电气工程及其自动化专业英语(2)

1、电气工程及其自动化专业教研室电气工程及其自动化专业教研室 电气工程及其自动化专业英语电气工程及其自动化专业英语 Specialized English for Electrical Engineering Its Automation 戴文进戴文进 主主 编编 杨植新杨植新 副主编副主编电气工程及其自动化专业教研室电气工程及其自动化专业教研室Part 2 Electric Machinery Unit 11 The Transformer on No Load Unit 13 Construction and Application of D.C. Machines Unit 16 Three

2、-Phase Induction (Asynchronous) Machine with the Rotor at Standstill Unit 19 Armature Reaction of Salient-Pole Synchronous Machine a Two-Reaction Theory 电气工程及其自动化专业教研室电气工程及其自动化专业教研室Unit 11 The Transformer on No Load-Specialized English Words in close proximity (to) 紧密耦合 permeability 磁导率 magnetizing

3、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 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 饱和电气工程及其自动化专业教研室电气工程及其自动化专业教研室Unit 11 The Transformer on No Load The Simple Two

4、-Coil Transformer The transformer is a straightforward application of Faradays Law of Electromagnetic Induction. The simple transformer consists 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 cur

5、rent (随时间交变随时间交变）. The other coil is linked by （与与-交链交链）most of this flux and thus has a mutually induced e.m.f. of value e2=N2d21/dt. This e.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

6、magnetic field（磁场媒介磁场媒介） from coil 1 to coil 2. 电气工程及其自动化专业教研室电气工程及其自动化专业教研室 The transformation could be from any convenient input voltage to any convenient output voltage. This apparently simple function of the transformer makes it as vital to modern industry as the gear train which, as a “transfor

7、mer” of speed and torque represents an interesting analogy（句子的主语是句子的主语是“function”，谓语为谓语为“make”，“as vitalas”意为意为“与与一样重要一样重要”，“which”引导一个定引导一个定语从句语从句“which represents an interesting analogy as atransformerof speed and torque”，修饰修饰“gear train”，意意为为“齿轮箱与变压器表现出一种有趣的相似，齿轮箱被称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

8、速度和转矩的变换器变换器。” The coils would be on an iron core (铁芯铁芯）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 r . 电气工程及其自动化专业教研室电气工程及其自动化专业教研室 The exciting or magnetizing current （励磁电流励磁电流）can

9、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 linking the N2 turns, is a much smaller fraction of the tota

10、l, making for(有助于有助于,倾向于倾向于) more efficient energy transfer. The mutual flux would be a much larger percentage of the total and the flux pattern (磁力线图磁力线图)would be rather more involved(复杂的复杂的), but simplified diagrams of this kind are quite adequate for the understanding of the principles to be disc

11、ussed in this chapter. The exciting coil which initiates (激励激励)the flux changes is called the primary winding, and the coupled coil which receives energy as a result (因此因此), is called the secondary winding.电气工程及其自动化专业教研室电气工程及其自动化专业教研室 It should not be difficult to realize that the two functions are

12、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 winding 1 exc

13、ited, the primary e.m.f. would be equal to N1d 11/dt. This is practically in phase opposition to (与与-反反相相)the applied terminal voltage V1 and limits the current to a very much smaller value than V1/R1, where R1 is the primary resistance(原边电阻原边电阻). As explained later, the resistance drop is normally

14、very small so that the back e.m.f. is virtually equal in magnitude to V1.电气工程及其自动化专业教研室电气工程及其自动化专业教研室 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

15、 producing 11 which rises and falls with it in time phase. It is therefore in quadrature with (与与-正交正交)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 componen

16、ts of flux linking N1 (与与N1交链的磁通交链的磁通)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(磁势磁势).电气工程及其自动化专业教研室电气工程及其自动化专业教研

17、室 The phase of component 1 is unchanged, however, since 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

18、primary current providing(=provided) the iron path is not greatly saturated(饱和饱和). The e.m.f. N1d 1/dt may thus be treated as if it were due to an unsaturated inductance of magnitude N121. The corresponding leakage reactance is a dominant factor in transformer behavior(characteristic). For the iron-

19、cored transformer which will form the subject of this chapter, 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(互感磁通互感磁通).电气工程及其自动化专业教研室电气工程及其自动化专业教研室 The first one will normally be treated in terms of

20、the voltage drop required to sustain the current. This is equal to +N1d 1/dt, or vectorially for frequency f it is given by j L1I1 =jX1I1which is a voltage leading the current by 90(领先电流领先电流90度度). The second component is due to the mutual flux and is represented by a vector E1, lagging 90behind the

21、flux (滞后磁通滞后磁通90度度)time vector. This too could be treated as a voltage drop jMI1N1/N2=jXmI1=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 windi

22、ng open circuited, the no-load condition. Allowance has been made for the iron losses (对铁耗损进行补对铁耗损进行补偿偿)which require a power component of current Ip.电气工程及其自动化专业教研室电气工程及其自动化专业教研室 This is drawn in phase with E1, the component of applied voltage necessary to sustain +E1. E1Ip is the iron loss in watts

23、. 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 made 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 asm and is equal to21 o

24、n no load. When the secondary carries current, I1 increases from I0;m is then due to the combined effect of primary and secondary ampere-turns, but is little changed from21. Consequently the magnetizing and power requirements of the flux are nearly constant so that I0 can be regarded as a substantia

25、lly constant component of I1 at any load.电气工程及其自动化专业教研室电气工程及其自动化专业教研室 It will be noticed from the diagram that since the e.m.f.s E1 and E2 are due to the same flux m, the voltage ratio E1/E2 is the same as the turns ratio N1/N2. In fact, on no load （空载时空载时）, the impedance drops I0R1 and I0X1 are so

26、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 transformed to (变换成变换成）any other voltage E2 by suitable choice of primary and secondary turns（通过适当的选择原副边匝数）通过适当的选择原副边匝数）. On load（负载时负载时）, the voltage at

27、the secondary terminals V 2 is measurably（obviously） different from （显著地不同于显著地不同于）E2 .电气工程及其自动化专业教研室电气工程及其自动化专业教研室The Circuit Equation for the Transformer on No Load From the vector diagram, and in accordance with circuit principle, we have Further, it shows the current split into components in phas

28、e 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 phase relationships. This figure can therefore be used to represent the transformer on no load; it is a

29、n equivalent circuit for this condition. The value of the magnetizing reactance xm depends on the saturation level(饱和程度饱和程度). The voltage drop across it is E1=jxmIm and it has already been pointed out that M is not constant with flux.100111VEI Rj I X 电气工程及其自动化专业教研室电气工程及其自动化专业教研室 However, the normal

30、operation of power transformers is at constant voltage and frequency so the peak value of fluxm is substantially unchanged with load. A value of xm corresponds to the average slope(斜率斜率) of the flux /current curve. The equivalent circuit could then be regarded as having constant parameters, the valu

31、es 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 respects (在某些方面在某些方面) and cannot be used to (用来用来)draw general

32、conclusions(得出一般的结论得出一般的结论). Though suitable for dealing with particular aspects of a problem involving saturation(饱和问题饱和问题), they are neither unique (only one of its kind) nor universal solutions.电气工程及其自动化专业教研室电气工程及其自动化专业教研室 It is important to realize the relative magnitudes of the various voltages

33、 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(没有过度饱和没有过度饱和). The high permeability of the magnetic circuit under these conditions, together with other design considerations, result

34、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. 22011()IRX电气工程及其自动化专业教研室电气工程及其自动化专业教研室 when the tran

35、sformer is fully loaded (额定运行额定运行)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 sub

36、stantially (largely) constant with 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 sint电气工程及其自动化专业教

37、研室电气工程及其自动化专业教研室 where m is the maximum value reached in the cycle. The induced e.m.f. is thus e= -Ndm/dt=-N m cost which 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)(有效值有效值). value is Applying above equation to the two coil

38、s:the primary e.m.f. due to mutual flux=4.44 fN1 m =E1 ;the secondary e.m.f. due to mutual flux =4.44 fN2 m =E2(1/2) 24.44mmffNNote: in each case (在每种情况下在每种情况下)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 vecto

39、rially(用矢量表示的用矢量表示的).电气工程及其自动化专业教研室电气工程及其自动化专业教研室 The instantaneous value e2 is shown in phase with e1 since this corresponds 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

40、closed, e2 would drive a current whose magnetic action would oppose the flux change by producing the induced current. This is in accordance with (符合符合)Lenzs law. The terminal marking A1 and a1 indicate cophasal potential variations. Obviously, the phase of e2 relative to the external secondary circu

41、it could be reversed by crossing over (交换交换）the connections. The applied voltage V1 is shown equal and opposite to e1 which is virtually true on no load.电气工程及其自动化专业教研室电气工程及其自动化专业教研室3词量的变化词量的变化 1 增词增词: 即增加原文中虽无其形但有其意的词汇即增加原文中虽无其形但有其意的词汇,或从词汇或从词汇要求要求,语法要求语法要求,逻辑要求和修辞要求等几个方面来考虑逻辑要求和修辞要求等几个方面来考虑. Electr

42、onics is the science of the electrons 电子学是电子学是研究研究电子的电子的一门一门科学科学. Having a lot of advantages, this imported foreign DC machine will eventually be displaced by home-made one. 尽管尽管这台国外进口直流电机有很多优点这台国外进口直流电机有很多优点,但它总有一天会但它总有一天会被国产直流电机取代被国产直流电机取代. It will be seen that the processes above involve a change

43、 in either the magnitude or the direction of the current of the surge arrester。 能够预见能够预见，上述过程不是涉及，上述过程不是涉及避雷针避雷针电流大小的变化，就电流大小的变化，就是涉及其方向的是涉及其方向的变化变化. 电气工程及其自动化专业教研室电气工程及其自动化专业教研室 2重复重复 It is called classical one if control theory is based on input-output relationships；modern one if control theory is

44、 based on direct use of the differential equations themselves。 如果控制理论是基于输入输出关系如果控制理论是基于输入输出关系,叫做古典控制理论叫做古典控制理论,如果如果控制理论是基于直接使用微分方程本身控制理论是基于直接使用微分方程本身,则叫做现代则叫做现代控制理论控制理论. 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你能大致给出这个电源装置的静态特性特性和

45、动态特性吗和动态特性吗? 3减词减词 In the past，to fly to the moon was out of the question。 过去飞往月球是不可能的事情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现在飞往月球是不成问题的.电气工程及其自动化专业教研室电气工程及其自动化专业教研室 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我厂生产

46、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参考价值. Because heat does not take up any room and it does not weigh anything, it is not material. 热不占有任何空间热不占有任何空间,也没有什么重量也没有什么重量,因此它不是物质因此它不是物质. There ar

47、e two kinds of new theories at present, neural network and wavelet ones, which are used in signal processing. 目前有两种新理论目前有两种新理论,即神经网络理论和小波理论即神经网络理论和小波理论,它们都能用它们都能用于信号处理于信号处理.电气工程及其自动化专业教研室电气工程及其自动化专业教研室 end shield （电机定子的）端盖（电机定子的）端盖 terminal box 出线盒出线盒 cast steel 铸钢铸钢 film of vanish 漆膜漆膜 wedge 槽楔槽楔 s

48、ilicon controlled rectifiers (SCRs)可控硅整流器可控硅整流器 cumulatively compounded self-excited machine 积复励自励积复励自励电机电机 brush holder 刷把刷把 cast iron 生铁生铁 ferromagnetic 铁磁性的铁磁性的 oxide coating 氧化层氧化层 centrifugal force 离心力离心力 cut-and-dried 不大会改变的，固定模式的不大会改变的，固定模式的Unit 13 Construction and Application of D.C. Machine

49、s电气工程及其自动化专业教研室电气工程及其自动化专业教研室Unit 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 （轭部轭部）inside a frame; excitation pol

50、es and winding; commutating poles（换向极换向极） (compoles) and winding; end shield （端盖端盖）with ball or sliding bearings（滑动轴承滑动轴承）; brushes and brush holders（刷握刷握）; the terminal box（接线盒接线盒）. 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

51、 has uniformly (均匀地均匀地）spaced slots into which the armature winding （电枢绕组电枢绕组）is fitted. A commutator（换向器换向器）, and often a fan, are also located on the machine shaft.电气工程及其自动化专业教研室电气工程及其自动化专业教研室 The frame（机座机座） is fixed to the floor by means of a bedplate and bolts. On low-power machines the frame a

52、nd yoke are one and the same components, through which the magnetic flux produced by the excitation poles （磁极产生的磁通磁极产生的磁通）closes（闭合）. The frame and the yoke are built of cast iron or cast steel or sometimes from welded steel plates（焊接钢板焊接钢板）. In low-power and controlled rectifier-supplied machines t

53、he yoke is built up of thin (0.51mm) laminated iron sheets（硅钢叠片）。（硅钢叠片）。 The yoke is usually mounted inside a non-ferromagnetic （非铁磁非铁磁）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 be

54、arings. 电气工程及其自动化专业教研室电气工程及其自动化专业教研室 The (main) excitation poles are built from 0.51mm iron sheets held together by riveted bolts. The poles are fixed into the frame by means of bolts. They support the windings carrying the excitation current. On the rotor side, at the end of the pole core is the so

55、-called pole-shoe which is meant to facilitate a given distribution of the magnetic flux through the air gap. The winding is placed inside an insulated core mounted on the frame（安装在机座上的铁心）（安装在机座上的铁心）, and secured by the pole-shoe. The excitation windings（励磁绕组励磁绕组） are made of insulated round or rect

56、angular （矩形矩形）conductors, and are connected either in series or in parallel. 电气工程及其自动化专业教研室电气工程及其自动化专业教研室 The windings are linked in such a way that the magnetic flux of one pole crossing the air gap is directed from the pole-shoe towards the armature (north pole), and the flux of the next pole is d

57、irected from the armature to the pole-shoe (south pole). The commutating poles, like the main poles, consist of a core ending in the pole-shoe and a winding wound round the core. They are located on the symmetry (neutral) axis between two main poles, and bolted on the yoke. Commutating poles are bui

58、lt either of cast-iron or iron sheets. The windings of the commutating poles are also made from insulated round or rectangular conductors. They are connected either in series or in parallel and carry the machines main current（armature current）.电气工程及其自动化专业教研室电气工程及其自动化专业教研室 The rotor core is built of

59、0.51mm silicon-alloy sheets. The sheets are insulated from one another by a thin film of varnish or by an oxide coating, both some 0.030.05mm thick. The purpose is to ensure a reduction of the eddy currents （涡流涡流）which arise in the core when it rotates inside the magnetic field. These currents cause

60、 energy losses which turn into heat. In solid cores（实心铁芯）（实心铁芯）, these losses could become very high, reducing machine efficiency and producing intense（过多的过多的） heating. The rotor core consists of a few packets of metal sheet. Redial or axial cooling ducts （径向或轴向通风道径向或轴向通风道）(810mm inside) are inserte