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Condition Monitoring Of High Voltage Machines By The Analysis of Electrical Partial Discharges

Condition Monitoring Of High Voltage Machines By The Analysis of Electrical Partial Discharges 22 April 04 Dino Kouadria PhD MSc BEng CEng MIEE MIEEE. CONTENT. What is Partial Discharge (PD) Analysis. Stator winding Common Faults . Basics Of Why & How To Measure PD. Case Studies.

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Condition Monitoring Of High Voltage Machines By The Analysis of Electrical Partial Discharges

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  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 electricalcondition 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. • LeaveMaintainReplace

  6. Why Do HV Stators Fail? • Failures due to windings’ insulation failure caused by the combined • electrical, thermal, environmental and mechanicalstress 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. Regardless of the type of defects, they all result in the generation of Electrical partial discharges. So what are partial discharges?

  8. Vs Cavity Vs = Applied voltage What is a partial discharge Local breakdown that short circuits part of theInsulation. • 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. + + - Patterns & location of pulses within AC cycle Is the key in defects identification Partial Discharges Basic Theory

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

  12. 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 installationtime. • 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 studies1 Contamination on old pump motor 11KV-3MW2 New motor manufacturing problem 13.8KV-12MW3 Coil Movement old motor 6.6KV-9MW4 Plastics plant old motor high PD 11KV-2.5MW

  19. 3MW Pump Motor Total Discharge Activity

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

  21. 13.8 kV 12.7 MW Gas Compressor

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

  23. 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 detectInter-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

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