Instrument Xmers - TESTING

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PTHV-IT, INABB

A/D conversion

Computer

Rb

METER

O/P

CVT CT

Instrument

TransformersProduct Training



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CT – Routine Tests

Tests as per IEC: 60044-1 and IS: 2705

Verification of Terminal Markings and Polarity

Power Frequency Withstand Test on Primary andSecondary

Partial Discharge Measurement

Inter-turn Over Voltage Test

Determination of Errors



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Tests as per IEC: 60044-1 and IS: 2705

Short Time Current Test

Temperature Rise Test

Lightning Impulse Test

Switching Impulse Test

Radio Interference Voltage Test

Determination of Errors

Facilities for conducting all Type Tests on CTs except ShortTime current Test (ERDA / CPRI) and Seismic test (IITChennai / University of Roorkee) are available at our works.

CT – Type Tests



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Tests as per IEC: 60044-1/ IS: 2705

Chopped Lightning Impulse Test

Measurement of Capacitance and Dielectric DissipationFactor

Multiple Chopped Impulse Test on Primary

Special tests as prescribed in CIGRE have also beenconducted

CT – Special Tests



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Figure: 1 Simple vector diagram for loss factor test

Test Setup:

V = Applied voltage

IT = Total current

IR = Resistive current

IC = Capacitive current

Dissipation factor = tangent δδδδ= IR/IC

Power factor = cosine θθθθ= IR/IT

H. V. Line

C4

R3

Test Object

R4

b

a

d

c

RX

CX

C1

D

D=Zero balance indicatorC1=Standard CapacitanceC4=Variable CapacitanceR3= Variable Resistance

Figure:2- Simple Schering bridge

Figure: 3- Test Set up for Capacitance & tandelta test

650V/750kV,

0-250V



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In case of cores it may bethe artificial primary

Figure: 1- Ratio and Phase angle measurement setup



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1.6.1 Test Setup



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TEST CERTIFICATE FOR CURRENT TRANSFORMER

Test Report No. CT/2008374 Date : 30/06/2008

CLIENT

CLIENT'S ORDER NO/LOA NO : 3191054331 DTD. 12-01-2008

WORK ORDER NO. 4200018667/30

DATE OF TESTING 30/06/2008

SPECIFICATION OF CURRENT TRANSFORMER

Sr. Nos. : 1108163

QTY. 01 No.

TYPE IMB 145

HIGHEST SYSTEM VOLTAGE 145 kV

RATED INSULATION LEVEL 145/275/650 kVRATED SHORT TIME THERMAL CURRENT: 40 kA, 3 Sec.

RATED PRIMARY NORMAL CURRENT: 1200 A

RATED CONTINUOUS THERMAL CURRENT: RATED PRI X 1.2

FREQUENCY 50 HZ

CORE :1 CORE : 2 & 3 CORE : 4

RATIO (AMP) 1200/1 1200/1 1200/1

BURDEN (VA) 50 -- 20

CLASS 0.2 PS 5P

ISF < 10 -- --

ALF -- -- 20

Vk (VOLTS) -- > 500 --

Io (mA) -- < 100 AT VK --RCT(OHMS) -- < 5 --

1.1 VERIFICATION OF TERMINAL MARKING & POLARITY TEST O.K. AS PER REF. STANDARDS

275 kV FOR 1 MINUTE : O.K.

5 kV FOR 1 MINUTE : O.K.

For ABB Ltd.

VIMAL PANDYA/S.R.SHAH

PTHV- IT-TESTING

STANDARD FOLLOWED : IS 2705/IEC 60044-1

THIS IS TO CERTIFY THAT THE ABOVE CURRENT TRANSFORMERS HAVE PASSED THE ROUTINE TESTS AS

PER IEC: 60044-1 & IS : 2705

1.3 PARTIAL DISCHARGE MEASUREMENT

1.4 POWER-FREQUENCY VOLTAGE WITHSTAND TEST ONSECONDARY WINDINGS ( All windings were tested individually )

1.5 INTER-TURN OVER VOLTAGE TEST O.K. AS PER REF. STANDARDS

1.2 POWER-FREQUENCY VOLTAGE WITHSTAND TEST ON

PRIMARY WINDING

5 pC AT 1.2 UM/ √3 & 10 pC AT UM

1.7 SEALING TEST (VISUAL) NO LEAKAGE OBSERVED

1.6 TURNS RATIO ERROR ( As per formula given in standard ) O.K. AS PER REF. STANDARDS



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Test Report No. CT/2008374 Limits

CT Sr.No. 1108163

2.0 Current error and phase angle error & TRE measurement PS cores

Ratio = 1200/1

Core Ratio Ph.Angle Ratio Ph.Angle TRE Rct (Ohm) Rct at 75°C

No. Error ( % ) Error(min.) Error ( % ) Error(min.) (%) at 32°C (Ohm) Ratio

AT 0 VA AT 10 VA (UPF) 32

2 0.00 0.20 -0.02 1.10 -0.015 6.30 7.317 1200/1 12

3 0.00 0.20 -0.02 0.80 -0.015 6.40 7.433 1200/1 12

2.0 Current error and phase angle error measurement for Protection core.

Core Primary Ratio Ph.Angle Ratio Ph.Angle Rct (Ohm) Rct at 75°C

No. current Error ( % ) Error(min.) Error ( % ) Error(min.) at 32°C (Ohm) Ratio

AT 50 VA 0.8 lag AT 12.5 VA 0.8 lag

1 60 -0.20 2.30 -0.06 1.00 4.40 5.807 800/1

1 240 -0.12 -0.10 -0.04 0.00

1 1200 -0.05 -1.40 -0.02 -0.50

1 1440 -0.06 -1.00 -0.02 -0.50

AT 50 VA 0.8 lag -- --

4 1200 -0.05 0.50 -- -- 9.00 10.452 1200/1

3.0 Knee point voltage ,Exciting current,composite error Test

Core Sec.Wdg. c t at 75°C Voltage Exc.current Remarks limit exc .

No. Terminals (ohm) ( Volts) mA Curr.(mA)

2 2S1-2S2 500 8.0 Vk> 500 <100 100

577 9.0

635 10.0

3 3S1-3S2 500 8.0 Vk> 500 <100 100

577 9.0

635 10.0

ISF Burden Sec.current Spec.ISF

1 1S1-1S2 5.807 113.0 > 1.0 2.025 50 1 < 10

Amp. C.E.% Burden Sec.current Spec.A.L.F.

4 4S1-4S2 1182 0.0110 0.055 50 1 20



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The values of knee pointvoltage and excitingcurrent shall be asguaranteed.

With the pri. open, the CT sec. will be excited ata voltage meant for measuring the excitingcurrent and the exciting current shall be lessthan the specified limit.

Then the sec. will be excited at rated Vk andcurrent is to be measured. This voltage will beincreased by 10% and again the current is to bemeasured. Increment in current should not be50% of the earlier value.

IS:2705 (PartIV) Cl. 6.1

11.0Measurementof Knee pointVoltage andexciting current

The Turns ratio error shallbe within ± 0.25 % or withinlimits specified in IS : 2705.

The error will be measured at 0VA and at 10 VAburden, having a power factor of 0.8 or unity.Turns ratio error will be calculated by thefollowing formula :

TRE=y[(A+R)/(B-A)]-x[1+(A+R)/(B-A)]

y = current error at 10 VA

A =0

R = Resistance of secondary winding

B = 10

x = current error at 0 burden

IS:2705 (Part-IV) Cl. 6.3

10.Turns Ratiotests forProtectionCore Cl. PS

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Rate

d

Volta

ge

(kV

rms)

Highest

System

Voltage

(kV rms)

One min. PF

withstand

Test Voltage

(kV rms)

PD Prestress

Voltage for

one min.

(IEC:60044-

1)

(kV rms)

PD

Measuring

Voltage for

30 sec ( for

two voltage

levels)

(kV rms)

PD Levels

in pC

CT Primary

Contact

Resistance

Capacitance Value in pF

66 72.5 140 11250

72.5

< 5

< 10

950 ± 15 %, (N-100),Alu

1500 ± 15% N, Cu,Dia

68/42

110 123 230 18485

123

< 5

< 10

132 145 275 220

100.5

145< 5

< 10

850 ± 15% N, Alu Sp.

1025 ± 15% N,Alu

1100 ± 15%N+200,Cu

1165 ± 15%N+200,Alu

1510 ± 15% N,Alu,Dia68/42

1465 ± 15% N,Cu,Dia 68/42

220 245 460 368

170

245

< 5

< 10

1110 ± 15% N ,Cu

1135 ± 15% N ,Alu

1225 ± 15% N+200 ,Cu

1250 ± 15% N+200 Alu

Pl refer Table

1 or

Annexure - 1

of instruction

1HYT600070

1175 ± 15 % for IMB 420

1250 ± 15 % for IMB 420Oval Conductor CT400 420 630 504

291

420291

420

< 5

< 10< 5

< 10125

maximum

700 ± 10% for TMBR l 420

CT



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CVT – Construction – EMU

HV Choke

PT

Bottom Tank

F R C i

r c u i t Resistor

Capacitor

FR Choke



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Step Down PT

HV Choke

C1

C2

V2

V1

Vs

FR CktResistor

Spark Gap

Sealed UnitProtects the EMU

from overvoltages

CVT - Schematic

I

mp

FR CktCharacteristic

Freq50



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WITNESS TEST REPORT FOR CVT

INSPECTION CALL NO:-

CLIENT : POWERGRID CORPORATION OF INDIA LTD.

WORKS ORDER NO. : 4200035285/10CLIENT ORDER NO. : ----

SUBSTATION : MAHARANIBAUG GIS

DATE OF TESTING : 29/06/2008

SPECIFICATIONS

Type : WS420N2

Rated Primary Voltage : 400/ √3 kVHighest System Voltage : 420 kVNominal Capacitance : 4400 pF + 10 % & - 5 %

Rated Insulation Level : 420/630/1425 kV Frequency : 50 HzSerial no. : 4208075Qty : 01 Nos.

No. of Secondaries : 3

Standards Applicable : IEC 60186, IS 3156

Rated Sec. Voltage

(volts)

Terminal marking Rated Burden (VA) Accuracy

Class

110 / √ 3 1a-1n 50 3P

110 / √ 3 2a-2n 50 3P110 / √ 3 3a-3n 50 0.2

100 0.2SIMULTANEOUS

BURDENS 150 3P

1.0 All the Capacitor Voltage Transformers have passed the following Routine tests.

1.1 Induced over voltage test on P.T. at 46 kV,150 Hz for 1 min : O.K.

1.2 Induced voltage test on choke at 10 kV, 150 Hz for 1 min : O.K.1.3 Voltage withstand test on secondary winding at 3 kV, 50 Hz for 1 min : O.K.

1.4 Verification of terminal marking & Polarity test : O.K.1.5 Sealing test : No leakage found at various sealing joints.

1.6 HV Test on earth terminal of CVD / HF Bushing at 10 kV for 1 min. : O.K.

For ABB Ltd. Witnessed by

VIMAL PANDYA/S.R.SHAH AJAY DINKAR

PTHV- IT-TESTING PGCIL , VADODARA



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2. Capacitance and Tan delta Measurement Test :

Sr. No. Capacitance(pF)

Tan delta(%)

H.V. withstandtest at 220.5 kV

for 1min.

Capacitance(pF)

Tan delta(%)

CVT SR. NO. 4208075

BEFORE H.V AFTER H.V

Unit 1- 73.0kV80.8 kV88.9 Kv

131561315613156

0.0770.0770.077

OK 131551315513155

0.0760.0760.077

Unit 2-73.0 kV80.8 kV88.9 Kv

131541315413154

0.0780.0780.078

OK 131541315413154

0.0770.0770.077

Unit 3-73.0 kV80.8 kV88.9 kV

131111311113111

0.0790.0790.079

OK 131101311013110

0.0780.0780.078

3.0 Partial Discharge TestPre-stress voltage = 0.8*630*1/3*1.05= 176.4kV for 60 sec.Measuring voltage MV-1 = Um*1/3*1.05=147 kV for 30 sec.

Measuring voltage MV-2 = 1.2*Um/ √ 3*1/3*1.05=102.0 kV for 30 sec.

Sr. No. Voltage

Level

Unit-1 Unit-2 Unit-3 Limit in Pc

M.V. -1 1 pC 1 pC 1 pC ≤ 104208075

M.V. -2 1 pC 1 pC 1 Pc ≤ 5

4.0 Accuracy measurement as a function of voltage and burden:

CVT SR. NO. 4208075

Voltage(%)

WindingUnderTest

Burden VA 0.8 lag VoltageError

(%)

PhaseAngle error(min.)

Frequency(Hz )

Wdg.1 Wdg.2 Wdg.3100 1a – 1n 12.5 0 0 0.56 0.9 50.00

100 1a – 1n 50 0 0 0.50 0.9 50.00100 1a – 1n 50 50 50 0.38 6.9 50.00

100 2a – 2n 0 12.5 0 0.46 6.9 50.00

100 2a – 2n 0 50 0 0.50 6.9 50.00100 2a – 2n 50 50 50 0.36 6.9 50.00

100 3a – 3n 0 0 12.5 0.11 6.9 50.00

100 3a – 3n 0 0 50 -0.02 6.9 50.00

100 3a – 3n 12.5 12.5 50 -0.05 4.9 50.00



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~

Care for CTs and CVTs

Incase of saturation of CT core during fault, they arerequired to be Demagnetized in order to let them performaccurately after the fault is cleared. The following method

may be adopted

Gradually excite the core upto its Output Voltage andreduce it to zero.

Repeat it 3 – 4 times. This will make the core free ofResidual flux and it is now ready to function as desired.



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The change in capacitance value

between before & after HV test shall

not be more than that caused by

failure of 1/3rd element of the

capacitor coil. Pl refer Annexure –II

for detailed values of capacitance.

Simillarly the change in Tan Delta

value shall not be more than 0.001(in

abs. value).+

Same as mentioned in 2 aboveIEC:358

Cl. 7 & 8/ IS:9348

Cl. 8.3

5. Capacitance &Tan Delta after HV

test

No puncture or flash over should occur.4/10 kV will be applied between theearth terminal ( Outdoor HF Bushing )and the tank and will be maintainedfor 1 minute. (4 kV in case ofenclosed CVT Terminal)

IEC:358 Cl. 10/ IS:9348 Cl. 8.54. Voltagewithstand test onearth terminal ofCVD

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Sr No Permissible changein values of

Capacitance (

Before And After

HV Test )

400kV (Total 3 capacitorunits) 245kV( Total 2

capacitor

units)

145kV ( onecapacitor unit) 66kV( one capacitor

unit)

1 Rated Capacitanceof CVT

4400pF 8800pF 6600pF 4400pF 5500pF 4400pF

2 Permissible increase

in Capacitance**

124pF 78pF* 165pF 70pF 34pF 37pF

* A failure inside the capacitor element or coil will increase the capacitance of the capacitor unit.Value for complete CVT

** A failure inside the capacitor element or coil will increase the capacitance of the capacitor unit.

Value for individual unit of CVT.

Note: 1

In case of 220 and 400 kV CVTs, if the test is made on one capacitor stack, then the applied voltage per stack will be calculated as

Voltage to be applied on stack = 1.05 x Voltage to be applied per unit x (Rated voltage of stack/Rated voltage of unit)



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