电气毕业设计外文翻译(共5页)

1、精选优质文档-倾情为你奉上Transformer One of the most valuable apparatus in electric power system is the transformer, 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

2、，which is most desirable economicallyStepping up of this generated voltage to high voltage，extra-high 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 transmi

3、ssion voltage level is then stepped down in many stages for distribution and utilization purposes A transformer 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 be

4、tween circuits of different voltageA transformer has a magnetic core on which there are two or more windingsThese 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 im

5、mersion in mineral oil or other suitable liquid within an enclosing tankConnection to the windings is 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 i

6、s the ratio of the no-load voltagesWhen the unit is carrying load, the ratio of the actual voltages is 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". T

7、he amount of voltage drop varies with the power factor of the output even when the kilovolt-amperes remain constantPractically 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 com

8、pensate for varying voltage drop in the system and to assure that the transformer operates as nearly as possible 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 rati

9、o will need to be changed only infrequently, because of load growth or some seasonal changeThe desired tap is selected 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 tap

10、It seldom makes much difference to the user which winding or windings are tapped；therefore，the choice is usually 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 requir

11、e special considerations to arrive at an optimum location for the LTC equipmentStep down units usually have LTC in 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 affo

12、rds cost savings over two-winding unitsThe nearer the voltages are to each other, the smaller will be the autotransformer 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 standa

13、rd American practice to add a low capacity, delta windingThis is frequently referred to as a “delta tertiary“Its 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 t

14、he neutral and to ground the system betterIn recent years，the use of shielded telephone cable has reduced the requirements 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

15、 the otherThis difficulty is minimized by solidly grounding the neutral of the autotransformer. Solidly grounding 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. Autotransfor

16、mers are not inherently self-protecting and, therefore，all windings must be examined for mechanical strength as applied 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 bul

17、k of a11 transformers，except for large extra-high voltage(EHV)and distribution units are three-phase units In the 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 limitat

18、ions for certain large EHV units now require this designThe distribution systems serve mainly single-phase loads in residential areas and are served from single-phase transformers中文译文： 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

19、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。

20、“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