机电专业英语 教学课件 作者 杨寿智 刘水平 机电专业英语.Lesson 30.ppt

《机电专业英语 教学课件 作者 杨寿智 刘水平 机电专业英语.Lesson 30.ppt》由会员上传分享，免费在线阅读，更多相关内容在应用文档-天天文库。

1、Lesson30PowernetworkstructureTextItisnotpracticallyfeasiblewiththepresentstateofthetechnologytogeneratetheelectricenergyatthelocationofitsuse.Localgenerationwouldbeunacceptableforeconomic,environmental,andreliabilityreasons.Consequently,electricitymus

2、tbegeneratedinbulkquantitiesinpowerstationsorcenters.Asthecustomerlocationsvaryovervastgeographicareas,theelectricenergymustbetransmittedoveranelectricpowernetworkconnectingthepowerstationswitheverycustomer①.Thelocationsofthepowercentersaredictatedbya

3、numberoffactors.Fuelavailabilityisoneimportantsuchfactor.Forexample,coal-firedgeneratorunitsareoftenlocatedinthevicinityofvastcoaldeposits.Itisobviouslymorepracticalandeconomicaltotransporttheenergytotheuserinelectricformonelectrictransmissionlinestha

4、nintheformofcoalshipments②.Environmentalfactorsarebecomingincreasingimportantinpower-stationsiting.Soisavailabilityofcondenser-coolingwater.Asthisisbeingwritten,thevariousprosandconsofnuclearpowerstationsandtheirsitingproblemsarebeinghotlydebated.Thes

5、izeofgeneratorunitsarebecomingincreasinglylarger.Powerratingsinexcessof1000MWarenotuncommon.Forcomparison,in1976intheUnitedStates,a1000-MWunitwillsatisfythevariedelectricpowerneedsofacitywithapopulationofabouthalfamillionpeople.Theelectricpowernetwork

6、mustbedesignedsoastomeettheneedofeverycustomerandatthesametimepermitenergyshipmentsinthe1000-MWrange③.Immediately,onenoticestheanalogybetweenanelectricpowernetworkandawell-designedtransportationsystem.Theinerstatesuperhighwaysystemhandleshugeblocksoft

7、ruck,bus,andlong-distanceautotraffic.Statehighwaystakecareofmedium-distancetraffic.Thesmallandlightlytraveledurbanandruralroadsandlanesservethelocaltrafficneeds.Inapowernetworkthehugeblocksofelectricpowermoveonthegridortransmissionlinks.Fromthegrid,po

8、werisbeingsubdividedintosmallerblocksandfedintothesubtransmissionportionsofthepowernetwork④.Finally,theindividualsmallcustomersarebeingservicedfromthedistributionnetwork.Frombothanoperationalandfunctionalpointofviewthepowernetworkcanbedividedi