《电气毕业设计外文翻译.doc》由会员分享,可在线阅读,更多相关《电气毕业设计外文翻译.doc(13页珍藏版)》请在taowenge.com淘文阁网|工程机械CAD图纸|机械工程制图|CAD装配图下载|SolidWorks_CaTia_CAD_UG_PROE_设计图分享下载上搜索。
1、本科毕业设计外文文献及译文文献、资料题目:Special English for Architectural Electric Engineering and Automation文献、资料来源:期刊(著作、网络等)文献、资料发表(出版)日期:2006.4院 (部): 信息与电气工程学院学院专 业: 电气工程与自动化班 级: 电气093姓 名: 孙德艺学 号: 指导教师: 陈红艳翻译日期: 2013.6.30外文文献一:Transformer One of the most valuable apparatus in electric power system is the transform
2、er, for it enables us to utilize different voltage levels across the system for the most economical value. Generation of power at the synchronous machine level is normally at a relatively low voltage,which is most desirable economicallyStepping up of this generated voltage to high voltage,extra-high
3、 voltage or even to ultra-high voltage is done through power transformers to suit the power transmission requirement to minimize losses and increase the transmission capacity of the linesThis transmission voltage level is then stepped down in many stages for distribution and utilization purposes A t
4、ransformer is a static device for transferring electric energy from one circuit to another electromagnetically,that is,by induction instead of by conductionIts usual function is to transfer energy between circuits of different voltageA transformer has a magnetic core on which there are two or more w
5、indingsThese windings are insulated from each other and from groundIn autotransformers,however,the windings are connected togetherThe assembly of core and coils is normally insulated and cooled by immersion in mineral oil or other suitable liquid within an enclosing tankConnection to the windings is
6、 by means of insulating bushings,usually through the cover.The “ratio of transformation” is determined by the relative number of turns in each of he windingsThis is known as the “turn ratio” and it is the ratio of the no-load voltagesWhen the unit is carrying load, the ratio of the actual voltages i
7、s slightly different because of the drop caused by the flow of 1oad current through the impedance of the transformer windingsAt rated load, this drop is known as the voltage regulation. The amount of voltage drop varies with the power factor of the output even when the kilovolt-amperes remain consta
8、ntPractically all power transformers and many distribution transformers have taps in one or more windings for changing the turn ratioChanging the ratio is desirable for two reasons to compensate for varying voltage drop in the system and to assure that the transformer operates as nearly as possible
9、at the correct core densityFor the latter purpose, the taps should be in the winding subject to the voltage variation. De-energized tap changers are used when it is expected that the ratio will need to be changed only infrequently, because of load growth or some seasonal changeThe desired tap is sel
10、ected by means of a ratio adjuster(no load taps)Load tap changer(LTC)is used when changes in ratio may be frequent or when it is undesirable to de-energize the transformer to change a tapIt seldom makes much difference to the user which winding or windings are tapped;therefore,the choice is usually
11、made by the designer on the basis of cost and good design. Both winding current and voltage must be considered when applying LTC equipmentHigh voltage and high current applications require special considerations to arrive at an optimum location for the LTC equipmentStep down units usually have LTC i
12、n the low-voltage winding and de-energized taps in the high voltage windingWhen energy is to be transferred between two circuits of nearly the same voltageThe use of autotransformers affords cost savings over two-winding unitsThe nearer the voltages are to each other, the smaller will be the autotra
13、nsformer per kilovolt-ampere of output,and the greater the savingsThe simplicity of phasing out systems has increased its useMost autotransformers are Y-connected,and it has been a standard American practice to add a low capacity, delta windingThis is frequently referred to as a “delta tertiary“Its
14、primary purpose has been to provide an internal path for the third harmonic currents (required for excitation),thus reducing those currents on the power systemIt also helps to stabilize the neutral and to ground the system betterIn recent years,the use of shielded telephone cable has reduced the req
15、uirements for the delta tertiary. Because an autotransformer does not afford electrical separation between the two circuits, disturbances originating on one circuit can be communicated to the otherThis difficulty is minimized by solidly grounding the neutral of the autotransformer. Solidly grounding
16、 the neutral,however, causes(among other things)current of short-circuit magnitude to flow through the delta-connected tertiary winding during ground faults on either system. Autotransformers are not inherently self-protecting and, therefore,all windings must be examined for mechanical strength as a
17、pplied to the system where they will be used . Tertiaries are normally 35of the physical size of the largest winding of the autotransformer, unless otherwise specified by the user.The bulk of a11 transformers,except for large extra-high voltage(EHV)and distribution units are three-phase units In the
18、 early days of the industry,It was almost universal practice in the United States to use three single-phase units connected in a three-phase bankInsulation clearances and shipping limitations for certain large EHV units now require this designThe distribution systems serve mainly single-phase loads
19、in residential areas and are served from single-phase transformers中文译文一: 变压器 在电力系统中最有价值的一个装置是变压器,因为它使我们能够在系统中利用不同的电压水平获得最经济的价值。同步电机的发电电压水平通常是在一个相对较低的电压,这是最令人满意也是最经济的。把发电电压升高到高电压,超高压甚至超高电压是通过电源变压器实现的,这样可以适应电力传输要求,减少电压损失,提高线路的传输容量。在不同的阶段,我们可以根据配电和使用目的的要求把高电压通过变压器降到低电压。 一个变压器是一个静态装置,因为电能量从一个电路转移到另一个电路是
20、通过电磁的形式实现的,也就是说,能量的转移是通过感应而不是通过传导。变压器通常的功能是传递不同电压等级电路之间的能量。 变压器有一个磁芯,磁芯上有两个或两个以上的绕组,这些绕组相互之间是绝缘的并且与大地也是绝缘的。 然而自藕变压器中的绕组是直接连在一起的的。 磁芯和绕组的组装通常是在密闭容器内进行的并且浸没在矿物油或其他适当的液体中。线圈的连接是通过绝缘套管,通常穿过表面。“变压比”是由每个绕组上线圈的相对匝数决定的。我们称为“匝数比”,这也是空载电压比。当变压器承载负荷时,实际电压的比例略有不同,因为当负载电流通过变压器时会因为绕组阻抗而使电压产生降落。在额定负载下,这种电压降落被称为“电压
21、调整”。 电压降落的大小随输出的功率因数的变化而变化即使总的视在功率保持不变。 几乎所有的电力变压器和输电变压器在一个或多个线圈上都有改变变压器变比的开关。改变变比有两个令人满意的理由:补偿系统中变化的电压降落以及确保变压器尽可能的在正确的中心密度下操作。为了达到后边的目的,改变变比的开关通常放在变压器的绕组中并且受电压变化的控制。当变比不经常改变时,例如负荷的增加或者季节的变化,我们常用断距抽头转换开关。 理想的开关是由比例调节器选择的。当变比变化比较频繁或者不希望断开变压器去改变抽头时,我们常用负载抽头转换开关(LTC)。 当线圈或线圈组都是抽头时对使用者这几乎没有任何区别;因此,设计师通
22、常根据成本和良好的设计来做出选择。应用LTC设备时绕组电流和电压都是必须考虑的。高电压和大电流在应用中需要特殊考虑才能达到负载抽头转换开关(LTC)设备的最佳使用条件。在降压变压器中,低压绕组通常用LTC(负载抽头转换开关),高压绕组通常用断距抽头转换开关。当两个具有相同的电压的电路之间转移能量时,使用自耦变压器要比使用两个绕组单元更能够节约成本。两个电路的电压越接近,自耦变压器输出的每千伏安越小,也就越节约成本。一些简单落后的系统往往常用它。很多自耦变压器是星形连接,这已经成为一个标准,但美国人尝试采用低容量三角形连接的自耦变压器。这是经常被称为是一个“三角洲三级“牵引,主要目的是为三次谐波
23、(用来激发)提供一个内部路径,从而减少在电力系统的谐波。这也有助于稳定中性点并且使接地系统更好的工作。在最近几年,屏蔽电话电缆的使用已经降低了对三角洲三级的要求。?因为一个自耦变压器不负担两个电路之间的电气隔离, 来源于一个电路的干扰可以传达到另一个电路。这一困难可以通过将自耦变压器的中性点直接接地来解决。然而,中性点直接接地,在系统发生接地故障时会(在其他事物之中)引起短路电流流过三角接法的第三相绕组。第三绕组的物理尺寸通常为自耦变压器最大的绕组的35%,除非用户另有指定。自耦变压器就不具有自我保护的功能,因此, 所有的绕组在使用之前都必须经过机械强度检查以确定是否适用于该系统。?除了大型超
24、高压(超高压)和配电设备,大部分变压器都是三相的。在美国早期的工业中, 把三个单相单位连接成一个三相的组合设备是一个非常普遍的经验。某些大型超高压单位的绝缘间隙和运输限制现在就需要这个设计。配电系统主要服务于居民区的单相负载并且电能是引自单相变压器。外文文献二: Selection and Cooling of Power TransformerThe selection of the transformer can have a major impact on the cost a substation,since the transformer represents the major c
25、ost itemNameplate rating is only a guide to transformer application,and should only be used as a first step in the selection process. The transformer is available as a self-cooled unit,or it can be purchased with additional steps of forced cooling that use fan or fans and oil pumpsTransformer rating
26、s can be increased from 25 to 66 by the addition of fans and pumpsThe nameplate rating is based on a continuous load producing a 55 to 65 conductor temperature rise over ambient. Since many transformers do not carry continuous loads,advantage can be gained from the thermal time lag to carry higher p
27、eak loads without exceeding the temperature limits .Transformer ratings are based on the assumption that only an extremely slow deterioration of insulation will take place with normal operationA substantial increase in rating can be achieved by accelerating the loss of insulation lifeThis increase i
28、n rating might approach 200for an hour or two, and approximately 120for 24 hoursFor substations that are designed to carry full load under the outage of any one transformer, a high emergency rating for a 24-hour period (e.g. until the failed unit can be replaced) could mean the selection of smaller
29、transformers and a substantial saving in substation cost The selection of the transformer should involve a careful evaluation of a number of other factors: (1)Impedances should be selected considering their effect on short-circuit duties and low-side breaker ratings both for initial and future stati
30、on developmentsIn addition,impedance is important to achieve a proper load division in the parallel operation of transformers. (2)No load tap ranges should be selected to provide an adequate low-side bus voltage.(3)If the high-side or low-side voltages vary over a wide range during the load cycle, i
31、t may be necessary to provide bus regulationThe actual regulation can be calculated using the system and load characteristicsIf regulating equipment is needed,it may be desirable to provide it in the transformer by using load tap changer(LTC) equipment. If the need for bus regulation is not presentl
32、y evident, but may be required in the future, it may be economical to leave space in the station for future regulators, and buy transformers without LTC equipment.A great many transformers, including all the large ones and all the high voltage ones are immersed in mineral oil which serves the double
33、 purpose of cooling and insulating the windings. Small transformers have enough tank surface to radiate a11 the heat caused by their losses without exceeding the permissible temperature riseAs size increases,the losses increase faster than the tank surface which soon becomes inadequateVarious method
34、s have been developed to get the heat out of the tank more effectivelyLarge power transformer being built today are commonly of the forced-oil-cooled typeIn this design the oil is pumped both through the external cooling devices(air or water heat-exchangers)and through internal channels that are loc
35、ated nearest the points where the heat is generatedThus the transfer of heat to and from the oil is far more effective than in the plain self-cooled or fan-cooled unit where the oil is allowed to circulate by convection. When oil-to-air heat exchanger(a group fans on each radiator)is used,this cooli
36、ng type is designated as type of FOAWhile oil-to-water heat exchanger is used,it is called FOWFor applications where any liquid,even a nonflammable one,is objectionable,the dry-type transformer is usedThe ventilated dry-type unit is cooled by a continuous natural draft of air and consequently is not
37、 suitable for locations where the air is wet or dirty. For these locations a completely enclosed unit,the sealed dry-type,is available,having a core-and-coil in a tank that is sealed and filled with an insulating gas. Dry-type transformers are completely nonflammable,using organic material such as e
38、poxy resin.中文译文二: 电力变压器的选择和冷却 变压器的选择对变电所的建造成本具有重大影响,因为变压器是主要的成本项目。铭牌定额只是变压器应用的指南,它只应该用作变压器选择过程的第一步。变压器可以是自冷式单位,也可以购买额外的冷却装置,如强制冷却风机或机组和柴油泵。根据额外的冷却机组和柴油泵,变压器评级可以从25%增加到66%。铭牌评级是基于连续负荷产生超过环境55到65导体温升而评定的。?因为很多变压器不带连续负载,优势可以获得从热滞后时间进行更高的高峰负荷而不超过温度限制。变压器的评级是基于假设:正常操作下的绝缘老化只是一个极其缓慢的过程。通过加速绝缘老化的进程可以大幅度的提高
39、评定等级。在一两个小时左右评级可能增长接近200%,而在在二十四小时左右评级则增长大约120%。因为变电站的设计要保证在任何一个变压器断电的情况下都要满足全负荷运行,为24变电站设计将满载在停机的任何一个变压器,因此在二十四小时内的较高的紧急评级(例如直到失败的单位可以更换)可能意味着选择较小的变压器和节约大量的变电所成本。 变压器的选择应该涉及对其他影响因素的审慎评估:(1)阻抗应该被选择的考虑到他们对短路职责和下部断路器评级的影响对初始和未来空间站发展。此外,阻抗在并行变压器的操作中获得一个合适的负载也是十分重要的.(2)无载分接范围应该选择提供一个足够的下部总线电压。(3)如果高压侧或低
40、压侧电压在负载周期内变化很大的话,可能有必要提供总线监管。通过系统和负载特性实际监管和控制是可以被计算和描绘的。如果调节设备是必要的,在变压器内使用负载抽头转换开关(LTC)设备来提供监管是可取的。如果需要总线监管目前是不需要的,但可能在未来需要的,那么在变电站预留未来安装设备的空间并且购买没有LTC设备的变压器是十分经济的。许多变压器,包括所有的大体积的和所有的高电压的变压器都是沉浸在矿物油,矿物油有双重目的:冷却和绝缘绕组。小变压器有足够的容器表面辐射a11热引起的损失而不超过容许温度上升范围。随着体积的增加,损失增加的速度会加快,这时容器表面会变得不适宜。很多的方法已经被改进以使的容器的
41、散热更有效。今天一般建造的大型电力变压器都是强制循环油冷却类型的。在这个设计中矿物油通过油泵不仅流进外部冷却设备(空气或水热交换器),而且流过内部最靠近热源的凹槽。因此通过矿物油对热量进行转移的方式要比一般的自冷装置和风冷装置要有效的多,因为油是允许通过对流循环的。当油空气热交换器(在每个散热器有一组风机)被使用时,这种冷却类型被指定为FOA。当油水热交换器被使用时,则被称为FOW。因为无论变压器是采用何种液体都是不受欢迎的,即使这种液体不易燃,所以干式变压器得到普遍的应用。通风式的干式变压器通常是通过自然风来使变压器冷却的,所以这种变压器不适于潮湿和恶劣的环境。如果铁芯和线圈是在一个充满绝缘
42、气体的封闭装置中则干式变压器在潮湿恶劣环境中是完全可以正常运行的的。干式变压器是完全不燃烧的,因为它使用了有机材料如环氧树脂。外文文献三:Circuit BreaksWithin a few years of the introduction of the fuse,the growing electrical industry startedlooking for an alternative method of providing protection for electric circuitsThey wanted a device that would not be destroyed
43、 by its operation,that could simply be reset to restore power, and that could also be used as a means of switching for the circuitOut of this development work came the circuit breakerwhich is an electromechanical deviceThe circuit breaker is defined as a device designed to open and close a circuit b
44、y non-automatic means and to open the circuit automatically on a predetermined over-current without injure to itself when properly applied within its rating. As with other equipment,circuit breakers are divided into those rated for 1 000 volts and less and those rated for more than 1000 voltsLow-vol
45、tage circuit breakers were also divided into two distinct categories,molded-case and power typesHowever,in the past few years the distinction between these two types has become less clea-cut as a new type of encased breaker are universally operated in air, so it is not necessary to designate them as
46、 air circuit breakers as this understoodMedium and highvoltage breakers,on the other hand,use mediums other than air in which to open the circuit and therefore must be designated as being air, gas,and so on Apart from having different voltage and continuous current ratingsbreakers have widely differ
47、ent interrupting ratings,response characteristics,and methods of operationThe proper application of circuit breakers requires a good knowledge of all the characteristics and options available for each typeThe simplest circuitopening device is the manually operated knife switchThis switch has the bas
48、ic parts required of any circuitopening device:a fixed contact, a moving,an operating handle,and a baseplate or flameHowever as anyone who has opened a knife switch under load has witnessed,there is a luminous discharge drawn between the separating contacts of the switchThis discharge is called an a
49、rc,and it consists of a stream of positive and negative ions. The current flowing in a circuit cannot be instantaneously interruptedAs a result,the arc continues until the switch contacts have separated far enough to finally extinguish the arcThe arc can make the opening of the switch very unsafe and unre