TRNG-6 Potential Transformer

(1)

Doble Testing

Potential Transformers ( PT’s )

Bob Sarni

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Doble Testing Potential Transformers 2

Potential Transformers (PTs)

H1 H0 I_surface Secondary Windings Not Shown Cascade Type

(3)

Potential Transformers (PTs)

H1 CH CHX CHY X1 X2 X3 Y1 Y2 Y3

(4)

Doble Testing Potential Transformers 4 X1 X2 X3 Y1 Y2 Y3 C_H1 C_H2 C_HY C_HX

Potential Transformers (PTs)

H1 H2 Line To Line PT

(5)

Recommended Test Voltage

Liquid-Filled Line-to-Line PTs Rated Below 15 kV Insulation Class

PT Voltage Rating Test Voltage (kV)

7.2 to 8.7 5.0

4.2 to 5.0 2.5

2.4 2.0

(6)

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-to-Ground Voltage, Whichever is Lower

(7)

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

(8)

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

(9)

Test Procedure - Single Phase - P T

Test No.

Test

Mode Energize Ground Guard UST Test Description

1 GST H1, H2 X1,Y1 - - 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

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Test Procedure - Single Phase - P T

X1 X2 X3 Y1 Y2 Y3 C_H1 C_H2 C_HY C_HX

Test #1 : GST Ground - No LV Lead Required Measure: CH1+CHX+CHY+CH2

H1 H0

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Test Procedure - Single Phase - P T

Test #2: GST-Guard (Cross-Check Test #1)

•Measure: CH1+ 1/2CHX + 1/2CHY X1 X2 X3 Y1 Y2 H1 H0 C_H1 C_HX C_H2 C_HY HV Lead LV Lead

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Test Procedure - Single Phase - P T

Test #3: GST-Guard (Cross-Check Test #2)

•Measure: CH2+ 1/2CHX + 1/2CHY X1 X2 X3 Y1 Y2 Y3 H1 H0 C_H1 C_HX C_H2 C_HY HV Lead LV Lead

(13)

Test Procedure - Single Phase - P T

X1 X2 X3 Y1 Y2 H1 H0 C_H1 C_HX C_H2 C_HY HV Lead LV Lead

Test #4: Ungrounded Specimen Test (UST) Measure: Excitation Current

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Test Procedure - Single Phase - P T

X1 X2 X3 Y1 Y2 Y3 H1 H0 C_H1 C_HX C_H2 C_HY HV Lead LV Lead

Test #5: Ungrounded Specimen Test (UST) Measure: Excitation Current

(15)

Supplementary Tests - Single-Phase P T

Test No.

Test

Mode Energize Ground Guard UST Test Description

6 UST H1, H2 Yn - Xn CHX 7 UST H1, H2 Xn - Yn CHY 8 GST H1 - H2, Xn, Yn - Bushing H1 9 GST H2 - H1, Xn, Yn - Bushing H2

(16)

Doble Testing Potential Transformers 16 X1 X2 X3 Y1 Y2 Y3 C_H1 C_H2 C_HY C_HX Test #6 : UST Measure: C_HX H1 _H0 HV Lead LV Lead

Supplementary Tests - Single-Phase P T

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X1 X2 X3 Y1 C_H1 C_H2 C_HY C_HX Test #7 : UST Measure: C_HY H1 _H0 HV Lead

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Test Procedure - Single Phase - P T

X1 X2 X3 Y1 Y2 Y3 H1 _H0 C_H1 C_HX C_H2 C_HY HV Lead LV Lead

Test #8: GST-Guard Red & Blue Measure: C_H1

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Test Procedure - Single Phase - P T

X1 X2 X3 Y1 Y2 H1 _H0 C_H1 C_HX C_H2 C_HY HV Lead LV Lead

Test #9: GST-Guard Red & Blue Measure: C_H2

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Single Phase Internally Grounded PT

H1

CH

CHX

CHY

Neutral Shown Internally Grounded H0

X1 X2 X3 Y1 Y2 Y3

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Test No. Mode Energize Ground Guard UST

1 UST H1 HO ---- X1,Y1

2 GST H1 HO X1,Y1

----Test No. 1: Measures Line-End Interwinding Insulation

Test No. 2: Measure Excitation Current

Single Phase Internally Grounded PT

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Cascade Potential Transformers

H₀

H₁

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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)

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Cascade Potential Transformers

Test #1: GST-Ground

H₀

H₁

Ground Lead HV Cable

Test Voltage for Tests 1, 3, 4, 5 Limited by Rating of Neutral Bushing (5 kV)

Secondary Windings Not Shown

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H₁

Cascade Potential Transformers

H₀ HV Cable Test #2: GST-Guard Measure: Cross-Check #1 LV Lead Secondary Windings Not Shown

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Cascade Potential Transformers

Test #3: GST-Guard Measure: Cross-Check #2 H₀ HV Cable Ground Lead H₁ LV Lead

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Cascade Potential Transformers

H₀

HV Cable

Test #4: UST

Measure: Excitation Current

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Cascade Potential Transformers

H₀ HV Cable Ground Lead H₁ LV Lead Test #5: UST

Measure: Excitation Current

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Cascade Potential Transformers

Test No. Test Mode Energize Ground Floating Test Description

1A GST H0 X1, X2, X3 H1 Overall

Y1, Y2, Y3

Tests 2 Through 5 - Same as

Conventional PT

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Cascade Potential Transformers

H₀

HV Cable

Ground Lead H₁

Test #1A: GST-Ground

No Short Circuit on Primary Winding

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Use of Guard Collar on Cascade PT

H1 Connect to Guard I_surface Secondary Windings Not Shown

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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

(34)

Analysis of Results: PTs

PT #1

Test No. mA Watts %PF

1 (Overall) 2.540 0.104 0.41 2 (H1 Cross-check) 1.256 0.056 0.45 3 (H2 Cross-check) 1.248 0.046 0.37

Examples:

PT #2

Test No. mA Watts %PF

1 (Overall) 2.650 0.354 1.32 2 (H1 Cross-check) 1.356 0.313 2.31 3 (H2 Cross-check) 1.248 0.055 0.44

(35)

What is Wrong With PT #2?

Analysis of Results: PTs

•Consider Performing Supplemental Tests to Locate

Cause of Problem

(36)

Test No.

mA

Watts % Power Factor

1 (Overall)

3.040

0.152

0.50 2 (H1 Cross-Check)

0.278 0.0312

1.12 3 (H0 Cross-Check)

2.810

0.128

0.46 Typical Good Unit

(37)

TRNG-6 Potential Transformer

Doble Testing

Potential Transformers ( PT’s )

Bob Sarni

Potential Transformers (PTs)

Potential Transformers (PTs)

Potential Transformers (PTs)

Recommended Test Voltage

Recommended Test Voltage

Test Procedure - Single Phase - P T

Test Procedure - Single Phase - P T

Test Procedure - Single Phase - P T

Test Procedure - Single Phase - P T

Test Procedure - Single Phase - P T

Test Procedure - Single Phase - P T

Supplementary Tests - Single-Phase P T

Supplementary Tests - Single-Phase P T

Test Procedure - Single Phase - P T

Test Procedure - Single Phase - P T

Single Phase Internally Grounded PT

Single Phase Internally Grounded PT

Cascade Potential Transformers

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)

Cascade Potential Transformers

Cascade Potential Transformers

Cascade Potential Transformers

Cascade Potential Transformers

Cascade Potential Transformers

Cascade Potential Transformers

Tests 2 Through 5 - Same as

Conventional PT

Cascade Potential Transformers

Use of Guard Collar on Cascade PT

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

Analysis of Results: PTs

What is Wrong With PT #2?

Analysis of Results: PTs

•Consider Performing Supplemental Tests to Locate

Cause of Problem

Test No.

mA

Watts % Power Factor

1 (Overall)

3.040

0.152

0.50

2 (H1 Cross-Check)

0.278

0.0312

1.12

3 (H0 Cross-Check)

2.810

0.128

0.46

Typical Good Unit

Analysis of Results: PTs

Test No.

mA

Watts % Power Factor

1 (Overall)

3.080

0.181

0.58

2 (H1 Cross-Check)

0.311 0.0682

2.19

3 (H0 Cross-Check)