分类宝典 较杂乱

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Overcoming the Problem of Waste Many large cities are anything but beautiful.Streets are littered with trash.In this trash,however, (C.there is still something that can be useful). If people want to solve the problem of waste, (A.there is no time to be lost).They must work out ways of making use of good things which are just thrown away as waste.>>>>>>But if the metal that the car was made of is still good, (D.it can be put to use again).When a bottle is empty,>>>>>> Furthermore,garbage can also be a good source for making building blocks,which are then covered with concrete.Now, (E.more and more machines are designed for this purpose).Some day,people will watch films in a great cinema which has been built out of garbage.Future buildings,roads,and cities may be made from garbage.But so far, (B.building beautiful cityes out of garbage is only a dream). Secondary equipment in power system The secondary equipments in power system are (B.the equipments that provide protecting,monitoring),measuring,regulating,>>>>>>or maintenance persons,and (D.the equipments that send the command signals).The electric circuit connected with the secondary>>>>>>to secondary system. The voltage and (E.current values in secondary system) are:110V,220V DC operating voltages,100V rated voltage of the potential transformer secondary winding and (A.5A rated current of the current transformer secondary winding).The related parameter values of secondary system afrer weak electrification are:24V,48V,60V DC operating voltages, (C.50V rated voltage of PT secondary side),0.5A rated current of CT secondary Switching overvoltage A sudden change in the configuration of transmission network caused (E.by the operation of a circuit breaker) or by the appearance>>>>>>It is these switching overvoltages which in general (A.determine the insulation requirements of transmission lines).Limitating these overvoltages is of extremely importance,because they have an important effect on both (B.the cost of transmission and line failure rate). These switching overvoltages can occur (C.at both opening and closing of circuit breakers).If non-restriking circuit breakers is not used,>>>>>>This switching overvoltage is usually limited (D.by means of circuit breaker closing resistor in 500KV system). Transmission line and distribution line The high voltage power line through which power is (A.transmitted from power plant's step-up substation to step-down substation) is called power transmission line.>>>>>>High voltage distribution line is (D.the power line that transmits the power from step-down substation) to distribution transformers.>>>>>>line is 380V. The special sections of (B.the overhead transmission line) refer to the sections with large spnning,serious pollution, (C.lightning frequently happening and heavy raining).The overhead line section whose span is 1000 m and longer or the height of the pole or tower is 100 m and higher is called market The electricity (http://doc.xuehai.netrge spanning

line section). The aim of introducing market mechanism is to bring various parties more economic benefit through equitable competition,thereby promote economic development. Like other markets,it needs (B.a wholesale market) where the sellers and buyers(suppliers) can trade electricity,and needs (D.a retail market) where the suppliers can sell electricity to final customers.As in other markets,the participants need (A.to agree on the price and quantity to be traded).Competition is introduced into generation and retail supplied to customers.Customers are free (E.to choose electricity suppliers).If a customer chooses to buy>>>>>>he will need (C.to register as a market customer).Power generation is disaggregated into separate companies to ensure adequate Electric power Electric power is a most convenient,cleam,>>>>>>At the present time (C.the lack of electricity(a blackout)) is newsworthy.Electric power is so vital to the lives of people that (B.its unavailability) causes inconvenience,>>>>>>could lead to (D.social disorder,and even national tragedy).With the developing of industry and improving in living standard,the electric power demand is growing continuously and (A.its growth rate) is much greater than that of all other forms of energy.Now (E.high electric power consumption per capita) has one of the indications of modernization of a country. Electrical energy

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