power transformers case studies

Power Transformers

Al-Khobar, Kingdom of Saudi ArabiaRiesa, GermanyHeidenau, GermanyIreland

Case Studies:

2

Diagnosis Measurements on Power Transformer in Al-Khobar, Kingdom of Saudi Arabia

Part 1 – GT 14Part 2 – GT 4Part 3 – GT 2

1. Partial Discharge Measurement

2. Dielectric Loss Analysis (DLA)

3. Sweep Frequency Response Analysis (SFRA)

3

1. Setup of the PDM system incl. the UHF-PD-sensor

2. Frequency analysis for determination of the measuring frequency (Zero-span-mode measurement)

3. Instrument Performance Check

4. Recording of the measuring signals for the measuring cycle of 120 second

5. Evaluation of the measuring recordings by using the LDS-6/UHF Analysis software: PRPD Pattern Recognition and Replay-Mode for signal evaluation

1. PD Measurement in Al-Khobar, Kingdom of Saudi Arabia (Part 1 & 2)

4

The main constituent parts of the PD measurement system are the inductive loop as non-conventional sensor, the handheld detector LDP-5, at least of the measurement instrument LDS-6 as used for the phase resolved PD pattern recognition.

Fig. 2: Sensor placement for the acoustic transformer inspection

Fig. 1: Schematic diagram of the PD measuring setup (non-conventional; inductive decoupling)

1. PD Measurement in Al-Khobar, Kingdom of Saudi Arabia (Part 3)

A) Inductive Decoupling at the earth lead

1. Calibration of the PDM System as reduced charge

2. Recording of the measuring signals for the measuring cycle of 120 second

3. Evaluation of the measuring recordings by using the LDS-6 Analysis software: PRPD Pattern Recognition and Replay-Mode for signal evaluation

B) Acoustic Decoupling at transformer tank

Acoustic inspection of the transformer at four positions of the tank each transformer side

5

2. DLA Measurement in Al-Khobar, Kingdom of Saudi Arabia

1. De-Energization of the Power Transformer and isolation from the power system completely.

2. Connection & configuration of the measuring system.

3. Performing the test in different configuration (GST, GUARD, UST).

4. Restoring the electrical connections of the power transformer to the network for the service operation.

5. Energization of the Power Transformer.

6

3. SFRA Measurement in Al-Khobar, Kingdom of Saudi Arabia

1. De-Energization of the Power Transformer and isolation from the power system completely.

2. Connecting & configuration of the measuring system.

3. Performing the test in different configurations. Fingerprints-Recording in the different measuring configurations (Fig. 4) for open and short-circuit (LV) winding.

4. Restoring the electrical connections of the power transformer to the network for the service operation

5. Energization of the Power Transformer

7

Part 1 – GT 14

1. Partial Discharge Measurement

2. Dielectric Loss Analysis (DLA)

3. Sweep Frequency Response Analysis (SFRA)

Part 1: Results of the PD Measurement

9

Part 1: Results of the DLA Measurement

19020,6319020,9619022,6919017,3219016,02

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Voltage [kV]

Capa

city

[pF]

7828,41 7830,57 7831,17 7830,28 7830,86

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Voltage [kV]

Capa

city

[pF]

11182,39 11184,32 11184,75 11186,22 11186,09

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Voltage [kV]

Capa

city

[pF]

15228,215228,3215226,7215223,6315225,28

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Voltage [kV]

Capa

city

[pF]

4040,83 4040,12 4040,14 4040,82 4040,46

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Voltage [kV]

Capa

city

[pF]

11183,47 11184,22 11184,46 11186,28 11186,09

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Voltage [kV]

Capa

city

[pF]

CH+CHL CH CHL

CLCL+CHL CHL

Part 1: Results of the SFRA Measurement

11

Part1: Results of the SFRA Measurement

Fingerprints all phases overlapped: Open Circuit H1-H0, H1-H0, H3-H0; (h1/h2/h3 open)

Fingerprints all phases overlapped: Short Circuit H1-H0, H1-H0, H3-H0; (h1/h2/h3 shorted)

The SFRA Measurement at the power transformer GT14 has been performed as base line fingerprint to compare measurements in future.

This initial measurement of SFRA is based on a subjective comparison of the traces.

The traces are analyzed for changes between responses of the three investigated phases of the same transformer.

The responses, short circuit measurement, as well as open circuit measurement, for all three phases are nearly similar.

Measurements in future should be compared with these base lines to check the mechanical integrity of the investigated power transformer.

12

Part 2 – GT 4

1. Partial Discharge Measurement

2. Dielectric Loss Analysis (DLA)

3. Sweep Frequency Response Analysis (SFRA)

Part 2: Results of the PD Measurement

Part 2: Results of the DLA Measurement I

CH+CHL CH CHL

CLCL+CHL CHL

13549,38 13549,19 13551,17 13552,18 13551,56

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Voltage [kV]

Cap

acity

[pF]

20288,6 20291,72 20296,89 20292,43 20293,43

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Voltage [kV]

Cap

acity

[pF]

3079,293079,53079,513079,873080,71

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Voltage [kV]

Cap

acity

[pF]

9819,249818,19818,59817,249816,98

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Voltage [kV]

Cap

acity

[pF]

10471,9110469,9710469,8410469,4210468,18

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Voltage [kV]

Cap

acity

[pF]

10472,8810470,4110469,3710468,6210467,86

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Voltage [kV]

Cap

acity

[pF]

Part 2: Results of the DLA Measurement II

CH+CHL CH CHL

CLCL+CHL CHL

0,7490,7470,7470,7480,746

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0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

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Voltage [kV]

Loss

Fac

tor

0,779 0,779 0,778 0,781 0,784

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0,5

0,6

0,7

0,8

0,9

1

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Voltage [kV]

Loss

Fac

tor

0,910,9090,9090,9080,94

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0,5

0,6

0,7

0,8

0,9

1

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Voltage [kV]

Loss

Fac

tor

0,8470,8450,8440,8440,842

0

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0,4

0,5

0,6

0,7

0,8

0,9

1

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Voltage [kV]

Loss

Fac

tor

0,6970,6960,6970,6950,693

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0,5

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0,7

0,8

0,9

1

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Voltage [kV]

Loss

Fac

tor

0,7110,710,710,7080,706

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0,9

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Loss

Fac

tor

16

Part 2: Results of the DLA Measurement

I) The recorded PF values are increased.

The insulation PF values more than 0.5%, between 0.7% and 0.8%.

Tendency the insulation values are increasing slightly more then 0.9 %.

Data should be analyzed on basis of prior tests on the same unit.

II) The results of the capacitance readings have to be compared with previously

measurements.

Capacitance is a function of winding geometry, and is expected to be stable with

temperature and age.

Change of capacitance is an indication of winding movement such as might occur

as a result of a through fault.

Part 2: Results of the SFRA Measurement

18

Part2: Results of the SFRA Measurement

Fingerprints all phases overlapped: Short Circuit H1-H0, H1-H0, H3-H0; (h1/h2/h3 shorted)

Fingerprints all phases overlapped: Open Circuit H1-H0, H1-H0, H3-H0; (h1/h2/h3 open)

1) The SFRA Measurement at the power transformer GT4 has been performed as base line fingerprint to compare measurements in future.

This initial measurement of SFRA is based on a subjective comparison of the traces. The traces are analyzed for changes between responses of the three investigated phases of the same transformer.

2) The responses, short circuit measurement, as well as open circuit measurement, for all three phases differ. All measurements of the phases differ considerable starting from 100 kHz.

The recorded fingerprints have to be compared with previously measurements at the power transformer if they are performed. Phase B, the open circuit measurement differ from both other phases over the complete recorded frequency range.

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Part 3 – GT 2

1. Partial Discharge Measurement

2. Dielectric Loss Analysis (DLA)

3. Sweep Frequency Response Analysis (SFRA)

Part 3: Results of the PD Measurement

PD Reading – Reduced Charge: QR = 68 pC

Part 3: Results of the DLA Measurement I

CH+CHL CH CHL

CLCL+CHL CHL

0,904 0,901 0,899 0,904 0,902

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0,9

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Loss

Fac

tor

0,7760,7750,7730,770,763

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0,9

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Loss

Fac

tor

0,535 0,536 0,538 0,534 0,536

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0,9

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Voltage [kV]Lo

ss F

acto

r

0,4140,4150,4140,4120,417

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Voltage [kV]

Loss

Fac

tor

0,991,010,97

1,051,01

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0,9

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Loss

Fac

tor

1,0451,0451,0461,0371,013

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0,50,6

0,7

0,8

0,9

1

1,1

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Voltage [kV]

Loss

Fac

tor

Part 3: Results of the DLA Measurement II

CH+CHL CH CHL

CLCL+CHL CHL

14930,5214929,1414930,9214927,8614931,15

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Voltage [kV]

Capa

city

[pF]

2573,16 2573,24 2572,86 2572,65 2571,79

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Voltage [kV]

Capa

city

[pF]

12357,68 12355,99 12356,73 12356,65 12357,21

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Voltage [kV]

Capa

city

[pF]

21183,91 21188,39 21194,63 21193,16 21195,6

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Voltage [kV]

Cap

acity

[pF]

8826,51 8829,2 8829,43 8830,17 8830,24

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Cap

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[pF]

12357,64 12356,51 12357,85 12360,14 12361,22

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23

Part 3: Results of the DLA Measurement

1) The recorded PF values are high increased, more than 0.9%.

Older power transformer may have insulation PF values in excess of 0.5%.

Data should be analyzed on basis of prior tests on the same unit too.

2) The results of the capacitance readings have to be compared with previously measurements.

Capacitance is a function of winding geometry, and is expected to be stable with temperature and age.

Change of capacitance is an indication of winding movement such as might occur as a result of a through fault.

Part 3: Results of the SFRA Measurement

Part3: Results of the SFRA Measurement

Fingerprints all phases overlapped: Short Circuit H1-H0, H1-H0, H3-H0; (h1/h2/h3 shorted)

Fingerprints all phases overlapped: Open Circuit H1-H0, H1-H0, H3-H0; (h1/h2/h3 open)

The SFRA Measurement at the power transformer GT2 has been performed as base line fingerprint to compare measurements in future.

This initial measurement of SFRA is based on a subjective comparison of the traces.

The traces are analyzed for changes between responses of the three investigated phases of the same transformer.

The responses, short circuit measurement, as well as open circuit measurement, for all three phases have minimal deviation. Phase B, short circuit measurement, the curve differed at 2-3 kHz.

26

UHF PD measurement in Riesa, Germany

27

UHF PD measurement in Riesa, Germany

Transformer

Drain valve

UHF PD probe DN80

Output

Input

Pre-amplifier

High-pass filter

Measuring results at 690 MHz

Installed UHF PD probe DN80

Application benefit:

• PD measurement with the UHF probe DN 80 on the drain valve of a 110 kV transformer

• Installation of the PD measurement equipment online• Based on receiving electromagnetic fields transmitted by the

PD source• The UHF probe used at online and on-site PD measurements• High noise reduction level, because the probe is located in the

inner transformer tank in a shielded area

28

UHF PD measurement in Heidenau, Germany

29

on a 3-phase 40 MVA Power Transformer

Application benefit:

customer wanted to verify the electric PD monitoring results

full in-service UHF sensor application, performance check and measurement

Strong noises clearly identifiable

UHF noise; amplified Performance Check; >300MHz

UHF PD measurement in Heidenau, Germany

30

UHF PD measurement in Ireland

31

UHF PD measurement in Ireland

Application benefit:

• Tested measurements have been performed using non-conventional decoupling methods taking advantage of electromagnetic field coupling

• PD measurements on the power transformers have been functioned on the drain valves of the three phase power transformers with the help of the UHF probe DN 50

• Three transformers with minor PD activity, one transformer with clear PD

Location:

• Louth (T2101; T2103)

• Dublin (T102)

• Ardnacrusha (T142)

• Cashla (T2101, T2102)

32

Drain Valve

Applied UHF Drain Valve Sensor

Mounting of the UHF Probe DN50 (with Adapter DN50/DN80)

Measuring System LDS-6/UHF

Measuring Instrument:

• PD Measuring System LDS-6/UHF• UHF Probe DN50 (with Adapter DN50/DN80)• UHF Calibrator LDC-6/UHF• Pre Amplifier LDA-5/GIS

UHF PD measurements in Ireland

33

UHF PD measurement in Louth, Dublin, Ardnacrusha, Cashla (Ireland)

V ≈ 550 mV at measuring frequency 560 MHzV ≈ 238 mV at measuring frequency 560 MHz

V ≈ 139 mV at measuring frequency 560 MHz V ≈ 128 mV at measuring frequency 520 MHz

34

UHF PD measurement in Jizan, Saudi Arabia

35

UHF PD measurement in Jizan, Saudi Arabia

Drain Valve Power Transformer

on 33/13,8 KV Power Transformers GT14 and GT4

Measuring Instrument:

• UHF Probe DN50

• Calibrator LDC-6/UHF

• PD measurement instrument LDS-6/UHF

36

UHF PD measurement in Jizan, Saudi Arabia

PRPD Pattern at the measuring frequency of 400 MHz V = 177 mV

PRPD Pattern at the measuring frequency of 400 MHz V = 288 mV