【正文】 ical column of water and because the outlet of he draft tube is larger than the throat just below the runner, thus utilizing a part of the kiic energy of the water leaving the runner blades. propeller runners nherently suitable for lowhead developments, the propellertype unit has effected marked economics within the range of head to which it is adapted. The higher speed of this type of turbine results in a lowercost generator and somewhat smaller powerhouse substructure and superstructure. Propellertype runners for low heads and small outputs are sometimes constructed of cast iron. For heads above 20 ft, they are made of cast steel, a much more reliable material. Largediameter propellers may have individual blades fastened to the hub. adjustableblade runners The adjustableblade propeller type is a development from the fixedblade propeller wheel. One of the bestknown units of this type is the Kaplan unit, in which the blades may be rotated to the most efficient angle by a hydraulic servomotor. A cam on the governor is used to cause the blade angle to change with the gate position so that high efficiency is always obtained at almost any percentage of full load. By reason of its high efficiency at all gate openings, the adjustableblade propellertype unit is particularly applicable to lowhead developments where conditions are such that the units must be operated at varying load and varying head. Capital cost and maintenance for such units are necessarily higher than for fixedblade propellertype units operated at the point of maximum efficiency. 西華大學(xué)外文資料翻譯 3 hydroelectric power Faraday had shown that when a coil is rotated in a magic field electricity is generated. Thus, in order to produce electrical energy, it is necessary that we should produce mechanical energy, which can be used to rotate the ‘coil’. The mechanical energy is produced by running a prime mover (known as turbine ) by the energy of fuels or flowing water. This mechanical power is converted into electrical power by electric generator which is directly coupled to the shaft of turbine and is thus run by turbine. The electrical power, which is consequently obtained at the terminals of the generator, is then transited to the area where it is to be used for doing work. he plant or machinery which is required to produce electricity (. prime mover +electric generator) is collectively known as power plant. The building, in which the entire machinery along with other auxiliary units is installed, is known as power house. 1 thermal and hydropower As stated earlier, the turbine blades can be made to run by the energy of fuels or flowing water. When fuel is used to produce steam for running the steam turbine, then the power generated is known as thermal power. The fuel which is to be used for generating steam may either be an ordinary fuel such as coal, fuel oil, etc., or atomic fuel or nuclear fuel. Coal is simply burnt to produce steam from water and is the simplest and oldest type of fuel. Diesel oil, etc. may also be used as fuels for producing steam. Atomic fuels such as uranium or thorium may also be used to produce steam. When conventional type of fuels such s coal, oil, etc. (called fossils ) is used to produce steam for running the turbines, the power house is generally called an Ordinary thermal power station or Thermal power station. But when atomic fuel is used to produce steam, the power station, which is essentially a thermal power station, is called an atomic power station or nuclear power station. In an ordinary thermal power station, steam is produced in a water boiler, while in the atomic power station。 the boiler is replaced y a nuclear reactor and steam generator for raising steam. The electric power generated in both these cases is known as thermal power and the scheme is called thermal power scheme. But, when the energy of the flowing water is used to run the turbines, the