楼上翻译的不错,但是电力方面的一些术语翻译的尚不准确或不恰当,我再此完善一下.
Fig.4.4 shows a minimum power system.
图4.4所示为一个简化的电力系统.
The system consists of an energy source,a prime mover,a generator,and a load.
系统由一个能量源（即原动力转换装置）一个发电机,和一个负载组成.
“ ,a prime mover,”是对energy source的进一步解释,相当于汉语中用括号对主词进行说明.
The energy may be coal,gas,or oil burned in a furnace to heat water and generator steam in a boiler.
获得能量的原料可以是煤炭,天然气或者某种燃油,通过其燃烧来加热锅炉中的水,以产生蒸汽.
The prime mover may be a steam-driven turbine,a hydraulic or water wheel,or an internal combustion engine.
原动力转换装置可以是一个由蒸汽驱动、液力驱动或水轮驱动的轮机,亦或是内燃机.
Each one of these prime movers has the ability to convert energy in the form of heat,falling water,or fuel into rotation of a shaft,which in turn will drive the generator.
无论哪种动力转换装置,都可以将热能或势能转换为机械能,用以驱动发电机转子主轴旋转从而最终转换为电能.
The electrical load on the generator may be lights,motors,heaters,or other devices,alone or in combination.
发电机上的电力负载可以是单独使用或混合使用的照明灯具,电动机,加热装置或其他设备.
The control system functions to keep speed of the machines substantially constant and the voltage within prescribed limits,even the load may change.
控制系统的功能是在负载随时变化的工况下,确保机组转速恒定,并使电压输出控制在要求范围之内,
The control system may include a man stationed in the power plant who watches a set of meters on the generator-output terminals and makes the necessary adjustments manually.
电厂中的控制系统包括一个人工监测站,工作人员随时监测发电机终端的输出电量的变化,以便在需要的时候对机组状态进行人工调整.
In a modern station,the control system is a servomechanism that senses a generator-output conditions and automatically makes the necessary changes in energy input and field current to hold the electrical output within certain specifications.
现代化的电厂中,控制系统通常采用自动控制装置,通过传感器探测发电机的输出电量的变化,从而自动调整能量输入和励磁电流,以保持机组各项输出参数的稳定.
Modern power systems are usually large-scale,geographically distributed,and with hundreds to thousands of generators operating in parallel and synchronously.
现代化的电力系统通常采用大规模,大区域的机组群同步并机运行的模式.
They may vary in size and structure from one to another,but they all have basic characteristics:
一般根据规模或结构形式加以区分,但都具有以下的共同特征：
(1)Are comprised of three-phase AC systems operating essentially at constant voltage.Generation and transmission facilities use three-phase equipment.Industrial loads are invariably three-phase; single-phase residential and commercial loads are distributed equally among the phases so as to effectively from a balanced three-phase system.
（1）都由以电压稳定为主要特征的三相交流电运行系统组成.发电与传输设备也采用三相装置.工业用电始终使用三相电源.民用与商业用电使用单相电源并被平均分配于三相电源中,从而实现三相交流电的平衡.
(2)Use synchronous machines for generation of electricity.Prime moves convert the primary energy ( fossil,nuclear,and hydraulic) to mechanical energy that is,in turn,converted to electrical energy by synchronous generators.
电力生产均使用同步机组.原动力转换装置将最初的能源（矿物,核能或液力）转换成机械能,同步发电机在原动力转换装置的带动下旋转并产生电能.
3)Transmit power over significant distances to consumers spread over a wide area.This requires a transmission system comprising subsystems operating at different voltage levels
将产生的电力通过远距离传输,输送给分布在广大区域的终端用户.这就要建立完善的输变电系统,该系统由不同电压等级的配电子系统构成.