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1、Chapter 6 Electric Power Systems,Section 1 Introduction,Text,New Words and Expressions,Exercises,End,Translation of Negative Sentences,Section 1 Introduction,The modern society depends on the electricity supply more heavily than ever before. It can not be imagined what the world should be if the ele
2、ctricity supply were interrupted all over the world. Electric power systems (or electric energy systems), providing electricity to the modern society, have become indispensable components of the industrial world.,Section 1 Introduction,The first complete electric power system (comprising a generator
3、, cable, fuse, meter, and loads) was built by Thomas Edison the historic Pearl Street Station in New York City which began operation in September 1882. This was a DC system consisting of a steam-engine-driven DC generator supplying power to 59 customers within an area roughly 1.5 km in radius. The l
4、oad, which consisted entirely of incandescent lamps, was supplied at 110 V through an underground cable system. Within a few years similar systems were in,Section 1 Introduction,operation in most large cities throughout the world. With the development of motors by Frank Sprague in 1884, motor loads
5、were added to such systems. This was the beginning of what would develop into one of the largest industries in the world. In spite of the initial widespread use of DC systems, they were almost completely superseded by AC systems. By 1886, the limitations of DC systems were becoming increasingly appa
6、rent. They could deliver power only a short distance from generators. To keep transmission power losses (I2R) and voltage drops,Section 1 Introduction,to acceptable levels, voltage levels had to be high for long-distance power transmission. Such high voltages were not acceptable for generation and c
7、onsumption of power; therefore, a convenient means for voltage transformation became a necessity.The development of the transformer and AC transmission by L. Gaulard and J.D. Gibbs of Paris, France, led to AC electric power systems. In 1889, the first AC transmission line in North America was put in
8、to operation in Oregon between Willamette,Section 1 Introduction,Falls and Portland. It was a single-phase line transmitting power at 4,000 V over a distance of 21 km. With the development of polyphase systems by Nikola Tesla, the AC system became even more attractive. By 1888, Tesla held several pa
9、tents on AC motors, generators, transformers, and transmission systems. Westinghouse bought the patents to these early inventions, and they formed the basis of the present-day AC systems.,Section 1 Introduction,In the 1890s, there was considerable controversy over whether the electric utility indust
10、ry should be standardized on DC or AC. By the turn of the century, the AC system had won out over the DC system for the following reasons: （1）Voltage levels can be easily transformed in AC systems, thus providing the flexibility for use of different voltages for generation, transmission, and consump
11、tion. （2）AC generators are much simpler than DC generators.,Section 1 Introduction,（3）AC motors are much simpler and cheaper than DC motors.The first three-phase line in North America went into operation in 1893a 2,300 V, 12 km line in southern California. In the early period of AC power transmissio
12、n, frequency was not standardized. Many different frequencies were in use: 25, 50, 60, 125, and 133 Hz. This poses a problem for interconnection. Eventually 60 Hz was adopted as standard in North America, although 50 Hz was used in many other countries.,Section 1 Introduction,The increasing need for
13、 transmitting large amounts of power over longer distance created an incentive to use progressively high voltage levels. To avoid the proliferation of an unlimited number of voltages, the industry has standardized voltage levels. In U.S.A., the standards are 115, 138, 161, and 230 kV for the high vo
14、ltage (HV) class, and 345, 500 and 765 kV for the extra-high voltage (EHV) class. In China, the voltage levels in use are 10, 35, 110 for HV class, and 220, 330 (only in Northwest China) and 500 kV for EHV class . The first 750 kV,Section 1 Introduction,transmission line will be built in the near fu
15、ture in Northwest China.With the development of the AC/DC converting equipment, high voltage DC (HVDC) transmission systems have become more attractive and economical in special situations. The HVDC transmission can be used for transmission of large blocks of power over long distance, and providing
16、an asynchronous link between systems where AC interconnection would be impractical because of system stability consideration or because nominal frequencies of the systems are different.,Section 1 Introduction,The basic requirement to a power system is to provide an uninterrupted energy supply to cus
17、tomers with acceptable voltages and frequency. Because electricity can not be massively stored under a simple and economic way, the production and consumption of electricity must be done simultaneously. A fault or misoperation in any stages of a power system may possibly result in interruption of electricity supply to the customers. Therefore, a normal continuous operation of the power system to provide a reliable power supply to the customers is of paramount importance.,
