毕业设计水利水电工程英文文献翻译

外文文献：hydraulicturbinesandhydro-electricpowerAbstractPowermaybedevelopedfromwaterbythreefundamentalprocesses:byactionofitsweight,ofitspressure,orofitsvelocity,orbyacombinationofanyorallthree.InmodernpracticethePeltonorimpulsewheelistheonlytypewhichobtainspowerbyasingleprocesstheactionofoneormorehigh-velocityjets.Thistypeofwheelisusuallyfoundinhigh-headdevelopments.Faradayhadshownthatwhenacoilisrotatedinamagneticfieldelectricityisgenerated.Thus,inordertoproduceelectricalenergy,itisnecessarythatweshouldproducemechanicalenergy,whichcanbeusedtorotatethe‘coil’.Themechanicalenergyisproducedbyrunningaprimemover(knownasturbine)bytheenergyoffuelsorflowingwater.Thismechanicalpowerisconvertedintoelectricalpowerbyelectricgeneratorwhichisdirectlycoupledtotheshaftofturbineandisthusrunbyturbine.Theelectricalpower,whichisconsequentlyobtainedattheterminalsofthegenerator,isthentransitedtotheareawhereitistobeusedfordoingwork.heplantormachinerywhichisrequiredtoproduceelectricity(i.e.primemover+electricgenerator)iscollectivelyknownaspowerplant.Thebuilding,inwhichtheentiremachineryalongwithotherauxiliaryunitsisinstalled,isknownaspowerhouse.Keywordshydraulicturbineshydro-electricpowerclassificationofhydelplantsheadschemeTherehasbeenpracticallynoincreaseintheefficiencyofhydraulicturbinessinceabout1925,whenmaximumefficienciesreached93%ormore.Asfarasmaximumefficiencyisconcerned,thehydraulicturbinehasaboutreachedthepracticablelimitofdevelopment.Nevertheless,inrecentyears,therehasbeenarapidandmarkedincreaseinthephysicalsizeandhorsepowercapacityofindividualunits.Inaddition,therehasbeenconsiderableresearchintothecauseandpreventionofcavitation,whichallowstheadvantagesofhigherspecificspeedstobeobtainedathigherheadsthanformerlywereconsideredadvisable.Theneteffectofthisprogresswithlargerunits,higherspecificspeed,andsimplificationandimprovementsindesignhasbeentoretainforthehydraulicturbinetheimportantplacewhichithaslongheldatoneofthemostimportantprimemovers.1.typesofhydraulicturbinesHydraulicturbinesmaybegroupedintwogeneralclasses:theimpulsetypewhichutilizesthekineticenergyofahigh-velocityjetwhichactsupononlyasmallpartofthecircumferenceatanyinstant,andthereactiontypewhichdevelopspowerfromthecombinedactionofpressureandvelocityofthewaterthatcompletelyfillstherunnerandwaterpassages.Thereactiongroupisdividedintotwogeneraltypes:theFrancis,sometimescalledthereactiontype,andthepropellertype.Thepropellerclassisalsofurthersubdividedintothefixed-bladepropellertype,andtheadjustable-bladetypeofwhichtheKaplanisrepresentative.1.1impulsewheelsWiththeimpulsewheelthepotentialenergyofthewaterinthepenstockistransformedintokineticenergyinajetissuingfromtheorificeofanozzle.Thisjetdischargefreelyintotheatmosphereinsidethewheelhousingandstrikesagainstthebowl-shapedbucketsoftherunner.Ateachrevolutionthebucketenters,passesthrough,andpassesoutofthejet,duringwhichtimeitreceivesthefullimpactforceofthejet.Thisproducesarapidhammerblowuponthebucket.Atthesametimethebucketissubjectedtothecentrifugalforcetendingtoseparatethebucketfromitsdisk.Onaccountofthestressessoproducedandalsothescouringeffectsofthewaterflowingovertheworkingsurfaceofthebowl,materialofhighqualityofresistanceagainsthydraulicwearandfatigueisrequired.Onlyforverylowheadscancastironbeemployed.Bronzeandannealedcaststeelarenormallyused.1.2FrancisrunnersWiththeFrancistypethewaterentersfromacasingorflumewitharelativelylowvelocity,passesthroughguidevanesorgateslocatedaroundthecircumstance,andflowsthroughtherunner,fromwhichitdischargesintoadrafttubesealedbelowthetail-waterlevel.Alltherunnerpassagesarecompletelyfilledwithwater,whichactsuponthewholecircumferenceoftherunner.Onlyaportionofthepowerisderivedfromthedynamicactionduetothevelocityofthewater,alargepartofthepowerbeingobtainedfromthedifferenceinpressureactingonthefrontandbackoftherunnerbuckets.Thedrafttubeallowsmaximumutilizationoftheavailablehead,bothbecauseofthesuctioncreatedbelowtherunnerbytheverticalcolumnofwaterandbecausetheoutletofhedrafttubeislargerthanthethroatjustbelowtherunner,thusutilizingapartofthekineticenergyofthewaterleavingtherunnerblades.1.3propellerrunnersnherentlysuitableforlow-headdevelopments,thepropeller-typeunithaseffectedmarkedeconomicswithintherangeofheadtowhichitisadapted.Thehigherspeedofthistypeofturbineresultsinalower-costgeneratorandsomewhatsmallerpowerhousesubstructureandsuperstructure.Propeller-typerunnersforlowheadsandsmalloutputsaresometimesconstructedofcastiron.Forheadsabove20ft,theyaremadeofcaststeel,amuchmorereliablematerial.Large-diameterpropellersmayhaveindividualbladesfastenedtothehub.1.4adjustable-bladerunnersTheadjustable-bladepropellertypeisadevelopmentfromthefixed-bladepropellerwheel.Oneofthebest-knownunitsofthistypeistheKaplanunit,inwhichthebladesmayberotatedtothemostefficientanglebyahydraulicservomotor.Acamonthegovernorisusedtocausethebladeangletochangewiththegatepositionsothathighefficiencyisalwaysobtainedatalmostanypercentageoffullload.Byreasonofitshighefficiencyatallgateopenings,theadjustable-bladepropeller-typeunit