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									Special English 2009

Unit 4

Unit Four
Electric Power System
Section 1 Electric Power and Power System
Electric power is the most convenient, clean, safe, and useful form of energy which supplies the major portion of energy needs of a modern society. At the present time the lack of electricity (a blackout) is newsworthy. Electric power is so vital to the lives of people that its unavailability causes inconvenience, loss of production, and danger to many individuals who are in operation in hospitals. A prolonged blackout, which is inevitable when a growing load is combined with no generation additions, could lead to social disorder, and even national tragedy. Electric power is generated in power generating stations (plants), or simply known as power stations (plants). Power generation means conversion of energy from a primary form to the electrical form. The current sources of nearly all the electrical energy generated come from: the conversion of chemical energy of fossil fuels, nuclear fission energy, and the kinetic energy of water which is allowed to fall through a difference of elevation, they are referred to as fossil-fired power, nuclear power and hydro power respectively. The voltage is usually transformed to a high level at the power plant and then via high voltage or extra-high voltage transmission lines the electric power is transmitted to general power consumption areas (load areas). Electric power is transmitted at high voltage level either because of the distance or because of the amount of power, or because of their combination. Before electric power is delivered to the electric power consumers or users, there may be more voltage transformations. First at primary substations, the voltage is reduced and then transmitted to local substations via subtransmission lines. Then another voltage reduction is experienced in local substations and the electric power is delivered to the power consumers (loads) via distribution systems. In distribution system, electric power is directly delivered to electric users via feeders. Thus the entire system consisting electrically of power stations, substation, power consumers, transmission lines and feeders is called a power system. In functional terms, a power system includes power generation, power transmission, power transformation, power distribution and power utilization. The connection between the power stations and loads is not a simple path but a complex network. The electric power utilities will plan, design, build and operate their power systems.

Words and Expressions
blackout [5blAkaut] load feeder plan n. 停电 n. 负荷 n. 馈电线路 n. 规划 fossil [5fCsl] fuel fission kinetic[kai5netik] energy hydro power 矿物燃料 n. 裂变 动能 水电

By Zhao Xia

1

Special English 2009

Unit 4

Section 2

The Characteristics of Electric Power

The electric power has unique technical characteristics which give the power industry certain unique business characteristics. a. Intangibility([in9tAndVE5biliti] n.无形性). The customer cannot directly detect a kilowatt-hour with any of his physical senses. The result of the kilowatt-hour of service (light, heat, work output from a motor) can be detected and for this he is willing to pay. Devices called kilowatt-hour meters are used to measure this intangible electrical energy delivered to customers. b. Quality. Although electricity is intangible, it can be measured in amount and quality. The quality of service can be measured by service continuity or reliability, uniformity ([7ju:ni5fC:miti] n.一致,均匀) of voltage at the proper level, proper and uniform frequency of the alternating voltage. Also, the shape of the voltage-time curve and its smoothness or wave shape is a measure of quality. c. Product storage. Unlike most businesses, the electric power utility must create its product simultaneously with its use because there is no storage of electricity. The storage battery has chemical not electrical storage, but the production of large blocks of power by chemical action so far is both technically and economically unsatisfactory. This simultaneous generation and transmission with use requires power system capacity to meet the load demand at whatever moment it occurs. Thus a maximum or peak demand of only a moment’s duration requires that the necessary equipment be in place throughout the entire year. d. Responsibility for power service. Because the utility delivers its product to the customer’s premises it must assume responsibility for the safe and reliable delivery of its product. The necessary transmission and distribution lines must be available and kept in service (or promptly returned to service after interruption) despite wind, lighting, ice, and so on. e. Public safety. Electricity is a very useful servant when it is kept under control; however, it can be very destructive if control is lost because it can shock, burn and kill. The utility must provide reasonably adequate protection for the public and its own skilled workers. Of the characteristics of electric power, the primary concern of the electric power system engineers is to maintain a constant operating frequency. This job is normally assigned to an automatic control system that maintain at all times real power balance in the system. A mismatch in real power results in a frequency deviation([7di:vi5eiFEn] n. 偏移). The next most important job is to maintain a proper profile([5prEufail]n.轮廓、分布)throughout the system. This is accomplished by proper flows of reactive power on the various lines.

By Zhao Xia

2

Special English 2009

Unit 4

Exercise
Translate the following passages into Chinese.
Transmission Line Parameters In this chapter, we discuss the four basic transmission-line parameters: series resistance, series inductance, shunt capacitance, and shunt conductance. We also investigate transmission-line electric and magnetic fields. Series resistance accounts for ohmic (I2R) line losses. Series impedance, including resistance and inductive reactance, gives rise to series-voltage drops along the line. Shunt capacitance gives rise to line-charging currents. Shunt conductance accounts for V2G line losses due to leakage currents between conductors or between conductors and ground. Shunt conductance of overhead lines is usually neglected. Although the ideas developed in this chapter can be applied to under-ground transmission and distribution, the primary focus here is on overhead lines. Underground transmission in the United States presently accounts for less than 1% of total transmission, and is found mostly in large cities or under waterways. There is, however, a large application for underground cable in distribution systems.

输电线路参数 本章我们讨论输电线路的四个基本参数:串联电阻,串联电感,并联电容和并联电 导。我们也研究输电线路的电磁场问题。 串联电阻表征线路的欧姆损耗(I2R)。串联阻抗,包括电阻和感抗,产生沿线的 电压降落。并联电容产生充电电流。并联电导表征线路上由导体和导体之间或导体和大 地之间的泄露电流产生的 V2G 损耗。架空线的并联电导一般忽略不计。 尽管本章的思想同样适用于地下输配电系统,这里我们主要考虑架空线路。目前 美国的地下输电线路不到输电线路总长的 1%,多为大城市或者水下输电系统。而在配 电系统中,地下电缆则有广泛应用。

References
[1] 苏小林,顾雪平. 电气工程及其自动化专业英语. 北京:中国电力出版社,2005 [2] 屠志健. 电力专业英语阅读与翻译. 上海:上海外语教育出版社,2000 [3] Glover J D, Sarma M S. Power System Analysis and Design. 北京:机械工业出版社,2004

By Zhao Xia

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