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
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学 号： **********
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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 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，which is most desirable economically．Stepping 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 loss and increa the transmission capacity of the lines．This transmission voltage level is then stepped down in many stages for distribution and utilization purpos．
A transformer is a static device for transferring electric energy from one circuit to another electromagnetically，that is，by induction instead of by conduction．Its usual function is to transfer energy between circuits of different voltage．A transformer has a magnetic core on which there are two or more windings．The windings are insulated from each other and from ground．In autotransformers，however，the windings are connected together．The asmbly of core and coils is normally insulated and cooled by immersion in mineral oil or other suitable liquid within an enclosing tank．Connection 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 windings．This is known as the “turn ratio” and it is the ratio of the no-load voltages．When the unit is carrying load, the ratio of the actual voltages is slightly different becau of the drop caud by the flow of 1oad current through the impedance of the transformer windings．At 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 constant．
Practically all power transformers and many distribution transformers have taps in one or more windings for changing the turn ratio．Changing 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 at the correct core density．For the latter purpo, the taps should be in the winding subject to the voltage variation. De-energized tap changers are ud when it is expected that the ratio will need to be changed only infrequently, becau of load growth or some asonal change．The desired tap is lected by means of a ratio adjuster(no load taps)．Load tap changer(LTC)is ud when changes in ratio may be frequent or when it is undesirable to de-energize the transformer to change a tap．It ldom makes much difference to the ur 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 equipment．High voltage and high current applications require special considerations to arrive at an optimum location for the LTC equipment．Step down units usually have LTC in the low-voltage winding and de-energized taps in the high voltage winding．
When energy is to be transferred between two circuits of nearly the same voltage．The u of autotransformers affords cost savings over two-winding units．The nearer the voltages are to each other, the smaller will be the autotransformer per kilovolt-ampere of output，and the greater the savings．The simplicity of phasing out systems has incread its u．Most autotransformers are Y-connected，and it has been a standard American practice to add a low capacity, delta winding．This is frequently referred to as a “delta tertiary“．Its primary purpo has been to provide an internal path for the third harmonic currents (required for excitation)，thus reducing tho currents on the power system．It also helps to stabilize the neutral and to ground the system better．In recent years，the u of shielded telephone cable has reduced the requirements for the delta tertiary. Becau an autotransformer does not afford electrical paration between the two circuits, disturbances originating on one circuit can be communicated to the other．This difficulty is minimized by solidly grounding the neutral of the autotransformer. Solidly grounding the neutral，however, caus(among other things)current of short-circuit magnitude to flow through the delta-connected tertiary winding during ground faults on eit
her system. Autotransformers are not inherently lf-protecting and, therefore，all windings must be examined for mechanical strength as applied to the system where they will be ud . Tertiaries are normally 35％of the physical size of the largest winding of the autotransformer, unless otherwi specified by the ur.
The bulk of a11 transformers，except for large extra-high voltage(EHV)and distribution units are three-pha units． In the early days of the industry，It was almost universal practice in the United States to u three single-pha units connected in a three-pha bank．Insulation clearances and shipping limitations for certain large EHV units now require this design．The distribution systems rve mainly single-pha loads in residential areas and are rved from single-pha 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。
