水利水电工程毕业设计外文翻译.doc

西华大学外文资料翻译外文资料翻译学院(直属系): 能源与环境学院 年级、 专业: 2009级 水利水电工程 学 生 姓 名: 李 巧 龙 学 号: 312009080801230 指 导 教 师: 杨 耀 完 成 时 间: 2013年 5 月 27 日 hydraulic turbines1 introductionPower 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 type 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.There has been practically no increase 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 increase 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 effect 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.2 types of hydraulic turbinesHydraulic turbines may be grouped 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 fills 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 representative.2.1 impulse wheelsWith 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 buckets 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 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 and annealed cast steel are normally used.2.2 Francis runnersWith 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 sealed 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 difference 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 runner, thus utilizing a part of the kinetic energy of the water leaving the runner blades.2.3 propeller runnersnherently 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 turbine 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 propellers may have individual blades fastened to the hub.2.4 adjustable-blade runnersThe 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 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 adjustable-blade propeller-type unit is particularly 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. hydro-electric powerFaraday had shown that when a coil is rotated in a magnetic 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 (i.e. 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 hydropowerAs 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, then the electricity generated is called hydroelectric power. This scheme is known as hydro scheme, and the power house 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 chapter, we are concerned with hydel scheme only.2 classification of hydel plantsHydro-plants may be classified on the basis of hydraulic characteristics as follow: run-off river plants ; storage plants ; pumped storage plants ; tidal plants. they are described below: (1) Run-off river plants.These plants are those which utilize the minimum flow in a river having no appreciable pondage on its upstream side. A weir or a barrage is sometimes constructed across a river simply to raise and maintain the water level at a pre-determined level within narrow limits of fluctuations, either solely for the power plants or for some other purpose where the power plant may be incidental. Such a scheme is essentially a low head scheme and may be suitable only on a perennial river having sufficient dry weather flow of such a magnitude as to make the development worthwhile.Run-off river plants generally have a very limited storage capacity, and can use water only when it comes. This small storage capacity is provided for meeting the hourly fluctuations of load. When the available discharge at site is more than the demand (during off-peak hours ) the excess water is temporarily stored in the pond on the upstream side of the barrage, which is then utilized during the peak hours.he various examples of run-off the river pant are: Ganguwal and Kolta power houses located on Nangal Hydel Channel, Mohammad Pur and Pathri power houses on Ganga Canal and Sarda power house on Sarda Canal.The various stations constructed on irrigation channels at the sites of falls, also fall under this category of plants.(2) Storage plantsA storage plant is essentially having an upstream storage reservoir of sufficient size so as to permit, sufficient carryover storage from the monsoon season to the dry summer season, and thus to develop a firm flow substantially more than minimum natural flow. In this scheme, a dam is constructed across the river and the power house may be located at the foot of the dam such as in Bhakra, Hirakud, Rihand projects etc. the power house may sometimes be located much away from the dam (on the downstream side). In such a case, the power house is located at the end of tunnels which carry water from the reservoir. The tunnels are connected to the power house machines by means of pressure pen-stocks which may either be underground (as in Mainthon and Koyna projects) or may be kept exposed (as in Kundah project).When the power house is located near the dam, as is generally done in the low head installations ; it is known as concentrated fall hydroelectric development. But when the water is carried to the power house at a considerable distance from the dam through a canal, tunnel, or pen-stock; it is known as a divided fall development.(3) Pumped storage plants.A pumped storage plant generates power during peak hours, but during the off-peak hours, water is pumped back from the tail water pool to the headwater pool for future use. The pumps are run by some secondary power from some other plant in the system. The plant is thus primarily meant for assisting an existing thermal plant or some other hydel plant.During peak hours, the water flows from the reservoir to the turbine and electricity is generated. During off-peak hours, the excess power is available from some other plant, and is utilized for pumping water from the tail pool to the head pool, this minor plant thus supplements the power of another major plant. In such a scheme, the same water is utilized again and again and no water is wasted.For heads varying between 15m to 90m, reservoir pump turbines have been devised, which can function both as a turbine as well as a pump. Such reversible turbines can work at relatively high efficiencies and can help in reducing the cost of such a plant. Similarly, the same electrical machine can be used both as a generator as well as a motor by reversing the poles. The provision of such a scheme helps considerably in improving the load factor of the power system.(4) Tidal plantsTidal plants for generation of electric power are the recent and modern advancements, and essentially work on the principle that there is a rise in seawater during high tide period and a fall during the low ebb period. The water rises and falls twice a day; each fall cycle occupying about 12 hours and 25 minutes. The advantage of this rise and fall of water is taken in a tidal plant. In other words, the tidal range, i.e. the difference between high and low tide levels is utilized to generate power. This is accomplished by constructing a basin separated from the ocean by a partition wall and installing turbines in opening through this wall.Water passes from the ocean to the basin during high tides, and thus running the turbines and generating electric power. During low tide, the water from the basin runs back to ocean, which can also be utilized to generate electric power, provided special turbines which can generate power for either direction of flow are installed. Such plants are useful at places where tidal range is high. Rance power station in France is an example of this type of power station. The tidal range at this place is of the order of 11 meters. This power house contains 9 units of 38,000 kW.Hydro-plants or hydroelectric schemes may be classified on the basis of operating head on turbines as follows: low head scheme (head60m). They are described below:(1) Low head scheme.A low head scheme is one which uses water head of less than 15 meters or so. A run off river plant is essentially a low head scheme, a weir or a barrage is constructed to raise the water level, and the power house is constructed either in continuation with the barrage or at some distance downstream of the barrage, where water is taken to the power house through an intake canal.(2) Medium head schemeA medium head scheme is one which used water head varying between 15 to 60 meters or so. This scheme is thus essentially a dam reservoir scheme, although the dam height is mediocre. This scheme is having features somewhere between low had scheme and high head scheme.(3) High head scheme.A high head scheme is one which uses water head of more than 60m or so. A dam of sufficient height is, therefore, required to be constructed, so as to store water on the upstream side and to utilize this water throughout the year. High head schemes up to heights of 1,800 meters have been developed. The common examples of such a scheme are: Bhakra dam in (Punjab), Rihand dam in (U.P.), and Hoover dam in (U.S.A), etc.The naturally available high falls can also be developed for generating electric power. The common examples of such power developments are: Jog Falls in India, and Niagara Falls in U.S.A.水轮机1.概述水的能量可以通过三种基本方法来获得：利用水的重力作用、水的压力作用或水的流速作用，或者其中任意两种或全部三种作用的组合。在如今的实际应用中，佩尔顿式水轮机或冲击式水轮机是唯一只利用其中一种方法来获取水能的，即利用一束或者好几束高速的水流的作用获得能量的一种水轮机。这种类型的水轮机通常应用在高水头电站上。从1925年开始，水轮机的最高效率达到93%或稍微高一点就没有再提高了。就最大效率而言，水轮机的对水能的利用率已经达到了实际发展的极限了。然而，在最近几年里，水轮机的大小和单机容量却增长的很快。另外，人们还对引起空蚀的原因以及怎样预防空蚀做了很多的研究，这些研究使得我们能够在高于以前认为的合适水头下获得更高的比转速。更大的机组，更高的比转速，以及水轮机的设计上的简化和改进，这几个方面的进步使得水轮机一直以来在作为原动力之一拥有很重要的地位。2.水轮机的类型水轮机可以分为两大类：冲击式水轮机利用高速水流冲击水轮机的一小部分时产生的动能；反击式水轮机利用充满转轮和过水道的水流所拥有的水的压力和流速两者相结合来获得动力。反击式系列又分成两种通用的型式：弗朗西斯式（有时称作反击式）以及旋桨式。旋桨式又进一步再分为定轮叶式水轮机和以卡普兰式代表的转叶式水轮机。2.1冲击式水轮机在冲击式水轮机上，压力钢管中的水从喷嘴孔口中射出，这时水的的势能转换成动能。射流自由地射入水轮室内的空气中，撞击在转轮的碗状戽斗上。戽斗每旋转一周进入射流、经过并从射流转出一次。在这段时间内戽斗承受着射流的全部冲击力。这种冲击力产生一个高速锤击冲打在戽斗上。与此同时，戽斗受到离心力的作用而有脱离它的座盘的趋势，由此而产生的应力以及水流在戽斗的碗状工作面上的冲刷作用都很大，因而需要选用能抵御水力磨损和疲劳的高质量材料，一般都采用青铜和韧化铸钢，只有水头很低时才能用铸铁。2.2弗朗西斯式转轮就弗朗西斯式水轮机来说，来自蜗壳或水槽内的流速较低的水，通过位于转轮周围的导叶或一些闸门，然后流经转轮，并从转轮泄入安置在尾水位以下而不与大气相通的尾水管内。由于水充满所有的水道并作用在转轮的整个周围，因此，仅有一小部分动力来自水的流速所引起的动力作用，而大部分动力则都通过作用在转轮叶片前后工作面上的压力差取得。尾水管可以使能利用的水头得到充分的利用，这一方面是由于转轮下面垂直水柱所产生的吸出作用，另一方面是由于尾水管的出口面积大于紧接转轮下喉管的面积，从而使水流离开转轮叶片时的一部分动能得以利用。2.3旋桨式转轮旋桨式机组最适用于低水头电站，在它适用的水头范围内，已产生了显著的经济效果。这种水轮机的转速比较高，以致使发电机的价格较低，并使发电厂房的水下结构和水上结构的尺寸都比较小。低水头、小功率的旋桨式转轮，有时用铸铁来制造。水头高于20英寸时，都用一种更为可靠的材料铸钢来制造。大直径的螺旋桨可用单个叶片固定在轮毂上制成。2.4转叶式水轮机转叶旋桨式水轮机是从定轮叶旋桨式水轮机发展而成的。卡普兰式水轮机是这类水轮机中为人们最为熟悉的一种。它的叶片可由液压伺服器调整到效率最大的角度。利用伺服器上的凸轮能使叶片的角度随阀门的开启位置而变化，从而在所有各种满负载百分率情况下都能保持高效率。由于转叶旋桨式水轮机组在闸门各种开度情况下效率都高，因此，它特别适用于那些必须在变负载和变水头条件下运行的低水头电站上。当然，这种机组的投资费用和维护费用要高于只能在一个最大效率点上运行的定轮叶旋桨式水轮机组。水力发电法拉第曾经指出：线圈在磁场中旋转，就产生了电。因此，为了获得电能，我们必须产生使“线圈”旋转的机械能。用燃料或流水的能量带动原动机（称为涡轮机）就产生了机械能。这种机械能转换成电能是通过电动机来实现的，电动机直接连接在涡轮机轴上，由涡轮机驱动。因此，就在发电机的出线端获得电能，然后输送到需要它做功的地区。发电需要的装置或机械（即原动机+发电机）统称为动力设备。安置所有机械和其他辅助设施的建筑称为发电厂。1火电和水电如上所述，涡轮机叶片是由燃料或流水的能量带动的。用燃料产生蒸汽驱动蒸汽涡轮机时，所产生的电称为火电。由于产生蒸汽的燃料是一般燃料如煤、燃料油等，或是原子能燃料即核燃料。直接燃烧煤产生水蒸气，煤是最简便、最古老的一种燃料。柴油等也可以作为产生蒸汽的燃料。原子燃料如铀、钍也可用于产生蒸汽。用传统燃料如煤、燃料油等（称为矿物燃料）产生蒸汽来带动水轮机时，这种发电厂一般称为普通火力发电厂或热电厂。但当原子燃料用于产生蒸汽时，这种发电厂（基本上属于火力发电厂）称为原子能发电厂或核电厂。一般火力发电厂是用锅炉产生蒸汽的，而原子能发电站是用核反应堆和蒸汽发生器代替锅炉产生蒸汽的。这两种情况产生的电能称为火电。该系统称为火力发电系统。然而，用流水的能量驱动水轮机时，所产生的电称为水电。