TRNG-6 Potential Transformer

Doble Testing Potential Transformers ( PT’s ) Bob Sarni Doble Engineering Company

Doble Engineering Company

85 Walnut Street, Watertown, MA 02472

Potential Transformers (PTs) H1

Isurface

Secondary Windings Not Shown

H0

Cascade Type Doble Testing Potential Transformers

2


CHX

CH

CHY H0 Doble Testing Potential Transformers

X1 X2 X3 Y1 Y2 Y3 Line To Ground PT 3


H2

CH1

CHX

CH2 X1 X2 X3

CHY

Y1 Y2 Y3

Line To Line PT Doble Testing Potential Transformers

4

Recommended Test Voltage Liquid-Filled Line-to-Line PTs Rated Below 15 kV Insulation Class PT Voltage Rating 7.2 to 8.7 4.2 to 5.0 2.4

Test Voltage (kV) 5.0 2.5 2.0

*For Units Rated 15 kV and Above, Perform Tests at 10 kV

Doble Testing Potential Transformers

5

Recommended Test Voltage Liquid-Filled Line-to-Ground PTs a) Perform Test At the Rated Voltage of the Neutral Bushing b) Cross-Check Tests are Performed at 10 kV or at Rated Line-toGround Voltage, Whichever is Lower


6

Recommended Test Voltage Dry-Type Line-to-Line PTs Rated Below 15 kV Insulation Class PT Voltage Rating Test Voltage (kV) Overall a. 2 kV b. Line-to-Ground Voltage* c. 10% to 25% Above Line-to-Ground operating Voltage Cross-Check

a. 2 kV b. Line-to-Ground Operating Voltage

Exciting Current

a. Line-to-Ground Operating Voltage

*Note: Power Factor Tip Up Test Doble Testing Potential Transformers

7

Recommended Test Voltage Dry-Type Line-to-Ground PTs Rated Below 15 kV Insulation Class •Perform Test at a Voltage Not to Exceed the Neutral Bushing Rating as Outlined in Previous Section

•Cross-Checks are Performed at 10 kV or Rated Line-to-Ground Voltage, Whichever is Lower •For Units Rated Above 15 kV, Perform Tests at 2 and 10 kV to Determine Tip-Up Value


8

Test Procedure - Single Phase - P T Test No. 1

Test Mode Energize Ground GST H1, H2 X1,Y1

Guard UST -

Test Description Overall

2

GST

H1

X1Y1

H2

-

H1 Cross Check

3

GST

H2

X1Y1

H1

-

H2 Cross-Check

4

UST

H1

X1Y1

-

H2

Excitation H1 to H2

5

UST

H2

X1Y1

-

H1

Excitation H2 to H1

6

Supplementary Hot-Collar tests on the primary line-terminal bushings


9

Test Procedure - Single Phase - P T Test #1 : GST Ground - No LV Lead Required Measure: CH1+CHX+CHY+CH2 H0

H1

HV Lead

CH1

CHX

CH2 X1 X2 X3

CHY Y1 Y2 Y3


10

Test Procedure - Single Phase - P T Test #2: GST-Guard (Cross-Check Test #1) •Measure: CH1+ 1/2CHX + 1/2CHY H1

HV Lead

CH1

H0

CHX

LV Lead

CH2 X1 X2 X3

CHY

Y1 Y2 Y3


11

Test Procedure - Single Phase - P T Test #3: GST-Guard (Cross-Check Test #2) •Measure: CH2+ 1/2CHX + 1/2CHY LV Lead

CH1

H1

H0

CHX

HV Lead

CH2 X1 X2 X3

CHY

Y1 Y2 Y3


12

Test Procedure - Single Phase - P T Test #4: Ungrounded Specimen Test (UST) Measure: Excitation Current H1

HV Lead

CH1

H0

CHX

LV Lead

CH2 X1 X2 X3

CHY

Y1 Y2 Y3


13

Test Procedure - Single Phase - P T Test #5: Ungrounded Specimen Test (UST) Measure: Excitation Current LV Lead

CH1

H1

H0

CHX

HV Lead

CH2 X1 X2 X3

CHY

Y1 Y2 Y3


14

Supplementary Tests - Single-Phase P T Test No. 6

Test Mode UST

Energize H1, H2

Ground Yn

Guard -

UST Xn

Test Description CHX

7

UST

H1, H2

Xn

-

Yn

CHY

8

GST

H1

-

-

Bushing H1

9

GST

H2

-

H2, Xn, Yn H1, Xn, Yn

-

Bushing H2

Note: n designates any winding connection, 1, 2 or 3


15

Supplementary Tests - Single-Phase P T Test #6 : UST Measure: CHX

H1

H0

HV Lead

CH1

CHX

CH2 X1 X2 X3

CHY Y1 Y2 Y3

LV Lead Doble Testing Potential Transformers

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Supplementary Tests - Single-Phase P T Test #7 : UST Measure: CHY

H1

H0

HV Lead

CH1

CHX

CH2 X1 X2 X3

CHY Y1 Y2

LV Lead

Y3 Doble Testing Potential Transformers

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Test Procedure - Single Phase - P T Test #8: GST-Guard Red & Blue Measure: CH1 H1

LV Lead

H0

HV Lead LV Lead

CH1

CHX

CH2 X1 X2 X3

CHY

Y1 Y2 Y3


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Test Procedure - Single Phase - P T Test #9: GST-Guard Red & Blue Measure: CH2 H1

HV Lead H0

LV Lead LV Lead

CH1

CHX

CH2 X1 X2 X3

CHY

Y1 Y2 Y3


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Single Phase Internally Grounded PT H1

CHX

CH

CHY

Neutral Shown Internally Grounded Doble Testing Potential Transformers

X1 X2 X3 Y1 Y2 Y3

H0 20

Single Phase Internally Grounded PT Test Procedure Test No. 1 2

Mode Energize UST H1 GST H1

Ground HO HO

Guard ---X1,Y1

UST X1,Y1 ----

Test No. 1: Measures Line-End Interwinding Insulation Test No. 2: Measure Excitation Current


21

Cascade Potential Transformers H1

H0 Ground Lead


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Cascade Potential Transformers •Test Preparation - Single Phase Line-to-Ground PT •One Side Of Each Secondary Winding Grounded •Remove Ground Link From Neutral •Short Circuit H1(Line) to H0 (Neutral) •Test No. 1 Only NOTE: Test Voltage for Tests 1, 3, 4, 5 Limited by Rating of Neutral Bushing (5 kV)


23

Cascade Potential Transformers Test #1: GST-Ground

H1

HV Cable

Secondary Windings Not Shown H0 Ground Lead Test Voltage for Tests 1, 3, 4, 5 Limited by Rating of Neutral Bushing (5 kV) Doble Testing Potential Transformers

24

Cascade Potential Transformers Test #2: GST-Guard Measure: Cross-Check #1

H1 HV Cable

H0

LV Lead



Ground Lead

25

Cascade Potential Transformers Test #3: GST-Guard Measure: Cross-Check #2

H1 LV Lead

H0


HV Cable

Ground Lead Test Voltage for Tests 1, 3, 4, 5 Limited by Rating of Neutral Bushing (5 kV) Doble Testing Potential Transformers

26

Cascade Potential Transformers Test #4: UST Measure: Excitation Current HV Cable

H0


Ground Lead


27

Cascade Potential Transformers Test #5: UST Measure: Excitation Current H1 LV Lead

H0


HV Cable


28

Cascade Potential Transformers Alternative Method for Performing the Overall Test* Test No.

Test Mode

Energize

Ground

Floating

1A

GST

H0

X1, X2, X3

H1

Test Description Overall

Y1, Y2, Y3

Tests 2 Through 5 - Same as Conventional PT *Note: No Short Circuit Used Between H1 & H0 Doble Testing Potential Transformers

29

Cascade Potential Transformers Test #1A: GST-Ground No Short Circuit on Primary Winding H1

H0


HV Cable


30

Use of Guard Collar on Cascade PT H1

Isurface


Connect to Guard H0


31

Test Procedure-Single-Phase PT - DTA


32

Analysis of Results: PTs •Compare Overall Power Factor Test Values to Previous Test Results •Compare Overall Power Factor Values to Similar Units (Doble Test-Data-Reference-Book) •Compare Cross-Check Power Factors •Most PTs Test Results are Similar


33

Analysis of Results: PTs Examples: PT #1 Test No. 1 (Overall) 2 (H1 Cross-check) 3 (H2 Cross-check)

mA 2.540 1.256 1.248

Watts 0.104 0.056 0.046

%PF 0.41 0.45 0.37

PT #2 Test No. 1 (Overall) 2 (H1 Cross-check) 3 (H2 Cross-check)

mA 2.650 1.356 1.248

Watts 0.354 0.313 0.055

%PF 1.32 2.31 0.44


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Analysis of Results: PTs

What is Wrong With PT #2?

•Consider Performing Supplemental Tests to Locate Cause of Problem •Refer to Doble Test Equipment Instruction Manual


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Analysis of Results: PTs Typical Good Unit

Test No. 1 (Overall) 2 (H1 Cross-Check) 3 (H0 Cross-Check)

mA 3.040 0.278 2.810


Watts % Power Factor 0.152 0.50 0.0312 1.12 0.128 0.46

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Analysis of Results: PTs Questionable Unit

Test No. 1 (Overall) 2 (H1 Cross-Check) 3 (H0 Cross-Check)

mA Watts % Power Factor 3.080 0.181 0.58 0.311 0.0682 2.19 2.810 0.128 0.46


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TRNG-6 Potential Transformer

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