trng-6 potential transformer
TRANSCRIPT
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Doble Testing
Potential Transformers ( PT’s )
Bob Sarni
Doble Engineering Company
Doble Engineering Company 85 Walnut Street, Watertown, MA 02472
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Doble Testing Potential Transformers 2
Potential Transformers (PTs)
H1
H0
Isurface
Secondary Windings
Not Shown
Cascade Type
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Doble Testing Potential Transformers 3
Potential Transformers (PTs)
H1
CH
CHX
CHY
X1
X2
X3
Y1
Y2
Y3
H0 Line To Ground PT
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Doble Testing Potential Transformers 4
X1X2
X3
Y1
Y2Y3
CH1 CH2
CHY
CHX
Potential Transformers (PTs)
H1 H2
Line To Line PT
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Doble Testing Potential Transformers 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
*For Units Rated 15 kV and Above, Perform Tests at 10 kV
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Doble Testing Potential Transformers 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
Recommended Test Voltage
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Doble Testing Potential Transformers 7
Dry-Type Line-to-Line PTs Rated Below 15 kV Insulation ClassPT 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
Recommended Test Voltage
*Note: Power Factor Tip Up Test
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Doble Testing Potential Transformers 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
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Doble Testing Potential Transformers 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-terminalbushings
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Doble Testing Potential Transformers 10
Test Procedure - Single Phase - P T
X1X2X3
Y1Y2Y3
CH1 CH2
CHY
CHX
Test #1 : GST Ground - No LV Lead Required
Measure: CH1+CHX+CHY+CH2
H1 H0HV Lead
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Doble Testing Potential Transformers 11
Test Procedure - Single Phase - P T
Test #2: GST-Guard (Cross-Check Test #1)
•Measure: CH1+ 1/2CHX + 1/2CHY
X1X2X3
Y1Y2Y3
H1 H0
CH1 CHX CH2
CHY
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
X1X2X3
Y1Y2Y3
H1 H0
CH1 CHX CH2
CHY
HV LeadLV Lead
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Doble Testing Potential Transformers 13
Test Procedure - Single Phase - P T
X1X2X3
Y1Y2Y3
H1 H0
CH1 CHX CH2
CHY
HV Lead LV Lead
Test #4: Ungrounded Specimen Test (UST)
Measure: Excitation Current
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Doble Testing Potential Transformers 14
Test Procedure - Single Phase - P T
X1X2X3
Y1Y2Y3
H1 H0
CH1 CHX CH2
CHY
HV LeadLV Lead
Test #5: Ungrounded Specimen Test (UST)
Measure: Excitation Current
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Doble Testing Potential Transformers 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
Note: n designates any winding connection, 1, 2 or 3
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Doble Testing Potential Transformers 16
X1X2X3
Y1Y2Y3
CH1 CH2
CHY
CHX
Test #6 : UST
Measure: CHXH1 H0
HV Lead
LV Lead
Supplementary Tests - Single-Phase P T
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Doble Testing Potential Transformers 17
X1X2X3
Y1Y2
Y3
CH1 CH2
CHY
CHX
Test #7 : UST
Measure: CHYH1 H0
HV Lead
LV Lead
Supplementary Tests - Single-Phase P T
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Doble Testing Potential Transformers 18
Test Procedure - Single Phase - P T
X1X2X3
Y1Y2Y3
H1 H0
CH1 CHX CH2
CHY
HV Lead
LV Lead
Test #8: GST-Guard Red & Blue
Measure: CH1
LV Lead
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Doble Testing Potential Transformers 19
Test Procedure - Single Phase - P T
X1X2X3
Y1Y2Y3
H1 H0
CH1 CHX CH2
CHY
HV Lead
LV Lead
Test #9: GST-Guard Red & Blue
Measure: CH2
LV Lead
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Doble Testing Potential Transformers 20
Single Phase Internally Grounded PT
H1
CH
CHX
CHY
Neutral Shown Internally Grounded H0
X1
X2X3
Y1Y2Y3
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Doble Testing Potential Transformers 21
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
Test Procedure
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Doble Testing Potential Transformers 22
Cascade Potential Transformers
H0
H1
Ground Lead
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Doble Testing Potential Transformers 23
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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Doble Testing Potential Transformers 24
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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Doble Testing Potential Transformers 25
H1
Cascade Potential Transformers
H0
HV Cable
Ground Lead
Test #2: GST-Guard
Measure: Cross-Check #1
LV Lead
Secondary Windings
Not Shown
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Doble Testing Potential Transformers 26
Cascade Potential Transformers
Test #3: GST-Guard
Measure: Cross-Check #2
H0
HV CableGround Lead
H1
LV Lead
Test Voltage for Tests 1, 3, 4, 5 Limited by Rating of Neutral Bushing (5 kV)
Secondary Windings
Not Shown
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Doble Testing Potential Transformers 27
Cascade Potential Transformers
H0
HV Cable
Ground Lead
Test #4: UST
Measure: Excitation Current
Secondary Windings
Not Shown
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Doble Testing Potential Transformers 28
Cascade Potential Transformers
H0
HV CableGround Lead
H1
LV Lead
Test #5: UST
Measure: Excitation Current
Test Voltage for Tests 1, 3, 4, 5 Limited by Rating of Neutral Bushing (5 kV)
Secondary Windings
Not Shown
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Doble Testing Potential Transformers 29
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
Alternative Method for Performing the Overall Test*
*Note: No Short Circuit Used Between H1 & H0
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Doble Testing Potential Transformers 30
Cascade Potential Transformers
H0
HV CableGround Lead
H1
Test #1A: GST-Ground
Test Voltage for Tests 1, 3, 4, 5 Limited by Rating of Neutral Bushing (5 kV)
No Short Circuit on Primary Winding
Secondary Windings
Not Shown
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Doble Testing Potential Transformers 31
Use of Guard Collar on Cascade PT
H1
H0
Connect to Guard
Isurface
Secondary Windings
Not Shown
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Doble Testing Potential Transformers 32
Test Procedure-Single-Phase PT - DTA
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Doble Testing Potential Transformers 33
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
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Doble Testing Potential Transformers 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
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Doble Testing Potential Transformers 35
What is Wrong With PT #2?
Analysis of Results: PTs
•Consider Performing Supplemental Tests to Locate
Cause of Problem
•Refer to Doble Test Equipment Instruction Manual
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Doble Testing Potential Transformers 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
Analysis of Results: PTs
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Doble Testing Potential Transformers 37
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) 2.810 0.128 0.46
Questionable Unit