电气工程及其自动化专业英语课件

Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,11/7/2009,#,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,电气工程及其自动化专业英语,Specialized English for Electrical Engineering,Its Automation,Contents,Part 1 Electrics and Electronics,Part 2 Electric Machinery,Part 3 Electrical Engineering,Part 4 Modern Computer Control Techniques,ContentsPart 1 Electrics an,Unit 1 Specialized English Words,circuit components,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,e.m.f.,electromotive force,电动势,unidirectional current,单方向电流,circuit diagram,电路图,load characteristic,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-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 Wor,Unit 1 Circuit Elements and Parameters,An electric circuit (or network) is an interconnection of physical electrical devices. The purpose of electric circuits is,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, 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 Pa,Events in a circuit,can be defined,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 voltages, 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,）,.,Events in a circuit can be def,Fig.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 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 is,seldom,if ever, met with in practice,.,Practical circuits may contain a large,number of sources and loads,interconnected in a variety of ways,Fig.1.1,（按不同方式连接的）,.,Fig.1.1 shows in simplified fo,To 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.,Such 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,R,S, and the load,resistance (which includes the,resistance of the conductors),R,(Fig.1.2) Fig.1.2,To simplify analysis of actual,Whatever 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,the source,E,= 1 2 =,V,12 (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 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 e.m.f. because of the voltage drop,V,S,inside the source, that is, across the source resistance,R,S,V,S,=,R,S,I,Whatever its origin (thermal,Fig.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,I,I,1,causes the terminal voltage of the source to decrease linearly,V,12,=,V,=,E,V,S,=,E,R,S,I,Fig.1.3,In other words, the,voltage drop V,S,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, the,proportionality 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 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-cal,The power delivered by a source is given by the equality,（等式）,P,S,=,EI,(1.2),where,P,S,is the power of the source.,It seems relevant at this point to dispel a,common,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 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 sourc,The load resistance,R,as a generalized circuit element, gives,an idea about,the consumption of energy, that is ,the conversion of electric energy into heat, and is defined as,P,=,RI,2,(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 resistance 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 known as,volt-ampere characteristics.,The load resistance R as a gen,Fig.1.4 shows,volt-ampere curves,for a metal-filament lamp,V,1,(,I,), and for a carbon-filament lamp,V,2,(,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.,Fig.1.4,Electric 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 curv,If the e.m.f. 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 characteristic,V,1,(,I,) of the loads will be linear.,Electric circuits containing only elements with linear characteristic are called linear.,Fig.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=interesting,If the e.m.f. and internal res,Unit 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,receiving end,接收端,leakage current,漏电流,ideal current source,理想电流源,Unit 2 Specialized English Wo,Unit 2 Ideal Sources Series and Parallel Equivalent Circuits,Consider,an elementary circuit containing a single source of e.m.f.,E,and of internal resistance,R,S, 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, 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 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,=,I,ab,.,Unit 2 Ideal Sources Series an,We shall,show that,the,circuit,of Fig.2.1,containing a source of 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 V,S,= E R,S,I (2.1),On the other hand, 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,=,R,S,I,+,RI (2.3),And,I,=,E,/ (,R,S,+,R,),V,= ,a, ,b,=,RI,(2.2),We shall show that the cir,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 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-,戴维宁等效电源,).,Depending on the relative,magnitude of the voltages,across R,s,and R, we can,develop two modifications,of the,series equivalent,circuit,（串联等效电路）,.,Fig.2.2,From the last equation we conc,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.m.f. E,and,the voltage drop,V,.,If,R,S,R,and, for the same current,V,S,V,(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,V,S,=,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 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 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 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,R,S,E,/,R,S,=,I,+,V,/,R,S,=,I,+,Vg,S,or,J,=,I,+,I,S,(2.4),where,J,=,E,/,R,S,current,with,the source,short-circuited,(with,R,=0);,I,S,=,V,/,R,S,=,Vg,S,- 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 resistance,R,S,is placed,in parallel with,（与,-,并联）,the load resistance,R.,If,g,S,R,and, for the,same voltages across,R,S,and,R,the current,I,S,0 and,i,0. 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.4.1,The number of cycles or periods per second is the frequency of a periodic current. It is reciprocal of its period,f,=1/,T,It 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.4.1 shows an example of th,A 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 zero, or,The 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 t