1、中文 3840 字 外文文献： hydraulicturbines and hydro-electric power Abstract Power may be developed from water by three fundamental processes : by action of its weight, of its pressure, or of its velocity, or by a combination of any or all three. In modern practice the Pelton or impulse wheel is the only typ
2、e which obtains power by a single process the action of one or more high-velocity jets. This type of wheel is usually found in high-head developments. Faraday had shown that when a coil is rotated in a magnetic field electricity is generated. Thus, in order to produce electrical energy, it is necess
3、ary 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
4、 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 (i.e. prime mover +e
5、lectric 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. Keywords hydraulic turbines hydro-electric power classification of hydel plants head scheme There has been practically no incre
6、ase in the efficiency of hydraulic turbines since about 1925, when maximum efficiencies reached 93% or more. As far as maximum efficiency is concerned, the hydraulic turbine has about reached the practicable limit of development. Nevertheless, in recent years, there has been a rapid and marked incre
7、ase in the physical size and horsepower capacity of individual units. In addition, there has been considerable research into the cause and prevention of cavitation, which allows the advantages of higher specific speeds to be obtained at higher heads than formerly were considered advisable. The net e
8、ffect of this progress with larger units, higher specific speed, and simplification and improvements in design has been to retain for the hydraulic turbine the important place which it has long held at one of the most important prime movers. 1. types of hydraulic turbines Hydraulic turbines may be g
9、rouped in two general classes: the impulse type which utilizes the kinetic energy of a high-velocity jet which acts upon only a small part of the circumference at any instant, and the reaction type which develops power from the combined action of pressure and velocity of the water that completely fi
10、lls the runner and water passages. The reaction group is divided into two general types: the Francis, sometimes called the reaction type, and the propeller type. The propeller class is also further subdivided into the fixed-blade propeller type, and the adjustable-blade type of which the Kaplan is r
11、epresentative. 1.1 impulse wheels With the impulse wheel the potential energy of the water in the penstock is transformed into kinetic energy in a jet issuing from the orifice of a nozzle. This jet discharge freely into the atmosphere inside the wheel housing and strikes against the bowl-shaped buck
12、ets of the runner. At each revolution the bucket enters, passes through, and passes out of the jet, during which time it receives the full impact force of the jet. This produces a rapid hammer blow upon the bucket. At the same time the bucket is subjected to the centrifugal force tending to separate
13、 the bucket from its disk. On account of the stresses so produced and also the scouring effects of the water flowing over the working surface of the bowl, material of high quality of resistance against hydraulic wear and fatigue is required. Only for very low heads can cast iron be employed. Bronze
14、and annealed cast steel are normally used. 1.2 Francis runners With the Francis type the water enters from a casing or flume with a relatively low velocity, passes through guide vanes or gates located around the circumstance, and flows through the runner, from which it discharges into a draft tube s
15、ealed below the tail-water level. All the runner passages are completely filled with water, which acts upon the whole circumference of the runner. Only a portion of the power is derived from the dynamic action due to the velocity of the water, a large part of the power being obtained from the differ
16、ence in pressure acting on the front and back of the runner buckets. The draft tube allows maximum utilization of the available head, both because of the suction created below the runner by the vertical column of water and because the outlet of he draft tube is larger than the throat just below the
17、runner, thus utilizing a part of the kinetic energy of the water leaving the runner blades. 1.3 propeller runners nherently suitable for low-head developments, the propeller-type unit has effected marked economics within the range of head to which it is adapted. The higher speed of this type of turb
18、ine results in a lower-cost generator and somewhat smaller powerhouse substructure and superstructure. Propeller-type 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. Large-diameter prop
19、ellers may have individual blades fastened to the hub. 1.4 adjustable-blade runners The adjustable-blade propeller type is a development from the fixed-blade propeller wheel. One of the best-known units of this type is the Kaplan unit, in which the blades may be rotated to the most efficient angle b
20、y 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 adjustable-blade propeller-type unit is parti
21、cularly applicable to low-head 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 fixed-blade propeller-type units operated at the point of maximum efficiency. 2. thermal
22、 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 o
23、rdinary 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
24、 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
25、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 elec
26、tric 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, then the electricity generated is called hydroelectric power. This scheme is known as hydro scheme, and the power h
27、ouse is known as hydel power station or hydroelectric power station. In a hydro scheme, a certain quantity of water at a certain potential head is essentially made to flow through the turbines. The head causing flow runs the turbine blades, and thus producing electricity from the generator coupled to turbine. In this
