section 6-2

Section 2 Components of Power Systems
three-phase; single-phase residential and commercial loads are distributed equally among the phases so as to effectively form a balanced threephase system. （2）Use synchronous machines for generation of electricity. Prime movers convert the primary energy (fossil, nuclear, and hydraulic) to mechanical energy that is, in turn, converted to electrical energy by synchronous generators.
New Words and Expressions
in parallel 并联地 synchronously ad. 同步地 facility n. ①容易，方便 ②灵活，熟练 ③ （便利）条件 ④（常用复数）设备，装置，工 具，器材 primary energy 一次能源 fossil n. 化石，石块 hydraulic a. 水力[学]的，水压的，液压的，液 力的 mechanical energy 机械能
Section 2 Components of Power Systems
bulk power system. The subtransmisson system transmits power in small quantities from the transmission substations to the distribution substations. Large industrial customers are commonly supplied directly from the subtransmission system. In some systems, there is no clear demarcation between subtransmission and transmission circuits. As the system expands and higher voltage levels become necessary for transmission, the older transmission lines are often relegated to subtransmission function.
Chapter 6
Electric Power Systems
Section 2 Components of Power Systems
Text
New Woation of Negative Sentences
Exercises
End
Section 2 Components of Power Systems
transmission network into the following subsystems: Transmission system; Subtransmission system; Distribution system.
Section 2 Components of Power Systems
The distribution system represents the final stage in the transfer of power to the individual customers. The primary distribution voltage is typically between 4.0 kV and 34.5 kV. Small industrial customers are supplied by primary feeders at this voltage level. The secondary distribution feeders supply residential and commercial customers at 120/240 V.
Translation of Negative Sentences
四、意义上的肯定
英语中有的否定词与其他词连用形成一个固定结 构，这种结构在形式上是否定的，但意义上是肯定的， 常 见 的 有 nothing like （ 没 有 什 么 比 得 上 …… ） ， cannot… too（越……越好），no/not/nothing + more + than（不过），no/not/nothing + less + than（多达）等。
Section 2 Components of Power Systems
Fig.6-1 Basic elements of a power system
Section 2 Components of Power Systems
The transmission system interconnects all major generating stations and main load centers in the system. It forms the backbone of the integrated power system and operates at the highest voltage levels (typically, 230 kV and above in U.S.A.). The generator voltages are usually in the range of 11 to 35 kV. These are stepped up to the transmission voltage level, and power is transmitted to transmission substations where the voltages are stepped down to the subtransmission level (typically, 69 to 138 kV). The generation and transmission subsystems are often referred to as the
（1）The importance of the project can hardly be exaggerated.
这项工程的重要性怎么说也不过分。
Translation of Negative Sentences
四、意义上的肯定 （2）It is impossible to overestimate the value of the invention.
五、含蓄否定
英语里有些词或词组形式上是肯定的，但意义往 往是否定的。由这类词或词组表达的否定称为含蓄否 定。翻译时，一般要把否定的意义明确译出，可译成 “不”、“没”、“没有”、“非”等。
Section 2 Components of Power Systems
Small generating plants located near the load are also connected to the subtransmission or distribution system directly. Interconnections to neighboring power systems are usually formed at the transmission system level. The overall system thus consists of multiple generating sources and several layers of transmission networks. This provides a high degree of structural redundancy that enables the system to withstand unusual contingencies without service disruption to the customers. Return
New Words and Expressions
switching device 开关装置，开关设备 subtransmission n. 二次输电 subtransmission system 分支输电系统，二次 输电系统 distribution system 配电系统 substation n. 变电所，变电站，分站，分所 feeder n. 馈线，馈电电路 redundancy n. 多余，冗余 contingency n. 意外事故，偶然事故 Return
Section 2 Components of Power Systems
（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. The basic elements of a modern power system in U.S.A. are shown in Fig.6-1. Electric power is produced at generating stations (GS) and transmitted to consumers through a complex network of individual components, including transmission lines, transformers, and switching devices. It is common practice to classify the