section 6課件

1、section 6,Chapter 6 Electric Power Systems,section 6,Section 2 Components of Power Systems,Text,New Words and Expressions,Exercises,End,Translation of Negative Sentences,section 6,Section 2 Components of Power Systems,Modern power systems are usually large-scale, geographically distributed, and with

2、 hundreds to thousands of generators operating in parallel and synchronously. They may vary in size and structure from one to another, but they all have the same basic characteristics: （1）Are comprised of three-phase AC systems operating essentially at constant voltage. Generation and transmission f

3、acilities use three-phase equipment . Industrial loads are invariably,section 6,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 three-phase system. （2）Use synchronous machin

4、es 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.,section 6,Section 2 Components of Power Systems,（3）Transmit power over significant distances to

5、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

6、a complex network of individual components, including transmission lines, transformers, and switching devices. It is common practice to classify the,section 6,Section 2 Components of Power Systems,transmission network into the following subsystems: Transmission system; Subtransmission system; Distri

7、bution system.,section 6,Section 2 Components of Power Systems,Fig.6-1 Basic elements of a power system,section 6,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 pow

8、er 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 do

9、wn to the subtransmission level (typically, 69 to 138 kV). The generation and transmission subsystems are often referred to as the,section 6,Section 2 Components of Power Systems,bulk power system. The subtransmisson system transmits power in small quantities from the transmission substations to the

10、 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, t

11、he older transmission lines are often relegated to subtransmission function.,section 6,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

12、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.,section 6,Section 2 Components of Power Systems,Small generating plants located near the load are also connected to the s

13、ubtransmission 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 re

14、dundancy that enables the system to withstand unusual contingencies without service disruption to the customers.,Return,section 6,New Words and Expressions,in parallel 并聯(lián)地 synchronously ad. 同步地 facilityn. 容易，方便 靈活，熟練 （便利）條件 （常用復數(shù)）設備，裝置，工具，器材 primary energy 一次能源 fossil n. 化石，石塊 hydraulic a. 水力學的，水壓的，

15、液壓的，液力的 mechanical energy機械能,section 6,New Words and Expressions,switching device開關裝置，開關設備 subtransmission n. 二次輸電 subtransmission system分支輸電系統(tǒng)，二次輸電系統(tǒng) distribution system配電系統(tǒng) substation n. 變電所，變電站，分站，分所 feedern. 饋線，饋電電路 redundancyn. 多余，冗余 contingencyn. 意外事故，偶然事故,Return,section 6,Translation of Negat

16、ive Sentences,四、意義上的肯定 英語中有的否定詞與其他詞連用形成一個固定結(jié)構(gòu)，這種結(jié)構(gòu)在形式上是否定的，但意義上是肯定的，常見的有nothing like（沒有什么比得上），cannot too（越越好），no/not/nothing + more + than（不過），no/not/nothing + less + than（多達）等。 （1）The importance of the project can hardly be exaggerated. 這項工程的重要性怎么說也不過分。,section 6,Translation of Negative Sentences,四

17、、意義上的肯定 （2）It is impossible to overestimate the value of the invention. 這項發(fā)明的價值無論怎樣估計也不會太高。 （3）Pesticides can cause a lot of harm, so you can never be too careful when using pesticides. 殺蟲劑會造成很大危害，所以當使用殺蟲劑時應特別小心。,section 6,Translation of Negative Sentences,五、含蓄否定 英語里有些詞或詞組形式上是肯定的，但意義往往是否定的。由這類詞或詞組表達

18、的否定稱為含蓄否定。翻譯時，一般要把否定的意義明確譯出，可譯成“不”、“沒”、“沒有”、“非”等。 1. 動詞或動詞短語引起的否定 常見的有deny拒絕，否認，fail失敗，lack缺乏，refuse拒絕，stop停止 protect from, 保護免受，keep from避免，overlook 忽視，忽略，miss失敗，錯過等。,section 6,Translation of Negative Sentences,五、含蓄否定 1. 動詞或動詞短語引起的否定 (1) The experiment failed of success. 實驗沒有成功。 (2) The value of lo

19、ss in this equation is so small that we can overlook it . 在此方程中，損耗值太小，可以忽略不計。 (3) The specification lacks detail. 這份說明書不夠詳盡。,section 6,Translation of Negative Sentences,五、含蓄否定 2. 名詞引起的否定 常見的有neglect忽視，absence缺乏，loss失去，exclusion排除，ignorance無知等。 A few instruments are in a state of neglect. 一些儀器處于無人管理狀

20、態(tài)。,section 6,Translation of Negative Sentences,五、含蓄否定 3. 形容詞或形容詞短語引起的否定 常見的有free from不受影響，ignorant of 不知道，short of缺乏，last最不，little少，few少等。 (1) The precision instrument must be kept free from dust. 精密儀器必須保持無塵。 (2) This equation is far from being complicated. 這個方程式一點也不復雜。,section 6,Translation of Nega

21、tive Sentences,五、含蓄否定 4. 介詞或介詞短語引起的否定 常見的有beyond 超出，above超出之外，beneath不值得，beside同無關，instead of而不是等。 (1) The problem is beyond the reach of my understanding. 這個問題我無法理解。 (2)The Theory of Relativity worked out by Einstein is now above many peoples comprehension. 愛因斯坦提出的“相對論”，現(xiàn)在還有不少人理解不了,section 6,Transl

22、ation of Negative Sentences,五、含蓄否定 5. 連詞及其某些短語引起的否定 常見的有before在以前，尚未，but而不，would ratherthan 寧可而不愿，與其不如，rather than 而不，tooto太不等。 Never start to do the experiment before you have checked the meter. 沒有檢查好儀表，切勿開始做試驗。,Return,section 6,Exercises,I. Choose the best answer into the blank,1. In power plants

23、convert the primary energy to mechanical energy, and con- vert mechanical energy to electric energy. A. synchronous generators, prime movers B. prime movers, synchronous generators C. prime movers, asynchronous generators D. prime movers, prime movers,section 6,Exercises,I. Choose the best answer in

24、to the blank,2. The generator voltages are usually stepped up to the transmission voltage level by . A. series capacitorsB. parallel reactors C. step-up transformersD. step-down transformers 3. Residential and commercial customers are supplied by the secondary distribution feeders at . A. 120/240 VB

25、. 220/380 V C.110/220 VD. 48/110 V,section 6,Exercises,I. Choose the best answer into the blank,4. In U.S.A., the voltages of the transmission system are typically . A. 345kV B. 500kV C. 230kV and above D. 115kV and above,section 6,Exercises,II. Answer the following questions according to the text,1

26、. What components is a modern power system comprised of? 2. What is the function of the distribution system? 3. What is the function of the transmission system? 4. What is the function of the subtransmission system? 5. What is the characteristics of a modern power system in network structure?,section 6,Exercises,III. Translate the following into Chinese,Instability may also be encountered without loss of synchronism. For example, a system consisting of a synchronous generator feeding an induction motor loa