US HPP Overhaul

8/2/2019 US HPP Overhaul

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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

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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.

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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

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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

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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

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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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_ 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.

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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


13/39

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


14/39

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


15/39

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.


16/39

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


17/39

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.


18/39

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


19/39

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


20/39

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


21/39

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


22/39


23/39

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


31/39

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.


32/39

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.

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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

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