电气工程及其自动化专业英语.ppt

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1、 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ContentsPart 1 Electrics and ElectronicsPart 2 Electric Machinery Part 3 Electrical Engineering Part 4 Modern Computer Control Techniques Unit 1 Specialized English Wordscircuit compon

2、ents 电路元件 circuit 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.electromotive force 电动势 unidirectional current 单方向电流circuit diagram 电路图 load characte

3、ristic 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

4、 volt-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 Circuit Elements and ParametersAn electric circuit(or network)is an interconnection of physical electrical devices.The purpose of electric circuits is to distribute and convert

5、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）（连接它们的）.An energy source(a primary or secondary cell,a generator and the like)converts chemical,mechanical,thermal or some oth

6、er forms of energy into（将（将-转换成转换成-）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.Events in a circuit can be defined in terms of（用（用-，根据，根据-）.(or voltage)and current.When ele

7、ctric 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 voltages,the magnetic and electric fields of the associated electric plant a

8、re also time-invariant.This is the reason why no of self-(or mutual-)induction（自感或互感）（自感或互感）appear in D.C.circuits,nor are there（倒装结构）（倒装结构）any displacement currents（位移电流）（位移电流）in the dielectric surrounding the conductors(导体周围的电介导体周围的电介质质）.Fig.1.1 shows in simplified form a hypothetical circuit with

9、 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 a closed conducting path.The.of the source causes a continuous and unidirectional current to ci

10、rculate 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 loads interconnected in a variety of ways（按不同方式连接的）（按不同方式连接的）.To simplify analysis of actual circuits,it is u

11、sual 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.Such a diagram consists of interconnected symbols called circuit elements or circuit parameters.Two elements are necessary to represent process

12、es in a D.C.circuit.These are a source of.E and of internal(or source)resistance RS,and the load resistance(which includes the resistance of the conductors)RWhatever its origin(thermal,contact,etc.),the source.E(Fig.1.2(a)is numerically equal to the potential difference between terminals 1 and 2 wit

13、h the external circuit open,that is,when there is no current flowing through the source E=1 2=V12 (1.1)The source.is directed from the terminal at a lower potential to that（代替代替terminal）at a higher one（代替代替potential）.On diagram,this is shown by arrows（箭箭头）.When a load is connected to the source term

14、inals(the circuit is then said to be loaded)and the circuit is closed,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.because of the voltage drop VS inside the source,that is,across the source resistance RS VS=RSIFig.

15、1.3 shows a typical so-called 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=ERSI In other words,the voltage drop

16、VS across 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）（不再是）linear.This dec

17、rease in voltage may be caused by a reduction in the source voltage,by an increase in the internal resistance,or both.The power delivered by a source is given by the equality（等式）（等式）PS=EI (1.2)where PS is the power of the source.It seems relevant at this point to dispel a common misconception about

18、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 energy generated,delivered,transmitt

19、ed 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 load resistance R as a generalized circuit element,gives an idea about the consumption of energy,that is,the conversion of electric energy

20、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（用符号）号）the function R(I).By Ohms law,the voltage across a resistance is V=RI (1.4)In circuit analysis,use is often made of the reciprocal of

21、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 known as volt-ampere characteristics.Fig.1.4 shows volt-ampere curves for a metal-filame

22、nt 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-filament lamp increases,and that of the carbon-filament lamp decreases with increase of current.Electric circuits containing co

23、mponents with non-linear characteristic（含有非线性特性元件的）（含有非线性特性元件的）are called non-linear.If the.and internal resistances of sources and associated 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 cha

24、racteristic V1(I)of the loads will be linear.Electric circuits containing only elements with linear characteristic are called linear.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 i

25、nterest=interestingUnit 2 Specialized English Words ideal source 理想电源 series and parallel equivalent 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 receiv

26、ing end 接收端 leakage current 漏电流 ideal current source 理想电流源 Unit 2 Ideal Sources Series and Parallel Equivalent CircuitsConsider an elementary circuit containing a single source of.E and of internal resistance RS,and a single load R(Fig.2.1).The resistance of the conductors of this type of circuit ma

27、y be neglected.In the external portion of the circuit,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 arr

28、owhead or by supplying the current symbol with a double subscript whose first digit identifies the junction at a higher potential and the second(省略了省略了identifies)the junction at a lower potential.Thus for the circuit of Fig.2.1,the current I=Iab.We shall show that the circuit of Fig.2.1 containing a

29、 source of known.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.by an amount equal to the voltage drop across the source resistance V=1 2=E VS=E RSI (2.1)On the other hand,the voltag

30、e across the load resistance R is 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)From the last equation we conclude that the current through the source is controlled by both the load resistance and the source resistance.Therefore,in an e

31、quivalent circuit diagram the source resistance R may be shown connected in series with（与（与-串联）串联）the load resistance R.This configuration may be called the series equivalent circuit(usually known as the Thevenin equivalent source-戴维宁等效电源戴维宁等效电源).Depending on the relative magnitude of the voltages a

32、cross Rs and R,we can develop two modifications of the series equivalent circuit（串联等效电路）（串联等效电路）.In the equivalent circuit of Fig.2.2(a),V is controlled by the load current and is decided by the difference between the source.E and the voltage drop V.If RSR and,for the same current,VSV(that is,if the

33、 source is operating under conditions very close to（接近）（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.2.2(b).What we have got is a source whose internal resistance is zero(R=0).It is called an ideal voltage so

34、urce.In diagrams it is symbolized by（用（用-符号表示）符号表示）a circle with(with结结构）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 source.The terminal voltage（端电压）（端电压）of an ideal voltage source is independent of the load resistance a

35、nd is always equal to the.E of the practical source it represents.Its external characteristic is a straight line parallel to the x-axis（与（与X轴平行轴平行的）的）(the dotted line 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 equi

36、valent-诺顿等效电路诺顿等效电路).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 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

37、source resistance（-与与-的比率）的比率）;I=V/R=Vg-load current.Eq.(2.4)is satisfied by the equivalent circuit of Fig.2.3(a)in which the source resistance RS is placed in parallel with（与（与-并联）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 cu

38、rve between points a and b or O and c cover a complete cycle of current alternations over one period.The number of cycles or periods 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 sec

39、ond（每秒周数每秒周数）.Thus the frequency of a periodic current will be 1 cycle per second,if its period is 1 second,or 1 cycle/sec.A direct current may be regarded as a special case of a periodic current whose period is infinitely long（无穷大）（无穷大）and the frequency is thus zero.The term（术语）（术语）alternating curr

40、ent is often used in the narrow sense of a periodic current whose constant(direct-current)component is zero,orThe frequencies of alternating current encountered in practice（在实际中遇到的）（在实际中遇到的）range over（涉及）（涉及）very wide values.The mains frequency is 50Hz in the Soviet Union and Europe,and 60Hz in the

41、United States.Some industrial processes use frequencies from 10 Hz to 2.5109 Hz.in radio practice（在无线电应用中）（在无线电应用中）,frequencies up to 31010 Hz are employed.The definitions for currents just introduced(and,indeed,those that will be introduced shortly)fully apply to periodic voltages,magnetic fluxes a

42、nd any other electrical and magnetic quantities.Some additional remarks are only needed with regard to the sign of alternating voltages and.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 d

43、irection from A to B（沿沿A到到B的方向的方向）,it will be negative in the direction 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 a

44、nd is regarded to be the positive reference direction of a voltage(or of an.).Electrical engineering uses the simplest and commonest type of alternating current,the one which varies sinusoidally with time;(按正弦规律变化）按正弦规律变化）hence the term（is called/termed）a harmonic or a sinusoidal current.The prefere

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

46、rol,etc.)also uses sinusoidal 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 pr

47、imary importance.The 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.They are ener

48、gized 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.induced in a stator conductor

49、 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.Since l and v are constant,the induced.will vary exactly as B varies.If the induced.is to be sinusoidal(which

50、 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.will undergo p cycles of changes every revolution.If the speed of the rotor is revolutions per minute(r/min),this works out to pn cycles