pd

1. 14 April 2019
Localizing partial discharge in power transformers by
acoustic method
Sridhar Shenoy

2. Introduction
Partial Discharges (PD)
"…local electrical discharges which only partially bridge the insulation
between electrical conductors ....”
[IEC 60270:2000]
…generate electromagnetic signals
…generate acoustic signals
measurable
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3. Acoustic Measurement at Transformer
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PD
Piezo-
Sensor
Cabling
Winding
...to get a closer look

4. Acoustic signal emission
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• PD signals emit part of the energy converted as a sound wave.
• The propagation medium and sound transducer have strong
influence on the shape of the measured signal.
• Acoustic data does not provide any direct information on type of
fault or intensity of Partial Discharge activity.
• Unlike electrical PD measurement, it is not possible to define limit
values.
• Used for fault localization determined through differences in signal
arrival time at sensor location.

5. Acoustic Signal Propagation from Source to Tank Wall
Time-base Localization
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Source: IEEE Std C57.127-2007 „IEEE Guide for the Detection and Location of Acoustic
Emissions from Partial Discharges in Oil-Immersed Power Transformers and Reactors”

6. Page: 6
Sensors
AES 075
Resonance frequency 75 kHz
Lower frequency limit 30 kHz
Upper frequency limit 120 kHz
Gain 40dB
Source: L.E.Lundgaard „Partial Discharge – Part XIV: Acoustic
Partial Discharge Detection – Practical Application“, IEEE El.
Insulation Magazine Sep 1992 Vol.8,No.5

7. 1250
1260
1270
1280
1290
1300
1310
0 200 400 600 800 1000 1200
Velocity
(m/s)
Frequency (kHz)
Acoustic Signal Propagation Speed in Oil
Howells, E. ; Norton, E.T.: “Parameters affecting the velocity of sound in transformer oil”
IEEE Transactions on Power Apparatus and Systems (1984)”
1000
1100
1200
1300
1400
1500
1600
-40 -20 0 20 40 60 80 100 120 140
Velocity
(m/s)
Temperature ( °
C)
@150 kHz
@ 65 °
C

8. Propagation Path
Material Speed [m/s]
Steel Longitudinal 5900
Steel Transversal 3200
Oil 20°
C 1413
Oil 80°
C 1200
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Source: IEEE Std C57.127-2007 „IEEE Guide for the Detection and Location of Acoustic
Emissions from Partial Discharges in Oil-Immersed Power Transformers and Reactors”

9. Propagation Path
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Winding
Transformer Tank
Sensor

10. Propagation Path
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Winding
Transformer Tank
Steel Part
Direct Oil Part
Source: Lue RiCheng, Li WeiGou, Lie ChenRong and Xiong Hao „Study
on PD Localization by Ultrasonic Measuring im Power Transformer
Based on Particle Swarm Optimization” G-003, ISH, Beijing, China
Aug 2005

11. Propagation Path
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Winding
Transformer Tank
Rearrangement of the
acoustic sensors (if possible)

12. Localization Algorithm - Triangulation
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Source: L.E.Lundgaard „Partial Discharge – Part XIV: Acoustic Partial Discharge
Detection – Practical Application“, IEEE El. Insulation Magazine Sep 1992 Vol.8,No.5
Absolute times tx Relative times ∆txy

13. Test Set-up
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• Approx. 2 – 3 hours usually required
• Place the sensors on transformer tank
• Perform operational check; ensure sensitivity of all
sensors
• To start with, place sensors in general area of bottom
connection of each bushings
• Place the sensors below the oil level
• Prepare Transformer model as accurate as possible
• Measure correct distances where the sensors are
mounted

14. Test Set-up
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Do’s & Don’ts:
• Contact between transducer and transformer tank is critical. It is
advisable to clean the area free of dirt, oil etc. and polish with
abrasive cloth before placing the sensors.
• Acoustic couplant is essential for enhancing the mechanical &
acoustic coupling between transducer & tank surface. It should
be evenly applied to the clean mounting surface of sensor.
• If possible, avoid locations where there is magnetic or non-
magnetic tank shielding, which will cause signal attenuation.
• Avoid mounting sensors on tank stiffeners
• For safety reasons, do not place sensors in areas of high voltage
• Do not mount sensors on control boxes
• Provide sufficient spacing between sensors to insure
independent signals.

15. Area Localization
Absolute times tx Relative times ∆txy

16. Point Localization
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17. Measurement setup
IEEE Guide: C57.127 for Transformers
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18. Setup example
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MPD with
HFCT

19. Electrical Trigger
HFCT
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MPD 600
HFCT

20. Electrical Trigger
Measurement Setup UHF
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21. Electrical Trigger
Measurement Setup UHF
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MPD 600 &
UHF 608
UPG 620
UVS 610

22. Electrical Trigger
Bushing Test Tap
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MPD 600
CPL 542

23. Measurement Setup
• 16 MVA three-phase power transformer 150 kV / 20 kV (Yyn0)
• PDL 650 (PDLocator) for acoustic PD measurements/localization
• MPD 600 for PD measurements according to IEC 60270
N
U
V
W
U V W
CPL
542A
CPL
542A
MPD
600
PDL
650
PC
MPD
600
Fig.1 Localization of PD sensors

24. Conventional PD measurements
Figure: Decoupling of PD signal on bushing of phase W

25. Results of Conventional PD Measurement
Figure The measurement was performed at 85 kV.
• Due to the high PD level on phase W it is assumed that the PD is located near
phase W
• Measurement Frequency 175-825kHz
Phase V
Phase W

26. Conclusion: Yellow and Black sensor are nearer to the PD defect, red sensor is farther
away and blue the farthest. Decision to change of position of sensor red was undertaken.
Calculated defect location: 2.7 m | 1.2 m | 1.7 m.
Results of Acoustic Localization
Sensor Arrival
time
Max. Amplitude (roughly)
Blue 0.804 ms 420 mV
Yellow 0.175 ms 825 mV
Red 0.746 ms 630 mV
Black 0.409 ms 770 mV

27. Sensor Arrival
time
Max. Amplitude (roughly)
Blue 0.515 ms 610 mV
Yellow 0.183 ms 680 mV
Red 0.567 ms 585 mV
Black 0.447 ms 655 mV
Conclusion: Yellow sensor is nearest to the PD defect, black sensor is farther away and
blue and red the farthest. Calculated defect location: 2.6 m | 1.1 m | 1.4 m.
Results of Acoustic Localization

28. Findings

29. 500 MVA Autotransformer
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Autotransformer:
400kV/220kV/33kV
YNa0d11 (50Hz)
500 MVA
Installation Date:
Oct 2011
Red
Yellow
Blue
LV
HV

30. DGA – Anomaly
> Sharp rise of H2
> Methane is still quite low and Acetylene is zero.
> Assumption: no arcing and no heavy discharges, but PD
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31. Electrical and Acoustic Measurement
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Red
Yellow
Blue
LV
HV
Neutral
MPD600
1.1
MPD600
1.2
MPD600
1.3
MPD600
1.4
Acoustic
Sensors
PDL 650
tap changer

32. Acoustic Measurement at transformer tank
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Non of the electrical
measured impulse were
convenient to trigger a
acoustic measurement
-> Next step are
all acoustic measurement

33. Acoustic Measurement
at transformer tank (top)
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Acoustic measurements at
the side walls of the tank
was not successful
-> Acoustic sensors on top
of the transformer

34. 1. Trial:
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4 Sensors on the Top
Sensor X [m] Y [m] Z [m]
Blue 2.64 1.74 3.99
Yellow 4.06 3.22 3.99
Red 6.63 3.27 3.99
Black 8.08 1.95 3.99
0/0/0

35. 1. Trial
Acoustic PD pulses were detectable

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1. Trial
Interpretation:
PD source is likely at tap changer, bushing or at the connection to
the winding of the yellow phase.
-> rearrange the sensor position close to Bushing and tap changer

37. 2. Trial
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Rearranged position of the sensors
Sensor X [m] Y [m] Z [m]
Blue 4.84 1.40 3.99
Yellow 5.60 0.00 3.60
Red
(attached to the
bushing / LV Yellow)
4.52 0.62 4.10
Black 5.50 1.00 3.99

38. 4/14/2019 38
Acoustic signal arrives first at
sensor Black and Blue and
later Yellow and than Red
Acoustic
Sensor
1 Blue 56 us
2 Yellow 473 us
3 Red 561 us
4 Black 0 us

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Conclusion

41. Summary
> Acoustic measurement / localization
> can localize PD inside of power transformer.
> can help to reduce repair time of a transformer at
the factory.
> can help assess the transformer on-site.
> Important is
> understanding of the acoustic propagation.
> knowledge about the inner construction.
> sufficient workflow.
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42. Thank you for your attention
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