电气工程及其自动化专业英语课件

1、 电气工程及其自动化专业英语 Specialized English for Electrical Engineering Its Automation ContentsPart 1 Electrics and ElectronicsPart 2 Electric Machinery Part 3 Electrical Engineering Part 4 Modern Computer Control Techniques ContentsPart 1 Electrics anUnit 1 Specialized English Wordscircuit components 电路元件 ci

2、rcuit parameters 电路参数the dielectric 电介质 storage battery 蓄电池electric circuit 电路 wire导线electrical device 电气设备 electric energy 电能energy source 电源 primary cell 原生电池secondary cell 再生电池 energy converter 电能转换器e.m.f.electromotive force 电动势 unidirectional current 单方向电流circuit diagram 电路图 load characteristic

3、负载特性terminal voltage 端电压 external characteristic 外特性Conductor 导体 load resistance 负载电阻generator 发电机 heating appliance 电热器direct-current(D.C.) circuit 直流电路 magnetic and electric field 电磁场time-invariant 时不变的 self-(or mutual-)induction 自（互）感displacement current 位移电流 voltage drop 电压降 conductance 电导 volt-

4、ampere characteristics 伏安特性metal-filament lamp 金属丝灯泡 carbon-filament lamp 碳丝灯泡non-linear characteristics 非线性特性Unit 1 Specialized English WorUnit 1 Circuit Elements and ParametersAn electric circuit (or network) is an interconnection of physical electrical devices. The purpose of electric circuits is

5、 to distribute and convert energy into some other forms. Accordingly, the basic circuit components are an energy source (or sources), an energy converter (or converters) and conductors connecting them（连接它们的）.An energy source (a primary or secondary cell, a generator and the like) converts chemical,

6、mechanical, thermal or some other forms of energy into （将-转换成-）electric energy. An energy converter, also called load (such as a lamp, heating appliance or electric motor), converts electric energy into light, heat, mechanical work and so on.Unit 1 Circuit Elements and PaEvents in a circuit can be d

7、efined in terms of （用-，根据-）e.m.f. (or voltage) and current. When electric energy is generated, transmitted and converted under conditions such that the currents and voltages involved remain constant with time, one usually speaks of direct-current (D.C.) circuits. With time-invariant currents and vol

8、tages, the magnetic and electric fields of the associated electric plant are also time-invariant. This is the reason why no e.m.f.s of self- (or mutual-)induction（自感或互感）appear in D.C. circuits, nor are there （倒装结构）any displacement currents （位移电流）in the dielectric surrounding the conductors(导体周围的电介质）

9、.Events in a circuit can be defFig.1.1 shows in simplified form a hypothetical circuit with a storage battery as the source and a lamp as the load. The terminals of the source and load are interconnected by conductors (generally but not always wires). As is seen, the source, load and conductors form

10、 a closed conducting path. The e.m.f. of the source causes a continuous and unidirectional current to circulate round this closed path.This simple circuit made up of a source, a load and two wires isseldom, if ever, met with in practice. Practical circuits may contain a large number of sources and l

11、oads interconnected in a variety of ways Fig.1.1（按不同方式连接的）. Fig.1.1 shows in simplified foTo simplify analysis of actual circuits, it is usual to show them symbolically in a diagram called a circuit diagram, which is in fact a fictitious or, rather, idealized model of an actual circuit of network. S

12、uch a diagram consists of interconnected symbols called circuit elements or circuit parameters. Two elements are necessary to represent processes in a D.C. circuit. These are a source of e.m.f. E and of internal (or source) resistance RS, and the load resistance (which includes the resistance of the

13、 conductors) R (Fig.1.2) Fig.1.2To simplify analysis of actualWhatever its origin (thermal, contact, etc.), the source e.m.f. E (Fig.1.2 (a) is numerically equal to the potential difference between terminals 1 and 2 with the external circuit open, that is, when there is no current flowing through th

14、e source E = 1 2 =V12 (1.1) The source e.m.f. is directed from the terminal at a lower potential to that （代替terminal） at a higher one（代替potential）. On diagram, this is shown by arrows（箭头）.When a load is connected to the source terminals (the circuit is then said to be loaded) and the circuit is clos

15、ed, a current begins to flow round it. Now the voltage between source terminals 1 and 2 (called the terminal voltage) is not equal to its e.m.f. because of the voltage drop VS inside the source, that is, across the source resistance RS VS=RSIWhatever its origin (thermal, Fig.1.3 shows a typical so-c

16、alled external characteristic V = 1 2 =V(I) of a loaded source (hence another name is the load characteristic of a source). As is seen, increase of current from zero to II1 causes the terminal voltage of the source to decrease linearly V12=V=EVS=ERSIFig.1.3 In other words, the voltage drop VS across

17、 the source resistance rises in proportion to the current. This goes on until a certain limit is reached. Then as the current keeps rising, theproportionality between its value and the voltage drop across the source is upset, and the external characteristic ceases to be （不再是）linear. This decrease in

18、 voltage may be caused by a reduction in the source voltage, by an increase in the internal resistance, or both.Fig.1.3 shows a typical so-calThe power delivered by a source is given by the equality（等式） PS=EI (1.2) where PS is the power of the source.It seems relevant at this point to dispel a commo

19、n misconception about power. Thus one may hear that power is generated, delivered, consumed, transmitted, lost, etc. In point of fact, however, it is energy that can be generated, delivered, consumed, transmitted or lost. Power is just the rate of energy input or conversion, that is, the quantity of

20、 energy generated, delivered, transmitted etc per unit time. So, it would be more correct to use the term energy instead of power in the above context. Yet, we would rather fall in with the tradition.The power delivered by a sourcThe load resistance R as a generalized circuit element, gives an idea

21、about the consumption of energy, that is ,the conversion of electric energy into heat, and is defined as P=RI2 (1.3 )In the general case, the load resistance depends solely on the current through the load, which in fact is symbolized by（用符号） the function R(I).By Ohms law, the voltage across a resist

22、ance is V=RI (1.4) In circuit analysis, use is often made of the reciprocal of the resistance, termed the conductance, which is defined as g = 1/ R In practical problems, one often specifies the voltage across a resistance as a function of current V(I), or the inverse relation I(V) have come to be k

23、nown as volt-ampere characteristics. The load resistance R as a genFig.1.4 shows volt-ampere curves for a metal-filament lamp V1(I), and for a carbon-filament lamp V2(I). As is seen, the relation between the voltage and the current in each lamp is other than linear. The resistance of the metal-filam

24、ent lamp increases, and that of the carbon-filament lamp decreases with increase of current. Fig.1.4Electric circuits containing components with non-linear characteristic （含有非线性特性元件的）are called non-linear. Fig.1.4 shows volt-ampere curvIf the e.m.f. and internal resistances of sources and associated

25、 load resistances are assumed to be independent of the current and voltage, respectively, the external characteristic V(I) of the sources and the volt-ampere characteristic V1(I) of the loads will be linear. Electric circuits containing only elements with linear characteristic are called linear. Fig

26、.1.5 Most practical circuits may be classed as linear. Therefore, a study into the properties and analysis of linear circuits is of both theoretical and applied interest. of interest=interestingIf the e.m.f. and internal resUnit 2 Specialized English Words ideal source 理想电源 series and parallel equiv

27、alent circuit 串并联等值电路 internal resistance 内阻 double subscript 双下标 ideal voltage source 理想电压源 active circuit elements有源电路元件 passive circuit elements 无源电路元件 power transmission line 输电线 sending end 发送端 receiving end 接收端 leakage current 漏电流 ideal current source 理想电流源 Unit 2 Specialized English WoUnit 2

28、Ideal Sources Series and Parallel Equivalent CircuitsConsider an elementary circuit containing a single source of e.m.f. E and of internal resistance RS, and a single load R (Fig.2.1). The resistance of the conductors of this type of circuit may be neglected. In the external portion of the circuit,

29、that is, in the load R, the current is assumed to flow from the junction a (which is at a higher potential such that a = 1 ) to the junction b (which is at a lower potential such that b = 2 ). The direction of current flow may be shown either by a hollow arrowhead or by supplying the current symbol

30、with a double subscript whose first digit identifies the junction at a higher potential and the second (省略了identifies) the junction at a lower potential. Thus for the circuit of Fig.2.1, the current I=Iab .Unit 2 Ideal Sources Series an We shall show that the circuit of Fig.2.1 containing a source o

31、f known e.m.f. E and source resistance R may be represented by two types of equivalent circuits. As already started, the terminal voltage of a loaded source is lower than the source e.m.f. by an amount equal to the voltage drop across the source resistance V = 1 2 = E VS = E RSI (2.1) On the other h

32、and, the voltage across the load resistance R is Fig.2.1 Since 1 = a and 2 = b , from Eqs.(2.1) and (2.2) it follows that E-RsI=RI, or E=RSI+RI (2.3) And I=E/ (RS+R)V = a b = RI (2.2) We shall show that the cirFrom the last equation we conclude that the current through the source is controlled by bo

33、th the load resistance and the source resistance. Therefore, in an equivalent circuit diagram the source resistance R may be shown connected in series with （与-串联） the load resistance R. This configuration may be called the series equivalent circuit (usually known as the Thevenin equivalent source-戴维

34、宁等效电源).Depending on the relative magnitude of the voltages across Rs and R, we can develop two modifications of the series equivalent circuit（串联等效电路）. Fig.2.2From the last equation we concIn the equivalent circuit of Fig.2.2(a), V is controlled by the load current and is decided by the difference be

35、tween the source e.m.f. E and the voltage drop V. If RSR and, for the same current, VSV (that is, if the source is operating under conditions very close to（接近） no-load or an open-circuit), we may neglect the internal voltage drop, put VS=RI=0 (very nearly) and obtain the equivalent circuit of Fig.2.

36、2(b). What we have got is a source whose internal resistance is zero (R=0). It is called an ideal voltage source. In diagrams it is symbolized by （用-符号表示）a circle with (with结构）an arrow inside and the letter E beside it. When applied to a network, it is called a driving force or an impressed voltage

37、source. In the equivalent circuit of F The terminal voltage （端电压）of an ideal voltage source is independent of the load resistance and is always equal to the e.m.f. E of the practical source it represents. Its external characteristic is a straight line parallel to the x-axis（与X轴平行的） (the dotted line

38、ab in Fig.1.3). The other equivalent circuit in Fig.2.3 may be called the parallel equivalent circuit (usually known as the Norton equivalent-诺顿等效电路). It may also have two modifications. To prove this, we divide the right- and left-hand sides of Eq.(2.3) by RS E/RS=I+V/RS=I+VgS or J=I+IS (2.4)where

39、J=E/RS ,current with the source short-circuited (with R=0);IS=V/RS=VgS - current equal to the ratio of the terminal source voltage to the source resistance（-与-的比率）;I=V/R=Vg - load current. The terminal voltage （端电压Eq.(2.4) is satisfied by the equivalent circuit of Fig.2.3(a) in which the source resi

40、stance RS is placed in parallel with （与-并联）the load resistance R.If gSR and, for the same voltages across RS and R, the current IS0 and i0. The segments of the curve between points a and b or O and c cover a complete cycle of current alternations over one period.Fig.4.1The number of cycles or period

41、s per second is the frequency of a periodic current. It is reciprocal of its period f =1/TIt is usually to specify the frequency of any periodic quantity in cycles per second（每秒周数）. Thus the frequency of a periodic current will be 1 cycle per second, if its period is 1 second, or 1 cycle/sec. Fig.4.

42、1 shows an example of thA direct current may be regarded as a special case of a periodic current whose period is infinitely long（无穷大） and the frequency is thus zero.The term（术语） alternating current is often used in the narrow sense of a periodic current whose constant (direct-current) component is z

43、ero, orThe frequencies of alternating current encountered in practice （在实际中遇到的）range over （涉及）very wide values. The mains frequency is 50Hz in the Soviet Union and Europe, and 60Hz in the United States. Some industrial processes use frequencies from 10 Hz to 2.5109 Hz. in radio practice（在无线电应用中）, fr

44、equencies up to 31010 Hz are employed.A direct current may be regardThe definitions for currents just introduced (and, indeed, those that will be introduced shortly) fully apply to periodic voltages, e.m.f.s, magnetic fluxes and any other electrical and magnetic quantities.Some additional remarks ar

45、e only needed with regard to the sign of alternating voltages and e.m.f.s.An alternating voltage between two points A and B, determined along a specified path l, periodically changes sign, so that if it is assumed to be positive in the direction from A to B（沿A到B的方向）, it will be negative in the direc

46、tion from B to A at the same instant of time【1】. This is why it is important to label which of the two directions is assumed positive. In diagrams, such a direction is labeled either by arrows or subscripts in the symbols for voltages and is regarded to be the positive reference direction of a volta

47、ge (or of an e.m.f.).The definitions for currents jElectrical engineering uses the simplest and commonest type of alternating current, the one which varies sinusoidally with time; (按正弦规律变化）hence the term （is called/termed）a harmonic or a sinusoidal current. The preference for sinusoidal currents is

48、explained by the fact that non-sinusoidal currents entail increased energy losses, induced over-voltages, and excessive interference with （对-的干扰）communications circuits.The transmission of information over a distance (wire or radio communications circuits, remote control, etc.) also uses sinusoidal

49、currents modulated by the signal in amplitude, frequency or phase. Periodic non-sinusoidal currents may likewise be treated as composed of sinusoidal currents at a variety of frequencies occurring simultaneously. This is why thorough of sinusoidal- current circuits is of primary importance.Electrica

50、l engineering uses thThe A.C. GeneratorAn A.C. generator consists of a stationary part, the stator, and a revolving part, the rotor. As a rule the rotor carries magnetic poles with coils around them. These are the field coils of the generator, because they establish a magnetic field in the machine.

51、They are energized with direct current through slip rings and brushes. The slots of the stator stacked up from electrical-sheet steel punchings receive the coils of the stator winding【2】. The stator coils are connected in series, as shown by the full and dotted lines in the drawing.The e.m.f. induce

52、d in a stator conductor is given by E=Blvwhere Bmagnetic induction of the field moving relative to the conductor;lactive length of the conductor;vspeed with which the magnetic field moves relative to the conductor.The A.C. GeneratorSince l and v are constant, the induced e.m.f. will vary exactly as

53、B varies. If the induced e.m.f. is to be sinusoidal (which is usually sought), the distribution of B around the circumference of the stator should be as close to sinusoidal as practicable.With p pole-pairs on the rotor, the e.m.f. will undergo p cycles of changes every revolution. If the speed of th

54、e rotor is revolutions per minute (r/min), this works out to pn cycles per minute, and the frequency of the induced e.m.f. is f =pn/60Since l and v are constant, thFor f =50Hz, the rotor of a generator with one pair of poles should run at 3000 r/min. and with two pole-pairs, at 1500 r/min. With spee

55、ds like this, rotors are usually fabricated with non-salient piles for greater mechanical strength.High-frequency generators operating at 800 to 8000Hz are all of special designs. Their uses are in the heat-treatment and induction-heating field. Still higher frequencies are generated by valve and se

56、miconductor oscillators.For f =50Hz, the rotor of a geSinusoidal CurrentThe instantaneous value of a sinusoidal current is given by (4.1)where Im is the peak value or amplitude of the current, and is the phase of the current. The quantity is the initial phase of the current (for t=0) and is termed the ep