closed position kV

(RMS value)Breaker in opened position kV

(RMS value)

300

362

420

525

765

380

450

520

620

830

435

520

610

760

1100

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11. INSULATION TESTING

11.1 PRINCIPLE

This test consists in measuring the insulation between electrical parts and the earth. The first insulation test has to be done for the links between active conductors (all receptors and the sources being disonnected).

11.2 EQUIPMENT TO BE CHECKED

- LV equipment (50 V < U < 500 V) with 500 V magneto,- MV equipment 5,5 kV with 5000 V magneto,- cables links,- receptors and sensors,- LV circuits.

11.3 PRINCIPLE OF INSULATION MEASURE FOR A LV CIRCUIT

78


Two possibilities :

1. insulation measurement of separate sections,

2. ensure that all intermediate apparatuses are closed, then carry out a global measurement.

11.4 INSULATION VALUES

Low voltage U < 500 volts.According to UTE standards, following values, are allowed : 1000 ohms/volts of the nominal voltage of the installation (C 15100 Chap. 621).

NOTA : Insulation resistance must not be under 250 000 ohms for each section which canbe isolated by a fuse or a cutting device. Insulation measurement will be carried out with a 500 V magneto.

Setting of permanent insulation controller (C15100 Art. 533.4.4)

In normal operation the operating threshold of a permanent insulation controller must be setted at about 20 % lower than insulation resistance of the total installation. This insulation resistance is higher than 1,25 of the maximum value of setting rang of PIC, this one must be setted at that max value.

Sometimes the signalling alarm of the P.I.C can operate, it is not due to a real insulation fault, but due to a decrease of insulation concerning the whole installation. This can appear for example if a part or all the installation has been switched off for a long time, then the insulation has been affected by humidity. In such a case after energizing the complete installation, the insulation will increase above the threshold of the P.I.C.

79


12. MAX RESISTANCE AUTHORISED BETWEEN FRAME AND MAIN EQUIPOTENTIAL EARTHCIRCUIT(extract from C 15100 standard)

TABLE 62 GB

In (A) FUSEPROTECTION (°)

MAIN CIRCUIT BREAKERS

PROTECTION (°°)

SMALL CIRCUITBREAKERS

NOMINAL CURRENT

TYPE U TYPE L

gl aM In (A) (size)

10 1,06 0,59 0,50 14 (15) 0,45 1,0016 0,57 0,37 0,31 15 (17) 0,42 0,9520 0,47 0,29 0,25 20 (22) 0,31 0,7225 0,36 0,24 0,20 25 (28) 0,25 0,5732 0,29 0,18 0,16 32 (35) 0,20 0,4540 0,23 0,15 0,125 38 (42) 0,17 0,3850 0,18 0,12 0,10 47 (52) 0,13 0,3063 0,14 0,09 0,08 60 (65) 0,11 0,2480 0,11 0,075 0,062 75 (82) 0,08 0,19

100 0,08 0,06 0,05 95 (104) 0,07 0,15125 0,065 0,47 0,04 117 (130) 0,05 0,12160 0,051 0,037 0,031200 0,039 0,030 0,025250 0,030 0,024 0,020315 0,023 0,019 0,016400 0,018 0,015 0,012500 0,014 0,012 0,010630 0,009 0,009 0,008800 0,007 0,007 0,0061000 0,005 0,006 0,005

(°) When protected by fuse, those values must be divided by :2. when the conventional voltage is limited at 25 Volts4. when the conventional voltage is limited at 12 Volts, according to standarts (481.1.2) chapter 48.

(°°) Those values has been determined for a ratio between the magnetic threshold and the adjusted current equal to 10.

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13. MEASURE OF STEP AND TOUCH VOLTAGE

13.1 PRINCIPLE

Measurement of voltage (or current) between 2 points or things being 1 meter apart when the earth brings a current.

Then by a simple proportion bring that measure at the value of the real homopolar current fault.

Measuring

Use a voltmeter with great accuracy and with internal resistance equivalent to the body resistance (about 5000 - 10000 ohms).

To ensure ground contact, use square metallic plates of 20 cm.

Measures will be carried out near underground conductors and in substation access areas (fence, transformer room gate...).

Take into account the characteristics of ground (dry, wet, in depth or superficially).

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13.2 METHOD

Injection of a current of 50 A under about 100 to 250 V into the ground-grid network of the substation between main earth of the network and an auxiliary rod.

Diagram

Test equipment used

16 mm2 cable,Ammeter 0-100 A,Voltmeter 0-250 V,Insulation transformer 400 V/250 V - 200 V - 150 V - 100 V about 15 kVA.

E : auxiliary earthing electrode.

To improve the impedance of the injection loop, the auxiliary earthing electrode E can be made of:

1. several electrodes in parallel,

2. the earth of another substation

- earth resistance value : about 1 ohm,- value of injection loop impedance : about 4 to 5 ohms.

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13.3 STEP VOLTAGE MEASUREMENT (Foot to foot contact)

Schematic diagrams

1) Current measurement 2) Voltage measurement

Carry out several measures with Use a voltmeter with a great accuracy and highdifferent resistance of 2000 ohms, internal resistance (5000 to 10000 ohms). 5000 ohms, 10000 ohms The connecting cables of the voltmeter willRecord the corresponding currents. be armoured.

Security

The manpower who carry out the test will be equiped with rubber boots.

Measurement points

- near fence,- far from fence,- entry of substation,- near the close network of the substation,- out of the close network of the substation,- transformer area,- technical gallery (cable trays),- near steel structures of substation.

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13.4 TOUCH VOLTAGE MEASUREMENT (Foot to hand contact)

Schematic diagram

Current measurement Voltage measurement

Carry out several measurements with Use an accurate voltmeter with highdifferent resistances 2000 ohms, 5000 ohms, internal resistance (5000 to 10000 ohms).10000 ohms The connecting cables of the voltmer will beRecord the corresponding currents. armoured.

Safety

The manpower who carry out the test will be equiped with rubber boots.

Measurement points

- between wire netting and earth,- between fence and earth,- between steel structure and earth,- between flight of stairs and earth,- between tap and earth (administrative building),- between machine frame and earth (workshop).

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13.5 CALCULATION OF POTENTIAL GRADIENT

Gp = 0,16 PID2

D Distance from center in meterP Resistivity in ohm / meterI Earth flowing currentGp Gradient in Volt

Earth resistivity (UTE 15.120)

Characteristics of earth Resistivity (ohms / m)

Marshy earth up to 30Limon or silt 20 to 100Humus 10 to 150Moist peat 5 to 100Malleable clay 50Dense clay an marl 100 to 200Clayed sand 50 to 500Siliceous sand 200 to 3000Bare stony ground 1500 to 3000Stony ground with grass 300 to 500Soft chalk 100 to 300Dense chalk 1000 to 5000Spiled chalk 500 to 1000Schist 50 to 300Micaschist 800Granite and sericin according weathering 1500 to 10000Granite and sericin very weathered 100 to 600Rich soils, dense and moist backfillings 50Poor soils, gravel, rouhg backfillings 500Bare stony soils, dry sand, impermeable rocks 3000

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s13.6 CURRENT ALLOWED DURING 1 SECOND (Amperes)

Section

(mm2)

Steel

(67 A / mm2)

Aluminium

(105 A / mm2)

Copper

(160 A / mm2)

16

25

35

50

70

100

200

3 300

4 700

6 700

13 500

2 700

3 700

5 300

7 400

10 500

21 000

2 500

4 000

5 500

8 000

11 500

16 000

32 000

CONCLUSION - RESULTS ANALYSIS

Danger is essentially based on the value of the current crossing through the body, on its crossing duration and on the parts of the body crossed by the current.

The following values have to be kept in mind :

- threshold of sensitiveness : 1 mA,

- threshold of crispation : 10 to 15 mA,

- Cardiac fibrillation : possible at 100 mA,

(for a duration of 1 second).

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The safety will be ensured if the value measured doesn't exceed the values given in the table here under.

Those values are dependant of :

- the time of fault clearance,

- the type of building or room.

TABLE 41.A (EXTRACT FROM STANDARD NF C15 100

WHERE T : MAXIMUM FAULT CLEARANCE TIME IN SECONDS

WHERE UL : SECURITY LIMIT VOLTAGE IN VOLTS)

TIME (s)VALUE OF UL (Volts)

Wet buildings Normal conditions

no limit

5

1

0,5

0,2

0,1

0,05

0,03

0,02

0,01

< 24

25

50

70

110

150

220

280

350

500

<50

50

75

90

110

150

220

280

350

500

Safety

During the above described tests, no personnel should be present on the site.

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14. SEARCH OF FAULTS

14.1 FAULT ON CABLE

14.1.1 Use of an echometer

14.1.2 Voltage drop method

Connect the two cable ends with a very short conductor of large section.

The measured values by V1 and V2 are proportionnal to voltage drop on DCB/Earth or(2L - x) and Earth/A or x, therfore :

V1 = 2L - x Þ V1 = 2L - 1 Þ V1 + 1 = 2LV2 x V2 x V2 x

And V1 + V2 = 2L Þ x = 2LV2V2 x V1 + V2

Characteristics

Cable section : mm2

Resistivity : ohm/kmLength : kmTotal resistance : ohmUsing of battery : V (according to R cable)Using of rheostat : 5 A

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14.1.3 Loop method

Connect the 2 ends of the 2 cables with a cable of large section :

P : Calibrated potentiometera : Potentiometer resistance between D and cursorb : Potentiometer resistance between A and cursor

A = 0 if : a = 2L - x Þ x = 2L . bb x a+b

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14.2 SHORT-CIRCUIT BETWEEN 2 CABLES

Method : connection in Wheaststone bridge

R : resistance in ohm / m of the conductor

1) Measure with bridge between A & D

Measure x = c a = R. 2d Þ d = xb 2R

2) Measure with bridge B & C

It gives a new value d' which locates the default on one section of cable between d and d' enough reduce.

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15. MV 5,5 KV TO 30 KV CIRCUITS. CONTINUITY OF MV CIRCUITS

15.1 METHOD

The test consists to inject successively a current equal to at least 50 % of the nominal current In on each bar (see following scheme).

The measured voltage between the incoming (MV bar) and the out going (cable) must be below 5 Volts.

15.2 SCHEMATIC DIAGRAM FOR THE PHASE TO PHASE TEST

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16. MEASURE OF CONTACT RESISTANCES ON BUSBARS

16.1 METHOD

Test : Inject successively a DC current of 100 A for each phase at level of connections.

16.2 TESTING DIAGRAM

Material : 100 A DC generator ammeter and accurate 100 A shuntmillivolmeter

or use an apparatus with direct reading (micro ohmeter), injection 100 A - 200 A DC current.

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17. CABLES CHECKING

17.1 GENERALITIES

17.1.1 Lineic resistance of cable

R = p L/S

R = resistance in W

p = resistivity in W mm2/m

L = length in meters

For the copper : p = 0,017241 W mm2/m

For the aluminium : p = 0,028264 W mm2/m

17.1.2 Variation of the resistance with the temperature

The resistance of a conductor in DC at the temperature

q (°C) is fonction of the resistance at 20°C by :

Rq = R 20 (1 + µ20 (q - 20))

µ20 = variation coefficient of the resistance at 20°C

for the copper = µ20 = 3,93.10-3

for the aluminium = µ20 = 4,03.10-3

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94


The following table gives the value of the coefficient(1 + µ20 (q - 20) ) fonction of q

qTemperature of conductor

(C°)

(1 + µ20 (q - 20) )

Copper Aluminium05

101520253035404550556065707580859095100

0,9210,9410,9510,9801,0001,0201,0391,0591,0791,0981,1181,1381,1571,1771,1971,2161,2361,2551,2751,2951,314

0,9190,9400,9600,9801,0001,0201,0401,0601,0811,1011,1211,1411,1611,1811,2021,2221,2421,2621,2821,3021,322

17.1.3 Classes of cables (tables entracted from SILEC book, 1984)

- Cores of conductors and rigid cables for firm installation

- Class 1 = solid conductors

- Class 2 = stranded conductors

- Cores of conductors and flexible cables ; classes 5 and 6.According to the flexibility level, the standart gives for each nominal section, the minimal quantity of consecutive wires (rigid cores) or the maximal diameter of these wires (flexible cores).

The nominal sections defined don't constitute strict geometrical values.It is the value of the lineic resistance of the core cable in DC current at 20°C, which is a rule fonction of the nominal section and the flexibility level required.The followings tables, show the nominal sections for each class of flexibility, the compositions and the corresponding lineic resistances.

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CLASS 1

SOLID CORE IN COPPER AND ALUMINIUM

FOR SINGLE AND MULTICONDUCTORS CABLES

Maximum lineic resistance at 20°CNominal Cores in copper circular section Circular cores or sectoralsection Untinned wires Tinned wires section in aluminium

mm2 W/km W/km W/km

0,5

0,75

1

1,5

2,5

4

6

10

16

25

35

50

70

95

120

150

185

240

300

36,0

24,5

18,1

12,1

7,41

4,61

3,08

1,83

1,15

0,727

0,524

0,387

0,268

0,193

0,153

0,124

__

__

__

36,7

24,8

18,2

12,2

7,56

4,70

3,11

1,84

1,16

__

__

__

__

__

__

__

__

__

__

__

__

__

18,1

12,1

7,41

4,61

3,08

1,91

1,20

0,868

0,641

0,443

0,320

0,253

0,206

0,164

0,125

0,100

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CLASS 2

STRANDED CORES IN COPPER AND ALUMINIUM


Nominal Minimal number of wires Maximum resistance at 20°CSection Circular Circular Sectoral Copper core Aluminium

mm2 core core core Untinned Tinned core

unannealed unannealed wires wires

mm2 Cu Al Cu Al Cu Al W/km W/km W/km

0,50,75

11,52,546

101625355070951201501852403004005006308001000

77777777777

19191937373761616161919191

__________777777

19191937373761616161919191

______666666666

121518183034345353535353

________________6666

121515153030305353535353

__________________666

12151818303434535353____

__________________666

12151515303030535353____

36,024,518,112,17,414,613,081,831,150,7270,5240,3870,2680,1930,1530,124

0,09910,07540,06010,04700,03660,02830,02210,0176

36,724,818,212,27,564,703,111,841,160,7340,5290,3910,2700,1950,1540,1260,100

0,07620,06070,04750,03690,02860,02240,0177

__________

7,414,613,081,911,200,8680,6410,4430,3200,2530,2060,1640,1250,1000,07780,06050,04690,03670,0291

1200(1 400) (2)

1 600(1 800) (2)

2 000

(1)(1)(1)(1)(1)

(1)(1)(1)(1)(1)

__________

0,01510,01290,01130,01010,0090

0,02470,02120,01860,01650,0149

(1) minimal number of wires unspecified

(2) sections into brackets are not preferentials

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CLASS 5FLEXIBLE CORES IN COPPER


Nominal Maximal Max lineic resistance at 20°Csection diameter of wires Untinned wires Tinned wires

mm2 mm W/km W/km

0,50,75

11,52,54610162535507095120150185240300400500630

0,210,210,210,260,260,310,310,410,410,410,410,410,510,510,510,510,510,510,510,510,610,61

39,026,019,513,37,984,953,301,911,210,7800,5540,3860,2720,2060,1610,1290,1060,08010,06410,04860,03840,0287

40,126,720,013,78,215,093,391,951,240,7950,5650,3930,2770,2100,1640,1320,1080,08170,06540,04950,03910,0292

CLASS 6FLEXIBLE CORES IN COPPER


Nominal Maximal Max lineic resistance at 20°Csection diameter of wires Untinned wires Tinned wires

mm2 mm W/km W/km

0,50,75

11,52,54610162535507095120150185240300

0,160,160,160,160,160,160,210,210,210,210,210,310,310,310,310,310,410,410,41

39,026,019,513,37,984,953,301,911,210,7800,5540,3860,2720,2060,1610,1290,1060,08010,0641

40,126,720,013,78,215,093,391,951,240,7950,5650,3930,2770,2100,1640,1320,1080,08170,0654

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17.2 MV CABLES (NOMINAL VOLTAGE 6-30 KV)

17.2.1 General visual inspection

Cable laying : joinedunjoinedover loadedtightened

Conformity of terminalsearthing

17.2.2 Checking

- terminals at each end

- marking

- continuity

17.2.3 Insulation

Before the final connection of the cable on both ends, it is necessary to check the insulation with a 5 kV Megger tester.

1) between each conductor and screen connected to the earth

2) between one conductor and the others connected together and to the earth.

17.2.4 Testing scheme

100



This test must be done only when the complete installation of the cable and accessories has been finished (including the ends of cables). The test will be done under an alternative voltage of Ö3Uo or a DC voltage of 4Uo during 15 mn.

Method : disconnect the cable on both ends, apply a voltage between theconductor and the screen connected to the earth, the other conductors also connected to the earth. Repeat the same test for each conductor by circular permutation.

OVERSHEATH TEST

Test done by applying a DC voltage of 7 Kv or on AC voltage of 2 Kv during 1 mn between the conductor and the external part of the sheath.

17.2.6 Testing diagram :

101


17.3 LV CABLES (50 V £ U £ 500 V)

17.3.1 General visual inspection

- Cable laying : joinedunjoinedoverloadedtinghtened

- Conformity of terminals

17.3.2 Checking

- terminals at each end- marking- continuity

17.3.3 Insulation

Before the final connection of the cable on both ends, it is necessary to check the insulation with a 500 V Megger tester.

1) between each conductor and earth2) between one conductor and the others connected together and to the earth.

17.3.4 Testing diagram

102



This test must be done only when the complete installation of the cable and accessories has been finished (including the ends of cables). The test will be done under an alternative voltage of 2 Uo + 1 kV at industrial frequency during 1 minute.

Method : Disconnect the cable on both ends, apply a voltage between the othersconnected to the earth. Repeat the same test for each conductor by circular permutation.

17.3.6 Over sheath test

Tests done by applying a DC voltage of 7 Kv or an AC voltage of 2 Kv during 1 mn between the conductor and the external part of the sheath.

Testing diagram :

17.4 CONTROL COMMAND CABLES

17.4.1 Checking


- marking (cables and wires)

- the way of laying : a distance must be respected between power cable traysand main control cable trays (around 1 foot, or 200 mm following the technical specification).

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17.4.2 Continuity

- ensure that no wires has been cut

- ensure that the good cable is at the right place

Method : By short circuiting each wire to earth successively (or wire 1 and 2, 1 and3...) at one end and checking at the other end that the signal is there (pulse, bell). See diagram on the following page.

17.4.3 Insulation

Before final connection on both ends, it is necessary to check with a 500 V Megger the insulation between :

- wire 1 and the others connected together and to the earth,


- and so on until the last wire,

Do it like that by permutation according to the number of wires.

17.4.4 Testing diagram :

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17.5 INSTRUMENTATION CABLES

17.5.1 Generalities

Cables carrying mA or mV.

In order to avoid interferences, these type of cables are usually screened.

- by pair,

- by multipair (general screen).

If is necessary to check that the complet circuit has been connected to the earth in accordance with the specification of the drawing office.

Example of a classic installation diagram :

105


17.5.2 Checking


- marking of cable and wires

- the way of laying : a distance must be respected between power cable trays andinstrumentation cable trays (around 2 feet or 400 mm following the technical specification).

17.5.3 Continuity

- ensure that no wires have been cut,

- ensure that the good cables are at the right place.

Method : by short circuiting each wire to earth successively (or wire 1 and 2, 1 and3 ...) at one end and checking at the other end that the signal is there (pulse, bell). See on the following diagram.

17.5.4 Insulation

Before final connection on both ends, it is necessary to check with a 100 V megger the insulation between :


- wire 2 and the others connected together and to the earth.

- and so on until the last wire

Do it like that by permutation according to the number of wires.

17.5.5 Testing diagram

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17.5.6 Cable resistance

Checking of the global loop resistance. This resistance must be lower than the value given by the constructor of the regulating device.

107


18. ON LOAD TEST

After the start up of equipments, it is necessary to check the correct operation of the apparatus.For each circuit the following points must be checked according to the effective load :

- Currents,- Voltage,- consumption,- Working conditions for diesels and motors for example.

During the tests, the operating values must be recorded as well as the test conditions like (temperature, humidity ...).

18.1 EHV, HV, MV, LV FEEDERS

Check and record the following values :

- Voltages phase to neutral, and phase to phase,- Currents for each phase and the neutral,- Power factor of the installation,- Transited power.

Check the compatibility.

18.2 TRANSFORMER OUTGOING FEEDERS

Check and record the following points :

- Primary voltages phase to neutral, and phase to phase.- Secondary voltages phase to neutral, and phase to phase.- Primary currents for each phase and neutral.- Secondary currents for each phase and neutral.- Voltage and currents without load, during the switching of transformer.- The power factor of the installation.- Transited power.- Oil and winding temperatures.

Check the compatibility

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18.3 MOTOR FEEDERS


- Voltages phase to neutral, phase to phase (with and without load).- Currents for each phase and neutral (with and without load).- Currents and voltages during the starting up of the motor (with and without load).- Starting times (with and without load).- Power used (with and without load).- Winding temperature.- Rotation speed.- Different pressures (according to the hydraulic command).


18.4 DIESEL ENGINE INCOMING


- Voltages phase to neutral, and phase to phase- Currents for each phase and neutral- Currents and voltage during switching of circuit breaker- Frequency- Transited powers- Power factor- Rotation speed- Temperatures of generator- Fuel consumption


109


19. IEC NORMS

IEC 52 Recommendations for voltage measurement by means of sphere-gaps (one sphereearthed)

IEC 55 Paper insulated metal shealted cables for rated voltages up to 18/30 kV

IEC 56 High voltage alternating current circuit breaker (frequencies £ 60 Hz)

IEC 70 Power capacitors

IEC 71 Insulation co-ordination

IEC 76 Power transformers

IEC 99 Surge arresters

IEC 141 Tests on oil-filled and gaz pressure cable and accessories (voltages £ 400 kV)

IEC 156 Determination of electric strength for insulating oils

IEC 157 Low voltage switchgear and controlgear (= IEC 947.2)

IEC 185 Current transformers

IEC 186 Voltage transformers

IEC 245 Rubber insulated cables of rated voltages up to and including 450/750 V

IEC 254 Lead-acid traction batteries

IEC 255 Electrical relays. Contact performance of electrical relays.

IEC 298 AC metal enclosed switchgear and controlgear for rated voltages between 1 kv andup to and including 52 kV.

IEC 353 Line traps

IEC 364 Electrical installation of buildings

IEC 408 Low voltage switches

IEC 439 Low voltage switchgear and controlgear assemblies.

IEC 502 Extruded solid dielectric insulated power cables for rated voltages between 1 kV up to30 kV

IEC 517 Gas insulated metal-enclosed switchgear for rated voltages of 72,5 kV and above.

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checking - site tests - energizing

Documents

continuity test

phase test

test sheets

ehv dielectric test

torque test

protection equipment

electrical tests

annex annex annex annex