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DOWDING & MILLS Condition Monitoring Of High Voltage Machines By The Analysis of Electrical Partial Discharges 22 April 04 Dino Kouadria PhD MSc BEng CEng.

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Presentation on theme: "DOWDING & MILLS Condition Monitoring Of High Voltage Machines By The Analysis of Electrical Partial Discharges 22 April 04 Dino Kouadria PhD MSc BEng CEng."— Presentation transcript:

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

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

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

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

6 DOWDING & MILLS 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 DOWDING & MILLS Regardless of the type of defects, they all result in the generation of Electrical partial discharges. So what are partial discharges?

8 DOWDING & MILLS What is a partial discharge Local breakdown that short circuits part of the Insulation. 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). Vs = Applied voltage Cavity VsVsVsVs

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

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

12 DOWDING & MILLS 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 DOWDING & MILLS Rogowski Coils: Typical Installation

14 DOWDING & MILLS Partial Discharge Analysis/Display: Typical Cycle

15 DOWDING & MILLS Partial Discharge Analysis/Display: Total Discharge Activity

16 DOWDING & MILLS Partial Discharge Analysis/Display: Pulse Height Analysis

17 DOWDING & MILLS CASE STUDIES

18 DOWDING & MILLS Case studies 1 Contamination on old pump motor 11KV-3MW 2 New motor manufacturing problem 13.8KV-12MW 3 Coil Movement old motor 6.6KV-9MW 4 Plastics plant old motor high PD 11KV-2.5MW Case studies 1 Contamination on old pump motor 11KV-3MW 2 New motor manufacturing problem 13.8KV-12MW 3 Coil Movement old motor 6.6KV-9MW 4 Plastics plant old motor high PD 11KV-2.5MW

19 DOWDING & MILLS Total Discharge Activity 3MW Pump Motor

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

21 DOWDING & MILLS 13.8 kV 12.7 MW Gas Compressor

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

23 DOWDING & MILLS Typical Detected Faults Damage due to wedge movement 13.8 kV 12.7 MW Gas Compressor

24 DOWDING & MILLS Banded Discharge is modulated which is due to coil movement MW Gas Compression Motor

25 DOWDING & MILLS 9MW Gas Compression Motor

26 DOWDING & MILLS Good Coil Air Duct Impressions 9MW Gas Compression Motor

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

28 DOWDING & MILLS Heavily Damaged Coil Due to impacting on slot bottom 9MW Gas Compression Motor

29 DOWDING & MILLS 2420KW 11kV ASEA synchronous compressor motor

30 DOWDING & MILLS 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 Outcome of A PD Analysis Survey

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

32 DOWDING & MILLS 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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