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    FACILITIES INSTRUCTIONS, STANDARDS, AND TECHNIQUES VOLUME 2-7

    MECHANICAL OVERHAUL PROCEDURES FOR HYDROELECTRIC UNITS

    Roger ClineJuly 1994GENERAL ENGINEERINGDIVISION OPERATION AND MAINTENANCE BRANCH

    UNITED STATES DEPARTMENT OF THE INTERIOR BUREAU OF RECLAMATION

    DENVER, COLORADO

    Section

    I. IntroductionII. Preparation

    2.1 Maintenancerecords

    2.2 Inspection2.3 Drawings

    2.4 Liftingdevicesandrigging

    2.5 Scheduling2.6 Hydraulic transientstudy

    2.7ProcurementofequipmentandsuppliesIII. Disassembly3.1Preshutdownandpreteardownreadings

    3.2 Labelingandmatch marking

    3.3 Disassembly Inspectionandrepairofunitcomponents4.1 Bearings

    4.2 Turbinerunner

    4.3 Wicketgates4.4 Facingplatesandwicketgatebushings

    4.5 Packingboxandshaftsleeve

    4.6 Servomotors

    4.7 Cooling coilsandgeneratorair coolers

    4.8 Exciter

    4.9 Generatorstructure

    4.10 Generatorbrakes

    V. Fieldmachiningprocedures

    5.1 Seal rings

    5.2 Facingplates

    5.3 Wicketgatebushing lineboring

    5.4 Redoweling

    5.5 Couplingboltholes

    VI. Reassembly

    6.1 Torqueorstretch ofbolts

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    6.2 Unitalignment6.3 Wicketgateadjustment6.4 Gasketsand

    packing6.5 Governor

    VII. Startup

    7.1 Final inspection

    7.2 Initial startup

    7.3 Operational readings

    CONTENTS

    CONTENTS-(continued) APPENDICES

    AppendixA-Seal ringdesignandspecificationsAppendix B-Sample calculationfor

    seal ringinstallationAppendix C-Tolerancesfor hydro unitassembly Appendix D-Wicketgateadjustmentprocedures

    ii

    MECHANICAL OVERHAUL PROCEDURES FOR HYDROELECTRIC UNITS

    I. INTRODUCTION

    Periodically, all hydroelectric generatorsrequireamajoroverhaul. Theextentoftheworkrequiredduringanoverhaul will dependagreatdeal onoperating conditions

    such aswaterquality and howthe unitwas loaded.Inorderfortheoverhaul to

    proceedsmoothly andtoaccomplish all theworkrequired, planningshouldstartwell beforetheoverhaul starts.

    II PREP ARA TION 2.1 Maintenance records

    Oneofthebestsourcesofinformationinplanningamajoroverhaul shouldbethe

    maintenancerecordsforthe unitor unitsinvolved. Theserecordsshouldprovidedetailsonthe history, presentcondition, andany unusual maintenanceproblemsofthe unit. This can helpidentify specific itemsthatmay needattentionduringthe

    overhaul. Reportsofpreviousoverhauls canpreventthesamemistakefrombeing

    madetwiceandmay providetipsthatcanexpeditetheoverhaul procedure. Themaintenancefilesmay alsoprovidenamesofsourcesforpartsandmaterials.

    2.2 Inspection

    Atleast6months, butpreferably a yearbeforetheplannedoverhaul, athorough

    inspectionofthe unitshouldbemadetodeterminethe conditionofthe

    equipment.Any itemsthatwill requiremaintenanceorreplacementshouldbedocumented. Many times, duetopowerorwaterdelivery constraints, the

    amountoftimeallowedforthe unitinspectionmay bevery limited. Becauseof

    this, any itemthatcanbeinspectedor checkedwithoutafull clearanceshouldbetaken careofpriorto, orfollowing, theoutageforthemaininspection. Thiswill

    allowmoretimeforathorough inspectionoftheotheritems.Theinspectionshouldinclude, butnotbe limited, tothefollowingitems:

    Turbine runner. Unwaterthe unitandinstall drafttubescaffoldingtoallowthe

    inspectionofthe undersideoftherunner. Checkeach bucketcarefully for

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    cavitationdamageand cracks.Ifpossible, usediepenetrantorother

    nondestructivetestto checkfor cracks. Compareseal ring clearancereadingswith design clearances. Openwicketgatestofull opentoallowinspectionof

    inletareaofrunner.Again lookfor cavitationdamageand cracks.

    Draft tube. Checkconditionofcoatingondrafttube liner Lookforanycavitationdamage, especially directly undertheturbinerunneronthethroatring. Tapdrafttube linerwith a hammertofindany voidsthatwill require

    grouting.

    Spiral case and penstock. Checkconditionofinterior coatingandexterior

    coatingofexposedportionsofpenstock. Pay special attentiontotheexteriorof

    thepenstockwhereitemergesfrom concrete.

    Wicket gates. With gatesopen, inspecteach gate, checkingthe conditionoftheseal area, thesurface coating, andforany cavitationdamage.Ifsealingsurfaces

    are unevenordamaged, they shouldberepairedby weldingandmachiningbacktodrawingdimensions. With thegates closed, checkthetopandbottomclearancesbetween-thegatesandthefacingplatesandthe clearancesbetween

    thegates. The heel andtoesidesofthegateshouldboth bemeasuredwhencheckingthetopandbottom clearances.In checkingthe clearancesbetween

    gates, checkthe clearanceatthetop, middle, andbottom. Checkconditionof

    facingplates lookingforany gallingorwearfrom contactwith thewicketgates.Ifthefacingplatesareseverely damaged, they will requirereplacementor

    resurfacing.

    Wicket gate operating linkage. Movegatesthrough theirfull rangeof

    movementinboth directionsseveral times. Watch forany lateral movementoftheshiftringorbacklash inthewicketgate linkage.Removethegatearmfrom

    onewicketgateandinspectthrustwasher. Checkwicketgatebushing clearance

    by jackingwicketgateshaftandmeasuringmovementwith dial indicators. This

    may notgiveatrueindicationofclearancedueto hardenedgreaseorother

    debrisinthebushings. Checkservomotorshaftforscoring.Ifpossible, remove

    servomotor cylinder headand checkcylinderboreforscoring.

    Bearings. Checkconditionanddimensionsofall spareguideandthrustbearings.Havebearingsrabbitedifnecessary.

    Generator rotor. Thoroughly inspectall stress carryingpartsofrotorfor cracks.Pay particularattentiontoweldsontherotorspider.

    Generator air coolers. Checkforany leaks.Ifpossible, inspectinterioroftubes

    forscalebuildupor corrosion.Ifspare coolersareavailable, makesurethey are

    ready forinstallation.

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    2.3DrawingsSeveral setsofmanufacturers as-builtdrawingsshouldbeobtainedforboth

    thegeneratorandturbine. Priortotheoverhaul, theoverhaul supervisorsshouldstudy thedrawingsandbecomefamiliarwith the

    Constructionofthemachine.Any specialinstructionsonany ofthedrawingsfordisassemblyorreassemblyshouldbenoted.Any special tools listednthedrawingsshouldbe located, orifnotonsite, purchasedorfabricated.

    A listofweightsofall ofthemachines componentsshouldbemadefromthe

    drawinginformation.Iftheweightsarenotlistedonthedrawing, approximate

    weightsmustbe calculated. This listisessential indeterminingwhatriggingwill

    berequiredfortheoverhaul.

    Drawingsofthepowerplantshouldalsobestudiedtodeterminewherethe

    major componentsfromthe unitcanbestored. Thespaceavailableandthe

    allowablefloor loadingmustbetakenintoaccount.Itmay benecessary tostoresomepartsoutsideoftheplant.Ifthisisrequired, someprovisionmustbemade

    toprotectthesepartsfromtheelements.

    2.4 Liftingdevicesandrigging

    All oftheriggingthatwill berequiredduringtheoverhaul, such asslings,

    eyebolts, andshackles, shouldbeon handwell beforetheoverhaul istobegin.

    Therequiredriggingforeach componentshouldbedeterminedbasedonthe list

    ofweights. Riggingalready onsiteshouldbeinspectedtomakesureitissafefor

    use. Special liftingdevicessuppliedby themanufacturer, such asforthe

    generatorrotororturbineshaft, shouldbe locatedandinspected.

    Dynamometersor cranescales canbeveryhelpfulduringanoverhaul.

    Acalibrateddynamometercantellhowmuch weightisbeing liftedduringasingle

    pointliftor howmuch weightone legofamultilegslingis lifting. This can

    preventoverloadingtheriggingwhen liftingpartsthatmay bestuck, such asthe

    turbine headcover, orwhensomeofthefasteners havebeenaccidently leftin

    place.Ifadynamometerisalready onsite, itshouldbe calibratedbeforethe

    overhaul begins.Sendingpersonnel whowill beinvolvedwith theriggingtoarigging classshould

    be considered. These classesprovidetraininginproperriggingprocedures,inspectionofcranesandriggingequipment, andproperoperatingprocedures

    for cranes.

    Asetoftwo-way radios canbevery helpful in communicatingwith the craneoperator. Voice-activated, headset-typeradioskeep handsfreetoallowthe

    signalertomake handsignalsandthe craneoperatortokeep his handsonthecontrols.

    A careful inspectionofthepowerplantcraneshouldalsobeaccomplishedbefore

    theoverhaul. Considerationshouldbegivento hiringa consultant, experiencedin craneinspections, to checkoutthe craneandproviderecommendations.

    Besidesinspectingthewirerope, brakes, hooks, hoistmotors, andgearboxes,

    operational testsshouldbeperformed.Itisvery

    3

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    importantthatbridge, trolley, and hoistcanbe joggedtoallowprecise

    positioningofthe load.Any problems or deficiencies with the crane must becorrected before the overhaul is started.

    Many timesitis helpful tofabricatespecial liftingdevicesorinstall atrolleytracktofacilitatedisassembly.Any shop-fabricated liftingdeviceorfixturemust

    bedesignedand certifiedby anengineerqualifiedinthisfieldandtestedat125percentoftheratedsafeworking load.All liftingdevicesandrigging hardwaremustbedesignedwith asafety factorofno lessthan5:1 basedonthetensile

    strength ofthematerialsofconstruction.

    2.5 SchedulingSupervisors, craftpersonnel, andengineersshouldmeettodiscusswhatwork

    will berequiredduringtheoverhaul sothattheschedule canbeoptimized.A

    critical path flowchartcanbevery helpful inschedulinganoverhaul. Typically,

    theflowchartshowstheorderinwhich varioustasksmusttakeplace, thetime

    requiredforeach task, andwhich tasks canbeaccomplished concurrently. Thereareanumberofcritical path methodsoftwarepackagesforpersonal

    computersavailabletoassistinsetting upaflowchart. Thissoftwareallowsthe

    scheduletobeeasily adjustedwhen unexpecteddelaysoccur. Many ofthesepackageswill alsoallowmanipulationoftheschedulebasedonavailable

    personnel.Insetting upthescheduleforamajoroverhaul, itisimportanttoberealistic and

    possibly a littlepessimistic inregardtowhatworkwill havetobedoneand how

    quickly itcanbeaccomplished. Onthefirstunittobeoverhauled, extratime

    shouldbeallowedfor unexpectedproblems.

    A checklistshouldalsobemaintainedtomakesureall tasksare completedandtorecordwhenthey were completed.-Astheoverhaul progresses, the list

    shouldbemodifiedtoincludeany itemsmissedontheoriginal listorremove

    any itemsnotrequired. The checklistshouldincludeany testingoradjustments

    thatwill berequiredbeforethe unitsarestartedorreleasedforoperation.

    2.6Hydraulic transientstudy

    Ifthe unitisbeing uprated, itis likely thatthe closurerateforthewicketgateswill havetobe changedtopreventoverpressuringthepenstockfollowinga load

    rejection. Todeterminewhatthenewwicketgatetimingshouldbe, awaterhammeror hydraulic transientstudy shouldbeperformedwith thenew

    parametersforthe uprated unit.Iftheoverhaul isnotan uprate, theoriginal test

    dataorrecordsshowingtherecommendedwicketgatetimingshouldbe located.Ifthisinformationisnotavailable, a hydraulic transientstudy shouldbe

    performed.Inthe caseofan uprateor losttestdata, loadrejectiontestsmustbeperformedfollowingtheoverhaul toverify theresultsofthe hydraulic transient

    study.

    4

    2.7 Procurementofequipmentandsupplies

    Basedontheinspectionofthe unitandonthediscussionsduringthescheduling

    meeting, a listofrequiredmaterials, tools, andservicesshouldbemade.

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    Specificationsformaterialsandtoolsrequiredfortheoverhaul shouldbe

    preparedaswell as StatementsofWorkfor contractservices.Ifitisnotcertainwhether contractservicewill berequired, the StatementofWorkshouldbe

    preparedsoitcanquickly beissuedonceitis confirmedthatitwill berequired.Donotwaituntil theoverhaul isinprogresstoorderparts. Someparts, because

    they are unusual orinshortsupply, may requireseveral months leadtimetoprocure.

    Thefollowingisa listofsuggestedmaterialsandtoolsto haveon handfora

    overhaul:

    Wicket gate bushings, thrust washers, linkage bushings, and shift ring

    bearing pads. Atleastonefull setofwicketgatebushings, thrustwashers,

    linkagebushings, andshiftringbearingpadsshouldbeprocuredandonsite

    priortotheoverhaul. Thewicketgatebushingsshould havean undersizedinner

    diametertoallowinplace lineboring.Ifthesparebushingssuppliedwith the

    turbinedonothavean undersizedinnerdiameter, anothersetofbushingsshouldbeordered.Abearingbronzesuch as UNS C93200 shouldbespecified.

    Thereareseveral typesofgreaselessorself-lubricatedbushingsavailablefromvariousmanufacturersfor useinwicketgateapplications. Each type hasitsownapplicationandinstallationrequirements. Conductextensiveresearch before

    switchingtoselflubricatedbushings. Remember, ifawicketgatebushingfailsinservice, inmostcasestheentire unitmustbedisassembledtomakerepairs.

    Contactfacilitiesthathaveinstalledthetypeofbushingbeing consideredtoget

    anaccountoftheirexperience. There havebeenfailuresofsometypesofself-

    lubricatedbushingsattributedto contaminationofsandorotherparticles

    betweenthebushingsandthejournals. These contaminantsareflushedoutbytheperiodic applicationofgreaseingrease-lubricatedbushings. Considerall

    factors, such asthe cleanlinessofthewaterandfrequency ofgateoperation,

    beforemakinga choice.Gasket and seals. Basedondrawingrecommendationsandonthe unit

    inspection, gasketmaterials, 0-rings, andothersealsshouldbeprocured. The

    seal materialsshouldbe compatiblefortheserviceforwhich they areintended.

    Gasketswill beneededonflangedoil andwaterpipe connections, oil tubs,

    generatorair coolers, thepackingbox, andothersimilarapplications. 0-ring

    materialismanytimesusedasasealontheheadcoverandoiltubcovers.Agasket

    cuttingkitcanspeed upthemakingofspecial gaskets. Silicon caulking

    5

    typegasketmaterial canbe useful duringanoverhaul, butonly thesiliconmaterial

    specifically formulatedfor useasgasketsshouldbe used, anditshouldonly be usedwherethepartswill nothavetobeshiftedafterinstallation. Thesiliconmanufacturersdirectionsshouldbefollowedregardingthematerials limitations.

    Markingtagsormarkedbins.Aspartsareremovedfromtheunit,they shouldbemarkedinsomeway toidentify wherethey goandstoredinamannersothatthey

    canbe conveniently locatedduringreassembly. Forsmall parts, such asnutsand

    bolts, storagebins labeledtoshowtheir contentsare helpful. For largeorbulky

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    parts, such aswicketgategrease lines, tagsdescribingwhatapartisandexactly

    whereitgoesarevery useful.Ifthepartitselfismarked, makesurethemarkingpenispermanentor useanengravertoetch thepart.

    Welding rod or wire. Ifthe unitinspectionindicatedthatsubstantial weldingrepairisrequired, asupply ofweldingrodorwireshouldbeobtained.Also, a

    weldingprocedurefortherequiredrepairsshouldbewrittenanddistributedtoallpersonnel thatwill beinvolvedinthewelding.

    Large rosebud or propane torches. Duringremoval ofthethrustblock, itis

    importantto heatitquickly sothatitexpandswithouttransferring heattothe

    generatorshaft. Several large weedburnertypepropanetorchesorrosebudoxyacetylenetorches canbe usedforthispurpose.Asthesetorchesarenotalways

    dependable, itisagoodideato haveatleasttwomorethanarerequiredtoactasbackups. Thesetorches canalsobe helpful inbreaking loosefrozenorseverely

    corrodedparts. Largerosebudtorches useagreatdeal ofacetyleneandsometimes

    requiretwoacetylenebottlestobemanifoldedtogether. Thesupplierofthetorch

    shouldbeabletoprovideinformationontheacetylenerequirementsforaparticulartorch.

    Hydraulic jacks. Various hydraulic jacks canbeinvaluableduringanoverhaul.

    Large hollow-corejacksarevery useful in loweringtheturbineandturbineshaft

    whenbreakingthe couplingandinpullingthe couplingbolts. Hydraulic wedgesand

    hydraulic ramsofvarioussizesare helpful inbreaking loosestuckparts.

    Hydraulic and pneumatic wrenches. Hydraulic-operatedwrenches cansavea

    greatdeal oftimeinremovingboltsthatwouldotherwiserequirethe useofasluggingwrench. Theirprimary useon hydrounitsarebreaking looseandtightening

    theshaftcoupling, boltsbuton large unitstheremay beanumberofother

    applications. Largepneumatic impactwrenches canalsogreatly speed

    6

    upthedisassembly andreassembly ofa unit. Cautionshouldbe usedin usingeitherhydraulic orpneumatic wrenchessoasnottooveror undertightenbolted

    connections.

    Magneticbaseddrill.Alargemagnetic-baseddrillcanbeespeciallyuseful duringan

    overhaul ifany componentsmustbeslightly shiftedandredoweledorifthereare

    othermodificationstotheequipment. Magnetic-baseddrillsallowfairly large holes

    tobeboredaccurately andalso canbe usedinreamingdowel holes.

    Shaft packing or seals. Whenevera unitisoverhauled, the compressionpackingof

    themainshaftandwicketgatesshouldbereplaced. Enough packingshouldbeorderedtoallowforerrorsin cuttingthepacking. Thereareanumberofdifferent

    typesofpackingavailable, sowhen choosingnewpacking, careshouldbetakento

    ensurethatitisthe correctsizeandtypefortheintendedapplication. Besuretotakeintoaccountall therelevantconditionsthepackingwill operate under, such as

    shaftsizeandrotational speed.Installingthewrongpacking canresultinexcessive

    leakage, reducedservice life, anddamagetotheshaftorsleeve. Wheremechanical

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    sealsare usedforthemainshaft, a completesetofseal segmentsshouldbeon hand

    in caseany ofthesegmentsaredamagedduringdisassembly.

    Micrometers and standards. Insideandoutsidemicrom, alongwith asetof

    standardsfor calibration, areessential fortheoverhaul ofa hydrounit. Micrometersarerequiredto checkdiametersofmainshaftbearingsandjournals, wicketgate

    bushingsandjournals, andotherwearpartstodetermineiftheyarewithintolerances.Anelectricmicrometermayalsoberequiredfor unit

    alignmentorinstallationofaboringbar.

    Boring bars. Evenifseal ringandwicketgatebushingreplacementarenotplanned,

    boringbarsforboth shouldbeavailablejustin caseofan unexpectedsituation.Suitableboringbarsshouldbe locatedandshippedtothejobsitewell beforethe

    overhaul.Ifboringisscheduled, theboringbarsoraccuratedrawingsoftheboringbarshouldbeavailablewell beforetheoverhaul sothatany modifications, such as

    mountingbracketsandboringanus, canbemade.

    Seal rings. On unitswith replaceableseal rings, asparesetofringsshouldbeonsite

    regardlessofwhetherornotreplacementisscheduled. On unitswherethe currentseal ringdesignisquestionableorwheretherotatingandstationary ringsareboth

    7

    stainlesssteel, anewdesignshouldbe considered. Formoreinformationonseal

    ringdesignandmaterial selection, refertoappendixA.

    Generator air coolers. Iftheinspectionormaintenancerecordsindicatethatthe

    generatorair coolersrequirerepair, specificationsfortherepairworkshouldbe

    prepared.Iftherepairworkcanbeaccomplishedby plantpersonnel, materialssuchassparetubesandall ofthetoolingrequiredforretubingshouldbeprocured.

    Scaffolding. Turbinepitscaffoldingtoprovideaccesstotheshaftcouplingandlowerguidebearing, anddrafttubescaffoldingtoprovideaccesstothedrafttubeandbottomoftheturbinerunner, arerequiredforany overhaul. Thescaffolding

    mustbedesignedtosupporttheweightofseveral maintenancepersonnel plus

    componentsfromthe unit, such asbearingsortherunner cone. Scaffoldingshould

    bedesigned, built, andinstalledinaccordancewith Reclamation Safety and Health

    StandardsandAmerican National StandardsInstitute (ANSI) StandardA10.8,

    Safety Requirementsfor Scaffolding.

    Cribbing material. Cribbingmaterial for cribbingpartsremovedfromthe unitshouldbeprocured. Largetimbersinvarious lengthsandwidthsshouldbeavailable

    toblockuptheparts, spreadoutthefloor loading, andprotectthefloor. timbers

    shouldbestressgradedandratedfor useas cribbing. Rough lumbermay nothavethe compressivestrength for heavy components.Insome cases, special jackstands

    may beneeded.Ifthesearerequired, they shouldbedesignedby anengineer

    competentinthefieldandfabricatedwell beforethey areneeded.

    Miscellaneous materials. Agoodsupply ofsteel plate, angleiron, steel barstock,

    etc., invariousthicknessesandsizesshouldbeon handforfabricatingspecial tools

    orbracketsthatmay berequiredduringtheoverhaul. Therearealwaysitemsthat

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    havetofabricatedoncetheoverhaul isinprocess, anddelays canbeavoidedifthe

    materialsareavailableonsite.

    Ill. DISASSEMBLY 3.1 Preshutdown and preteardown readings

    Thepurposeofpreshutdownandpreteardownreadingsaretodeterminethe

    conditionofthe unitpriortotheoverhaul sonecessary repairs canbemadeduringtheoverhaul. Operational readings, such asvibrationandtemperaturedata, can

    provideasignatureofthe conditionofthe unitbeforeteardown. Thepreteardown

    readingsarealso useful asreferencedataduringreassembly.Intakingthereadings,

    itisimportantthatall readingsare consistent. Forexample, thenorth, south, east,

    8

    andwestpositions usedfortheshaftalignmentreadingsdonotnecessarily haveto

    correspondexactly with theactual directions, butthepositionthebearing, seal ring,

    andairgapreadingsaretakenmustcorrespondwithinafewdegrees, with eachother, andthealignmentreadings. Referringtothereadingsasdownstream,

    upstream, right, and leftmay helpwith consistency. Preshutdownreadingsshouldincludeall pertinentinformationsuch asreservoirandtailraceelevations, wicket

    gateopening, and unitload.

    Preshutdown readings. Thepreshutdownreadingsshouldinclude, butnotbe

    limitedtothefollowing:

    _ Shaft runout readings-While shaft runout readings can be measured with dialindicators, the preferred method would be to install at least one pro3dmity probe at each

    guide bearing elevation and record the data to a strip chart recorder, tape recorder, orsome other type of data logging device. Readings should be taken at various loads from

    speed- no-load to full load including readings at any rough zone and with and without thefield voltage at speed-no-load.

    _ Bearing temperatures.-Bearing and oil temperatures should be recorded at variousloads. If a temperature recorder is part of the unit instrumentation, a recording of a

    normal startup showing the rate of temperature rise should be included. The unit load andwicket gate position should be noted on the recording.

    _ Pressures.-The normal operating pressure of the turbine bearing oil pumps,packing water supply, and cooling water supply should be recorded. The pressure of the

    thrust bearing, high-pressure lubrication system should be recorded during startup andshutdown.

    _ Permanent magnet generator (PMG) voltage.-The PMG voltage should bechecked and compared to rated voltage. If the measured voltage is more than 20 percent

    lower than the rated voltage, the field shouldberemagnetizedduringtheoverhaul.

    Facilities,Instructions, Standards, and Techniques (FIST), Volume 2-3, Mechanical

    Governors for Hydroelectric Unitshas a procedure for remagnetizing the rotor of aPMG in section II.

    Preteardown readings. Thepreteardownreadingsshouldbetakenafterthe unitis

    shutdownandthe clearance hasbeenissuedandshouldinclude, butnotbe limited

    to, thefollowing:

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    9

    _ Guide bearing and seal ring clearances.-Clearance readings should be taken on

    all guide bearings at least in four quadrants. On segmented shoe guide bearings, check theclearance of each bearing shoe. Top and bottom seal ring clearance should also be taken.

    _ Generator air gap.-Air gap readings should be taken at least in four quadrants and

    at the top and bottom of the rotor. For better accuracy in determining the position of therotor in the stator and for determining the shape of the stator, more readings may berequired.

    _ Shaft alignment readings.- Preteardown alignment readings may be taken with orwithout the guide bearings in place. With the bearings in place, the bearing centers can beplotted to determine their concentricity, but the shaft itself will not be free, and the shafts

    actual straightness may not be represented by readings. With the bearings and the packingremoved, the shaft should be hanging free, and the readings should represent the

    condition of the shaft, but the operating position of the shaft and bearings will not beknown. If the bearings are removed, a check of the static shaft runout should be made.

    3.2 Labeling and match marking

    Priortoremoval, mostpartsshouldbematch markedtomakesurethey are

    installedinexactlythesamepositionfromwhichtheywereremoved. Thisisespecially

    importantforpartsthatcanberotated, such asthrustblockkeys, orforpartssuch

    aswicketgates, thatcanbeinterchanged. Many partsaremarkedduringtheoriginalassembly.Ifthesemarkingsarevisibleandtheirmeaningsare clear, nomoremarks

    shouldbemade.Ifnewmatch marksor labelsaremade, theoriginal markings

    shouldbe completely removedsothereisno confusionduringreassembly.

    3.3 Disassembly

    Itisimportantduringdisassembly to checkthemanufacturersdrawings carefullytomakesureall partsareremovedinthe correctorderandthatall fasteners, piping

    connections, andwiringareremoved.Itisalsoimportantthatthevarious crafts

    coordinatetheiractivitiessothatthereisno unanticipateddelaysduetotheunavailability ofpersonnel.

    The listofweightsandariggingmanual shouldbe consultedoftenduringdisassembly., Theweightofany partshouldneverbe guessed,andtherigging

    shouldneverbeassumedtobestrongenough.Apartmay bemuch heavierthanit

    appears, andrigging, duetoslinganglesorother

    10

    factors, may be loadedmuch higherthanexpected. Theweightofeach component

    shouldalsobe consideredwhenstoringthepartssothattheallowablefloor loadingisnotexceeded.

    Thefollowingaregeneral proceduresfortheremoval ofsomeofthe

    commonpartsofahydrogenerator. Theactualproceduresusedwillprobably vary

    dependingonthedesignofthe unit.

    Permanent magnet generator.Afterdisconnectingthewiringfromthe PMGterminal block, removethemountingbolts, being careful notto losetheinsulating

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    washersandbushing. Centerthe craneoverthe PMG and liftitoffusingeyebolts

    installedinthe PMG case. Storetheinsulatinggasketbetweenthe PMG andtheexciter housingwith the PMG.

    Exciter. Afterremovingthebrushes, wiring, andexciter housingbolts, the craneshouldbe centeredas closeaspossibleovertheexciterandtherigging hooked upto

    theexciter housing. Topreventcontactbetweentheexciterstatorandrotor, stripsofthickgasketmaterial shouldbeinsertedintheexciterairgap, orifpossible, the

    entireexciterrotormay bewrappedwith gasketmaterial.

    Thrust block. Thethrustblockorthrustcollarisfittedtothegeneratorshaftwith a

    very tightfitandrequires heattoexpanditforremoval. Priortoremoval, the unitshouldbejackedandblockedonthejackssothatthereisnoweightonthethrust

    block. Theoil shouldbe completely drained, andbearing housing coversandvaporsealsshouldberemovedtoprovideaccesstotheblock. Theriggingto liftthethrust

    blockshouldincludeturnbucklessothattheblockcanbekeptlevel toprevent

    bindingwhenitis liftedofftheshaft.Ifthedesignallows, theriggingshouldbe

    attachedandadjustedbeforetheblockis heated. Somethrustblockdesignswill notallowthis, astheradial keysmustberemovedbeforetherigging canbeinstalled.

    The heatshouldbeappliedquickly sothattheblockcanexpandwithout

    transferring heattotheshaft. Toaccomplish this, several large weedburnertype

    propanetorchesorrosebudoxyacetylenetorchesshouldbe used. Careshouldbetakennotto heattheriggingexcessively. The length oftimerequiredto heatthe

    blockwill vary dependingonthe tightnessofthefitontheshaftandthe condition

    ofthematingsurfacesoftheblockandshaft.Inmostcases, whentheblockhas

    expanded, itwill dropslightly, allowingtheradial keystoberemovedandtheblock

    toberemoved. Thrustblocksthatrestonashoulderontheshaftwill notdrop, and

    the cranemustbe usedtoapply aslightupwardforceontheblockuntil itpops up.

    Inthese cases, adynamometerinstalledinone legoftherigging canbe helpful inpreventinganoverloadontheriggingbeforetheblockisexpandedsufficiently.

    11

    Generator rotor. Thegeneratorrotoris usually thesingle heaviestcomponentto

    beremovedduringanoverhaul.Inessentially all cases, special liftingdevicesanda

    pedestal forstorageareprovided. The liftingdevicesshouldbethoroughly

    inspected longbeforetherotorisremoved. Largegeneratorsmay requiretwo

    cranestobe hookedtothe liftingdevice. The craneoperatorsshouldfamiliarize

    themselveswith the useofthe liftingdeviceandsignalsfromthedesignated

    signaler.

    To uncouplethegeneratorshaftfromtheturbineshaft, all ofthe couplingbolts

    exceptfourshouldberemoved. Beforeremovingthefinal bolts, machinedsteelblocksshouldbesetundertheturbinerunneronthesupportledgeto limitthe

    amounttheturbinerunnerandshafthavetobe lowered. Theshaftandrunner can

    thenbe lowered usingthe lastfourboltsorby clampingthe couplingwith hydraulicjacks, removingthe lastbolts, and loweringtheshaftwith thejacks. Theturbine

    runnerisdesignedtosupportonly theweightoftheturbineshaftandtherunner

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    itself, soatnotimeshouldtheweightofthegeneratorrotorbeallowedtoreston

    theturbine.

    Plywoodstrips, 6to 10 incheswide, to3/8inch thick, and8feetlongshouldbe

    cuttofitinthegeneratorairgaptopreventtherotorfrom contactingthestatorwhiletherotorisbeingremoved. Sixormoremaintenancepersonnel shouldbe

    stationedaroundthestatorwith thestripsinsertedintheairgapmovingthem upanddown.Iftherotorgetstoo closetothestator, thestripswill becometight,

    alertingthe craneoperatorstostopandrecentertherotor.

    Guide bearings. Thebearingshoesofsegmentedshoeguidebearings can usually

    be liftedoutofthebearing housingby oneortwopeopleoncethebearing coverisremoved.

    Theturbinebearing, which isalmostalwaysasplitshell journal bearing, mustbeliftedoutofits housing using come-a-longsor chainfalls. Thebearingisthenseton

    blocksontopofthebearing housingand unboltedtosplititintwosothatitcanbe

    removedfromtheturbineshaft.

    Onsome units, the upperand lowergeneratorguidebearingsarealsosplitshell

    journal bearings.Inthe caseofthe upperguidebearing, itis usually onepieceand

    canbesimply liftedoffwith the craneoncetheexcitorandbearing coverareremoved. Special attentionshouldbegiventothe upperguidebearinginsulating

    gasketstopreventbreakingormisplacingany ofthesegments. The lowerguidebearing usually mustbe lowereddownintotheturbinepitusingthreadedrodsand

    nutsor come-a-longsaftertheoil potisremoved. Thebearingis loweredtoreston

    topoftheshaftcoupling, split, andthebearing halves loweredtothescaffolding.

    12

    Wicket gate linkage. Thewicketgateoperating linkage consistsoftheservomotors, shiftringoroperatingring, wicketgate links, andthewicketgate

    arms.Although thegate linksandgatearmsshould, intheory, beinterchangeable,

    they shouldbematchmarkedtotheirrespectivewicketgateandthegatesmarkedaccordingtotheirinstalledposition.Insome units, thegate linklength isadjustable

    topermitadjustmentinthe closureofthewicketgates. Careshouldbetakennotto

    disturbtheadjustmentofthesetype linkstoreducetheamountoftimerequiredtoadjustthewicketgatesduringreassembly.Anothermethodofadjustingthewicket

    gatesisthrough the useofeccentric pins locatedeitherintheshiftringorthegatearmendofthegate link. Thepositionofeach eccentric pinshouldbemarkedto

    reducetheamountofadjustmentduringreassembly.

    Headcover. Theturbine headcover, becauseofrust, many times canbevery difficulttobreakloose. Beforetryingto liftthe headcover, itshouldbebroken loose using

    hydraulic jacksbetweenthe upperand lowerfacingplates. Thiswill eliminateany

    chanceofoverstressingtheriggingorbouncingthe loadwith the crane.

    Turbine runner and shaft. With the headeoverremoved, theturbinerunnerand

    shaft, inmostcases, arefairly straightforwardtoremove. Thereis usually a lifting

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    devicethatattachesdirectly totheturbineshaft, andtheshaftandrunnerare

    simply liftedoutoftheturbinepit.

    IV.INSPECTION AND REPAIR OF UNIT COMPONENTS 4.1

    BearingsUponremoval, all guideandthrustbearingsshouldbethoroughly inspected. Minor

    scratchesandevensomedeepgouges canberepairedadequately by carefullyscrapingthe high spotsfromthebabbittsurface. Extreme caremustbetakenwhen

    scrapingabearingtopreventremovingtoomuch babbitt.Also checkthebondbetweenthebabbittandthebearingshell. Becauseofthedovetailsinthebearing

    shell, aguidebearing usually canoperatesatisfactorily with littlephysical bond

    betweenthebabbittandtheshell, butifthereisnoticeableseparation, itisagoodideatoinstall thesparebearingorto havethebearingrebabbittedbeforethe unitis

    reassembled.Also,whenthebabbittisseverelydamagedbyinadequatelubricationorif

    theinnerdiameterofjournal bearingsisbeyonddesigntolerances, thebearing

    shouldberebabbitted.

    Whenitisnecessary torebabbitbearings, anAmerican Society for TestingandMaterials (ASTM) B-23, grade 2 orgrade3tin-basedbabbittshouldbe used. Split

    shell journal bearings, andifpossiblesegmentedshoeguidebearings, shouldbe

    rebabbittedbycentrifugalcasting. Thrust

    13

    bearingshoesmustbepoured. Regardlessofthemethod usedtorebabbitthe

    bearings, ultrasonic testingshouldbeperformedtoverify theintegrity ofthebabbitttosteel bondandtheabsenceofporosity.Ababbitttosteel bondofno lessthan85

    percentshouldbespecified.Thebearingjournalsandthrustrunnershouldalsobeinspectedforany damage.

    Thejournalsshouldbe checkedforany scoringorotherdamage. Damageisrare,

    butinmostcasesscratchesorscoring canbeadequately repairedby s6ningtoremoveany high spots. Moreseveredamagemay requiremachining. Thethrust

    runnershouldbe checkedforscoringonthebearingsurfaceandforany frettingcorrosiondamagebetweentherunnerandthethrustblock.Iffretting corrosionis

    severe, checkthe contactareabetweentherunnerandthethrustblock.Iflessthan

    70 percent, machiningmay benecessary.Ifmachiningisrequired, chooseamachineshop carefully, asitis critical thatthethrustrunnersurfacebeperfectly

    perpendiculartotheshaft. Tolerancesforthrustrunnersare usually inthe 10-

    thousands-of-an-inch range.

    4.2 Turbinerunner

    Inmostcases, therepairofcavitationdamage canbeaccomplishedmuch moreeffectively with therunnerremovedfromtheturbinepit, astherunner canbe

    positionedforeasieraccess.

    Anoverhaulisanexcellentopportunitytorestoretherunnertolikenewcondition, orin

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    someinstances, betterthannew condition.FIST Volume 2-5, Turbine Repair,

    describestechniquesandproceduresforrepairingturbinerunners.

    4.3 Wicket gates

    Thewicketgatebushingandpackingjournalsshouldbemeasuredand checkedto

    drawingto

    leran

    ces.

    Thewi

    cketgates

    hafts

    ho

    uldbe

    che

    ckedforstraig

    htness.

    Thetopandbottomsealingsurfacesshouldalsobe checkedforwearor cavitation

    damage. The heel-to-toeseal areasshouldbe checkedforstraightnessandtoverifythattheseal surfacesareparallel tothegateshaft.

    Wornor corrodedjournalsthatoperateingreasedbronzewicketgatebushings

    shouldbebuiltupby weldingwith a309 stainlesssteel andmachinedbackto

    original diameters. Therepairtothetopandbottomsealingsurfaceswill dependon

    thedamageandonthefacingplatematerial.Ifthedamageisobviously from

    misalignedormisadjustedwicketgateswith noapparentgalling, andthematerialsofthegateandfacingplatesarenotpronetogalling, weldrepairwith amaterial

    similartothegatematerial shouldbesufficient.Ifgallingispresent, agalling

    resistantmaterial shouldbe usedtooverlay thetopandbottomsurfaces.Ifthefacingplateisabronze, astainlesssteel or Nitronic 60 stainlesssteel weldoverlay

    wouldberecommended.Ifthefacingplatesarestainlesssteel orsteel. Nitronic 60ornickel

    14

    4.4

    aluminumbronze, C95500 shouldbe used.Ifthe heel-to-toesealingsurfacesrequire

    repair, thesesurfacesshouldbebuiltupwith thesameorsimilarmaterial asoriginally used unlessthereisgallingorotherproblemsthatindicatea changein

    material isneeded.

    Inperformingweldrepairstothewicketgates, thefollowinggeneral proceduresshouldbefollowed.Inpreparationforwelding, thesurfacetobeweldedshouldbe

    machinedtosoundmaterial atleast0.125inch deeperthanthefinal dimension.

    Whereanoverlay ofadissimilarmaterial isbeing used, such asbronzeorstainless

    steel overmildsteel, enough material shouldberemovedtoallowatleastthree

    weldpassestobemade. Thiswill ensurethatthemetal atthefinishedsurfacewill

    be undilutedby theparentmaterial andthereforepossessthedesiredproperties.

    Aftertheweldingiscomplete,thegatesshouldbefinish machinedtothemanufacturers

    drawingdimensions.Itisimportantthatthefinish machiningbe completedafterall

    theweldingis completetoallowforthe correctionofany distortionthatmay occur

    fromthe heatofwelding.

    Facing plates and wicket gate bushingsThetopandbottomfacingplatessurfacesshouldbe checkedforwearandgalling.

    The headcovershouldbeinstalledwithoutthewicketgates.

    Alloftheheadcoversmountingboltsshouldbeinstalledandtightenedtofull torque

    to checkthefacingplatesfor level andparallel. Whiletheplatesshouldbe level, itis

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    moreimportantthatthey beparallel toeach otherandperpendiculartothewicket

    gatebushingstopreventbindingofthewicketgates. Parallelism canbe checkedbymeasuringthevertical distancebetweentheplateswith aninsidemicrometer. The

    plates canbe checkedfor level usingaprecision level ora laserdevicewithhorizontal sweep capability.Iftheplatesarenotparallel and/ornotlevel, the

    methodofcorrectionwill dependontheamounttheplatesareoffandtheamountofexcessmaterial availabletomachine.

    Theeasiestmethodofrepairistoinstall aboringbarandmachinethesurfaces level

    andparallel, butthis canonly bedoneifthereissufficientmaterial.Ifthisisdone,

    thetopandbottomsurfacesofthewicketgateswill havetobebuiltuptomaintainthedesign clearancesbetweenthegatesandtheplates.Ifthereisnotsufficient

    material formachiningtheplatestrueandifthe unitisdesignedforreplaceable

    plates, newplateswill havetobeinstalled. Building upthereplaceableplatesby

    weldingisnotrecommendedastheirrelatively thin crosssection canallowagreat

    deal ofdistortionfromwelding.

    Removingtheoldplatesnormally requires locatingtheretainingbolts, usuallytwist-offboltsthathavebeenweldedinplace, anddrillingthemout. Thenewfacing

    platesshould havesufficientthicknesstoallowformachiningto compensateforany

    unlevelnessintheplates. Theretainingboltholes canbedrilledand counterbored

    accordingtothemanufacturersdrawing, butifadrawingisnotavailableorifthereisany doubtasto

    15

    theaccuracy ofthedrawingdimensions, theoldfacingplatesshouldbe usedto layouttheboltpattern. Twist-offboltsare usually usedtoretainthefacingplates.A

    neckeddownportionoftheboltallowsthe hexofthebolttotwistoffat

    predeterminedtorquevalue leavingtheboltheadflush with thefacingplatesurface.The headisthentackweldedtotheplatetopreventitfrombackingout.

    Oncethenewplatesareinstalled, aboringbarwith a horizontal feedingtool slide

    canbe usedtomachinetheplates level andparallel toeach other. Toachievethis,

    theinstallationandalignmentoftheboringbaris critical. Theboringbarmustbe

    plumbandthetool slidefeedperpendiculartotheboringbar.Aftermachining, thevertical distancebetweenplatesshouldequal thewicketgate heightplusthe

    recommendedamountofclearancebetweenthegatesandtheplates.

    Thediameterofthewicketgatebushingsshouldbemeasuredand comparedtothe

    drawingtolerances. Whenthe headcoverisinstalledto checkthefacingplates, the

    wicketgatebushingsshouldalsobe checkedfor concentricity andforperpendicularity tothefacingplates.Ifitwasdeterminedthatthebushingsare

    wornbeyondtheallowabletolerance, thebushingsshouldberemovedfromthe

    headcoverandbottomringandthebushingfits checkedfor concentricity and

    perpendicularity. Nonperpendicularity ofthebushingandfacingplatesshould have

    beennotedduringpreteardown checksofthetopandbottom clearancesofthewicketgates.Ifthebushingsarenotperpendiculartothefacingplates, the clearance

    measurementswouldindicatethatthegatesareoperatingatanangletotheplates.

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    Concentricity canbe checkedby hangingasingletightwirethrough the centerof

    thebushings, orbushingfits, andmeasuringfromthewiretothebushingorfitsurfaces.Ifthebushingsorbushingfitsarenotconcentric ornotperpendicularto

    thefacingplates, thebushingsshouldbereplacedand linebored. Proceduresforlineboringarediscussedinsection V, entitled, Field Machining Procedures.Ifitis

    determinedthatthefitsforthebushingsare concentric, newbushings canbeinstalledwithoutlineboring. Whenthisisdone, thebushinginnerdiametermustbeslightly largerthanrequiredto compensateforthereductionindiameterthat

    occurswhenthebushingispressedinplace. This cantakesomeexperimentationto

    achievethe correctinstalledinnerdiameter. Tofacilitatetheinstallationofthe

    bushings, they shouldbeshrunkby packingindry iceorstoringinafreezer

    overnight.

    Insome cases, thetoptwobushingsorbushingfitswill bewithintolerancefor

    plumbandperpendicularity, butthebottombushingwill not.Inthisevent, thetop

    twobushingsarereplacedwithoutlineboring, andthebottombushingis lineboredconcentric tothetoptwo. Thissimplifiestheinstallationand lineboringprocedures

    significantly.

    Thebushingandpinsofthewicketgate linkageshouldbe checkedagainstdrawing

    tolerances. Thebushingsonthe linkage can usually justbepressedinplacealready

    finish machined.Aswith thewicketgate

    16

    bushings, theinnerdiameterwill havetobeslightly largerthanrequiredto

    compensateforthereductionindiameterthatoccurswhenthebushingsarepressedinplace.

    Thebearingplatesontheoperatingringshouldbe checkedforexcessivewearand

    replacedifnecessary. Thegreasegroovesoftheoriginalsshouldbeduplicatedonthenewbearingplates.

    4.5 Packing box and shaft sleeve

    Many timesthepackingboxwill beseverely corroded.Ifthemetal lossissignificant

    inthepackingboxbore, thepackingwill havetobeovercompressedinordertofill

    thebore. Thiswill leadtoshortenedpacking lifeandexcessivewearoftheshaft

    packingsleeve.Ifthepackingboxisstill structurally sound, theinteriorboreofthe

    box canbebuiltupwith aproperly appliedepoxy coating.Ifthe corrosion has

    reachedthepointthatthebox hasbeenweakenedsignificantly, someothermethod

    ofrepairor completereplacementmay berequired. Oncethesurfaces havebeen

    repaired, thepackingboxshouldbepainted.

    Theturbineshaftpackingsleeveis usually constructedintwopiecessothatitcan

    bereplacedwhenworn.Insome cases, thesleeve canbebuiltupby weldingand

    machinedbacktothedrawingdimensions.Weldingonthepackingsleevemustbeaccomplishedwith aminimumamountofheatinputtopreventinducingstressand

    distortingthesleeve.Anotheralternativeistoflamespray thesleevewith awear-resistantmaterial andmachineitbacktooriginal dimensions. The coating usedin

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    flamesprayingmustbe chosen carefully andtheproperprocedurefollowedto

    ensureproperbondingtotheparentmaterial.

    4.6 Servomotors

    Insomeinstances, dueto contaminantsintheoil ormisalignment, theservomotors

    forthe

    wi

    cket

    gates

    wi

    llreq

    uire

    repair.

    The

    most

    common

    types

    of

    damage

    are

    scoringinthe cylinderandscoringonthepistonrods. Scored cylindersmustbe

    boredoutand honedtoremovethescoring. Newpistonringsthenmustbefabricatedtomatch thenewinnerdiameterofthe cylinder. Torestorethepistonto

    cylinder clearance, bronzesleevesorbandsofphenolic material canbeinstalledon

    thepiston.

    Thefirststepinrepairingscoringonthepistonrodistoturndowntherodby

    machiningtoremovethescoring. Therodmustthenbebuiltuptoallowgrindingto

    thefinal diameter.Ifmildly scored, electroplatingwith industrial hard chromiummay be usedtorestoretheroddiameter.Ifthescoringwasdeep, itmay be

    necessary tobuildtherod upby weldingorothermeanstorestoreittoitsoriginal

    diameter.

    17

    4.7 Cooling coils and generator air coolers

    Thebearing cooling coilsandgeneratorair coolersshouldbethoroughly inspected

    for leaks, corrosion, andmineral buildup. Theendoftheair coolersshouldbe

    removedtoallowtheinspectionofthetubesheetandthe connectionofthetubes.

    Leakingtubesshouldbereplaced.Ifasignificantnumberoftubesare leakingorif

    theirgeneral conditionisquestionable, theentire coolershouldberetubed.Afterretubing, the coolershouldbe hydrostatically testedatapressureofatleast110

    percentoftheworkingpressureto checkfor leaks.

    Thebearing cooling coilsshouldbethoroughly inspectedand hydrostatically tested.Dueto corrosionandweakeningofjointsdueto yearsofvibration, itissometimes

    moreeconomical toreplacethe coolersratherthantryingtorepairthem.Ifitis

    determinedthatitisfeasibletorepairthe coils, a hydrostatic testshouldbe

    performedaftertherepairtoinsuretherepairwassuccessful andthatnonew leaks

    havedeveloped.

    Thepipingtotheair coolersand cooling coilsshouldbe checkedfor corrosionand

    mineral buildupandreplacedifnecessary.

    4.8 Exciter

    The conditionofcollectorringand commutatoroftheexciterrotorshouldbecheckedforroundnessandevidenceofwearorarcing. Thegrooveonthe

    commutatorshouldbethoroughly cleanedofcarbondustorother contaminants.If

    necessary, the collectorringsshouldbemachinedina lathetorestoretheirsurface

    finish androundness.

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    4.9 Generator structure

    With the unitdisassembled, itispossibletoperformathorough inspectionof

    componentsnotnormally accessible. The upperand lowerbridgesshouldbecheckedfor crackedweldsorothersignsofdamage. Thetorqueonthestatorframe

    boltsshouldbe checkedandthedowels checkedtomakesurethey haventbacked

    out. Therotorspidershouldbe checkedfor crackswith special attentiongiventowherethearms connecttothe hubandtherotorring. Thebrakeringshouldbe

    checkedfor unevenwearing, cracks, andevidenceofexcessive heating.

    4.10 Generator brakes

    Thegeneratorbrakesshouldbedisassembledforinspection.Ifthereis corrosionor

    scoringinthe cylinder, itshouldbereboredor honed, dependingontheextentofdamage, andifnecessary, anewpistonfabricatedandinstalled. Leatherpacking

    shouldbereplacedwith afluorocarbonorsimilarmaterial.

    18

    V.FIELD MACHINING PROCEDURES 5.1 Seal rings

    Oneofthemostcommonfieldmachiningoperationsperformedon hydroelectric

    unitsistheboringofthestationary seal rings.Inmostcases, theoperationinvolves

    boringnewseal rings, butitmay alsoincludethemachiningofthedischargering,throatring, and/or headcovertoacceptthenewrings.

    Theboringbarmustbeprecisely setupsothattheringsarebored concentric to

    each otherandtothe unitguidebearingsandgeneratorstator. Toaccomplish this,

    thedesired centerofthe unitwith referencetotheseal ringsmustbedetermined.

    Tofindthe units center, the upperbridgeand headcovershouldbeinstalledafter

    all therotatingparts havebeenremoved.Asingletightwireshouldbe hungthroughthe unitandreferencemeasurementstakenfromthestator, theturbinebearing

    housing, thepackingboxbore, andtotrammel pointsinthedrafttube. Thetrammel

    pointsmay beboltsweldedtothedrafttube linerwith the headsmachinedtomatch

    aninsidemicrometerorany markedpointwheremeasurements canberepeated

    exactly.

    Ifthegeneratorguidebearingsarenotadjustable, the lowerbridgeshouldalsobe

    installedandreferencemeasurementstakenfromthe lowerand upperbridges.Oncethemeasurements havebeentakenandthe centersplotted, itcanbe

    determinedwherethe centeroftheseal ringsshouldbe.Ideally, thegenerator

    stator, all oftheguidebearings, andtheseal ringsshouldbeperfectly concentric,butsome compromisewithintherecommendedtolerancesmay berequired.

    Indeterminingthe centerforboringtheseal rings, several thingsshouldbetaken

    into consideration.The centeroftheturbinebearing housingshouldbewithinthe

    allowabletolerancesfor centerofthestator(refertoappendix C).Although itisnot

    asimplejob, theturbinebearing housing, inmany cases, canbemovedto centerandredoweled.Iftheseal ringsmustbeboredsignificantly offcentertomakethem

    concentric tothe unitcenter, theremustbesufficientmeattoallowboringtothe

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    requireddiameter.Insome cases, thepackingboxisnotmovableandwill bethe

    limitingfactorin howfartheseal ring centers canbemoved.Ifthe calculationsshowthataftermovingtheseal ring centersasfarasthey canbemoved, thestator

    willstillbeexcessivelyoffcenter,itmaybenecessarytomovethestator.Asmovingthestator canbedifficult, itshouldonly beattemptedifabsolutely necessary andafter

    careful planning.Oncethe centerfortheseal rings hasbeendetermined, itcanbe helpful tomovethe

    plumbwiretothe centerpointandtakethefinal referencemeasurements. While

    thisisnotnecessary, itwill simplify the calculationsrequiredduringtheinstallation

    oftheboringbar. Theboringbarispositionedandplumbedby centeringitatthereferencepointsat

    19

    theturbinebearing housing (or head coveriftheturbinebearing housingisremoved)andthetrammel pointsinthedrafttube. Theinstallationprocedurewill

    vary with boringbardesign, butusually theboringbarthrustbearingandaguide

    bearingaremountedontheturbinebearing housingordirectly tothe headcover.Anotherguidebearingis usually mountedinaspidertypeframeweldedtothedraft

    tube liner. Theguidebearings usually havesomeadjustmenttoallowmovingthebarto center. Whentheboringbaris centeredanditsguidebearings lockedin

    place, theboringarmandtool slide canbeinstalled. Themotionofthetool slideshouldbeperfectly parallel tothebarforvertical cutsandperpendiculartothebar

    for horizontal cuts.Ifnecessary, thetool slideshouldbeshimmedwhereitmounts

    totheboringarmtomakeitperfectly parallel orperpendicular.

    Theboringbardrivespeedshouldbeadjustable, usingeitheranelectric motorwith

    solidstatefrequency controlsora hydraulic systemwith somemeansofvarying

    flow. The cuttingspeedforboxingwill dependonthetypeofmaterial beingmachined, thediameterofthering, thedepth ofcut, andthefeedrateofthetool

    slide.The Machinery Handbookandothermachiningreferencebooks listarangeof

    recommended cuttingspeedsbasedonthesefactors. Theoptimumspeed, cutdepth,

    andfeedratewill havetobedeterminedonsitethrough experimentation.

    5.2 Facing plates

    Asdiscussedintheprevioussection, itissometimesnecessary tomachinethefacing

    platesinordertomakethemtrueandparallel toeach other.Aboringbarwith atool

    slidewith a horizontal feed canbe usedtomachinethefacingplatessurfaces.Becauseoftheinterrupted cutcausedby the holesinthefacingplatesforthewicket

    gatebushings, the cuttingtool will seeagreatdeal ofshock. The cuttingspeedandfeedinmostcasesmustbereducedtopreventbreakingthetool bit.

    5.3 Wicket gate bushing line boring

    Whenitisnecessary to lineborethewicketgatebushings, theinstallationoftheboringbaris critical. Thebarmustbemadeplumb, positionedatthe correctradial

    distancefromthe unitcenter, andinthe correctangularpositionwith referenceto

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    theothergates. Whateverprocedureis usedtoaccomplish this, itmustberepeated

    16to 24 timesdependingonthenumberofwicketgates.

    Inmostcases, centeringtheboringbarintheintermediatebushingwill bewithin

    thetolerancefortheradial distancefromthe unitcenterandthedistancebetweengates. Theradial distanceshouldbeverifiedby measuringthedistancefromasingle

    plumbwire hungthrough the centerofthe unittotheboringbar. Thedistancebetweengatesshouldbemeasuredbetweentheboringbarandawire hungthrough

    the lastholebored. Thefirstholeboredwill bethereference.

    20

    5.4

    Themostcritical stepininstallingtheboringbarismakingthebarplumb.Ifthe

    barisnotinstalledplumb, therewill begapsbetweenthewicketgatesealingsurfaces, andinsevere cases, thetopandbottomsurfacesofthegatesmay bind

    againstthefacingplates. Thereareseveral proceduresforplumbingtheboring

    bar. Thebestoneforaparticular unitwill dependonthesizeanddesign.

    Plumbwires canbe usedtoplumbthebar.Ideally, fourwires hung 90 degreesapartwouldbe usedtoallowfora checkintheaccuracy ofthereadings.

    Realistically, thereisrarely roomforfourwires. Normally, awire hungthrough

    the centerofthe unit, which isalso usedfor checkingtheradial positionofthe

    bar, andwires hunginthe holesoneithersideofthe holebeingboredare used.

    Readingsshouldbetakenseveral timestoverify theiraccuracy.

    Ifthebushingdiameteris largeenough, anothermethod canbe usedwith plumb

    wires. Thismethod usesasinglewire hungthrough thebushingbores. Thewireis centeredintheintermediatebushing, andreferencemeasurementsaretaken

    fromthebushingstothewire. Thesereferencemeasurements canthenbe usedtopositiontheboringbarinthesamepositionasthewire. Sincethewire hangs

    plumb, theboringbarwill beplumb.

    Ifthefacingplatesarewithintolerancesforparallelismbutnotlevelness, thewicketgatesshouldbeboredperpendiculartothefacingplatesandnotplumb.

    Somefixtureorjigwill havetobefabricatedtomaketheboringbar

    perpendiculartotheplates.Ifthefacingplatesurfacesaresmooth, adialindicatorattachedtotheboringbar canbe usedtopositionthebar.

    Ifitwasdeterminedthatthetoptwobushingswerewithintoleranceforplumbandperpendicularity butthebottombushingwasnot, theboringbar canbeset

    upby centeringitinthetoptwobushings. Plumb, radial position, anddistance

    betweengatesstill shouldbe checkedby plumbwiresorothermeans.

    Appendix C liststolerancesforwicketgateinstallation. Thesestandardsareonly

    intendedtobe usedasaguidesincevariablesinthe constructionofthe unit

    may-make largerorsmallertolerancesacceptable.

    RedowelingUnitswith nonadjustableguidebearingsrequirethepreciseplacementofthe

    bearingbrackets. Bearingbracketsandother componentsthatneedtobe heldinan

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    exactpositionmany times usedowel pins. Theboltholesonthese componentsare

    usually oversizedtoallowthepartstobeshiftedslightly duringthealignmentprocess. Thedowels haveavery tightfittopreventthe componentsfromshifting

    oncethepartispositioned.

    21

    Thedowel pinsmay be hardenedor unhardenedsteel andmay bestraightor

    tapered. Taperedpinsareeasiertoremovethanstraightpins. Hardenedpinsare

    normally usedwherestrength, shock, orweararefactors.Ifthe componentsare

    heldtogetherwith threadedfasteners, andthepinswill see littleshearstressor

    wear, unhardeneddowel pinsaresufficient.

    Whendoweled componentsaremovedduringthealignmentprocessfollowingthe

    overhaul ofa unit, redowelingisnecessary. Dependingonthe locationandsizeofthedowelsandtheamountofavailableroom, itwill benecessary toeitherrelocate

    thedowelsorborethee2dsting holestoaccepta largerdowel.Ifthedowelsare

    relocatedon componentssubjecttovaryingtemperatures, such asthegenerator

    stator, careshouldbetakentoinstall thedowel sothatthey donotimpededifferential thermal expansion.

    Amagnetic-baseddrill shouldbe usedtoborethe holeforthedowel. Toensureatightfit, the holeisalwaysdrilled undersizedandreamedtomatch thedowel pin.

    Thereaming canbeaccomplished usingthemagnetic-baseddrill anda chuckingreamer, oritcanbedonewith a handreamerandawrench.Ifthedrill is used, care

    shouldbetakentoproperly alignthereamerandto choosetherightcuttingspeed

    topreventoversizedorbellmouth holesandtoachieveagoodfinish.Ifthecomponentswereonly movedafewthousandsofaninch, expansionreamers can

    sometimesbe usedtoreamthee2dsting holeto useaslightly oversizeddowel.

    5.5 Coupling boltholes

    Whennewturbinerunnersareinstalledaspartoftheoverhaul, itis usually

    necessary toreboretheturbineshafttoturbinerunner couplingboltholes. Onrareoccasions, the couplingboltsonthegenerator-turbineshaftcouplingmay gall upon

    removal tothepointreboringisrequired. Thenormal procedureistotemporarily

    bolttheshafttotherunnerortheshaftstogetherusingfourbolts.

    Theboltsshouldbetightenedsufficientlytoensurethematingsurfacesaremakingfull

    contact. rightwiresor laseralignmentequipmentisthen usedto checkfordoglegandoffset. Offsetcanbe correctedby shiftingtheshaft, butdoglegrequires

    remachiningtheshaftortherunnermatingface. Whenitisdeterminedthatthe

    shaftis correctly positioned, the holesareboredslightly oversizedfromtheoriginaldiametertoacceptnew couplingbolts.

    Theboringequipmentusedwill dependonthesizeofthe holebeingbored.Insome

    cases, amagnetic-baseddrill canbe usedwith aboringbar.Ifamagnetic-baseddrillis used, abearingfortheboringbarshouldbemountedatthebottomofthe holeto

    addadditional support. Cylinderboringmachinesforengines canalsobe usedinsomeinstances. Thesemachinesaredesignedtoborethe cylindersoflargediesel or

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    Anothermethodofstretchingboltsiswith the useofboltheaters.Theboltis

    measuredwhilestill coldandthenthe heaterisinsertedinanaxial holethrough thecenterofthebolt.Astheboltis heated, itexpands, andwhileitisstill hot, thenuts

    aretightenedtoretaintheexpansion.Thefinal stretch ismeasuredwith amicrometerafterthebolthas cooled. Thismethodwill usually takesometrial and

    errortoachievethedesiredstretch inthebolt.6.2 Unit alignment

    Itis critical thatthegeneratorandturbineshaftbeproperly plumbedandtheguide

    bearingsbemadeplumbandconcentric.

    Theexactprocedurewillvarydependingonthedesignofthethrustandtheguidebearings.FIST Volume 2-1,Alignment of Vertical Shaft Hydro Units, describesin

    detail thealignmentproceduresforthevarioustypeofbearingsaswell astolerancesforthealignment.

    Oncetheshaftalignmentisdeterminedtobeacceptable, preparationforinstalling

    theguidebearings canbegin. Sincethealignmentprocedures call forplumbingthe

    centerofrunoutandnottheshaft, theshaftwill notbeperfectly plumbandwillprobably notbeinthedesiredrunningpositionwith referencetothebearing

    centers. Thiswill notbeaproblemiftheguidebearingsareall nonadjustableand

    thebearing housings havealready beenmade concentric andplumbaspartofthe

    alignmentprocess.Inthis case, theshaftismovedto centerinthe uppergenerator

    guideandturbineguidebearing housingsandthebearingsinstalled.

    Ifthe upperand lowerguidebearingsaretheadjustablesegmentedshoetype, the

    shaftwill havetobepositionedsothatitcanbe usedasareferenceforsettingtheclearancesonthebearingsegments.Tomakethebearing centersall concentric, the

    shaftmustbeperfectly plumb. This canbeaccomplishedby installingtheturbine

    bearingandshimmingtheshaftto centerintheturbinebearing. Plumbreadings, arethentakentodeterminethepositionoftheshaft. Fromtheseplumbreadings, the

    topoftheshaftcanbemovedtomakeitplumb. The upperand lowerguidebearingsegments canthenbeinstalledandsetusingtheshaftasareference.

    24

    6.36.4

    Settingthe clearancesonsegmentedshoebearings canbea challenge. Mostdesignsallowthesegmentstopivotaroundtheadjustmentbolt. Sincethesegmentspivot,

    obtainingaccurate clearancereadingswith afeelergauge canbevery difficult.

    Whentakingreadingswith afeelergauge, itisessential thatthesegmentbe held

    level andtightagainsttheadjustingbolt. Wheninserted, thefeelergaugeshould

    extendall theway through thebearingtopreventobtainingafalse high readingatthetopofthesegmentwhenthebottomistightagainsttheshaft.Itisalso helpful to

    measurethe clearanceoneithersideofthepivotpointatthesametimetoprevent

    theshoefrompivotingtoonesideortheother.

    Anothermethodofsettingthe clearanceiswith adial indicatorontheadjusting

    bolt. Theboltisturnedintomakethebearingtightagainsttheshaft, andthedial

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    indicatorissetuponthe headoftheboltandzeroed. Theboltisthenbackedoutthe

    amountofthedesired clearanceandthe locknuttightened. The locknutmustbetightenedwith care;ifitisovertightened, itcanactually stretch theadjustingboltto

    thepointthatthe clearanceissignificantly reduced.Astheboltisstretchedbetweenthe locknutandtheshoe, therewill benoindicationonthedial indicator.

    Ifthedial indicatormethodis used, the clearancestill shouldbeverifiedwith feelergauges.

    Wicket gate adjustmentThe heel-to-toe clearancebetweenwicketgatesmustbeminimal topreventexcessive leakageoncethe unitiswatered up. Turnbucklesoreccentric adjustments

    areprovidedinthewicketgate linkagetoadjustthepositionofthegatesandthe

    clearancesbetweenthem. Proceduresforadjustingthegatesarefoundinappendix

    D.

    Thesqueezeonthegatesshouldalsobeadjusted. Thesqueezeistheamounttheservomotorstravel afterthegates contacteach other. Thesqueezetakes upthe

    slackinthegateoperatingmechanismand holdsthegatesshutwhenthespiral case

    iswatered up. Thesqueezemustbeadjustedsothateach servomotormovesthe

    sameamounttopreventdistortingtheoperatingring. PartIII, Section B, ofFIST

    Volume 2-3, Mechanical Governors For Hydroelectric Unitshasaprocedurefor

    adjustingthesqueezeonthewicketgates.

    Gaskets and packingThegasketsshouldbe cutpriortoreassembly usingtheoldgasketsasapatternif

    possible. Thematingsurfacesofthegasketedjointshouldbethoroughly cleanedand checkedforany largenicks, dentsorgouges, orany othersurfaceimperfectionsthatwouldpreventthegasketfromsealing.

    Thegasketmaterialusedmustbecompatiblewiththefluidbeingsealedandshouldbeas

    thinaspossiblewhilebeingthickenough toseal. Themanufacturers

    recommendationshouldbe usedifavailableortheoldgasketcanbe usedasaguide,

    keepinginmindthattheoldgasketisprobably somewhatdeformedby

    25

    compression. Theboltsshouldbetightenedto uniformly compressthegasket. This

    meansgoingfromonesidetotheotheraroundthejoint. Gasketedjointsshouldbe

    retorquedafterthe unithasbeeninoperationfor 1 or 2 days.

    Compressionpackingonwicketgateshaftsandtheturbineshaftshouldbeinstalled

    with thejointsstaggered 90 degreesapart.Itissometimes helpful to lubricatethepackingpriortoinstallation. Thepackingmanufacturershouldbe consultedfor

    recommendationsfora lubricantandforany special instructionsthatmay be

    requiredforthetypeofpackingbeing used. With all ofthepackingandthe lantern

    ring, ifsoequipped, inplace, thepackingglandshouldbeinstalledfingertight. The

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    wicketgatepacking canbesomewhattighterbecauseofthe limitedrotational

    movementofthewicketgates.

    Thereshouldbegenerous leakage upontheinitial startupaftertheinstallationof

    newturbineshaftpacking. Thepackingglandshouldbetightenedevenly andinsmall steps until the leakageisreducedsufficiently. Theglandshouldbetightened

    at15-to30-minuteintervalstoallowthepackingtimetobreakin. Thetemperatureofthewater leakingfromthepackingshouldbe cool or lukewarm, never hot.Ifthe

    wateris hot, backoffthepackinggland.

    Mechanical sealsaresometimes usedinsteadofcompressionpackingontheturbine

    shaft. Theseal consistsofsealingsegments, usually madeofcarbon, heldagainsttheshaftbyspringtensionandlubricatedbyathinfilmofwater.Agreasezerkisusually

    providedto lubricatethesealspriortostartupfollowinganoverhaul or lengthyoutage.

    Sincemechanical sealsareprecisely madeandrely onvery tighttolerancesinorder

    tooperatesuccessfully, agreatdeal ofcaremustbetakenduringtheinstallation.

    Justasmall amountofdirtorother contaminantsonthepolishedsealingsurfacescanallow leakagepasttheseal andreducetheseals life. Theseal segmentsarealso

    usuallyverybrittleandareeasilybroken.Asparesetofsegmentsshouldbeon handinthe

    eventany shouldbreak.

    6.5 Governor

    Ifpossible, thegovernorshouldbetestedandadjustedpriortostartup usinga PMG

    simulator. The PMG simulatorprovidesathree-phasealternating currentata

    voltageandfrequency thatmatchestheoutputofthe PMG. Thesimulatordrivesthe

    ballheadmotoratnormal synchronousspeedwhich makesthegovernoroperateas

    ifthe unitwasonline.Ifthe PMG simulatorisavailable, thesetests canbeperformed

    assoonastheservomotorandwicketgatesareoperational. ThetestsaredescribedinFIST Volume 2-3, Mechanical Governorsfor Hydroelectric Units.

    26

    Regardlessofwhetherornotthe PMG simulatorisavailable, the)full ratewicket

    gatetimingmustbesetbeforethe unitiswatered up.Asmentionedpreviously, the

    wicketgatetimeshouldbeobtainedfroma hydraulic transientstudy ortestreports.

    VII. STARTUP 7.1 Final inspection

    Onceall theitemsonthe checklist, otherthanoperational testsandadjustments, are

    completedandjustpriortostartingthe unitforthefirsttimefollowingtheoverhaul,

    afinal inspectionofthe unitshouldbemade. Someoftheitems listedbelowwillhavebeen checkedpreviously, butbecauseofpotential damagetothemachine, they

    shouldbe checkedagain. Thisinspectionshouldinclude, butnotbe limitedto, thefollowing:

    Visual inspection of generator housing and spiral case. Avery thorough

    inspectionofthegenerator housingandspiral caseshouldbemadeto checkforany

    bolts, nuts, tools, etc.Inthegenerator housing, checkontopofrotorarms, underfan

    covers, orany placethatapartortool couldpossibly havebeen left. Oncethese

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    areas havebeeninspectedandverifiedtobe clean, nooneshouldbeallowedback

    in.Ifitisnecessary forsomeonetogobackintotheseareas, they shouldremoveeverythingfromtheirpocketsandmakea listofevery tool thatistakeninsothat

    they canverify nothingis leftinsidewhenthey arefinished.

    Bearing lubricant levels. All bearing lubricantlevelsshouldbe checkedjustprior

    tostartup.Ifthe lubricantlevel isindicatedby asightglass, thevalvetothesightglassshouldbe checkedtomakesureitisopenandthe level inthesightglassis

    accurate.

    Cooling water supplies. Theflowandpressureofthe coolingwatertothe

    generatorandbearing coolersshouldbe checkedtomakesureitisadequate. Thepackingbox coolingwatersupply shouldalsobe checked.

    Clearances. Clearancesbetweenstationary androtatingpartsshouldbe checked.Bearing covers, vaporguards, rotorfanblades, etc., shouldbe checkedforadequate

    clearance.

    Bearing and PMG

    insulation. The upperguidebearing, thethrustbearing, andthePMG are usually insulatedfromtheframetopreventdamagethatcouldoccurfrom

    circulating currentspassingthrough them. Theinsulationshouldbe checkedwith

    anohmmeterpriortostartupfollowingtheprocedureinFIST Volume 3-11,Generator ThrustBearingInsulationand Oil Film Resistance.

    27

    Oil or water leaks. With full pressureandflow, checkthreadedandflangedjoints

    ofthevariouswater linestothe unitfor leaks. Checkoil pipingandbearingoil tubs

    for leaksatjoints.

    7.2 Initial startup

    Whenthe unitcheckouthasbeen completedandthe clearancefortheoverhaulreleased, the unitcanbewatered upforstartup. Maintenancepersonnel shouldbestationedwith two-way radiosatstrategic locationsnearthe unitto listenand

    watch foranything unusual whenthe unitisstarted. Thewicketgatesshouldbeopenedjustenough tostartthe unitturningandthenshut. Thisshouldbedone

    several timesto checkfor rubsorotherproblems.Ifnoproblemsarenoted, the

    wicketgatesshouldbeopenedtobringthe unitto 100-percentspeed.Ifatany pointany oftheobserversnoticeany unusual noiseorotherproblems, they shouldnotify

    theoperatortoimmediately shutthe unitdown.Ifnoproblemsarenoted, the unit

    should continuetooperateatspeed-no-load until bearingtemperaturesstabilize.

    Ifthegovernorwasnotadjustedbeforestartup, itispossiblethatthe unitwillhunt.Ifthisisthe case, gradually closethegovernordashpotneedle until the

    huntingstops. Thegovernor canbeadjustedforoptimumresponseafterthebearing

    temperaturesstabilize.

    7.3 Operational readings

    Onceitisdeterminedthatthe unitcanbeoperatedwith noproblems, thefollowing

    readingsshouldbetakenand comparedtothepreteardownreadings.Itisvery

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    likely that, dependingonwhatmodifications havebeenmadetothe unit, agreat

    deal ofothertestingbesidesthesereadingswill berequired. Thesereadingsaresuggestedonly asbasic indicationofthe units condition. Variousindexor

    acceptancetests, aswell asnumeroustestsoftheelectrical equipment, will berequiredfollowingany uprateormajoroverhaul.

    Bearing heat run. With the unitrunningatspeed-no-load, thebearingmetal andoiltemperaturesshouldberecorded until thetemperaturesstabilize.Ifadata loggeris

    notavailable, thetemperaturesshouldberecordedmanually every 5minutesfor

    thefirst30 minutesofoperationandevery 15minutesafterthatuntil the

    temperaturesstabilize.Afterthe unitisbroughtonline, againmonitortemperaturesasthe unitis loaded.

    Shaft runout readings. Therunoutreadings canbetakenwith dial indicatorsbutaremuch moremeaningful iftakenby proximity probes. Readingsshouldbetaken

    atvarious loadsfromspeed-no-loadtofull load. Special attentionshouldbegivento

    therunoutatany rough zonestheturbinemay have.Ifproximity probesare used,

    thesignal shouldberecordedwith astrip chartrecordersothatthewaveformoftherunoutcanbeanalyzed.Anormalrunout

    28

    patternwill beasinewavewith atimeperiod correspondingtotherotational

    speed.Ifproblemsareencountered, such asextremely high runoutmagnitudeora

    hotbearing, furtheranalysisshouldbeperformed.Iftwoproximity probesare

    mounted 90 degreesapartateach elevation, theiroutputcanbe hooked uptoatwo-

    channel oscilloscopetoplottheactual runoutorbitpattern. This canbe

    helpfulindetectingarubinthebearing.Aspectrumanalyzerisalsousefulwhen

    troubleshootingavibrationproblem. Thespectrumanalyzerbreaksdownthesignal

    fromtheproximity probesintoits componentfrequencies. Therunoutreadingstakenshouldalsobe comparedtothereadingstakenbeforethe unitwasshutdown

    fortheoverhaul.

    Load rejection tests. Ifa hydraulic transientstudy wasperformedtodeterminethe

    correctwicketgatetiming, eitherbecausethe unitwas upratedortheoriginal data

    was lost, loadrejectiontestsshouldbeperformedtoverify thefindingsofthestudy.

    Thestudy shouldprovidepredictedspiral casepressureversustimegraphsand

    unitoverspeedversustimegraphsfortheforebay andtailraceelevationsatthetimeofthetests. Thewicketgatetimingshould havebeensettothevaluerecommended

    by the hydraulic transientstudy beforethe unitwaswatered up.

    Loadrejectiontestsshouldbeperformedatlower loadsbeforeperformingafullloadrejection.Immediately followingatestata lower load, thetestdatashouldbe

    studiedtomakesurethatarejectionatthenexthigher load canbeperformed

    withoutexceedingdesign limits.If, fromthetestdata, itappearsthatthepressurecouldpossibly exceedthedesignpressureatfull load, thewicketgatetimingshould

    besloweddownbeforethefull loadrejectiontestisperformed.Ifpressureissignificantly lowerthanthe hydraulic transientstudy andtheoverspeed higher, the

    wicketgatetiming canbemadefaster.

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    Ifthe unitbeingtestedisequippedwith apressureregulatororanautomatic bypass

    valve, several loadrejectionsshouldbedonefromnotmorethan 15-percentgatetoverify thewicketgatetiming. Whilethewicketgatetimingstill shouldbesetwith

    the unitunwatered, someregulatordesignsaresuch thatthetiming canonly beaccurately testedduringanactual loadrejection.

    Immediately priortothetest, thefollowingdatashouldberecorded:

    y Gateposition Load Forebay elevation Tailraceelevation Spiral casepressure

    29

    Thefollowingshouldbemonitoredandrecordedby astrip chartrecorderduringa

    loadrejectiontest:

    Breaker position.-Areferencesignal todetermineexactly whenthebreakeropens

    canbe helpful. This canbeasignal fromthegenerator currenttransformerora

    breaker contactthatopensor closeswith themainbreaker.

    Gate position.-Astringtransducerorotherpositiontransducershouldbe

    connectedtooneoftheservomotorstomonitorwicketgateposition. Thestrip chart

    recordershouldbe calibratedfrom 100-to 0-percentgate.

    Unit speed.-Unitspeedshouldberecordedwith atachometerorfrequency

    transducerwith sufficientrangetomeasurethespeedfromzerotothepredicted

    maximumspeed.

    Spiral case pressure.-Spiral casepressureshouldbemonitoredby apressure

    transducer connectedtoavalvedtapinthespiral casemandoor.Ifatapisnotavailableinthemandoor, thetransducer canbeinstalleddirectly onthepiezometer

    ringjustupstreamfromthepenstock.Installationona long lineora linewith a

    bourdontubetypegaugeorsensor can leadtofalsedata.

    Surge tank pressure.-Apressuretransducershouldbemountedatthebaseofthe

    surgetanktomonitorwaterelevationinthetank. Underno circumstancesshould

    thewaterovertopthetank.

    Generator voltage.-Avoltagetransducer connectedtothegeneratorpotential

    transformershouldbe usedtomonitorgeneratorvoltage.

    Pressure regulator.-Ifapressureregulatororautomatic bypassvalveispresent,

    itspositionshouldbemonitoredby astringtransducerorotherposition

    transducers.

    Shaft runout.-Proximity probesshouldbeinstalledateach oftheguidebearingelevationstomonitorshaftrunoutduringthe loadrejectiontests.

    Afterthetest, thefollowingdatashouldberecorded:

    y Wicketgatetiming Maximumshaftspeed _ Maximumspiral casepressure _ Maximumgeneratorvoltage _ Maximumsurgetank

    pressureorelevation Regulatorvalve closuretime

    30

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    APPENDICES

    31

    Appendix A

    SEAL RING DESIGN AND SPECIFICATIONS

    32

    INTRODUCTION

    SEAL RING DESIGN AND SPECIFICATIONS

    Thepurposeofseal ringsorwearingrings, asthey arealso called, istoprovidea

    renewableseal or leakagejointbetweenaturbinerunnerandits casing. Thesmallclearancebetweenthestationary androtatingrings limitstheflowofwaterfrom

    the high pressureareasto lowpressureareasoftheturbine.Asthe clearance

    increasesovertime, theamountofwaterflowingthroughthesealringsincreases,decreasingtheefficiencyoftheturbine.

    Assealringclearancesincreaseto 200 percentofthemanufacturersdesign clearance,theefficiency candecreaseasmuch as 2 percent. Priortoascheduledoverhaul, the

    seal ring clearancesandthedesignoftheseal ringsshouldbeanalyzed.Iftheseal

    ring clearance hasincreasedsignificantly oriftheseal ringdesignisquestionable,replacementshouldbe considered.

    Seal ring designIdeally, seal ringsshould last20 yearsormore. Thistypeoflongevity isnotalways

    possible, buttoachievethe longestlifepossible, theseal ringsmustbe constructed

    ofmaterialsthatareresistanttowearand corrosion. Wear canoccurasaresultof

    cavitationorabrasiveerosion.Abrasiveerosion causedby siltorothersuspendedparticlesinthewateris usually nota concerninturbinesthatreceivetheirwaterfromdeepreservoirs, butitcanbeaprobleminpump-turbinesorturbinesthat

    receivetheirwaterfroma canal orothershallowwaterway. Cavitationerosionis

    dependentontheamountofheadofthe unit, theseal ring clearance, andthe

    hydraulic characteristicsoftheunit.

    Theoccurrenceofcorrosionwilldependonthesealringmaterialandthequality ofthewater.

    Thegallingresistancebetweentherotatingandstationary ringmaterialsmustalso

    be considered. Undernormal operating conditions, theringsshouldnevertouch.

    However, insome circumstancessuch asthefailureoftheturbineguidebearing,failureofaseal ring, orduring unitalignment, they can comein contact.Ifcontactis

    madebetweenmaterialsthatarepronetogalling, therings canbeseverelydamaged, andinextreme cases, theringsmay seize.

    Overthe years, seal ringdesigns havevaried.Insomeplants, caststeel ringsthatwereintegral partsoftheturbinerunnerand casingwere used. While caststeel is

    notpronetogalling, itissusceptibleto cavitationerosion, abrasiveerosion, and

    corrosion. The caststeel performedacceptably inmostcircumstances, butas

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    material technology improved, othermaterialsweretriedinanattempttoachieve

    longer life.

    Inthe 1950sand 1960s, the Bureau ofReclamation commonly specified hardened

    400 seriesmartensitic stainlesssteel forboth therotatingandstationary seal rings.

    Theseringsweremuch moreresistantto corrosionand cavitationerosionthanthe

    caststeel rings. Theringswere heattreatedtodifferenthardnessvalues, apparentlywith theideathatitwouldpreventgallingintheeventofcontactbetweentherings.

    Therotatingringwasashrinkfitontherunner, andthestationary rings consisted

    ofdovetail segments heldinplacewith softcopper caulkinginadovetail groove.

    Thisdesignwasnotsuccessful asthe copperwoulderodeovertimeallowingthesegmentsto come loose. Thestainlesssteel againststainlesssteel, evenwith the

    different

    33

    hardnessvalues, wasstill likely togall.Inoneinstance, the upperand lowerring

    both seizedwhenthestationary segments came loose.

    Anotherproblemencounteredwith martensitic stainlesssteel isitssusceptibility to

    stress corrosion crackingwhennotheattreatedproperly. Tempering 410 stainless

    steel between700 Fahrenheit(oF)and 1,050 oF resultsindecreased corrosionresistance. Rotatingringsfailedatseveral facilitiesduetospecifyinga hardnessthat

    requiredtemperingat900 oF.

    Tosolvethegallingproblem, dissimilarmetalsshouldbespecified.Astheresultof

    laboratory testing, austenitic stainlesssteel andaluminumbronzeweredetermined

    asthebestcombinationofmaterialsforseal zings.Inthetests, thesematerialswere

    foundtobenotonly resistanttogallingwhenbroughtintomoving contact, butboth

    materialsprovedtobemore cavitationresistantthanthemartensitic stainlesssteel.

    Toreplacethedovetailedsegmentsofthestationary ring, aluminumbronzesegmentsrolledfrombarstockand heldinplacewith radial fastenerswere used.

    Thisdesignalsoproved unsuccessful. Ringsofthisdesignfailedinarelatively shorttimeafterinstallation. Therolledbarstocktendedto loseitsrolleddimension,

    creatinga clearancebetweentheringanditsmatingsurface. The clearanceallowed

    theringtomove, creatingavibrationthatledtofatigue cracking. Therollingprocessitselfcaused crackstoformontheoutsidediameteroftherings. Otherfactorsthat

    may have contributedtothefailurewereovertorquingthefasteners, flawsinthefasteners, andstress concentration causedby theradial boltholes.

    Currentseal ringdesign callsformakingtheringsinonepiecewheneverpossible.

    Thepreferredmethodofmanufactureisby centrifugal casting. Centrifugal castingforcesthemetal outwardwhilethe lighterimpuritiesremainontheinsidediameter.

    Theimpuritiesareremovedby machining. Whentheringsarevery large,

    centrifugal castingmay notbepossible, andsand castingorringrolledforgingmaybe used. Ringrolledforgingisaprocessthatproducesa large-diameterseamless

    lingby rollinga heated, smaller-diameterringwith athickcrosssection, betweentworollers. Rotatingrings canalsobefabricatedby rollingbarstockandwelding

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    theends, butcastingispreferable. Whennewstainlesssteel turbinerunnersare

    installedtherotatingringsarespecifiedtobeanintegral partoftherunner.

    Thesinglepieceringsaredesignedtobeashrinkfitand usually dontrequire

    fasteners.Ifthestationary ring hastobeinstalledinsections, each sectionis cast, ortheringis castinonepieceand cutby wireelectrodischargemachining (EDM)

    process. EDM isspecifiedbecausethewidth ofcutby normal sawingtechniqueswouldbegreaterthan 0.020 inch wherethewidth ofawire EDM cutis lessthan

    0.010 inch.Iffastenersarerequired, they shouldbemadefrom Nitronic 60 stainless

    steel. Nitronic 60, unlikemoststainlesssteels, isresistanttogallingaswell asbeing

    resistantto cavitationerosionand corrosion.

    34

    REFERENCES

    Christenson, D.J., and Duncan, W. H., Turbineand Large Pump Seal Rings, WaterOperationand Maintenance Bulletin No. 159, March 1992.

    Peabody, S.C., United States Bureau ofReclamation, Wearing Ring Design,Preliminary Report, November 1991.

    35

    I. INTRODUCTION

    SAMPLE SPECIFICATIONS

    Thefollowingspecificationsspecify stainlesssteel fortherotatingringandnickel

    aluminumbronzeforthestationary ring.Inspecial circumstances, itmay bedesirabletomaketherotatingringbronzeandthestationary stainlesssteel.

    Centrifugal cast, singlepieceringsarepreferable, buton largerings, sand castingor

    ringrolledforgingmay berequired. Thesespecificationsareonly providedasa

    guide. Specificationsfornewseal ringsshouldbeissuedonly afteradequate

    research andanalysis hasbeenperformed.

    II

    GENERAL REQUIREMENTS

    A. Stationary seal ring. Each seal ringshall be castasonepiecefromnickelaluminumbronze, copperalloy C95500 or copperalloy C95800. Theseal rings

    shall be casttonominal sizeby sand castinginaccordancewith American

    Society for Testing Materials (ASTM) B148or centrifugally castinginaccordance

    with ASTM B27l, orthey shall be casttoasmallerdiameterwith athicker crosssectionandringrolledforgedtotherequired largerdiameter. Rings castfrom

    C95500 shall beannealedandtempered. Rings castfrom C95800 shall be

    annealed. The heattreatmentprocedureofthe castingshall besubmittedfor

    approval andshall includetheinitial annealingtemperaturerangeand coolingrateandthetemperingtemperaturerangeand coolingrateifapplicable.Ifthe

    contractorelectstoringroll forgeafter casting, theproceduremustbesubmittedforapproval.

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    Ifthezingistobesuppliedinsections, each sectionshall be castortheringmay

    be castinonepiece, finish machined, and cutintosections usingthewire EDMprocessorothermethodthatremovesnomorethan 0.010 inch ofmaterial per

    cut.

    B. Rotating seal rings. Each seal -ringshall be constructedofstainlesssteel ofthe

    chromiumnickel-alloy type, conformingtoASTM A743grade CF-8orCF10SMnN (Nitronic 60)ifcast, or conformingtoASTM A 167type304L if

    fabricated.Ifcast, theseal ringsshall be casttonominal size, orthey shall be cast

    toasmallerdiameterwith athicker crosssectionandringrolledforgedtothe

    required largerdiameter. Fabricatedringsshall berolledandweldedwith notmorethantwoweldseamsperring. Fabricatedringsshall bestressrelieved, and

    thestressreliefprocedureshall besubmittedforapproval. Castringsshall be

    heattreated, andthe heat-treatingprocedureshall besubmittedforapproval.If

    the contractorelectstoringroll forgeafter casting, theproceduremustbe

    submittedforapproval.36

    III. WELDING

    Majordefectsinthe castingsmay berepairedby weldingwith the consentofthecontractingofficer.Iftheringsarefabricatedfrommorethanonepiece, welding

    proceduresanddrawingsidentifyingtheweldsshallbesubmittedforapproval.Allweldsshallbe100-percentnondestructively inspectedby radiographic, dye

    penetrant, orothernondestructivemeans. Theseinspectionsshall beattheexpense

    ofthe contractor. Thequalificationofweldingprocedures, welders, andweldingoperatorsshall conformtosectionIXoftheAmerican Society ofMechanical

    Engineers (ASME) Boilerand Pressure Vessel Code.

    IV. LADLE ANALYSIS AND MECHANICAL PROPERTIESCertificatesshowingtheresultsofthe ladleanalysisandmechanical propertiestests

    shall besubmittedforapproval. Testcouponsformechanical propertiesshall beworkedand heattreatedinthesamemannerastheseal ringsandshall be

    destructively testedtodeterminetensilestrength, yieldstrength, and Brinell

    hardness. Mechanical propertiesshall meetthespecifiedvaluesintheaboveASTM

    codes.

    V. FINISH OF SEAL RINGS

    Thefinishedringsshall befreefromvoids, cracks, andsurfacedefects. Thefinished

    surfacesoftheseal ringsshall notexceed 125-microinchesmaximumsurface

    roughnessinaccordancewith American National StandardsInstitute (ANSI) 46.1.

    VI. FINAL INSPECTION

    Inspectionoftheseal ringswill bemadeby the contractingofficerorthe contracting

    officersrepresentativeatthepointofmanufacturepriortopreparationfor

    shipment.Amanufacturersinspectionreportwith final dimensionsofeach ring

    shall besubmittedtothe contractingofficerforapproval beforeshipment.

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    VII. SHIPPING

    Theseal ringsshall besufficiently supportedduringshipmenttoassurearigid

    retentionoftheirshape. Shippingwill betheresponsibility ofthe contractor.

    37

    Appendix BSAMPLE CALCULATION FOR SEAL RING INSTALLATION

    38

    SAMPLE CALCULATION FORSEALRINGINSTALLATION

    By Ernie Bachman

    Thefollowingisasample calculationfordeterminingthedimensionsfor

    replacementseal rings.Itisageneral exampleshowingtheformulasandassumptionsmadewhen calculatingthestressandfitofseal rings. Refertofigure Bl

    fordimensions. Only the calculationsforthetopseal ringsareshownasthey would

    beessentially thesameforthebottomrings.37

    ROTATING RING

    Step 1. Determine inner diameter of rotating seal ring. Thestressinducedinthe

    seal ringby theshrinkfit(i.e., thedifferencebetweentheinnerdiameteroftheseal

    zingtheouterdiameteroftheturbinerunner)inmostcasesshouldnotbemore

    thanone-thirdofyieldstrength ofringmaterial. Thedesired unitdeformation, or

    strain, is calculatedbasedonone-thirdofthe yieldstrength. Theamountofshrink

    fitisthendeterminedby multiplyingthestrainby thediameteroftherunner. This

    valueissubtractedfromthediameteroftherunnertoobtaintheinnerdiameterof

    theseal zing.Step 2. Determine stress in ring caused by centrifugal force. Thestressinthe

    ring causedby centrifugal forcewill bemaximumatrunaway speed. Comparethis

    valuetotheshrinkfitstress.Ifthestress causedby the centrifugal forceisgreaterthantheshrinkfitstress, thering couldbecome looseontherunner.

    38

    Step 3. Determine temperature required for installation. Theringmustbeexpandedby heatingforinstallation. Thetongueofthetongueandgroovefitofthe

    ringmustbe consideredinthe calculations. Thetotal amounttheringmustbeexpandedmustincludetheshrinkfitamount, twicethethicknessofthetongueon

    thering, plusthe clearancerequiredforinstallation.

    39

    STATIONARY RING

    Step 1. Determine outer diameter of stationary seal ring. Thetopstationary

    seal ringisashrinkfitinthe headcover. Theamountofinterferencebetweentheringandthe headcovershouldbesufficienttopreventtheringfrombecoming loose

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    whenthe unitiswatered up. Thestressinthezingshouldbe checked, butthe

    limitingfactorontheamountofinterferencewill betherequiredinstallationtemperature. Therequiredinstallationtemperatureshouldnotbe lowerthan-109

    oF, thetemperatureofdry ice. Lowertemperaturesareattainablewith other coolingmediumssuchasliquidnitrogen,butthisisnotpracticalwithlargerings.

    Astrainof0.0005inch perinch shouldprovideafitthatissufficiently tightandattainablewith dry ice.

    Step 2. Determinestressinring causedby shrinkfit.

    Step 3. Check effect of watering up. Assumingaworse caseofunitbeingdry and

    atatemperatureof70 oF andbeingwatered upsuddenly with 40 oF water,determinewhetherringwill remaintight.

    40

    Step 4. Determinerequiredtemperatureforinstallationofring. Verify thatinstallationtemperatureisabove-109 oF.

    Figure B1

    41

    Appendix C

    TOLERANCES FOR HYDROUNIT ASSEMBLY

    42

    Statorairgap

    MeasurementTolerance 5%ofnominal designairgap

    5%ofnominal designairgap 20%diametrical bearing clearance

    20%diametrical bearing clearance 10%diametrical seal ring clearance

    5%ofnominal designairgap 5%ofnominal designairgap 5%ofnominaldesignairgap