电力能源系统.docx

电力能源系统.docx

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电力能源系统

河南机电高等专科学校

ModernPowerSystems

课程名称：

自动化专业英语

课题名称：

ModernPowerSystems

系部名称：

自动控制系

专业班级：

生产过程自动化091

组员：

李敏杰张会珠李喜文张冬张志辉

2011年12月01日

ModernPowerSystems

Therearewellover80,000,000customersofelectricalutilitiescompaniesintheUnitedStatestoday。

Tomeetthisdemandforelectricalpower,powerCompaniescombinetoproduceStatestoday.Tomeetthisdemandforelectricalpower,powerCompaniescombinetoproduceabouttwomil1on-million（2,000,000×106）kilowatt-hoursofelectricalpower.Thisvastquantityofelectricalpowerissuppliedbyabout4000powerplants.Individualgeneratingunitswhichsupplyover1200megawattsofelectricalpowerarenowinpowerplants.

E1ectricalpowercanbeproducedinmanyways,suchasformchemicalreactions,heat,light,ormechanicalenergy.Thegreatmajorityofourelectricalpowerisproducedbypowerplantslocatedthroughoutourcountrywhichconverttheenergyproducedbyburningcoal,oil,ornaturalgas,thefallingofwater,orfromnuclearreactionsintoelectricalenergy.Electricalgeneratorsatthesepowerplantsaredrivenbysteamorgasturbinesorbyhydraulicturbines,inthecaseofhydroelectricplants.Thischapterwillinvestigatethetypesofpowersystemsthatproducethegreatestmajorityoftheelectricalpowerusedtoday.

Variousothermethods,someofwhichareintheexperimentalstages,maybeusedasfuturepowerproductionmethods.Theseincludesolarcells,geothermalsystems,wind-poweredsystems,magnetohydrodynamic（MHD）systems,nuclear-fusionsystems,andfuelcells.

ELECTRICALPOWERPLANTS

MostelectricalpowerintheUnitedStatesisproducedatpowerplantsthatareeitherfossil-fuelsteamplants,nuclear-fissionsteamplants,orhydroelectricplants,orhydroelectricplantsFossil-fue1andnuclear-fissionplantsutilizesteamturbinestodeliverthemechanicalenergyneededtorotatethelargethree-phasealternatorswhichproducemassivequantitiesofelectricalpowerHydroelectricplantsordinarilyuseverticallymountedhydraulicturbines.Theseunitsconverttheforceofflowingwaterintomechanicalenergytorotatethree-phasealternators.

Thepowerp1antsmaybelocatedneartheenergysources,nearcities,ornearthe1argeindustrieswheregreatamountsofelectricalpowerareconsumed.ThegeneratingcapacityofpowerplantsintheUnitedStatesisgreaterthanthecombinecapacityofthenextfourleadingcountriesoftheworld.Thus,wecanseehowdependentweareupontheefficientproductionofelectricalpower.

SupplyandDemand

Thesupp1yanddemandsituationforelectricalenergyismuchdifferentfromotherproductswhichareproducedbyanorganizationand,thenlater,soldtoconsumers.E1ectrica1energymustbesuppliedatthesametimethatitisdemandedbyconsumers.Thereisnosirnp1estoragesystemwhichmaybeusedtosupplyadditionalelectricalenergyatpeakdemandtimes.Thissituationisquiteuniqueandnecessitatestheproductionofsufficientquantitiesofelectricalenergytomeetthedemandoftheconsumersatanytime.Accurateforecastingofloadrequirementsatvariousgiventimesmustbemaintainedbyutilitiescompaniesinorderthattheymayrecommendthenecessarypowerplantoutputforaparticulartimeoftheyear,week,orday.

PlantLoadandCapacityFactors

Thereisasignificantvariationintheloadrequirementthatmustbemetatdifferenttimes.Thus,thepowerplantgeneratingcapacityissubjecttoacontinualchange.Fortheabovereasons,muchofthegeneratingcapacityofapowerplantmaybeidleduringlowdemandtimes.Thismeansthatnotallthegeneratorsattheplantwillbeinoperation.

Therearetwomathematicalratioswithwhichpowerplantsareconcerned.Theseratiosarecalledloadfactorandcapacityfactor.Theyareexpressedas:

Loadfactor=

Capacityfactor=

Itwouldbeideal,intermsofenergyconservation,tokeeptheseratiosasclosetounityaspossible.

FOSSILFUELSYSTEMS

Mi11onsofyearsago,largedepositsoforganicmaterialswereformedunderthesurfaceoftheearth.Thesedeposits,whichfurnishourcoal,oil,andnaturalgas,areknownasfossilfuels.Ofthese,themostabundantfossilfueliscoalandcoal-firedelectricalpowersystemsproduceaboutone-halfoftheelectricalpowerusedintheUnitedStates.Natural-gas-firedsystemsareusedforaboutone-fourthofourelectricalpower,whileoil-firedsystemsproduceAround10%ofthepoweratthepresenttime.TheserelativecontributionsofeachsystemtothetotalelectricalpowerproducedintheUnitedStatesaresubjecttochangeduetothe

additionofnewpowergenerationfacilitiesandfuelavailability.Atthepresenttime,over80%ofourelectricalenergyisproducedbyfossil-fuelsystems。

Abasicfossil-fuelpowersystemisshowninFig.7.4.1.Inthistypeofsystem,afossilfuel（coal,oil,orgas）isburnedtoproduceheatenergy.Theheatfromthecombustionprocessisconcentratedwithinaboilerwhereisconvertedwaterisconvertedtosteam.Thehigh-pressuresteamisusedtorotateaturbineshaftisconnecteddirectlytotheturbineshaftisconnectedelectricalgeneratorandprovidesthenecessarymechanicalenergytorotatethegenerator.Thegeneratorthenconvertsthemechanicalenergyintoelectrica1energy.

FossilFuels

Fossilfuelsareusedtosupplyheatbymeansoftheirchemicalreactionsformany

differentpurposes.Suchfuelscontaincarbonmaterialsthatareburnedasaresultoftheirreactionwithairoroxygen.Thesefossilfuelsareusedasadirectsourceofheatwhenburnedinafurmaceandareusedasaheatsourceforsteamproductionwhenusedinapower-plantboilersystem.Thesteamthatisgeneratedisusedforrotatingthesteamturbinesinthepowerplants.

Fossilfuelsvaryaccordingtotheirnaturalstate（solid,liquid,orgas）,accordingtotheirabilitytoproduceheat,andinthetypeofflameorheatthattheyproduce.Coalandcokearesolidfossilfuels,withcoalusedextensivelyforproducingheattosupportelectricalpowerproduction.Oil,gasoline,anddieselfuel,whichareliquidfossilfuelsderivedbypetroleumprocessing,areusedmostlyinconjunctionwithinternalcombustionengines.However,oilisusedasaheatsourceformanypowerplants.Naturalgasistheprimarygaseousfuelusedforelectricalpowerproduction.

HYDROELECTRICSYSTEMS

Theuseofwaterpowergoesbacktoancienttimes.Ithasbeendevelopedtoaveryhighdegree,butisnowtakingasecondaryroleduetotheemphasisonotherpowersourcesthatarebeingdevelopedinourcountrytoday.Electricalpowerproductionsystemsusingwaterpowerweredevelopedforuseintheearly20thCentury.

Theenergyofflowingwatermaybeusedtogenerateelectricalpower.ThismethodofpowerproductionisusedinhydroelectricpowersystemsasshownbythesimplesystemillustratedinthediagramofFig.7.4.2Water,whichisconfinedinalargereservoir,ischanneledthroughacontrolgatewhichadjuststheflowrate.Theflowingwaterpassesthroughthebladesandcontrolvanesofahydraulicturbinewhichproducesrotation.Thismechanicalenergyisusedtorotateageneratorthatisconnecteddirectlytotheturbineshaft.Rotationofthealternatorcauseselectricalpowertobeproduced.However,hydroelectricsystemsarelimitedbytheavailabilityoflargewatersupplies.Manyhydroelectricsystemsarepartofmultipurposefacilities.Forinstance,ahydroelectricpowersystemmaybepartof

aprojectplannedforfloodcontrol,recreation,orirrigation.

NUCLEAR-FISSIONSYSTEMS

Nuclearpowerplantsinoperationtodayutilizereactorwhichfunctionduetothenuclear-fissionprocess.Nuclearfissionisacomplexreactionwhichresultsinthedivisionofthenucleusofanatomintotwonuclei.Thissplittingoftheatomisbroughtaboutbythebombardmentofthenucleuswithneutrons,gammarays,orotherchargedparticlesandisreferredtoasinducedfission.Whenanatomissplit,itreleasesagreatamountofheat.

Inrecentyears,severalnuc1ear-fissionpowerplantshavebeenputintooperation.Anuclear-fissionpowersystem,showninFig.7.4.3,reliesuponheatproducedduringanuclearreactionprocess.Nuclearreactors“burn”nuc1ear1materialWhoseatomsaresplitcausingthereleaseofheat.Thisreactionisreferredtoasnuclearfission.Theheatfromthefission.Processisusedtochangecirculatingwaterintosteam.Thehigh-pressuresteamrotatesaturbine.Whichisconnectedtoanelectricalgenerator.

Thenuclear-fissionsystemisverysimilartofossilfuelsystemsinthatheatisusedtoproducehigh-pressuresteamwhichrotatesaturbine.Thesourceofheatinthenuclear-fissionsystemisanuclearreactionwhile,inthefossil-fuelsystem,heatisdevelopedintheUnitedStatescomesfromnuclear-fissionsources.However,thispercentageisalsosubjecttorapidchangeasnewpowerfacilitiesareputintooperation.

POTENTIALPOWERSOURCES

Solarpowerisonepotentialelectricalpowersource.Thelargestenergysourceavailabletodayisthesunwhichsuppliespracticallylimitlessenergy.Theenergyavailablefromthesunfarexceedsanyforeseeablefutureneed.Solarcellarenowbeingusedtoconvertlightenergyintosmallquantitiesofelectricalenergy.Possiblesolar-energysystemsmightincludehomeheatingorpowerproductionsystems,orbitingspacesystems,andsteam-drivenelectricalpowersystems.Eachofthesesystemsutilizessolarcollectorsthatconcentratethelightofthesunsothatalargequantityofheatwillbeproduced.Potentially,thisheatcouldbeusedtodrivedasteamturbineinordertogenerateadditionalelectricalenergy.

Geothermalsystemsalsohavepromiseasfutureenergysources.The