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1、Althoughourconcerninthisbookiswiththeelectricalaspectsofpowersystems,itisimportanttoknowwhatbasicenergysourcescanbeusedtoproduceelectricalenergyonalargescale・尽管这本书关注的是电力系统的电气方血,但了解哪些基本能源能够被用來大规模发电依然十分重要。Electricalenergysourcescanbebrokendownintotwobroadcategor
2、ies,thermalandnon-thermal电能可以被分为两人部分,热能和非热能Abriefdiscussionofvaryingalternativesfollowsbelow・以下简短讨论几个不同的选择ThermalSourcesCoal.Substantialreservesandthedevelopmentofthenecessarytechnologymeanthatcoalisandwillcontinuetobeamajorenergysource・热能源。煤。大量的储备和发达的关键技术使得煤在
3、现在,也在将來都是主要的能源。Presentlycoalrepresentsabout45%oftotalelectricalenergysources・目前,煤占总电能源的45%Generatorschangemechanicalenergyintoelectricalenergy.Motorschangeelectricalenergyintomechanicalenergy.・发电机把机械能转换成电能。电动机把电能转换为机械能。Generatorsandmotorsarealotalike.theyarema
4、deinthesamegeneralway.发电机和电动机冇很多相似z处,他们的制造方法基本相同。Further,theybothdependonthesameelectromagneticprinciplesfortheiropcration.另外,他们运根据相同的电磁原理运行。Somemotorsuseonepermanentmagnetandoneelectromagnet.Othersusetwoelectromagnets.有的电动机使用一块永磁铁和一块电磁铁,有的用两块电磁铁。Eitherway,ele
5、ctricalenergycreatesatleastoneofthemagneticfields.不管哪种方式,电能产生至少一个磁场。Then,theforcesbetweenthetwomagneticfieldscausethemotion.然后,磁场间的力促使转子转动。Lowercaselettersareusedtoindicateinstantaneousvalues,thatis,thatp,v,andimayvarywithtime.小写字母用來表示瞬时值,比如p,v和i会随时间变化。Highpow
6、erlevelsrequirehighvoltageandcurrentvalues.大功率等级的传输需要高电压和大电流。Foragivenvalueofcurrent,higherpowerflowsmaybeobtainedbyincreasingthevoltage,andcurrentvalues・对于一个给定的电流,抬高电压可以获得更多的电流传输,反之亦然。Unfortunately,theexistingtechnologysetspracticalupperlimitsonallowablecurre
7、ntsandvoltages不幸的是,现有技术存在允许电流和电压的上限。Whatarethelimitingfactorsforcurrent?Wefabricatepowerconductorsusingmaterialswithhighconductivity,appropriatemechanicalcharacteristics,什么限制了电流?我们用高导电性,适当机械性能的材料制造导体Andthatarceconomical:aluminumisthemostcommonchoice,withcopper
8、usedforsomeapplications从经济方面考虑,铝通常是最好的选择,有时也用铜。Thecurrent-carryingcapacityofaconductorisrelatedtoitsmaximumallowablecurrentdensityanditscross-sectionalarea导体通过电流的能力与导体的最大允许电流密度和导体的