cr4 - thread_ high pd value on 13.pdf

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parimalamActiveContributor

JoinDate:Feb2009Posts:16

HighPDvalueon13.8KV,12,5MWsteamturbinegenerator02/14/20099:24AM

Hi,Goodday.Thisismyfirstpostonthisforum.wehaveoneofour13.8KV,12.5MW,turbinealternatorhavinghighPDvalues,somespecilistsaysthisalternatorneedstoberewindedtoavoidfailureofwinding.presentlythisgeneratorisrunningonloadabout11MW.myquestionhereis,howexactlytheresultsarePDmeasurements,itisnecessarytodorewindingthisalternatortoavoidunexpectedfailure???isthereanywayonecanprolongthelifeofthisalternatorhavinghighPDvalue.Irequestspecilistinthisforumtorespondtothisqueryasquicklyaspossible,sothatitwillbehelpfultotakedecisiononthisissue.kparimalam@gmail.com,+6592326838

thanksandbestregardsK.Parimalam

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#5"Re:HighPDvalueon13.8KV,12,5MWsteamturbinegenerator"bySiswantoon02/15/200912:24PM(score2)

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CJMcGillGuru

JoinDate:Jul2008Location:SoCalUSAPosts:563GoodAnswers:24

Re:HighPDvalueon13.8KV,12,5MWsteamturbinegenerator02/15/200912:18AM

HiParimalam,welcome.

IthasbeenafewyearssinceIdealtwithlargemotorassessmentandrepair,andIamsurprisedthatyouhavenotreceivedanypostssofar,butIthinkyouwoulddowelltogetinputfromseveralsourcesthatoffertheseservicesprofessionally.

Partialdischarge(PD)whenidentifiedathighlevels,especiallywhenacontinuousmonitoringhasshowadramaticincreaseinlevels,isaverygoodindicatorofseriousdegradationintheinsulationorcracksinthebarsetc.Sometimeserrorsinplacingthewedgesorflawsinthemetalscanbegintoproducethesedischargepatterns,andusuallyseriousconsequencesarepending.

HereareafewquicklinksIfoundthatmayhelpyou.

discussioninformationanddefinitioninformationanda

supplierofequipmentandservicesspecifictoyourneed

Hopeyougetwhatinformationyouneedinatimelymanner.

Regards,CJ

__________________Idonot'knowitall',butiwilladmitthatIwouldliketo.CJM

myn1996Commentator

JoinDate:Jan2009Location:PhilippinesPosts:60


Parimalam,

AhighPDreadingdoesnotmeanthatthegeneratorneedsrewindingasap.Aswithallothermethodsoftestinganddiagnostics,PDisnotonlyasciencebutratheritisalsoanart.

Forexample,EquipmentAmightshowahigherPDvaluecomparedtoEquipmentB.However,experiencedoesnotalwaysshowthatEquipmentAfailedsoonerthanEquipmentB.InfactEquipmentAlastedtoitsnormallifespanasifitsPDvalueiswithinnormalrange.

Additionally,wasthisequipmenttestedbeforewithPD?Ifitwastested,whatwheretheresults?ComparedtothepastPDresults,isthe

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#5

GoodAnswers:4 presentPDvaluetoohigh?Istherateofincreaseacauseofalarm?

Now,thisiswheretheexperienceofthetestingengineercomesin.HistoricalPDdatawouldgreatlyhelpinanalyzingthepresentone.Awisetestingengineerwouldnotdependononlyjustonetestingmethod.Weretheretestsperformedonthisgeneratorbyyourspecialist?Whatarethesetests?Whatdidtheresultsimply?

AdditionaltestishighlyrecommendedtoconfirmthePDfindings.AnFDS(frequencydomainspectroscopy)orDFR(dielectricfrequencyresponse)ifyouwanttheotherterminology,isstronglyrecommendedforthissituation.

__________________Patriotismisthelastrefugeofscoundrels




DearCJMcGillPoweruser,myn1996Associate,InstruformParticipant,

Ithankallofyoufortakingtimeandprovidingguideline,andIamveryhappytoheartheresponsesandnowIwillfurtherexploreasperyourrecommendationsandalsotolookforthetestsuchasFDS(frequencydomainspectroscopy)orDFR(dielectricfrequencyresponse).canyoupleaseadvicemethebestmethodforPDmeasurement,asofnowwehavemeasuredwithonlinePDmeasurementonlyonceusingtoshibaequipmentandusedinternalsinglewindingtemperatureresistorasasensingelementforthistest.AlsowefoundlotsofwhitepowderonrunningturbinegeneratorandthiswhitepowderbecauseofPDactivityisitnot??.willCO2cleaningonrunninggeneratortoremovethesewhitepowderisnecessary,supposeweuseCO2cleaningisthereanychancethatwemaydamageinsulationfurtherleadingtoPD???advicerequired.

Thanksandbestregards

K.Parimalam

CJMcGillGuru

JoinDate:Jul2008Location:SoCalUSAPosts:563GoodAnswers:24

Re:HighPDvalueon13.8KV,12,5MWsteamturbinegenerator02/15/20091:34PM

BynowyouhavereadtheexcellentinformationfromSiswanto,withgreatdetailedphotos.(GA)

Inoticedthementionofwhitepowderspecificallyinconnectionwithgreasewhenloosetiesontheleadswerefound.

MyinstinctsleadmetorecognizethatthispowderwillhelpintheidentificationoflocationsaffectedbythePD,andcleaningmayerasetheevidence.Asfarascleaning,thatwoulddependonthepowderpropertiesandwhetherthepowderitselfwillcausefurtherproblems.

Iwillleavethefurtherdiscussionaboutthepowdertomoreexperiencedindividualswithspecificknowledge

__________________Idonot'knowitall',butiwilladmitthatIwouldliketo.CJM

InstruformAssociate



Ihaveover40yearsofPDtestingexperienceandwouldsupportwhatMyn1996&CJMcGillrecommend.PDlimitvaluestandardsaresetfornewmachinesandhaveonlybeensetinthelast5yearsaftersome20yearsoftrial.Forlifeexpectancyyouneedtoascertainthechangefrompreviousresults/reportstoevaluateyoursituation.Thatiswhywhentestingforservicelifeexpectancytheinception,extinctionvoltagesandthedischargeshapeareimportantreadings&observationsandtogetsomeconsistencythesameprofessional&experiencedtestershouldbeusedonaregularbasisifpossible.UnfortunatelyPDtestingisstillbothascience&aseatofthepantsfeel.Makepreparationsbyallmeans,havecoilsavailabletolimityouroutagetime,butdon'tpanicyoucouldstillhaveyearsofservicefromthemachine.

SiswantoCommentator

JoinDate:Mar2008Location:JAKARTA.INDONESIAPosts:73GoodAnswers:15


Dearparimalam:

Welcometothisforum

ourcolleagueCJMcGillandmynhasgiveagoodsharing,IwouldliketotryoffersolutionbasedonmyexperiencesduringrepairofGeneratorsinINDONESIA.

Since10yearsagoIjustfound2casesofPDFailureonGenerators,duetoitsnotdetectedandsettledatearlierstage.

HaveyoutestPDbefore?ifyes,plscomparedtheresulthowfastthePDlevelacceleration,andyouknowwhereisthePDactivitieslocation?

Attheendwinding?

intheslot?

attheoverhang?

intheinternalwindinginsulation?

IfPDactivitieshasfoundattheendwinding,slotandoverhang,itslittlebiteasytorepair,butiffoundwithinintheinsulationduetovoidsitsverydifficultandalmostimpossibletorepairexceptrewinding.

CanyoutoldmethePDlevelandlocation?whichbarsthathavehighPDlevel?

Followingarticlemaycanhelpyoutomadeadecision.Plsforgivemeifitsnotsufficientinformationforyou..

PARTIALDISCHARGEphenomenononElectricmachine

2

Coronaactivity

Coronaisdefineastheionizationofgaswhenexposedtoanintenseelectricfield,thedischargehaveawiderangeoffrequencies[40kHzto100MHz].

PartialDischarge(PD)inthelargegeneratorapplication,isusuallyassociatedwiththehighvoltagestatorconductorbars.

Coronaactivityintherotatingmachine:

SurfacedischargeduetoCoronaatendwinding(EndwindingDischarge)

InternaldischargeduetoCoronaatinsideoftheinsulation(voidsordelamination)

SlotdischargeCoronaatgroundwallinsulationresultingfromlosscontactbetweenbarandcore.(damagedonthesemiconductivecoatingonthestatorbar)

SurfacedischargeduetoCoronaatoverhangofwindingresultingfrombarvibration

Aproblemcommontomachineswiththermoplasticinsulationisthatthenormalthermalcyclingiscausescoilmovementintheslot,tendtogeneratecrackwithinthegroundwallinsulation.

Atapeseparationisaseparationoftapecoveringthewallinsulationofthecoilduetoaxialexpansionandcontractionoftheconductorsandtheopposingforcesoftheslotappliedtothewallinsulation.

Insomecasesonlythearmortapeisseparated,inothercasesthemicatapecomprisingthegroundwallinsulationisalsoaffected,whenthisoccurafewlayermaybeaffectedandthewholetapewillmovecreating"aneck"inthecoil.

FollowingaretypicalinsulationfailureduetoPDactivitiesbasedonoursiterepairexperiencesonGeneratorsinINDONESIA.basedonourexperiencessince10yearsago,wefound2caseswindingbreakdownduetoundetectedPDactivitiesonstatorwindinggenerators,wedomuchtorepairofsemiconductivecoatingandstressgradingtominimizeandpreventthePDonthewinding

A.PDInspection,

PDinspectiononAlstom87.5MVAafter18topbarscompletedremovedfromslot

Coronaprobemeasurements

Coronaprobetestingcanpinpointpartialdischargelocationineachslot.Itsupplementsonline/offlinepartialdischargetestsbypreciselylocatingpartialdischargetoaparticularcoiloraspot.ThecoronaprobecanalsobeusedasatestingtooltomeasurelevelsofPDactivity.Coronaprobetestingcanbeperformedeitherwiththerotorinoroutofthemachine

EndoscopicPDVisualinspectiononAlstom87.5MVA

PDVisualinspectionbyUVcameraon6.6KVMotors(figtakenfromOfil)

WindingInspection

FollowingaretypicalrootcauseofPDactivities

StatorwedgelooseonGEgenerator49,5MVA

WhenStatorwedgehasloose,followingpartsmayaffectedloosetoduetomovement.

FillerslipoutonMitsubishiGenerator125MVA.

Endwindingmovementduetostatorwedgesloose(notsufficienttokeepstatorcoilstayinplace)onGEGenerator237MVA

Loosesupportduetovibration

Typicalwindinginstallmentintheslot

Whenties,wedge,supporthasloose,statorbarswillmovementanddamaged.

HVCoil

Preventiveaction

WhenwedgewasfoundlooseandtheaccelerationofPDactivitiesInthewindinghasincreasewithcomparedtotheprevioustestorthePDtesthasoverorclosetothemaxthreshold,followinginspectionmustbedonetomadeadecisiontorepairorreplace.

1Checkthewedgetightness'foundloosemorethan30%mustbereplaced,concerntoreplacealsoforradialsprings,improvethematerials

2Checkthecoilblocking,ties,foundloose,break,toodry,missing,mustberepaired

3Checkthewindingsupport,surgerings,boltsetc,foundloosemustberepairedorretight

4PDwasfoundhighonthewinding/

IfPDactivitiescausedbyloosecontactbetweencoilbarstoslotwalls,dorepairthesemiconductivebycoatingorsemicondpainting

IfPDactivitiescausedbylooseorstressgradingdeteriorationatendwindingportion,dorepairstressgradingbycoating

IfPDactivitiescausedbyinternalinsulationvoid,wecan'tdonothingexceptrewinding

Followingarerepairreferenceswhenwerepaironlargegeneratorupto250MVA(basedonourexperiences).

Replaceofstatorwedgeandradialspring

TakenfromIRISEngineering

Repairblockingcoil,ties,support,etciffoundloose,defect

Injectthesideripplebysemiconductivepainting

Suggestionsolutionforyourproblems

Followingmysuggestion

1. IdentifiedthePDsources,trytorepairofsemiconductivecoatingintheslot,beforetorepairallstatorwedges,ripple(topifany),fillersmustberemovedfirst.

2. DoretestPDbyofflinemethod,andprovidewithbartobarscanningorbyprobetoidentifiedwhichcoilsarehavehighPDlevelwithvoltageUn/1.73(linevoltagetoground)

3. Inspectallwindingregion,insideslot,endwindingetc,useendoscopic(borescope)toinspectwindingintheslot4. Dotestinsulationtangentdelta,withvoltagetestsameforoflinePDtest.5. Replaceallstatorwedges,toprippleIfprovide)andflatfillers,iftheexistingarenotprovidebytopripple,andifthespaceis

possibleenoughtoaccommodateoftopspring,providethethespring,andimprovethematerialfromclassBtoclassF,NEMAG11isrecommended

6. Retightallwindingsupportandreplacethewindingtiesiffoundloose,missing,broken,etc7. Repairtheendwindingregioniffoundstressgradingdefectorreinsulatetheendwindingiffounddelaminationontheseareaand

applieditbystressgradingpaintafterreinsulation.8. Cleanupallwindingareas,9. DryoutthestatorwindingbyusingDCsupply,keepthetemperatureround8090degreecelround24hrsormoreifmoistureis

stillpresence10. Recoatingbyvarnishpainting11. Whengeneratorrunning,ifequipmentavailable,dotestPDonline.12. Recordallthetestresultasbasedline

GoodLuck

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HitoAll,

ItissimplygreatandInevergetsuchvaluableinformationanywerebutinthisforumitisamazingandIverymuchthankfultoallofyou.Iamgoingthroughalltheinformationandsuggestionandwilltaketimeformetounderstandfully.inthemeantimeIwillreplyfewanswerstothequestionspostedhere.

thisplant2x12.5MW,13.8KVsteammachines(FSO)runningcontinuouslyforthepast10yearsandnowonealreadyfailedandalsothefailuredamagedthecorelaminationsandendupwiththebigjob,rewindingandlaminationrepairsandthejobisongoingatpresent.Myquestionhereisthereyanywaywecouldhavepreventedcoredamageduetocoilgrounding???intermsoffastswitchingprotectionrelayetc..????

ThesemachinesnevercheckedforPDandnowonlyafterfailurewehavecheckedtherunningTAandfoundPDvalueisveryhigh(therewasnoearlierreadingforcomparisson).presneltywearerunningthisTAonlywith10%stationload,duetofear.Myquestionhere,runninglessloadwillhavelessPD???,eventhoughvoltageissame??curioustoknowsomesaynochangeinPDasthevoltageisthecreteriaforPDIamthinkinginotherwaybyhavinglowload,IreducethetemperatureandalsovibrationofcoilsomeextendreducedcanrunlongerperiodtocaterthestationloadtillwerepairanotherfailedTA.needadvice.

CananyonecansuggestonlindPDmetereconomicalmodelbrandforpurchaseinordertokeepitatsiteforfrequentmonitoring

restinnextpost.

SiswantoCommentator

JoinDate:Mar2008Location:JAKARTA.INDONESIAPosts:73GoodAnswers:15


Dearparimalam

Asyouknow,PDisassociatedwiththehighvoltagestatorconductorbars,PDwouldbestillproducedwhengeneratorisenergizeevennoload,ofcourseyes,reducedloadwouldbereducedalsotheaccelerationofPD,becauseyouhavereducedalsothevibrationandthermal.

Mysuggestion,whenyouscheduledtoshutdown,doinspectonyourwinding,

InspectthePDbyofflinemethod(probetestisrecommended,itsdesignedtocheckandidentifywhichcoilbarsarehavehighPDlevel,soyoucanrepaired,inmyopinionthehighPDlevelinyourwindingiscausedbysemiconductivedeterioration).YoucanalsocheckthePDactivitybyusingendoscopic(borescope),checkthePDviaventholes(airduct)ofwinding

ProvidealsoTangentDeltatest,isusefultoanalysisofyourwinding

Statorwedgetightens,looseonthispartswillcreatebigproblemsonyourwinding,suchas:

oDeteriorationonsemiconductivelayer,duetothestatorbarcoilswillmovemententireslot

oLooseendwindingblockingandties,itscancreateendwindingdeteriorationoninsulation,electricfieldconcentrationonendofcorecanoccurringwhenstressgradingfailure,mayalsocancreatedelaminationonscarfjoin,scarfjoinisinsulationtapejoinbetweenoverhangtoendwindingarea,thisistheweaknessinsulationjoin.

oWhenloosewedgeswasfound,itscanalsocreateinsulationvoidsacceleration,whenPDiscausedbythewindingvoids,youcan'tdoanythingtorepair,exceptrewinding

Note:torepairsemiconductivelayer,usematerialsasbellow:

Entireslot,use:"coronapainting",i.e.VonRollIsolaproducttypeP8003orequivalent.

Endwinding,use:"coronapainting",i.e.vonrollisolaproduct,typeP8001orequivalent

Cleanfirstanddryoutbeforeappliedthesematerials

oWhenyoufoundstatorwedgesloose,replaceandimprovethematerials,providewithradialspringsifthespaceispossibletoaccommodateit,forwedgematerialyoucanimprovebyNEMAG11materialorequivalent,andforradialspringimprovetoclassF

RetightorreplacetheendwindingandblockingcoiltiesbyusingbendingtapeclassF,alsoreplaceifyoufoundlooseormissingofblockingcoils,thefunctionofBlockingcoilsareusedtodeterminetheclearancebetweenthecoilsideattheendregion,toeliminate

mechanicalstressesarisingcoilmovement,thatwillberesultingcoiltouchingeachotherattheendwinding,Blockingcoilsarealmostmadefromsolidinsulationmaterials(suchastextolite,felt,etc)whichissoakedinresin.Blockingcoilisalwaysheldinplacewithties.Oftensolidseparatortendtolooseafterlongperiodofoperation,inseverecasesitwillfallfromthewinding.

Inspectalltiesonthesurgeringsupport,ndwindingandsurgeringsaresecuredwithties,aswiththeblockingcoilsties,whenexposedoveralongtimeoperation,tiestendto"dry",becomelooseduetolosevolume,brittle,broken,etcretightorreplaceitbyusingbendingtypeandsoakedwithresin

Inspecttightensofsupportstructures,foundsludgeorgreasingorwhitepowderisindicateloose,retight.

Inspectthedustunderwindingclosetocore,extractitandcheckit,foundmetaldustonit,indicatestatorcoreloose,checkthecorelooseness,retighttheboltssupportbasedonmanufacturerspecification,foundbent,brokencoreteeth,repairitandappliedepoxy/resinorRTVonitstopreventorminimizethecorevibration.

InspectthecorebyusingDigitalELCIDmethod,foundhotspot,repairedassoon,itsmustbedonewhenyouperformrewinding,recordedtheresultasbasedline,doregularlyin5years.

Corerepairandtest,seethefollowinglink.

http://cr4.globalspec.com/thread/32530/HowtoRepairaPartialCoreStatorGenerator

PDInstruments.

Youcanbrowsingintheinternet,itsmanysuppliercanprovide,orourcolleaguesheremaycanhelpyoutoprovidethetechnicalspecificationandsupplierfortheinstruments.

PDinstrumentforofflinetest,PDProbemaythecheapest,anditsusefultoquickidentifiedofPDlocation,

GoodLuck.

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cr4 - thread_ high pd value on 13.pdf

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