毕业设计水利水电工程英文文献翻译

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 plants

Tidal 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.

4.Hydro-plants or hydroelectric schemes may be classified on the basis of operating head on turbines as follows: ① low head scheme (head<15m),②medium head scheme (head varies between 15m to 60 m) ,③high head scheme (head>60m). 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 scheme

A 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.

水轮机和水力发电

摘要

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。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。

关键词水轮机水力发电水电站种类水头系统

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。

1.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。

1.1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。

1.2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。

1.3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。

1.4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。

2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