us hpp overhaul
Post on 06-Apr-2018
226 Views
Preview:
TRANSCRIPT
-
8/2/2019 US HPP Overhaul
1/39
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
-
8/2/2019 US HPP Overhaul
2/39
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
-
8/2/2019 US HPP Overhaul
3/39
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.
-
8/2/2019 US HPP Overhaul
4/39
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
-
8/2/2019 US HPP Overhaul
5/39
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.
-
8/2/2019 US HPP Overhaul
6/39
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
-
8/2/2019 US HPP Overhaul
7/39
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
-
8/2/2019 US HPP Overhaul
8/39
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
-
8/2/2019 US HPP Overhaul
9/39
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:
-
8/2/2019 US HPP Overhaul
10/39
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
-
8/2/2019 US HPP Overhaul
11/39
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
-
8/2/2019 US HPP Overhaul
12/39
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
-
8/2/2019 US HPP Overhaul
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
-
8/2/2019 US HPP Overhaul
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
-
8/2/2019 US HPP Overhaul
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.
-
8/2/2019 US HPP Overhaul
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
-
8/2/2019 US HPP Overhaul
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.
-
8/2/2019 US HPP Overhaul
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
-
8/2/2019 US HPP Overhaul
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
-
8/2/2019 US HPP Overhaul
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
-
8/2/2019 US HPP Overhaul
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
-
8/2/2019 US HPP Overhaul
22/39
-
8/2/2019 US HPP Overhaul
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
-
8/2/2019 US HPP Overhaul
24/39
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
-
8/2/2019 US HPP Overhaul
25/39
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
-
8/2/2019 US HPP Overhaul
26/39
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
-
8/2/2019 US HPP Overhaul
27/39
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.
-
8/2/2019 US HPP Overhaul
28/39
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
-
8/2/2019 US HPP Overhaul
29/39
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
-
8/2/2019 US HPP Overhaul
30/39
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
-
8/2/2019 US HPP Overhaul
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.
-
8/2/2019 US HPP Overhaul
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.
-
8/2/2019 US HPP Overhaul
33/39
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
-
8/2/2019 US HPP Overhaul
34/39
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
top related