1. Condition Monitoring Of High Voltage Machines By The Analysis of
Electrical Partial Discharges
22 April 04
Dino Kouadria
PhD MSc BEng CEng MIEE MIEEE

2. CONTENT What is Partial Discharge (PD) Analysis.
Stator winding Common Faults.
Basics Of Why & How To Measure PD.
Case Studies.
Open Discussions.

3. What is Partial Discharges Analysis
It is an electrical condition monitoring technique.
Used to assess the condition of hv insulation
Wider applications
static items i.E. Switchgear, cables transformers, etc.
Dynamic items i.E. Electrical machines

4. PDs Analysis On HV Windings
Apply to HV motors & generators (>5kv)
Online & off line tests.
Predominantly on-line tests - no shut down & tests under
normal stress condition.

5. PDs Analysis On HV Windings
Assess the current & development in condition of the
windings
Maintenance planning based on machines’ health.
Elimination of unwanted/unexpected shutdowns.
Assistance in targeting maintenance effort effectively.
Leave Maintain Replace

6. Why Do HV Stators Fail?
Failures due to windings’ insulation failure caused by the combined
electrical, thermal, environmental and mechanical stress factors.
Most common causes in modern insulation are mechanically induced defects i.E. Loose wedges, erosion due to bar vibration etc. - Short time degradation process.
Discharge between phases due to cracks / low spacing
Contamination of end windings.
Others: internal voids, insulation ageing, delamination.
Electrical partial discharges

7. Electrical partial discharges. So what are partial discharges?
Regardless of the type of defects, they all result in the generation of
Electrical partial discharges.
So what are partial discharges?

8. What is a partial discharge
Local breakdown that short circuits part of the Insulation.
Vs = Applied voltage
Cavity Vs
Formation of corrosive ions, acids, nitrogen oxides, ozone.
Detected using of chemical sensors for detection.
Emission of light, sound & electromagnetic waves.
Detected using ultrasonic devices, antennae, cameras..
Injection of high frequency current pulses.
Detected using electrical partial discharges measurement (pd).

9. Partial Discharges Basic Theory- +
Patterns & location of pulses within AC cycle
Is the key in defects identification

10. Importance Of Monitoring PDs
Different defects produce different PD patterns.
Complex PD patterns are produced when multiple defects are present.
Failures are due to localized defects.
PD pattern development over time represents developing degradation processes.
Provide an early warning of potential problems

11. Partial discharge monitoring over a machine life cycle
Discharge levels
Repair/action required
Curing Process
Fabrication Defects
Contamination
Mechanical failure
3 – 6 months
?? Years
Time

12. North sea oil industry – mainly Rogowski coils
PD Detection
Two main type of permanently installed sensors.
Capacitive couplers first developed in north america. Main users power industry.
Rogowski coils first developed for the north sea oil industry.
North sea oil industry – mainly Rogowski coils
Ease of installation: no disconnection of supply cables, less installation time.
Atex certified

13. Rogowski Coils: Typical Installation

14. Partial Discharge Analysis/Display: Typical Cycle

15. Partial Discharge Analysis/Display: Total Discharge Activity

16. Partial Discharge Analysis/Display: Pulse Height Analysis

17. CASE STUDIES

18. Case studies 1 Contamination on old pump motor
Case studies 1 Contamination on old pump motor 11KV-3MW 2 New motor manufacturing problem 13.8KV-12MW 3 Coil Movement old motor KV-9MW 4 Plastics plant old motor high PD 11KV-2.5MW

19. Total Discharge Activity
3MW Pump Motor
Total Discharge Activity

20. Typical Detected Faults Damage due to movement and contamination
3MW Pump Motor
Typical Detected Faults Damage due to movement and contamination
White power deposits clear
signs of discharge activity

21. 13.8 kV 12.7 MW Gas Compressor

22. 0ver 70% of wedges loose or missing
13.8 kV 12.7 MW Gas Compressor
0ver 70% of wedges loose or missing

23. Typical Detected Faults Damage due to wedge movement
13.8 kV 12.7 MW Gas Compressor
Typical Detected Faults Damage due to wedge movement

24. 9MW Gas Compression Motor
Banded Discharge is
modulated which is due to
coil movement .....

25. 9MW Gas Compression Motor

26. 9MW Gas Compression Motor
Good Coil
Air Duct Impressions

27. 9MW Gas Compression Motor
Damaged Coil
Air Ducts (no abrasion)
Lamination groves due to movement

28. 9MW Gas Compression Motor
Heavily Damaged Coil Due to impacting on slot bottom

29. 2420KW 11kV ASEA synchronous compressor motor

30. Outcome of A PD Analysis Survey
Detect any potential insulation problems.
The contribution of the different problems.
Location of problems within the winding.
Development in windings condition (through regular monitoring)
Early detection allows scheduling of remedial work/repairs.
“Provide the maintenance engineer with the information to make
The most cost effective decisions on planned maintenance”

31. Partial Discharge Analysis
Not an exact Science.
Does not predict when plant is likely to fail.
BUT will highlight which machines are most likely to fail.
Does not detect Inter-turn Faults
More room for improvement in defect recognition.
Future development in insulation/motor designs.

32. Condition Monitoring Of High Voltage Machines By The Analysis of
Electrical Partial Discharges
22 April 04
Dino Kouadria
PhD MSc BEng CEng MIEE MIEEE