電氣英文文獻翻譯

1、精選優(yōu)質(zhì)文檔-傾情為你奉上精選優(yōu)質(zhì)文檔-傾情為你奉上專心-專注-專業(yè)專心-專注-專業(yè)精選優(yōu)質(zhì)文檔-傾情為你奉上專心-專注-專業(yè) Elements of electrical power station design = 電站設(shè)計基礎(chǔ) / M. V. Deshpande. Wheeler Publishing, 1981 Where water resources are available, hydro-electrie power station are used to supply electrical energy to consumers.This type of station，ho

2、wever, cannot be located everywhere. First,there must be an ample quantity of water at sufficient hard, and suitable site must be available.Stream flow date for a number of years should be studied.The possibility of constructing a dam at a suitable site to store water in the catchment area and the a

3、vailability of water throughout the year are decisive factors. The amount of power that can be developed depends on the quantity of water available,the rate at which it is available,the head,etc.Hydro-electric projects involve a large amount of civil engineering construction work .Often the project

4、is a multipurpose one embracing irrigation and power,flood control and power,or flood control,navigation and power.One might imagine that hydro-electric power should be very cheap as water does not cost anything and there is no fuel cost,This ,however,is not true.To store water at enough head,it is

5、necessary to have a dam and civil engineering construction works. This costs money,and increases investment costs and fixed costs which are not required for other types of power plants,Whenever a hydro-electric project is considered for power purposes ,it is always necessary to work out the economic

6、s comparing hydro-electric power costs with the costs for other forms of station.7.2HydrologyWhen considering the possibility of a hydro-electric project,the first requirement is to obtain data regarding the stream flow of water that would be available,and to predict the yearly possible flow from th

7、e data ,The water cycle in general consists of evaporation from seas or oceans and/or other water surfaces on the earth due to heat from the sun,the formation of moist air and clouds ,the circulation in form of rain ,hail or snow .Determination of the amount of stream flow and its variation involves

8、 a study of hydrography (or hydrology) which deals with the occurrence and under the earths surface.The science of hydrology is based on meteorology ,geology,agricultural physics,chemistry,botany and data obtained by observation and measurement.It is necessary to calculate the mean annual rainfall i

9、n the area under consideration from a record of the annual rainfall for a number of years,say 25to30,and also to note the frequency of dry years.The precipitation or rainfall in a particular area can be measured by rain gauges at various places in the area.A rain gauge consists of a collecting cylin

10、der which exposes a circular gauge consists of a collecting cylinder which exposes a circular surface for collecting the rain and a storage vessel in which the water is retained until measured .Recording rain gauges ,giving a continuous record,are use where possible.Frequency of precipitation is als

11、o care fully noted.A curve of precipitation in millimetres plotted against percentage of time gives a range of able for a number of years,the range of distribution of mean monthly precipitation is obtained the general character of the periodic distribution of the rainfall tends to be similar each ye

12、ar in each locality .There is some variation in the occurrence of rainfall from year to year ,but when the record of a number of seasons is available ,it is usually found that the occurrences of rainfall for a given month in a given locality are similar.The frequency of occurrence of a dry year or t

13、wo consecutive dry years is also seen when records for a long period are available.Precipitation in a particular locality depends to a certain extent on altitude,The general and fundamental tendency is for the precipitation to increase as the altitude increases on the coastal side of a mountain rang

14、e,if the locality is not far from the general sources of water vapour.Date regarding maximum rainfall in a particular area and the nature of the drainage area help in the study of possible floods in the area.Knowledge of the frequency of high rainfall in the are is also helpful in the above studies.

15、The mean precipitation on a drainage area over a period of time can be obtained by plotting isohyets,or lines of equal precipitation,from the records available and then finding a weighted average by planimeter.Of the total precipitation ,some part of the water is lost.Sources of loss are evaporation

16、 from the water are ,soil evaporation ,interception and transpiration losses from land area.The stream flow is known when the water losses have been subtracted from the precipitation .Stream flow consists of surface flow and percolation through the ground.The various factors which affect the distrib

17、ution of precipitation are meteorological conditions, drainage area characteristics,topography of land,geology of land and vegetation in the area.Evaporation is effected by heat from the sun.Temperature and relative humidity affect evaporation,and so too does wind velocity.Plants absorb moisture fro

18、m the ground,giving it off to the atmosphere,the process being known as transpiration.During the process ,some water is lost,this is known as transpiration loss.Drainge area characteristics are the size and shape of the are .A small area tends to have a higher unit flood discharge than a large area.

19、The topography of land and surface slopes affects the surface flow of water.Steep slopes tend towards a rapid and large surface flow.The size of the water area affects the losses .A large percentage of water area tends to a diminished run-off.The geological characteristics of the watershed affect ru

20、n-off. Evaporation varies inversely with the porosity of soil.Percolation and water losses depend on whetner the soil is pervious or impervious.A large surface run-off is experienced when pervious ground is saturated with rainwater or when the ground is of impervious material such as rock or clay.Ev

21、aporation and percolation are increased by cultivation.Transpiration and interception losses occur owing to the presence of vegetation.To find the evaporation from a water surface a shallow pan is partly immersed in a lake or reservoir ,the evaporation being measured by the change in the water level

22、 in the pan, If the pan were placed on land, the temperature would differ from that of the lake.Humidity and wind,air and water temperatures are noted because evaporation varies with all these factors.Transpiration is estimated in a particular area in an approximate,empirical way.Changes in ground w

23、ater level are found by a water-level recorder.The amount of moisture in the soil above the water table is found by measuring the electrical resistance of gypsum blocks buried at different depths in the ground.The resistance of gypsum increases as it gets drier.The soil temperature is measured by me

24、ans of thermocouples placed near the gypsum blocks. In considering the factors affecting losses,the stream flow and the run-off available are determined.A drainage area and profile map is prepared.This shows the length of the river,the size and shape of the watershed,tributaries,lakes,reservoirs,etc

25、.The watershed or drainage area is sometimes called the catchment area with respect to precipitation.7.3Stream Flow :Hydrographs:Flow Duration CurvesFor water-power studies,it is essential to know the streamflow date,over a long period if available.Daily,weekly or monthly flow data for number of yea

26、rs at a site help in finding the average flow data for a number of years at a site help in finding the average flow and output power that are likely to be available from the stream flow.The head available is determined by surveying the site.The minimum or low water flow data help in estimating the f

27、irm power that will be available at the site .The maximum flow helps in estimating the floods and in designing the spillway.Estimating the stream flow helps in determining the capacity of storage reservoir for equalising the flow to a given minimum.Knowing the maximum stream flow conditions, it is p

28、ossible to estimate the necessary capacity of a flood-control reservoir for limiting the discharge to a pre-determined maximum under all conditions except extreme floods. When studing stream flow in a river,it is necessary to find the depth of the river at various sections by river gauging.The depth

29、 of the river is measured by wading in shallow water,by wire weight gauge,etc.Measurement of discharge in open channels is done by the velocity-area method or by the flow of water over a weir of known dimensions. In the velocity-area method,the discharge is obtained as the sum of the products of par

30、tial cross-sectional areas of the flowing water by the respective measured velocities in such areas.The cross-sectional areas are found by measuring the width and depth at suitably spaced points to show the shape of the river bed ,and summation of the partial areas is computed from these measurement

31、.Velocities in different areas are measured by float or current meters.Thee other method of computing the discharge is by observing the head on a weir and the known dimensions of the weir.The discharge ,or volume rate of flow ,Q,in cubic metres per second,is given by Q=CLh3/2Where L is the length of

32、 the weir in metres ,h is the head in metres,and C is a constant.For a sharp-crested weir ,C is 1.85 approximately. Hydrographs. When a river discharge has been measured ,a curve can be plotted showing discharge in cubic metres/second against time in hours.The curve is known as a hydrograph.The ordi

33、nates may be plotted in terms of the gauge height ,the number of cubic metres per second per square kilometre,the power in kilowatts that can be developed theoretically per metre of fall,or the energy in kilowatt-hours,days or weeks.A hydrograph shows the variation of flow with time.It will also ind

34、icate the power available from the stream at different times of the day or year.It is similar to the load curve used in the study of electrical power.Hydrographs help in noting the extremes of flow more readily than the inspection of tabular values of the discharge.Hydrographs are essential in studi

35、es of the effect of storage on flow. Flow duration curve. The flow duration curve is a very convenient form of hydrograph for determining the available power at the site.It indicates the daily ,weekly or monthly flows available as ordinates plotted against percentage of time.The flow is available,on

36、e can convert the cubic metres per second per week,or other unit of time.Knowing the head at which the flow is available,one can convert the cubic metres per second per weeks,or the discharge for the period,into power in kilowatts,so that the flow duration curve becomes the load duration curve for a

37、 hydro-electric plant .If storage is available at a site upstream from the power plant ,a flow duration curve as modified by the use of storage,will be necessary.Low water flow decides the primary power that can be developed.The flow duration curve also shows the possible heavy flood flow and the ti

38、me during which it may occur .The data are useful in designing a spillway on the dam to allow flood water to escape from the reservoir.It is easy to convert a hydrograph into a flow duration curve.The following examples illustrate the plotting of a hydrograph and flow duration curve from the flow da

39、ta in terms of discharge per week.7.5 Investigation of Site Preliminary investigations are made when selecting the site for a dam,The dam should be as close to the turbines as possible,and should have maximum size of pondage and the shortest length of conduit.The ideal site will be one where the dam

40、 will have the largest catchment area to store water at a high head,and yet be economical in construction.A general reconnaissance survey is first made from the air .Topographical mapping is then carried out by detailed surveying of the area,Geological studies are made.Methods of exploring the sub-s

41、urface are by digging pits ,shafts and/or tunnels,etc.Supplementary methods used are the measurement of electrical resistivity and seismic methods of prospecting.The electrical resistivity method depends on the difference between the resistivities of the ledge rock and the overburden.The seismic met

42、hod requires the measurement of the ratio of propagation of waves caused by explosion and is dependent on the difference in the elastic properties of the ledge rock and the overburden.Other methods of investigating the geological properties of rock are wash borings,churn drilling,rotary core drillin

43、g and diamond drilling.Sub-surface explorations should be made ,and condition of soil mechanics helps a great deal in this respect.Ti is necessary to investigate the possibility and availability of construction materials in the neighbourhood,namely,earth,gravel,concrete aggregates,etc.Foundation con

44、ditions have to be studied.水電站：初步設(shè)計I7.1介紹 水電站建在有水資源的地方，用于向消費者提供電能。 然而，這種類型的站，可以不設(shè)隨處可見。 首先，必須有足夠數(shù)量的水，足夠硬，必須提供合適的地點 。應(yīng)研究了數(shù)年的流量資料。在一個合適的集水區(qū)興建水壩和一年四季水的可用性是決定性的因素。可開發(fā)的發(fā)電量依賴于水量，它是可用率，源頭等水電項目涉及大量的土建施工工作。常見項目是一個多用途的包含灌溉電源，防洪電源，或者防洪，航運電源?？梢韵胂螅Πl(fā)電應(yīng)該是很便宜的，水不消耗什么，也沒有燃料成本。然而，這并不正確。要在源頭儲存足夠的水，它是需要有一個水壩和土建施工工程。這些

45、資金投入，增加投資成本，而不是其他類型電廠所需的固定成本。每當(dāng)一個水電項目作為電力用途考慮時，水力發(fā)電站與其他發(fā)電站的費用成本的經(jīng)濟性比較是很必要的。7.2水文當(dāng)考慮一個水電項目的可能性，第一個要求是獲取數(shù)據(jù)流的水流量，數(shù)據(jù)流將提供，并預(yù)測每年可能的水流量。一般的水循環(huán)包括從?；虼笱蠛?或其他地球上的水表面由于來自太陽，潮濕的空氣和云層的形成，暴雨，冰雹或雪的形式循環(huán)加熱蒸發(fā)。流流及其變化量的測定涉及發(fā)生在地球表面的水文學(xué)研究（水文）。水文科學(xué)是建立在氣象，地質(zhì)，農(nóng)業(yè)物理學(xué)，化學(xué)，植物學(xué)，通過觀察和測量獲得的數(shù)據(jù)基礎(chǔ)上的。在該地區(qū)的年平均降雨量計算中，要通過數(shù)年的年均降雨量紀(jì)錄考慮，25至30

46、年，并要注意干旱年的發(fā)生頻率。在某一特定地區(qū)的降水或降雨量可以通過在該地區(qū)各個地方的雨量計測量。雨量計由一個敞開的收集缸，一個圓形儀表組成。收集缸有一個敞開的圓弧面用來收集雨水并在容器中儲存，通過圓形儀表測量。雨量計在可用處記錄，并給出連續(xù)記錄。降水頻率也被仔細考慮到了。時間的百分比繪制毫米的降水曲線能夠數(shù)年的范圍內(nèi)給出，月平均降水量的分布范圍，并得到定期的降雨分布的一般性質(zhì)，每年相同地方，往往是相似的。有一些是每年的降雨量發(fā)生變化，但當(dāng)季節(jié)紀(jì)錄時，它通常在一個給定的地方給定月份的降雨量出現(xiàn)類似的。干旱一年或兩年連續(xù)干幾年發(fā)生的頻率也可從很長一段時間的記錄時得出。在某一特定地區(qū)的降水在一定程度

47、上取決于海拔高度。一般的和基本的趨勢是降水增加，沿海邊的山脈海拔增加如果地方不遠處就是一般水汽來源。對于在一個特定的區(qū)域和流域最大降雨量的數(shù)據(jù)，可以幫助該地區(qū)洪水性質(zhì)的研究。在該地區(qū)的高頻降雨量信息在上述研究也很有幫助。利用現(xiàn)有的記錄對流域面積超過一段時間的平均降水量繪制等雨量線，或平等降水線，然后通過所求積儀加權(quán)平均可以得到的。在總降水量中，水有某些部分損失。損失的的來源是從水的蒸發(fā)，土壤水分蒸發(fā)，截留和土地面積的蒸騰損失。水流量中，水的損失已經(jīng)從降水量減去。水流量包括通過地面的地表徑流和滲流。影響降水分布的各種因素有氣象條件，流域面積的特點，土地的地形，地質(zhì)土地，在該地區(qū)的植被。蒸發(fā),來自太陽的熱量。溫度、相對濕和風(fēng)速度影響蒸發(fā)。植物吸收來自地面的水分，排出給大氣，這一過程被稱為蒸騰。在這個過程中，失去了一些水，這被稱為蒸騰損失。流域特點的是大小和形狀。小面積的泄洪能力較大面積更強。土地和表面的斜坡地形影響表面流動的水。陡峭的山坡上傾向于迅速和大量的地表徑流。水面積的大小影響的水損失。一個面積很大水域很大比例減弱徑流損失。流域的地質(zhì)特征影響徑流損失。蒸發(fā)與土壤的孔隙率成反比。滲流和水的損失取決于土壤透水與否。一個大的地表徑流流過透水地面與雨水或地面時，像巖石或粘土防滲材料會飽和。通過種植增加蒸發(fā)和滲透。由于植被的存在減少蒸騰和攔截?fù)p失的發(fā)生