1、 电气工程及其自动化专业英语Specialized English for Electrical Engineering Its Automation戴文进 主 编杨植新 副主编Part 2 Electric Machinery Unit 11 The Transformer on No Load Unit 13 Construction and Application of D.C. Machines Unit 16 Three-Phase Induction (Asynchronous) Machine with the Rotor at Standstill Unit 19 Armatu
2、re Reaction of Salient-Pole Synchronous Machine a Two-Reaction Theory Unit 11 The Transformer on No Load-Specialized English Words in close proximity (to) 紧密耦合 permeability 磁导率 magnetizing current 激磁电流 power component of current 电流的有功分量 sinusoidal variations 正弦变量 a mutually induced e.m.f. 互感电动势 the
3、applied voltage 外施电压 zero-power-factor 零功率因数 the no-load power factor 空载功率因数 formulate 用公式表示 ,系统地阐述 saturation 饱和Unit 11 The Transformer on No Load The Simple Two-Coil TransformerThe transformer is a straightforward application of Faradays Law of Electromagnetic Induction. The simple transformer con
4、sists of two coils in close proximity. One coil of N1 turns is excited with alternating current and therefore establishes a flux 11 which alternates with the current (随时间交变 ） . The other coil is linked by （ 与 -交链 ） most of this flux and thus has a mutually induced e.m.f. of value e2= N2d21/dt.This e
5、.m.f. would drive a load current through any circuit connected to the terminals of the second coil. Energy would then be transferred through the medium of the magnetic field（ 磁场媒介 ） from coil 1 to coil 2. The transformation could be from any convenient input voltage to any convenient output voltage.
6、 This apparently simple function of the transformer makes it as vital to modern industry as the gear train which, as a “transformer” of speed and torque represents an interesting analogy（ 句子的主语是 “function”， 谓语为 “make”， “as vitalas” 意为 “与 一样重要 ”， “which”引导一个定语从句“which represents an interesting analog
7、y as atransformerof speed and torque”， 修饰 “gear train”， 意为 “齿轮箱与变压器表现出一种有趣的相似，齿轮箱被称为速度和转矩的 变换器 。 ” The coils would be on an iron core (铁芯 ） and so at the cost of introducing iron losses, the value of flux per ampere is increased several hundred times because of the change of permeability from 0 to 0
8、 r . The exciting or magnetizing current （ 励磁电流 ） can thus be very small. Further, the proportion of the total flux which is linked mutually by the two coils is greatly increased. Looked at another way, the leakage flux 1 which links N1 turns alone and “leaks” between the two windings without linkin
9、g the N2 turns, is a much smaller fraction of the total, making for(有助于 ,倾向于 ) more efficient energy transfer. The mutual flux would be a much larger percentage of the total and the flux pattern (磁力线图 )would be rather more involved(复杂的 ), but simplified diagrams of this kind are quite adequate for t
10、he understanding of the principles to be discussed in this chapter. The exciting coil which initiates (激励 )the flux changes is called the primary winding, and the coupled coil which receives energy as a result (因此 ), is called the secondary winding. It should not be difficult to realize that the two
11、 functions are interchangeable: if coil 2 were excited instead, a mutual e.m.f. would be induced in coil 1 which would then become the secondary winding(二次绕组 ). It should be obvious that since the primary winding also experiences flux changes, there is a primary e.m.f. self-induced this time. With w
12、inding 1 excited, the primary e.m.f. would be equal to N1d 11/dt. This is practically in phase opposition to (与 -反相)the applied terminal voltage V1 and limits the current to a very much smaller value than V1/R1, where R1 is the primary resistance(原边电阻 ). As explained later, the resistance drop is no
13、rmally very small so that the back e.m.f. is virtually equal in magnitude to V1. If the applied voltage is alternating sinusoidally at frequency f=/2 Hz, a vector diagram can be drawn, and for an air-core transformer, neglecting resistance. As shown I1 is the magnetizing current producing 11 which r
14、ises and falls with it in time phase. It is therefore in quadrature with (与 -正交 )V1 and the circuit is a zero-power-factor lagging load. With the secondary circuit open, the primary coil is an inductor whose voltage drop is +N1d 11/dt or in vector form=j L11I1. The two components of flux linking N1
15、(与 N1交链的磁通 )are shown and though I1 is in phase with both of them,it will be found that when the secondary is carrying current, the mutual flux is no longer in phase with the primary current due to the reaction of the secondary ampere-turns(磁势 ). The phase of component 1 is unchanged, however, since
16、 it is produced by primary current alone and is therefore in phase with it. Further, even with an iron core the reluctance offered to 1 is still predominantly due to its path in air so that the leakage flux remains virtually proportional to the primary current providing(=provided) the iron path is n
17、ot greatly saturated(饱和 ). The e.m.f. N1d 1/dt may thus be treated as if it were due to an unsaturated inductance of magnitude N12 1. The corresponding leakage reactance is a dominant factor in transformer behavior(characteristic). For the iron-cored transformer which will form the subject of this c
18、hapter, the total back e.m.f. of the primary, N1d 11/dt, will be considered in two components, the one due to leakage and the other due to the mutual flux(互感磁通 ). The first one will normally be treated in terms of the voltage drop required to sustain the current. This is equal to +N1d 1/dt, or vecto
19、rially for frequency f it is given by j L1I1 =jX1I1which is a voltage leading the current by 90(领先电流 90度 ). The second component is due to the mutual flux and is represented by a vector E1, lagging 90behind the flux (滞后磁通 90度 )time vector. This too could be treated as a voltage drop jMI1N1/N2=jXmI1=
20、 E1, but the mutual flux is in iron, subject to permeability changes and so the mutual inductance M varies with the flux level. Here is the vector diagram for an iron-cored transformer with its secondary winding open circuited, the no-load condition. Allowance has been made for the iron losses (对铁耗损
21、进行补偿)which require a power component of current Ip. This is drawn in phase with E1, the component of applied voltage necessary to sustain +E1. E1Ip is the iron loss in watts. The ampere-turns required to produce the flux are given by ImN1 so that on no load the primary takes a current I0 which is ma
22、de up of the two components Im and Ip. In practice Ip is very much smaller than Im and the no-load power factor is very low. The mutual flux is shown as m and is equal to 21 on no load. When the secondary carries current, I1 increases from I0;m is then due to the combined effect of primary and secon
23、dary ampere-turns, but is little changed from 21. Consequently the magnetizing and power requirements of the flux are nearly constant so that I0 can be regarded as a substantially constant component of I1 at any load. It will be noticed from the diagram that since the e.m.f.s E1 and E2 are due to th
24、e same flux m, the voltage ratio E1/E2 is the same as the turns ratio N1/N2. In fact, on no load （ 空载时 ） , the impedance drops I0R1 and I0X1 are so small that V1 is virtually the same magnitude as E1 and the turns ratio is equal to the no-load voltage ratio V 1/E2. Thus any voltage V 1 can be transf
25、ormed to (变换成 ） any other voltage E2 by suitable choice of primary and secondary turns（ 通过适当的选择原副边匝数） . On load（ 负载时 ） , the voltage at the secondary terminals V 2 is measurably（obviously） different from （ 显著地不同于 ） E2 .The Circuit Equation for the Transformer on No Load From the vector diagram, and
26、in accordance with circuit principle, we haveFurther, it shows the current split into components in phase and in quadrature with E1. The quadrature component Im flows through a pure reactance Xm and the in-phase component Ip flows through a pure resistance rm, thus giving the correct voltage/current
27、 phase relationships. This figure can therefore be used to represent the transformer on no load; it is an equivalent circuit for this condition. The value of the magnetizing reactance xm depends on the saturation level(饱和程度 ). The voltage drop across it is E1=jxmIm and it has already been pointed ou
28、t that M is not constant with flux. However, the normal operation of power transformers is at constant voltage and frequency so the peak value of flux m is substantially unchanged with load. A value of xm corresponds to the average slope(斜率 ) of the flux /current curve. The equivalent circuit could
29、then be regarded as having constant parameters, the values being determined by calculation or by test. It should be stressed here that any techniques described in the book which attempt to get a linear equivalent for a non-linear saturated circuit are inevitably deficient (imperfect) in some respect
30、s (在某些方面 ) and cannot be used to (用来 )draw general conclusions(得出一般的结论 ). Though suitable for dealing with particular aspects of a problem involving saturation(饱和问题 ), they are neither unique (only one of its kind) nor universal solutions. It is important to realize the relative magnitudes of the va
31、rious voltages in the circuit. A transformer is so designed that a mutual flux, sufficient to produce a voltage equal to that of the supply V1 is reached without undue saturation(没有过度饱和 ). The high permeability of the magnetic circuit under these conditions, together with other design considerations
32、, result in a no-load leakage impedance drop which is negligible by comparison with E1. The voltage drop vectors have thus been greatly exaggerated in order to demonstrate their phase relationship clearly and in practice, X1 may be very much larger than R. when the transformer is fully loaded (额定运行
33、)and the primary current increases from I to twentyfold or more, the voltage drop in the primary leakage impedance may be perhaps 3% of V1 in the normal transformer. Even then, however, flux will be little changed from the no-load condition. Im and Ip in turn are substantially (largely) constant wit
34、h load.The Transformer E.M.F. EquationThe induced e.m.f. due to mutual flux, -Ndm/dt, is conveniently formulated in a different way to deal with the special case of sinusoidal variations. The instantaneous value of flux may then be expressed as: m= m sin t where m is the maximum value reached in the
35、 cycle. The induced e.m.f. is thuse = -Ndm/dt=-N m costwhich is another sine wave lagging m by 90. The peak value of this e.m.f. is 2fNm .since =2f and the r(root).m(mean).s(square)(有效值 ). value is Applying above equation to the two coils:the primary e.m.f. due to mutual flux =4.44 fN1 m =E1 ;the se
36、condary e.m.f. due to mutual flux =4.44 fN2 m =E2Note: in each case (在每种情况下 )that the maximum value of mutual flux must be used. There are the flux and the two e.m.f. waves in a relationship already demonstrated vectorially(用矢量表示的 ). The instantaneous value e2 is shown in phase with e1 since this co
37、rresponds to its relationship with m . With the coils wound round the core in the same direction, the top ends must be positive at the same instant since if the secondary circuit were closed, e2 would drive a current whose magnetic action would oppose the flux change by producing the induced current
38、. This is in accordance with (符合 )Lenzs law. The terminal marking A1 and a1 indicate cophasal potential variations. Obviously, the phase of e2 relative to the external secondary circuit could be reversed by crossing over (交换 ） the connections. The applied voltage V1 is shown equal and opposite to e1
39、 which is virtually true on no load.3词量的变化 1 增词 : 即增加原文中虽无其形但有其意的词汇 ,或从词汇要求 ,语法要求 ,逻辑要求和修辞要求等几个方面来考虑 .Electronics is the science of the electrons电子学是 研究 电子的 一门 科学 .Having a lot of advantages, this imported foreign DC machine will eventually be displaced by home-made one.尽管 这台国外进口直流电机有很多优点 ,但它总有一天会被国
40、产直流电机取代 .It will be seen that the processes above involve a change in either the magnitude or the direction of the current of the surge arrester。能够预见 ，上述过程不是涉及 避雷针 电流大小的变化，就是涉及其方向的 变化 . 2重复It is called classical one if control theory is based on input-output relationships； modern one if control theo
41、ry is based on direct use of the differential equations themselves。如果控制理论是基于输入输出关系 ,叫做古典控制理论 ,如果控制理论是基于直接使用微分方程本身 ,则叫做现代 控制理论 .Can you roughly give the static and dynamic characteristics about this power supply apparatus？你能大致给出这个电源装置的静态 特性 和动态特性吗 ? 3减词In the past， to fly to the moon was out of the q
42、uestion。过去飞往月球是不可能的事情 .In these days， to fly to the moon is out of question。现在飞往月球是不成问题的 . The TV sets produced by our factory are good in quality and low in price. 我厂生产的电视机物美价廉 .The paper on computer control technology is thought of considerable value for reference. 这篇有关计算机控制技术的论文被认为有相当大的 参考价值 .Bec
43、ause heat does not take up any room and it does not weigh anything, it is not material. 热不占有任何空间 ,也没有什么重量 ,因此它不是物质 .There are two kinds of new theories at present, neural network and wavelet ones, which are used in signal processing. 目前有两种新理论 ,即神经网络理论和小波理论 ,它们都能用于信号处理 . end shield （电机定子的）端盖 terminal
44、 box 出线盒 cast steel 铸钢 film of vanish 漆膜 wedge 槽楔 silicon controlled rectifiers (SCRs)可控硅整流器 cumulatively compounded self-excited machine 积复励自励电机 brush holder 刷把 cast iron 生铁 ferromagnetic 铁磁性的 oxide coating 氧化层 centrifugal force 离心力 cut-and-dried 不大会改变的，固定模式的Unit 13 Construction and Application of
45、D.C. MachinesUnit 13 Construction and Principle of D.C. Machines Construction of D.C. Machines A D.C. machine is made up of two basic components: The stator which is the stationary part of the machine. It consists of the following elements: a yoke （ 轭部 ） inside a frame; excitation poles and winding;
46、 commutating poles（ 换向极 ） (compoles) and winding; end shield （ 端盖 ） with ball or sliding bearings（ 滑动轴承 ） ; brushes and brush holders（ 刷握 ） ; the terminal box（ 接线盒 ） . The rotor which is the moving part of the machine. It is made up of a core mounted on the machine shaft（轴） . This core has uniformly
47、 (均匀地 ） spaced slots into which the armature winding （ 电枢绕组 ） is fitted. A commutator（ 换向器 ） , and often a fan, are also located on the machine shaft. The frame（ 机座 ） is fixed to the floor by means of a bedplate and bolts. On low-power machines the frame and yoke are one and the same components, thr
48、ough which the magnetic flux produced by the excitation poles （ 磁极产生的磁通 ） closes（闭合） . The frame and the yoke are built of cast iron or cast steel or sometimes from welded steel plates（ 焊接钢板 ） . In low-power and controlled rectifier-supplied machines the yoke is built up of thin (0.5 1mm) laminated iron sheets（硅钢叠片）。 The yoke is usually mounted inside a non-ferromagnetic （ 非铁磁） frame (usually made of aluminum alloys, to keep down the weight). To either side of the frame there are bolted two end shields, which contain the ball or sliding bearings. The (main) excitation poles are built fr
