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

DOWDING & MILLS

Condition Monitoring Of High Voltage Condition Monitoring Of High Voltage

MachinesMachines

By The Analysis ofBy The Analysis of

Electrical Partial DischargesElectrical Partial Discharges

22 April 0422 April 04

Dino KouadriaDino KouadriaPhD MSc BEng CEng MIEE MIEEEPhD MSc BEng CEng MIEE MIEEE

DOWDING & MILLS

CONTENTCONTENT

What is Partial Discharge (PD) Analysis.What is Partial Discharge (PD) Analysis.

Stator winding Common FaultsStator winding Common Faults..

Basics Of Why & How To Measure PD.Basics Of Why & How To Measure PD.

Case Studies.Case Studies.

Open Discussions.Open Discussions.

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It is an It is an electricalelectrical condition monitoring condition monitoring

technique.technique.

Used to assess the condition of hv Used to assess the condition of hv

insulationinsulation

Wider applications Wider applications

static static itemsitems i.E. Switchgear, cables i.E. Switchgear, cables

transformers, etc. transformers, etc.

Dynamic items i.E. Dynamic items i.E. Electrical machinesElectrical machines

What is Partial Discharges AnalysisWhat is Partial Discharges Analysis

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Apply to HV motors & generators (>5kv)Apply to HV motors & generators (>5kv)

Online & off line tests.Online & off line tests.

Predominantly Predominantly on-line testson-line tests - - no shut no shut

downdown & & testtestss under under

normal stress normal stress condition.condition.

PDs Analysis On HV WindingsPDs Analysis On HV Windings

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Assess the current & development in Assess the current & development in

condition of the condition of the

windingswindings

Maintenance Maintenance planning planning based on machines’ based on machines’

health.health.

Elimination of unwanted/unexpected Elimination of unwanted/unexpected

shutdowns.shutdowns.

Assistance in Assistance in targeting maintenance effort targeting maintenance effort

effectivelyeffectively..

LeaveLeave MaintainMaintain

ReplaceReplace

PDs Analysis On HV WindingsPDs Analysis On HV Windings

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Why Do HV Stators Fail?

Failures due to windings’ insulation failureFailures due to windings’ insulation failure caused caused

by the combinedby the combined

electrical, thermal, environmental and electrical, thermal, environmental and mechanicalmechanical

stress factors.stress factors.

Most common causes in modern insulation are Most common causes in modern insulation are

mechanically induced defects i.E. mechanically induced defects i.E. Loose wedgesLoose wedges, ,

erosion due to erosion due to bar vibrationbar vibration etc. - etc. - Short time Short time

degradation process.degradation process.

Discharge between phases due to cracks / low Discharge between phases due to cracks / low

spacingspacing

Contamination of end windings.Contamination of end windings.

Others: internal voids, insulation ageing, Others: internal voids, insulation ageing,

delamination.delamination.

Electrical partial dischargesElectrical partial discharges

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Regardless of the type of defects, they Regardless of the type of defects, they

all result in the generation of all result in the generation of

Electrical partial discharges.Electrical partial discharges.

So what are partial discharges?So what are partial discharges?

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What is a partial dischargeLocal breakdown that short circuits part of theLocal breakdown that short circuits part of the Insulation.Insulation.

Formation of corrosive ions, acids, nitrogen oxides, ozone.Formation of corrosive ions, acids, nitrogen oxides, ozone.

Detected using Detected using of chemical sensors for detection.of chemical sensors for detection.

Emission of light, sound & electromagnetic waves. Emission of light, sound & electromagnetic waves.

Detected using Detected using ultrasonic devices, antennae, cameras..ultrasonic devices, antennae, cameras..

Injection of high frequency current pulses.Injection of high frequency current pulses.

Detected using Detected using electrical partial discharges measurement electrical partial discharges measurement

(pd).(pd).

Vs = Vs = AApplied voltagepplied voltage

CavityCavityVVss

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-

+ +

Patterns & location of pulses within AC cyclePatterns & location of pulses within AC cycleIs the key in defects identificationIs the key in defects identification

Partial Discharges Basic Partial Discharges Basic Theory Theory

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Importance Of Monitoring PDs Importance Of Monitoring PDs

Different defects produce different PD patterns.Different defects produce different PD patterns.

Complex PD patterns are produced when multiple defects Complex PD patterns are produced when multiple defects

are present.are present.

Failures are due to localized defects.Failures are due to localized defects.

PD pattern development over time represents developing PD pattern development over time represents developing

degradation processes.degradation processes.

Provide an early warning of potential problemsProvide an early warning of potential problems

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Discharge Discharge levelslevels

TimeTime

3 – 6 months3 – 6 months ?? Years?? Years

CuringCuring Process Process Fabrication Defects

Contamination

Mechanical failure

Partial discharge monitoring over a machine Partial discharge monitoring over a machine life cyclelife cycle

Repair/action required

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PD DetectionPD Detection

Two main type of permanently installed sensors.Two main type of permanently installed sensors.

Capacitive couplers first developed in north Capacitive couplers first developed in north

america. Main users power industry.america. Main users power industry.

Rogowski coils first developed for the north sea Rogowski coils first developed for the north sea

oil industry. oil industry.

North sea oil industry – mainly Rogowski coilsNorth sea oil industry – mainly Rogowski coils

Ease of Ease of installation: installation: no disconnection of supply no disconnection of supply

cables, cables, lessless installation installation timetime..

Atex certifiedAtex certified

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Rogowski Coils: Typical InstallationRogowski Coils: Typical Installation

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Partial DischargePartial Discharge Analysis/Display Analysis/Display: Typical : Typical Cycle Cycle

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Partial Discharge Partial Discharge Analysis/DisplayAnalysis/Display: Total : Total Discharge ActivityDischarge Activity

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Partial Discharge Partial Discharge Analysis/DisplayAnalysis/Display: : Pulse Pulse Height AnalysisHeight Analysis

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CASE STUDIESCASE STUDIES

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Case studiesCase studies

1 Contamination on old pump motor 1 Contamination on old pump motor 11KV-11KV-3MW3MW

2 New motor manufacturing problem 2 New motor manufacturing problem 13.8KV-12MW13.8KV-12MW

3 Coil Movement old motor 3 Coil Movement old motor 6.6KV-9MW6.6KV-9MW

4 Plastics plant old motor high PD 4 Plastics plant old motor high PD 11KV-2.5MW11KV-2.5MW

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Total Discharge ActivityTotal Discharge Activity

3MW Pump Motor

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White power deposits clear White power deposits clear signs of discharge activitysigns of discharge activity

Typical Detected Faults Damage due to movement and contaminationTypical Detected Faults Damage due to movement and contamination3MW Pump Motor

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13.8 kV 12.7 MW Gas Compressor13.8 kV 12.7 MW Gas Compressor

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13.8 kV 12.7 MW Gas Compressor13.8 kV 12.7 MW Gas Compressor

0ver 70% of wedges loose or missing

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Typical Detected Faults Damage due to wedge movementTypical Detected Faults Damage due to wedge movement

13.8 kV 12.7 MW Gas Compressor13.8 kV 12.7 MW Gas Compressor

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Banded Discharge is Banded Discharge is

modulated which is due to modulated which is due to

coil movement .....coil movement .....

9MW Gas Compression Motor

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9MW Gas Compression Motor

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Good Coil Good Coil

Air Duct ImpressionsAir Duct Impressions

9MW Gas Compression Motor

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Damaged Coil

Lamination groves due to movement

Air Ducts (no abrasion)

9MW Gas Compression Motor

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Heavily Damaged Coil Due to impacting on slot bottom

9MW Gas Compression Motor

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2420KW 11kV ASEA synchronous compressor motor

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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 SurveyOutcome of A PD Analysis Survey

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Partial Discharge AnalysisPartial Discharge Analysis

Not an exact Science.Not an exact Science.

Does not predict when plant is likely to Does not predict when plant is likely to

fail.fail.

BUTBUT will highlight which machines are will highlight which machines are

most likely to fail.most likely to fail.

Does not detectDoes not detect Inter-turn FaultsInter-turn Faults

More room for improvement in defect More room for improvement in defect

recognition.recognition.

Future development in insulation/motor Future development in insulation/motor

designs.designs.

DOWDING & MILLS

Condition Monitoring Of High Voltage Condition Monitoring Of High Voltage

MachinesMachines

By The Analysis ofBy The Analysis of

Electrical Partial DischargesElectrical Partial Discharges

22 April 0422 April 04

Dino KouadriaDino KouadriaPhD MSc BEng CEng MIEE MIEEEPhD MSc BEng CEng MIEE MIEEE