水利水电工程专业英语Word格式文档下载.docx

水利水电工程专业英语Word格式文档下载.docx

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1HYDROPOWERPLANT

1.1Hydropower

Itisthepowergeneratedbyusingwaterastheenergy-supplyingagent.Inthiscase,waterisallowedtoflowfromahigherleveltoalowerlevelthroughaturbinewherethepotentialenergyofwaterisconvertedintokineticenergyandtheturbine,inturn,rotatesageneratortoproduceelectricity.

Hydropowergenerationdependsupontheavailabilityofrainwater.Cloudsareformedbecauseoftheheatingofseawaterbythesun.Theymovetowardstheland,wherelow-pressurezonesareformedandastheygetcooled,moisturestartsprecipitating.Therainwaterstartsmovingtowardslowerlevelsbecauseofgravity,throughasystemofnaturaldrainsconsistingofnullahs,rivulets,riversandsoon.Thiswatercanbestoredinreservoirscreatedontherivers,byconstructionofdamsandcanbeusedtogeneratepower.Aftergeneration,thewaterisletoutintotheriverandgraduallytravelsfurtherandultimatelyreachesthesea.Hereitisheatedupbythesuntostartthenextcycle.Therefore,hydropowerisnothingbutconversionofsolarenergyintoelectricitythroughacircuitousroute.

1.2AdvantagesofHydropower

Hydropowergenerationisnon-wastingself-replenishingandnon-polluting.

Itisaphysicalphenomenonandnochemicalchangeisinvolved.Watercomeoutunchangedfromtheturbineafterimpartingitsenergyandcanbeusedagaineitherforpowergenerationorforirrigation.Infact,thisisdoneinmulti-purposeriver-valleyschemesliketheChambalValleydevelopmentinIndiaandtheTennesseeValleydevelopmentinU.S.A.InthecaseoftheChambalValleydevelopment,powerisgeneratedwiththehelpofthesamewaterinthreepowerhouses,situatedoneafteranotherontheriver,beforebeingreleasedintoirrigationcanals.Asagainstthis,coal,oilornuclearfuelcanonlybeusedonce.

Thesupplyofwaterisautomaticandthewaterutilizedinoneseasonisreplenishedbynatureinthenextseason.Thewaterreachesthepowerhousesiteonitsown-nominingoperationsandtransportationareinvolvedasinthecaseofcoaloroil.

Waterpoweriscleanasitdoesnotproduceanypollutants,whereasinthecaseofthermalornuclearpowergenerationpollutionisinevitable,astoxicby-productsareemitted.

Thehydropowerplantshaveveryhighefficiencies.Theturbineefficiencyisabove90percentandtheoverallefficiencycanbeabove80percentwhichismuchhigherthanthatofthermalplants.Thehydro-plantsarelonglastingandmanyplantsarestillinserviceeven40yearsaftercommissioning.Thepercentageofoutagesisverylow,asshutdownsforrepairsandmaintenancearefewer.Theplantsareavailableforinstantloadingandasetcanstarttakingfullloadwithinfiveminutes,startingfromthestandstillposition,whereasthermalplantsmaytakeaboutfivetosixhours.

1.3DisadvantageofaHydroplant

Theinitialinvestmentsareveryheavyandthespecificcostishighcomparedtoathermalplant.Thetimeneededforconstructionisquitelonganditaffectstheeconomyadverselyasreturnsstartflowinginlate.Whenalakeisformed,landsubmergencecreatesitsownproblem.

Astheavailabilityofwatervariesfromyeartoyear,inlowrainfallyearstheplantcapacityisunder-utilized.

Anywaytheadvantagesfaroutweighthedisadvantages.

1.4Multi-PurposeUses

Asalreadystartedearlier,anumberofadditionalbenefitscanbeobtainedfromwaterstoredbesidesgeneratingpower,suchasirrigation,floodcontrol,navigationandsoon.Themulti-purposeuseofwatergivesmuchbetterreturnsoninvestmentandthereismarkedimprovementinthecost-benefitratio.

1.4.1Irrigation

Thewaterbeingdischargedfromapowerhousecanbefedintoacanalnetworktoprovideirrigationfacilitiestolandsituateddownstream.Asamatteroffact,inmanymulti-purposeprojectsinIndia,waterisstoredpredominantlyforirrigationpurposeswithpowergenerationplayingasecondaryrole.

1.4.2Floodcontrol

Creationoflakeonariverhastheinherentpossibilitiesoffloodmoderation.Thefloodwatersmaybefullyorpartlyabsorbedinthelakeandonlyregulatedquantitiesofwaterareallowedtopassdownstream,protectingthelowerareasfromfloods.Thisaspectassumesgreatimportanceinthecaseofrivers,whichgoondevastatinglargetractsoffertilelandandvaluablepropertyyearafteryear.

1.4.3Navigation

Theformationofstoragereservoirincreasesthenormalwaterlevelinariver.Manypoolsandshallowstretchesoftherivergetsubmergedunderwaterandasufficientdepthofwaterbecomesavailableforshiptonavigatethesestretches.Thusfacilitateseconomictransportofcargoandpassengers.

Themulti-purposedevelopmentoftheriverDanubeinEuropeisatypicalexampleofcombiningnavigationwithpowergeneration.It’slinkingupwiththeriverRhinehasallowedtheshipstopassfromtheNorthSeatotheBlackSea.Barrageshavebeenconstructedatanumberofpointsintheriverincreasingtheupstreamwaterlevelsandpowerisbeinggeneratedattheseplaces.Theonlyadditionalconstructionneededistoprovidenavigationallocksatthesitesofthebarragefortheuninterruptedmovementofaship.

1.4.4Recreation

Creationareservoirofwaterconsiderablyenhancesthebeautyandcharmofsurroundingareasandtouristresortsandpicnicspotsarebeingdevelopedintheseareas.

1.4.5FishBreeding

Itcantakeplaceonalargescaleandfishcanbemadeavailableeconomicallytothepopulationlivingintheneighboringareas.

1.5TypicalComponentsofaHydroelectricPlant

Themaincomponentsare（Fig.1.1）:

（i）Thedam,（ii）Thewater-conduitsystem,（iii）Thepowerhouse,（iv）Thetail-watersystem,（v）Theswitchyard,and（vi）Thetransmissionlines.

1.5.1DamorBarrage

Adamorabarrageisconstructedontherivercourseresultinginanincreaseintheupstreamwaterlevelbecauseoftheformationofareservoirwhosestoragecapacityisdecidedbythewaterrequirementforpowergeneration.

1.5.2Water-ConduitSystem

Water-conduitsystemcarrieswaterfromthereservoirtothepowerstation.Itmayconsistofapressuretunneland/orpipescalledpenstockswhichmaybelaidabovegroundorunderground.Onepenstockmayfeedanumberofturbines,whereanumberofbrancheshavetotakeoff.Flow-controlvalvesmaybeprovidedbeforewaterisadmittedtotheturbines.Asurgetankisoccasionallyprovidedtorestricttheeffectsofwaterhammer.

Fig.1.1Typicallayoutofahighheadhydroelectricplant

1.5.3PowerHouse

Thepowerhouseaccommodatestheturbinesandgenerators,thecontrolequipmentandinsomecasesthetransformers.Itslocationcanbeeitheratthesurfaceorundergroundanditmaybeawayfrom,atthefootof,orinthebodyof,thedam.

1.5.4TailRace

Thewater,afterpassingthroughtheturbine,isdischargedintothetailracewhich,inturn,carriesittoariver.

Thetailracecanbeanopenchannelasinthecaseofasurfacepowerhouse,oratunnelasinthecaseofanundergroundpowerhouse.Thedischargefromalltheturbinesiscollectedinthetailraceatitsbeginningbymeansofbranchchannels.Thetailracemaydischargeintotheoriginalriveritselfor,inrarecases,someotherriverwhenthereisaninter-basintransferofwater.

1.5.5ElectricalPowerTransmission

Theelectricalpowergeneratedbythegeneratorsisfedtothestep-uptransformersbymeansofcablesasthegeneratingvoltagemaybemuchlessthanthetransmissionvoltage.Thepoweristhensuppliedtothetransmissionnetworkviaaswitchyardwheretheswitchingandprotectiveequipmentisinstalled.Theswitchyardislocatedwithinashortdistanceofthepowerhouse.

Transmissionlinestakeoffindifferentdirectionstosupplypowertotheconsumers.

Inthecaseofcombinedhydropowerandirrigationmulti-purposeprojects,acanalnetworkisestablisheddownstreamofdam.

1.6ClassificationofHydroelectricPlants

Theycanbeclassifiedonthebasisoftheoperatingheads,theoutputorsomeotherimportantfeatures,suchasthenatureofduty.

1.6.1Base-LoadandPeak-LoadPlants

Everyhydro-plantisanindividualentityandnotwoplantsareidenticalasregardsthehead,availabilityofpowerandsoon.Ahydro-plantworksasabase-loadplantifthereiscontinuouspowergeneration.Thisisespeciallythecaseiftheflowthroughtheriverhastobemaintainedconstantformeetingtheirrigationornavigationrequirements.

Iftheconditionsprevailingatthepowerstationpermitregulatedreleases,theplantcanbeusedtogeneratepeakpower.Forexample,theRoselandplant（France）isdesignedtomeetthepeakwinterdemandfromwaterlargelystoredduringthesummerperiod.

1.6.2Plantscanalsobeclassifiedasfollows:

（a）Conventionalhydro-plantswithvalleystorage.

（b）Run-of-the-riverplants.

（c）Diversiontypeofplants.

（d）Pumpedstorageplants.

（e）Tidal-powerplants.

Valleystorageplants

Inthecaseofconventionalhydro-plants,areservoirhastobecreatedontherivertostoresufficientrainwater,forpowergenerationthroughouttheyearbyconstructionofadam.Thesetypesofplantsaresub-dividedintohigh-headplants,medium-headplants,andlow-headplants（Fig.1.2）.

Itisdifficulttolaydownexactranges.However,thefollowinglimitsarerecommended（theyarearbitraryandareasgoodasanyotherarbitraryrangesrecommended）:

（i）High-headplants-havingheadsofmorethan250m.

（ii）Medium-headplants-havingheadsbetween50mand250m.

（iii）Low-headplants-havingheadslessthan50m.

Fig.1.2TheGeheyanvalleystorageplant（China）

Today,theplantcapacitiesrangefromafewhundredkilowattstothousandsofmegawattswi