水利毕业设计英文翻译水轮机和水力发电Word文档下载推荐.docx
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hydraulicturbinesandhydro-electricpower
Abstract
Powermaybedevelopedfromwaterbythreefundamentalprocesses:
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-electricpowerclassificationofhydelplants
headscheme
Therehasbeenpracticallynoincreaseintheefficiencyofhydraulicturbinessinceabout1925,whenmaximumefficienciesreached93%ormore.Asfarasmaximumefficiencyisconcerned,thehydraulicturbinehasaboutreachedthepracticablelimitofdevelopment.Nevertheless,inrecentyears,therehasbeenarapidandmarkedincreaseinthephysicalsizeandhorsepowercapacityofindividualunits.
Inaddition,therehasbeenconsiderableresearchintothecauseandpreventionofcavitation,whichallowstheadvantagesofhigherspecificspeedstobeobtainedathigherheadsthanformerlywereconsideredadvisable.Theneteffectofthisprogresswithlargerunits,higherspecificspeed,andsimplificationandimprovementsindesignhasbeentoretainforthehydraulicturbinetheimportantplacewhichithas
longheldatoneofthemostimportantprimemovers.
1.typesofhydraulicturbines
Hydraulicturbinesmaybegroupedintwogeneralclasses:
theimpulsetypewhichutilizesthekineticenergyofahigh-velocityjetwhichactsupononlyasmallpartofthecircumferenceatanyinstant,andthereactiontypewhichdevelopspowerfromthecombinedactionofpressureandvelocityofthewaterthatcompletelyfillstherunnerandwaterpassages.Thereactiongroupisdividedintotwogeneraltypes:
theFrancis,sometimescalledthereactiontype,andthepropellertype.Thepropellerclassisalsofurthersubdividedintothefixed-bladepropellertype,andtheadjustable-bladetypeofwhichtheKaplanisrepresentative.
1.1impulsewheels
Withtheimpulsewheelthepotentialenergyofthewaterinthepenstockistransformedintokineticenergyinajetissuingfromtheorificeofanozzle.Thisjetdischargefreelyintotheatmosphereinsidethewheelhousingandstrikesagainstthebowl-shapedbucketsoftherunner.Ateachrevolutionthebucketenters,passesthrough,andpassesoutofthejet,duringwhichtimeitreceivesthefullimpactforceofthejet.Thisproducesarapidhammerblowuponthebucket.Atthesametimethebucketissubjectedtothecentrifugalforcetendingtoseparatethebucketfromitsdisk.Onaccountofthestressessoproducedandalsothescouringeffectsofthewaterflowingovertheworkingsurfaceofthebowl,materialofhighqualityofresistanceagainsthydraulicwearandfatigueisrequired.Onlyforverylowheadscancastironbeemployed.Bronzeandannealedcaststeelarenormallyused.
1.2Francisrunners
WiththeFrancistypethewaterentersfromacasingorflumewitharelativelylowvelocity,passesthroughguidevanesorgateslocatedaroundthecircumstance,andflowsthroughtherunner,fromwhichitdischargesintoadrafttubesealedbelowthetail-waterlevel.Alltherunnerpassagesarecompletelyfilledwithwater,whichactsuponthewholecircumferenceoftherunner.Onlyaportionofthepowerisderivedfromthedynamicactionduetothevelocityofthewater,alargepartofthepowerbeingobtainedfromthedifferenceinpressureactingonthefrontandbackoftherunnerbuckets.Thedrafttubeallowsmaximumutilizationoftheavailablehead,bothbecauseofthesuctioncreatedbelowtherunnerbytheverticalcolumnofwaterandbecausetheoutletofhedrafttubeislargerthanthethroatjustbelowtherunner,thusutilizingapartofthekineticenergyofthewaterleavingtherunnerblades.
1.3propellerrunners
nherentlysuitableforlow-headdevelopment