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 ： 2009081102 指导教师： 陈红艳 翻译日期： 2013.6.30 山东建筑大学毕业设计外文文献及翻译 外文文献 一 ： Transformer One of the most valuable
2、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
3、 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 lines This transmission voltage level is then stepped down in ma
4、ny 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 conduction Its usual function is to transfer energy between circuits of different voltage A trans
5、former has a magnetic core on which there are two or more windings These windings are insulated from each other and from ground In autotransformers， however， the windings are connected together The assembly of core and coils is normally insulated and cooled by immersion in mineral oil or other suita
6、ble 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 voltag
7、es When 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 windings At rated load, this drop is known as the voltage regulation. The amount of voltage drop varies with the p
8、ower 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 山东建筑大学毕业设计外文文献及翻译 for two reasons to compensate for varying vol
9、tage drop in the system and to assure that the transformer operates as nearly as possible at the correct core density For 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 chan
10、ged only infrequently, because of load growth or some seasonal change The 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 It seldom makes muc
11、h 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 equipment High voltage and high current applications require special consid
12、erations 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 use of autotransformers affords cost savi
13、ngs 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 increased its use Most autotransformers are Y-connected， and it has been a standard Ameri
14、can practice to add a low capacity, delta winding This 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 system It also helps to stabilize the n
15、eutral and to ground the system better In 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 the other This 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.
