passage two.pptVIP

Passage Two Generators convert: 转换 mechanical: 机械的 transmit: 输送 remotely: 偏远的 point of application: 用户端 voltage: 电压 relatively: 相对的 commutator: 换向器 efficient:有效的 maintenance: 维护 plant: 设备 electric transformer: 变压器 rectify: 整流 invert：转向；反向 Generator(发电机) Electric generators convert（v.转换） mechanical(机械的) energy to electrical energy, which is more easily transmitted(输送) to remotely(遥远的;偏远的) located points of application. 发电机是将机械能转化成电能的电力设备，而电能可以很容易地传输给远距离的用户。 The first large electric generating systems used direct-current (DC) generators, mainly because direct current was better understood than alternating current (AC). 直流电机之所以首先被应用于大发电系统，主要是由于直流电流与交流电流相比较能更好地被人们理解。 However, DC generators are limited to(受限) generating power at relatively(相对的) low voltages, largely due to(由于) problems at their commutators(整流器). 然而，由于直流电机存在转向器的问题，所以仅仅用于低电压下的发电。 As power networks(电网) developed, higher and higher voltages were required to transmit large blocks of（大量的） power over longer and longer distance. 随着电网的发展，为了将大量的电力传输到越来越远的地方，电压也就要求越来越高。 Electric transformers can easily change the normally low voltage generated to the high voltages needed for efficient power transmission, and, of course, transformers only work on alternating current. 电力变压器能轻易地将电机正常发出来的低电压转变为所需要的高电压，以利于能源的有效传输。当然，变压器只能在交流状态下工作。 AC generators, or alternators as they are commonly called, are so much simpler mechanically, so much more efficient, and require so much less maintenance than DC machines that all large generating plants output alternating current today. 交流发电机通常称为交流电机，比起直流电机来机械结构更简单，使用效率更高，所需维修更少，所以今天大型电厂的输出都为交流电流。 Although DC transmission lines can transport extremely large blocks of power very efficiently over long distances, the power is always generated as alternating current, transformed to the voltage required, rectified(改正；校正) and transmitted as direct current, and then inverted(整流) back to alternating current at the point of application. 尽管直流输电能很有效地将绝对多的能源进行长距离传输，然而，电能还是先以交流电形式发出，再被转换到所要求的电