【文章內(nèi)容簡(jiǎn)介】 he Earth C. To get out into space we have to overe the Earth’s gravitational pull D. A satellite stays in orbit because the planet gravitational force keeps pulling it into a circleE. Artificial satellite can be used for various purposesPassage 12 Secondary equipment in power system The secondary equipments in power system are (1), measuring，regulating，controlling primary equipments, the equipments that supply information，working condition for the operator or maintenance persons, and (2). The electric circuit connected with the secondary winding of CT or PT is called secondary circuit. The secondary equipment and secondary circuit belong to secondary system. The voltage and (3) are：110V , 220V DC operating voltages, 100V rated voltage of the potential transformer secondary winding and (4). The related parameter values of secondary system after weak electrification are：24V 48V 60V DC operating voltages, (5), rated current of CT secondary side. A. 5A rated current of the current transformer secondary winding B. the equipments that provide protecting，monitoring C. 50V rated voltage of PT secondary side D. the equipments that send the mand signals E. current values in secondary systemPassage 13 Switching overvoltage A sudden change in the configuration of transmission network caused (1) or by the appearance of a fault can cause a rapid surge known as switching overvoltage, which propagates throughout the network. It is these switching overvoltages which in general (2), Limitating these overvoltages is of extremely importance, because they have an important effect on both (3). These switching overvoltages can occur (4). If nonrestriking circuit breakers is not used, it is at the instant of closing, and above all，reclosing of a line which has held a residual charge, that the strongest overvoltages will appear. This switching overvoltage is usually limited (5). A. determine the insulation requirements of transmission lines B. the cost of transmission and 1ine failure rate C. at both opening and closing of circuit breakers D. by means of circuit breaker closing resistor in 500kV system E. by the operation of a circuit breakerPassage 14 Transmission line and distribution line The high voltage power line through which power is (1) is called power transmission line. The voltage classes of 35kV and above are generally used. High voltage distribution line is (2) to distribution transformers. Low voltage distribution line is the line that transmits power from distribution transformer to the users. The normal voltage of power distribution line is 380V. The special sections of (3) refer to the sections with large spanning, serious pollution, (4)．The overhead line section whose span is 1000 m and longer or the height of the pole or tower is l00m and higher is called (5). A. transmitted from power plant’s stepup substation to stepdown substation B. the overhead transmission line C. lightning frequently happening and heavy raining D. the power line that transmits the power from stepdown substation E. 1arge spanning line sectionPassage 15 Transformer insulation The insulation of a transformer can be categorized into internal insulation and external insulation. (1). The external insulation is the insulation between the upper part of bushings and the ground and the insulation among the bushings. The internal insulation of transformer can be further subdivided into main insulation and longitudinal insulation (2). The longitudinal insulation refers the insulation between different parts of the same winding，such as insulation between different sections，layers and turns of the same winding. (3), insulating pressboard, cable paper, corrugated paper, etc. The oil in transformer has two functions, one is insulation, and the other is cooling (4) by the factors such as temperature is called insulation aging. (5), for every 6oC temperature rise the insulation life time of the paper used in transformer will decrease by half. A. The main insulation materials inside transformer are transformer oil B. The degradation of insulating properties of insulation materials under long period of influence C. The internal insulation refers to the insulation of various parts inside the oil tank D．If the winding temperature is within the scope of 80～140 oC E. The main insulation refers to the insulation between windings and grounding parts and the insulation between windingsPassage 16 The electricity market The aim of introducing market mechanism is to bring various parties more economic benefit through equitable petition，thereby promote economic development. Like other markets, it needs (1) where the sellers and buyers (suppliers) can trade electricity, and needs (2) where the suppliers can sell electricity to final customers. As in other markets，the participants need (3). Competition is introduced into generation and retail supplied to customers. Customers are free (4). If a customer chooses to buy electricity in the retail market, he should be able to choose electricity supply from one of several peting retailers. If a customer decides to purchase directly from the wholesale market, he will need (5). Power generation is disaggregated into separate panies to ensure adequate petition. A. to agree on the price and quantity to be traded B. a wholesale market C. to register as a market customer D. a retail market E. to choose electricity suppliersPassage 17 Electric power Electric power is a most convenient，clean，safe，and useful form of energy which supplies the major portion of energy needs of a modem society At the present time (1) is newsworthy. Electric power is so vital to the lives of people that (2) causes inconvenience, loss of production, and danger to many individuals who are in operation (such as cardiac operation) in hospital. A prolonged blackout, which is inevitable when a g