Testing and Commissioning Instrument-Transformers

7/28/2019 Testing and Commissioning Instrument-Transformers

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TESTING INSTRUMENT

TRANSFORMERS

CT Testing

Primary Insulation

Resistance

Dielectric Withstand Secondary Insulation

Resistance

Secondary Burden

Saturation Ratio and Polarity

Primary Ins. Resistance Test

For Bar and Primary wound

CTs

DC voltage test at the ratedcrest voltage on the primary

winding

Secondary grounded

1 minute test


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TESTING INSTRUMENT

TRANSFORMERSCT Insulation Resistance: Bar Type and Primary Wound

DC Voltage test

Isolate Primary

Isolate & Gnd Secondary

Connect HV lead to H1/H2

Connect LV to Gnd /

2ndary

Test for 1 minute Record test value


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TESTING INSTRUMENT

TRANSFORMERS

CT Testing

Primary Insulation

Resistance


Resistance

Secondary Burden


Dielectric Withstand Test

For Bar and Primary wound

CTs

AC voltage test at the 75%factory test voltage

Secondary grounded

1 minute test


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TESTING INSTRUMENT

TRANSFORMERSCT Dielectric Withstand: Bar Type and Primary Wound

AC Voltage test

Isolate & Gnd Secondary

Connect HV lead to H1/H2

Connect LV to Gnd /

2ndary

Test for 1 minute

Record test value


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TESTING INSTRUMENT

TRANSFORMERS

CT Testing

Primary Insulation

Resistance


Resistance

Secondary Burden


2ndary Ins. Resistance Test

Test for secondary wiring

Secondary wiring isolated

and ungrounded 1000 VDC

1 minute test


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TESTING INSTRUMENT

TRANSFORMERSCT Secondary Circuit Insulation Test


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TESTING INSTRUMENT

TRANSFORMERS

CT Testing

Primary Insulation

Resistance


Resistance

Secondary Burden


2ndary Burden Test

Conducted in 2 parts

Part 1, 1A current injection

Measure circuit burden Part 2, four-wire resistance

measurement

Measure secondary

winding resistance Burden = part 1 + part 2


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TESTING INSTRUMENT

TRANSFORMERSPart 1: CT Secondary Circuit Burden Measurement


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TESTING INSTRUMENT

TRANSFORMERSPart 2: CT Secondary Winding Resistance Measurement


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TESTING INSTRUMENT

TRANSFORMERS

Total burden calculation

ZT = RCT + (RL + ZB)

WhereZT = Total burden ()

RCT = DC Winding resistance ()

RL = Lead resistance ()ZB = Device impedance ()


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TESTING INSTRUMENT

TRANSFORMERS

CT Testing

Primary Insulation

Resistance


Resistance

Secondary Burden


Saturation Test

Secondary winding excitation

test

Primary open circuited Step voltage increase,

current proportional

Test for knee-point voltage

Rapid rise is I-excitation 10% V = 50% I


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TESTING INSTRUMENT

TRANSFORMERSCT Saturation test


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TESTING INSTRUMENT

TRANSFORMERS

CT Testing

Primary Insulation

Resistance


Resistance

Secondary Burden


Ratio and Polarity test

Secondary winding excited at

1V per turn

Primary open circuited H1-H2 compared to X1-X2

Phase measured, ratio

calculated

Phase difference 0 meanspolarity correct


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TESTING INSTRUMENT

TRANSFORMERSCT Ratio and Polarity Test


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TESTING INSTRUMENT

TRANSFORMERS

CT Testing

Primary Insulation

Resistance


Resistance

Secondary Burden


Ratio and Polarity test (ALT)

Use individual meters, phase

angle and voltmeter

Secondary winding excited at1V per turn

Primary open circuited

H1-H2 compared to X1-X2

Phase measured, ratiocalculated

Phase difference 0 means

polarity correct


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TESTING INSTRUMENT

TRANSFORMERSCT Ratio and Polarity Test (alternate connections)


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TESTING INSTRUMENT

TRANSFORMERS

VT Testing

Insulation Resistance

Dielectric Withstand

Ratio and Polarity


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TESTING INSTRUMENT

TRANSFORMERS

VT Testing



Ratio and Polarity

Insulation Resistance Test

DC voltage test at the rated

crest voltage

3 tests HV to Gnd

HV to LV

LV to Gnd


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TESTING INSTRUMENT

TRANSFORMERSVT Insulation Resistance Tests


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TESTING INSTRUMENT

TRANSFORMERS

VT Testing



Ratio and Polarity

Dielectric Withstand Test

AC voltage test at the 75%

factory test voltage

Secondary grounded 1 minute test


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TESTING INSTRUMENT

TRANSFORMERSVT Dielectric Withstand Tests


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TESTING INSTRUMENT

TRANSFORMERS

VT Testing



Ratio and Polarity

Ratio and Polarity test

Primary winding excited at

1V per turns ratio

Secondary open circuited X1-X2 compared to H1-H2

Phase measured, ratio

calculated

Phase difference 0 meanspolarity correct

Compare ratio with

nameplate


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NETA STANDARD

5. NETA Acceptance Testing Procedure

5.1 Visual and Mechanical Inspection

5.2 Electrical Test 5.2.1 Current Transformer

5.2.2 Voltage Transformer

5.3 Test Value Analysis 5.3.1 Visual and Mechanical

5.3.2 CT Electrical Test

5.3.3 VT Electrical Test


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TEST SET MANUAL

Module 3:

CT Tester

Module 2:

15 KV Insulation Resistance Test set

AC High Potential Test set

DC High Potential Test set

Digital Low Resistance Test set


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TEST FORMS

Current Transformer Test Form

Voltage Transformer Test Form


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Documents

Testing and Commissioning Instrument-Transformers