trng-6 potential transformer

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Doble Testing Potential Transformers ( PTs )Bob Sarni Doble Engineering Company

Doble Engineering Company

85 Walnut Street, Watertown, MA 02472

Potential Transformers (PTs)H1

Isurface

H0

Secondary Windings Not Shown

Cascade TypeDoble Testing Potential Transformers 2

Potential Transformers (PTs)H1

CHX

CH

CHYH0Doble Testing Potential Transformers

X1 X2 X3 Y1 Y2 Y3 Line To Ground PT3

Potential Transformers (PTs)H1 H2

CH1 CHY

CHX

CH2 X1 X2 X3 Y1 Y2 Y3

Line To Line PTDoble Testing Potential Transformers 4

Recommended Test VoltageLiquid-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 VoltageLiquid-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

Doble Testing Potential Transformers

6

Recommended Test VoltageDry-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 a. Line-to-Ground Operating Voltage

Exciting Current

*Note: Power Factor Tip Up TestDoble Testing Potential Transformers 7

Recommended Test VoltageDry-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

Doble Testing Potential Transformers

8

Test Procedure - Single Phase - P TTest No. 1 2 3 4 5 6 Test Mode Energize Ground GST H1, H2 X1,Y1 GST GST UST UST H1 H2 H1 H2 X1Y1 X1Y1 X1Y1 X1Y1

Guard UST H2 H1 H2 H1

Test Description Overall H1 Cross Check H2 Cross-Check Excitation H1 to H2 Excitation H2 to H1

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

Doble Testing Potential Transformers

9

Test Procedure - Single Phase - P TTest #1 : GST Ground - No LV Lead Required Measure: CH1+CHX+CHY+CH2HV LeadH1 H0

CH1 CHY

CHX

CH2X1 X2 X3 Y1 Y2 Y310

Doble Testing Potential Transformers

Test Procedure - Single Phase - P TTest #2: GST-Guard (Cross-Check Test #1) Measure: CH1+ 1/2CHX + 1/2CHYHV Lead H1 H0 LV Lead

CH1CHY

CHX

CH2X1 X2 X3

Y1 Y2 Y311

Doble Testing Potential Transformers

Test Procedure - Single Phase - P TTest #3: GST-Guard (Cross-Check Test #2) Measure: CH2+ 1/2CHX + 1/2CHYLV Lead H1 H0 HV Lead

CH1CHY

CHX

CH2X1 X2 X3

Y1 Y2 Y312

Doble Testing Potential Transformers

Test Procedure - Single Phase - P TTest #4: Ungrounded Specimen Test (UST) Measure: Excitation CurrentHV Lead H1 H0 LV Lead

CH1CHY

CHX

CH2X1 X2 X3

Y1 Y2 Y313

Doble Testing Potential Transformers

Test Procedure - Single Phase - P TTest #5: Ungrounded Specimen Test (UST) Measure: Excitation CurrentLV Lead H1 H0 HV Lead

CH1CHY

CHX

CH2X1 X2 X3

Y1 Y2 Y314

Doble Testing Potential Transformers

Supplementary Tests - Single-Phase P TTest No. 6 7 8 9 Test Mode UST UST GST GST

Energize H1, H2 H1, H2 H1 H2

Ground Yn Xn -

Guard H2, Xn, Yn H1, Xn, Yn

UST Xn Yn -

Test Description CHX CHY Bushing H1 Bushing H2

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

Doble Testing Potential Transformers

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Supplementary Tests - Single-Phase P TTest #6 : UST Measure: CHXHV LeadH1 H0

CH1 CHY

CHX

CH2X1 X2 X3 Y1 Y2 Y3 LV Lead16

Doble Testing Potential Transformers

Supplementary Tests - Single-Phase P TTest #7 : UST Measure: CHYHV LeadH1 H0

CH1 CHY

CHX

CH2X1 X2 X3 Y1 Y2 Y3 LV Lead

Doble Testing Potential Transformers

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Test Procedure - Single Phase - P TTest #8: GST-Guard Red & Blue Measure: CH1H1 H0 LV Lead

HV LeadLV Lead

CH1CHY

CHX

CH2X1 X2 X3

Y1 Y2 Y318

Doble Testing Potential Transformers

Test Procedure - Single Phase - P TTest #9: GST-Guard Red & Blue Measure: CH2H1 LV Lead LV Lead HV Lead H0

CH1CHY

CHX

CH2X1 X2 X3

Y1 Y2 Y319

Doble Testing Potential Transformers

Single Phase Internally Grounded PTH1

CHX

CH

CHY H0

X1 X2 X3 Y1 Y2 Y3

Neutral Shown Internally GroundedDoble Testing Potential Transformers

20

Single Phase Internally Grounded PTTest ProcedureTest 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

Doble Testing Potential Transformers

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Cascade Potential TransformersH1

H0Ground Lead

Doble Testing Potential Transformers

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Cascade Potential TransformersTest 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 OnlyNOTE: Test Voltage for Tests 1, 3, 4, 5 Limited by Rating of Neutral Bushing (5 kV)

Doble Testing Potential Transformers

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Cascade Potential TransformersTest #1: GST-GroundH1

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 TransformersTest #2: GST-Guard Measure: Cross-Check #1H1 HV Cable

H0

Secondary Windings Not Shown

LV Lead

Ground Lead

Doble Testing Potential Transformers

25

Cascade Potential TransformersTest #3: GST-Guard Measure: Cross-Check #2H1 LV Lead

H0

Secondary Windings Not Shown

Ground Lead Test Voltage for Tests 1, 3, 4, 5 Limited by Rating of Neutral Bushing (5 kV)Doble Testing Potential Transformers 26

HV Cable

Cascade Potential TransformersTest #4: UST Measure: Excitation CurrentHV Cable

H0

Secondary Windings Not Shown

Ground Lead

Doble Testing Potential Transformers

27

Cascade Potential TransformersTest #5: UST Measure: Excitation Current H1LV Lead

H0

Secondary Windings Not Shown

Ground Lead Test Voltage for Tests 1, 3, 4, 5 Limited by Rating of Neutral Bushing (5 kV)Doble Testing Potential Transformers 28

HV Cable

Cascade Potential TransformersAlternative Method for Performing the Overall Test*Test No. 1A Test Mode GST Energize H0 Ground X1, X2, X3 Y1, Y2, Y3 Floating H1 Test Description Overall

Tests 2 Through 5 - Same as Conventional PT*Note: No Short Circuit Used Between H1 & H0Doble Testing Potential Transformers 29

Cascade Potential TransformersTest #1A: GST-Ground No Short Circuit on Primary WindingH1

H0

Secondary Windings Not Shown

Ground Lead Test Voltage for Tests 1, 3, 4, 5 Limited by Rating of Neutral Bushing (5 kV)Doble Testing Potential Transformers 30

HV Cable

Use of Guard Collar on Cascade PTH1

Isurface

Connect to Guard H0

Secondary Windings Not Shown

Doble Testing Potential Transformers

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Test Procedure-Single-Phase PT - DTA

Doble Testing Potential Transformers

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Analysis of Results: PTsCompare 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

Doble Testing Potential Transformers

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

mA 2.540 1.256 1.248 mA 2.650 1.356 1.248

Watts 0.104 0.056 0.046 Watts 0.354 0.313 0.055

%PF 0.41 0.45 0.37 %PF 1.32 2.31 0.4434

Doble Testing Potential Transformers

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

Doble Testing Potential Transformers

35

Analysis of Results: PTsTypical 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

Doble Testing Potential Transformers

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Analysis of Results: PTsQuestionable 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

Doble Testing Potential Transformers

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