Power Stations 2
Coal-Fired Power Stations 4
Oil-Fired Power Stations 5
Nuclear Power Stations 5
Electric Power Stations 6
نیروگاه ها ۷
نیروگاه های زغال سوز ۹
نیروگاه های نفت سوز ۹
نیروگاه های هسته ای ۱۰
نیروگاه های هیدروالکتریکی ۱۰
نیروگاههای الکتریکی ۱۱
مشخصات موثر بر تولید و انتقال ۱۱
عایق بندی الکتریکی ۱۲
سیستم توزیع ۱۵

Section one: Reading Comprehension

Power Stations
There are five sources of energy which together account for nearly all the world’s electricity. They are local, oil, natural gas, hydroelectric power and nuclear energy. Coal, oil and nuclear plants use the steam power station uses very pure water in a closed cycle. First it is heated in the boilers to produce steam at high pressure and high temperature, typically 150 atmospheres and 550 ºC in a modern station. This high-pressure steam drives the turbines which in turn drive the electric generators, to which they are directly coupled. The maximum amount of energy will be transferred from the steam to the turbines only if the latter are allowed to exhaust at a very low pressure, ideally a vaccum. This can be achieved by considering the outlet steam into water. The water is then pumped back into the boilers and the cycle begins again. At the considering stage a large quantity of heat has to be extracted from the system.
This heat is removed in the condenser which is a form of heat exchanger. A much larger quantity of cold impure water enters one side of the condenser and leaves as warm water, having extracted enough heat from the exhaust steam to condense it back into water. At no point must the two water systems mix. At a coastal site the warmed impure water is simply returned to the sea at a point a short distance away. A 2 GW station needs about 60 tons of sea water each second. This is no problem to the coast, but inland very few sites could supply so much water all the year round. The alternative is to recirculate the impure water. Cooling towers are used to cool the impure water so that it can be returned to the condensers, the same water being cycled continuously. A cooling tower is the familiar concrete structure like a very board chimney and acts in a similar way, in that it induces a natural draught. A large volume of air is drawn in round the base and leaves through the open top. The warm, impure water is sprayed into the interior of the tower from a large number of fine jets, and as it falls it is cooled by the rising air, finally being collected in a pond under the tower. The cooling tower is really a second heat exchanger where the heat in the impure water is passed to the atmospheric air, but unlike the first heat exchanger, the two fluids are allowed to come into contact and as a consequence some of the water is lost by evaporation.