第一章第一节电力系统基本结构Part 1 Basic Construction of Electric Power SystemBasic Concepts of Electric Power System电能是一种理想的能力形式，便于传输和使用，而且很清洁，对环境和大气无污染，因此自被发现以来，电能发展迅速并且利用广泛。
电能的产生、输送和消耗过程就在这一被称为电力系统的整体化系统中实现。
Electricity is an ideal energy form, which is convenient to deliver and use, and is clean without polluting our environmentand atmosphere. The generation, delivery and consumption of electricity are realized in an integrated system which is calledelectric power system or power system.一个电力系统包括三个基本部分：发电系统、输电系统和配电系统，如图1-1 所示An electric power system consists of three principal divisions: power generation, power transmission system, and powerdistribution systems, as shown in Fig.1.1图1-1 电力系统的三个基本部分用户从电力系统取用的所有电能都是在某种形式的电厂（或者称作电站）中产生的。
发电是整个电能利用过程的第一环节。
All the electricity the consumers take from the power system is generated in a power plant, or called power station, of somekind. Power generation is the first stage of the whole progress of the utilization of electric energy.输电系统连接发电和配电系统，并经过网络互连通向其他电力系统。
配电系统在执行电压变换和开关功能的变电站将所有单个负荷接连到输电线路。
Transmission systems are the connecting links between thegeneration plants and the distribution systems and lead to otherpower systems over interconnections. A distribution system connects all the individual loads to the transmission lines at thesubstations which perform voltage transformation and switching functions.地处负荷区的附近的小型电厂，通常直接连接到中压输电系统或配电系统。
Small generating plants located near the load are often connected to the subtransmission or distribution system directly.通常，在输电系统水平上形成相邻电力系统间的互联。
Interconnection to neighboring power systems are usually formed at the transmission system level.因而整个电力系统包括多个电源和若干层次的输电网络。
这提供了高度的结构化冗余，使系统能够承受罕见的意外事故而不会中断对用户的供电。
The overall system thus consists of multiple generating sources and several layers of transmission networks. This provides ahigh degree of structural redundancy that enables the system to withstand unusual contingencies without service disruption tothe consumers.第二节电力系统典型的网络拓扑结构Part 2 Typical Topologies of Electric Power System构成电力系统的设备，其布局取决于当地的负荷增长方式，并且随时可能重新调整。
The equipments which form an electric system are arranged depending on the manner in which load grows in the area and may berearranged from time to time.然而，也可以采取办法对系统进行分类。
以下列举三类：辐射状系统、环状系统和网状系统。
However, there are certain plans into which a particular system design may be classified. Three types are illustrated: theradial system, the loop system and the network system.如图1-2 所示，在辐射系统中，线路从电源呈树状向外延伸。
打开任一段线路都会导致一个或多个负荷停电。
In a rad ial system, as shown in Fig. 1.1, the lines form a“ tr espreading out from the power source. Opening any linewill result in interruption of power to one or more of the loads.环状系统如图1-3 所示。
这样接线，即使一条线路退出运行，仍能保证给所有负荷供电。
The loop system is illustrated in Fig. 1.2. With this arrangementall loads may be served even though one line section isremoved from service.图1-4 所示的是同样的负载由网状方式供电。
这样设计，保证了每个负荷有两条或多条线路为其供电。
Fig. 1.3 shows the same loads being served by a network. With this arrangement each load has two or more circuits over whichit is fed.通常将配电线路设计成辐射状或环状，但是大多数高压输电线路则按网状布局，主要电力系统的互联形成由多个线路段组成的网络。
Distribution circuits are commonly designed so that they may be classified as radial or loop circuit. The high-voltagetransmission lines of most power systems are arranged as networks. The interconnection of major power systems result innetworks made up many line sections.第三节大多数电力系统的特点Part 3 Characteristics of Most Power System第一个完整的电力系统是直流系统。
交流输电的发展，促成了交流电力系统的产生。
由于下列原因，交流系统已经完全取代直流系统。
The first complete electric power system was a direct current (DC) system. The development of alternating current (AC)transmission led to AC electric power system. The AC system had won out over the DC system for the following reasons:(1) 交流系统易于转换电压等级，因而提供了以不同电压水平进行发电、输电和用电的灵活性。
i ) V oltage levels can be easily transformed in AC systems, thus providing the flexibility for use of different voltage forgeneration, transmission, and consumption.(2) 与直流电机相比，交流电机要更加简单和便宜。
ii) AC electric machines are much simpler or cheaper than DC electric machines.电力系统的大小和结构组成可能不同。
然而，它们有相同的基本特点Electric power systems vary in size and structural components. However, they all have the same basic characteristics:（1）电力系统都是由基本运行在恒定电压的三相交流系统构成。
发电和输电设备都是三相元件。
工业负荷总是三相负载；单相居民负荷和商业在各相之间均匀分配，以有效地构成平衡的三相系统。
i） Are comprised of three-phase AC systems operating essentially at constant voltage. Generation and transmission facilitiesuse three-phase equipment. Industrial loads are invariably three-phase; single-phase residential and commercial loads aredistributed equally among the phases so as to effectively form a balanced three-phase system.（2）都使用同步电机发电。