电气工程及其自动化专业英语.ppt

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 AutomationContents Part 1 Electrics and Electronics Part 2 Electric Machinery Part 3 Electrical Engineering Part 4 Modern Computer Control Techniques Unit 1 Specialized English Wordscircuit 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 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）（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（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-）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）（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 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 isseldom, 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）（按不同方式连接的）. 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 RS, and the load resistance (which includes the resistance of the conductors) R (Fig.1.2) Fig.1.2 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 =V12 (1.1) The source e.m.f. 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 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 VS inside the source, that is, across the source resistance RS VS=RSI 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 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 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 decrease in voltage may be