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1、电气工程英语复习资料 Flemings left-hand rule:Place the thumb and the first and second finger of the left hand so that all three are mutually perpendicular to each other.With the first finger in the direction of the field and the second finger in the direction of the current,the thumb indicates the direction o
2、f the force.弗莱明左手定则：伸出左手大拇指、食指以及中指并使它们相互垂直。使食指指向磁场的方向，中指指向电流的方向，那么拇指所指的方向是力的方向。The air gaps of turbine generators usually are much longer than in other types of machines.A long air gap reduces the reactance of the armature winding and improves voltage regulation and stability.It is also necessary fo
3、r ventilation.An obvious disadvantage of a long air gap is that it necessitates a greater field mmf to produce a specified air-gap flux.汽轮发电机的气隙通常比其它类型的电机大得多，这么大的气隙使电枢绕组的电抗减小并增大了电压调节范围和稳定性。对于通风来说它也是必要的。大气隙的一个明显缺点是它需要一个较大的励磁磁动势来产生一定的磁通。A transformer is a device that changes AC electric energy at one
4、voltage level into AC electric energy at another voltage level through the action of a magnetic field.It consists of two or more coils of wire wrapped around a common ferromagnetic core.These coils are(usually)not directly connected.The only connection between the coils is the common magnetic flux p
5、resent within the core 变压器是一种设备，这种设备通过磁场作用将一种电压等级的交流电能转换成另外一种电压等级的交流电能。变压器由两个或多个缠绕在共用铁心上的线圈组成，这些线圈通常不是直接连接在一起，线圈之间唯一的连接是存在于铁心中的共同的磁通量。Copper(Rt)losses,Copper losses are the 1.铜耗 Rr 铜耗是变压器一次绕组和二次绕组中的电阻性热损耗。铜耗正比于绕组电流的平方。第六章 With the development of the AC/DC converting equipment,high voltage DC(HVDC)tr
6、ansmission systems have become more attractive and economical in special situations.The HVDC transmission can be used for transmission of large blocks of power over long distance,and providing an asynchronous link between systems where AC interconnection would be impractical because of system stabil
7、ity consideration or because nominal frequencies of the systems are different.随着交直流转换装置的发展,高压直流(HVDC)传输系统已经变得更加经济性而且具有吸引力在一些特殊的情况下。高压直流输电系统可用于支持大功率的远距离输送,并可以链接出于对系统稳定性的考虑或者是频率不同的交流系统不可行的系统 Power system stability may be broadly defined as the property of a power system that enables it to remain in a
8、state of operating equilibrium under normal operating conditions and to regain an acceptable state of equilibrium after being subjected to a disturbance.电力系统稳定性广义上包括了电力系统的性质,使其保持在一个平衡的状态下运行工况和恢复正常平衡状态后可以承受的干扰能力。Instability in a power system may be manifested in many different ways depending on the s
9、ystem configuration and operating mode.Traditionally,the stability problem has been one of maintaining synchronous operation.Since power systems rely on synchronous machines for generation of electrical power,a necessary condition for satisfactory system operation is that all synchronous machines re
10、main in synchronism or,colloquially in step.This aspect of stability is influenced by the dynamics of generator rotor angles and power-angle relationships,and then referred to rotor angle stability.电力系统的不稳定可能会因为不同的系统配置和运行模式而体现出很多不同的方式。传统意义上，稳定性问题一直是保持同步操作问题之一。因为动力系统依靠同步机直接产生的电功率，一个令人满意的系统运行的必要条件是，所有
11、机器保持同步或同步通俗的讲“一步”。这一方面的稳定是受到发电机转子的动态角度和功角之间的关系，然后关系到“转子角稳定”。The basic elements of a modern power system in U.S.A.are shown in Fig.6-1.Electric power is produced at generating stations(GS)and transmitted to consumers through a complex network of individual components,including transmission lines,tran
12、sformers,and switching devices.It is common practice to classify the transmission network into the following subsystems:Transmission system;Subtransmission system;Distribution system.在美国，一个现代化电力系统的基本要素如 Fig.6-1 显示。电功率由发电厂（GS）生产 后通过复杂的网络组件,包括输电线路、变压器和开关传递给消费者。最常用的网络传输系统由以下系统构成：输电系统；变电系统、配电系统。Rotor an
13、gle stability is the ability of interconnected synchronous machines of a power system to remain in synchronism.It is most important to power system stability problems.The stability problem involves the study of the electromechanical oscillations inherent in power system.A fundamental factor in this
14、problem is the manner in which the power outputs of synchronous machines vary as their rotors oscillate.转子转角的稳定性反映了电力系统中相互关联的同步电机保持同步运转的能力。这是电力系统稳定性中最重要的问题。涉及的稳定性问题的研究动力系统固有的机电振动。在这个问题上,一个基本要素是能量的输出方式变化是因为同步机转子的振荡。The purpose of a power system is to deliver the power the customers require in real ti
15、me,on demand,within acceptable voltage and frequency limits,and in a reliable and economic manner.In normal operation of a power system,the total power generation is balanced by the total load and transmission losses.The system frequency and voltages on all the buses are within the required limits,w
16、hile no overloads on lines or equipment are resulted.However,loads are constantly changed in small or large extents,so some control actions must be applied to maintain the power system in the normal and economic operation state 电力系统的目的是为了提供电力客实时的需求的电压、频率范围内,并在一个可靠的和经济的方式下进行。在正常运行的电力系统,总发电是由总负载传输损失平衡
17、。这个系统的频率和电压满足对所有的需求和限制,而没有导致设备或线路超载。然而,在荷载作用下会产生或大或小的变化,所以必须采取一些控制措施维护电力系统运行在正常和经济的状态。For satisfactory operation of a power system,the frequency should remain nearly constant.Relatively close control of frequency ensures constancy of speed of induction and synchronous motors.Constancy of speed of mo
18、tor drives is particularly important for satisfactory performance of all the auxiliary drives associated with the fuel,the feed-water and the combustion air supply systems.In a network,considerable drop in frequency could result in high magnetizing currents in induction motors and transformers.The e
19、xtensive use of electric clocks and the use of frequency for other timing purpose require accurate maintenance of synchronous time which is proportional to integral of frequency.As a consequence,it is necessary to regulate not only the frequency itself but also its integral.The frequency of a system
20、 is dependant on active power balance.As frequency is a common factor throughout the system,a change in active power demand at one point is reflected throughout the system by a change in frequency.Because there are many generators supplying power into the system,some means must be provided to alloca
21、techange in demand to the generators.A speed governor on each generating unit provides the primary speed control function,while supplementary control originating at a central control center allocates generation.The problem of maintaining voltages within the required limits is complicated by the fact
22、 that the power system supplies power to a vast number of loads and is fed from many generating units.As loads vary,the reactive power requirements of the transmission system vary.Since reactive power can not transmitted over long distances,voltage control has to be effected by using special devices
23、 dispersed throughout the system.This is in contrast to the control of frequency which depends on the overall system active power balance.The proper selection and coordination of equipment forcontrolling reactive power and voltage are among the major challenges of power system engineering.Stability
24、is a condition of equilibrium between opposing forces.The mechanism by which interconnected synchronous machines maintain synchronism with one another is through restoring forces,which act whenever there are forces tending to accelerate or decelerate one or more machines with respect to other machin
25、es.Under stead-state conditions,there is equilibrium between the input mechanical torque and the output electrical torque of each machine,and the speed remains constant.If the system is perturbed,by some disturbances such as load changes,line outages and short-circuit faults,etc.,this equilibrium wi
26、ll be upset,resulting in acceleration or deceleration of the rotors of themachines according to the laws of motion of a rotating body.If one generator temporarily runs faster than another,the angular position of its rotor relative to that of the slower machine will advance.The resulting angular diff
27、erence transfers part of the load from the slow machine to the fast machine,depending on the power-angle relationship.This tends to reduce the speed difference and hence the angular separation.The power-angle relationship,as discussed above,is highly nonlinear,beyond a certain limit,an increase in a
28、ngular separation is accompanied by a decrease in power transfer ;this increases the angular separation further and leads to instability.For any given situation,the stability of the system depends on whether or not the deviations in angular positions of the rotors result in sufficient restoring torq
29、ues.Transient stability is the ability of the power system to maintain synchronism when subjected to a severe transient disturbance.The resulting system response involves large excursions of generator rotor angles and is influenced by the nonlinear power-angle relationship.Stability depends on both
30、the initial operating state of the system and the severity of the disturbance.Usually,the system is altered so that the post-disturbance steady-state operation differs from that prior to the disturbance.暂态稳定是反映电力系统在严重的瞬时干扰保持同步的能力,。结果反映了系统包括响应的受到非线性干扰时大型发电机转子角功角之间的关系。最初的稳定性取决于系统遇到严重的骚乱运行状态,。通常,这个系统是如
31、此的改变不同稳态操作之前的干扰。1.The thumb is in the direction of in Flemings right-hand rule.A.the field B.rotation of the magnetic field C.the induced voltage D.the relative motion of conductor 2.In induction motors the speed of the rotating rotor the speed of the rotating magnetic field.A.equals to B.is much gr
32、eater than C.never reaches D.keeps the same as 3.When the speed of the rotor is zero,the slip of induction machine is .A.0.0 B.0.1 C.1.0 D.0.3 4.Form-wound coils are widely used for motors.A.small-size AC B.medium-size AC C.large AC D.large DC 1.When a induction motor with 10 poles is supplied by 50
33、Hz three-phase ac power source,the synchronous revolutions per minute is .A.1000 B.900 C.700 D.600 2.If the difference in speed between the rotor and the air-gap rotating magnetic field is smaller,the corresponding slip is .A.smalle B.greater C.equal D.indefinite 3.The electric machine that operates
34、 at speeds above synchronous speed works in region.A.motoring B.generating C.plugging D.stopping 4.The breakdown torque of a motor is the torque that it generates?A.minimum B.maximum C.locked-rotor D.synchronous 1.The speed of a synchronous machine is directly proportional to in its armature under s
35、teady-state conditions.A.the amplitude of the current B.the frequency of the current C.the amplitude of the voltage D.the flux 2.The field winding in a synchronous generator is supplied by power source.A.a DC B.an AC C.no D.any type 3.The cylindrical rotor machine is used in .A.low-speed motorsB.hig
36、h-speed motors C.high-speed steam-turbine-driven generators D.low-speed hydro-turbine-driven generators 4.The turbine generators with two poles for 60-cps are machines.A.3600-rpm B.1800-rpm C.5400-rpm D.2400-rpm 5.The field current of a turbine generator is usually obtained from .A.a motor B.an AC g
37、enerator C.an exciter D.a battery 1.A transformer is a device that can converter one ac voltage to another ac voltage through the action of .A.an electric circuit B.a magnetic field C.an electric field D.a coupling circuit 2.The primary winding is connected to .A.the power source B.the load C.the me
38、asurement instrument D.the motor 3.The core construction consisting of a three-legged laminated core with the windings wrapped around the centre leg is called .A.core form B.shell form C.cylindrical form D.global form 4.The transformer that takes the distribution voltage and steps it down to the fin
39、al voltage at which the power is actually used is called a .A.distribution transformer B.unit transformer C.substation transformer D.potential transformer 5.Copper losses are losses in the primary and secondary windings of the transformer core.A.inductive B.Capacitive C.Resistive D.reactive 1.The fi
40、rst complete power system was built in ,it was power system.A.1889,an AC B.1882,a DC C.1882,an AC D.1889,a DC 2.The first three-phase AC transmission line in North America was put into operation in .A.1889 B.1882 C.1893 D.1890 3.Power system interconnections are usually formed at the level.A.transmi
41、ssion system B.subtransmission system C.distribution system D.generating station 4.In North American is adopted as standard frequency in electric power system.A.25Hz B.50Hz C.60Hz D.125Hz 1.In power plants convert the primary energy to mechanical energy,and con-vert mechanical energy to electric ene
42、rgy.A.synchronous generators,prime movers B.prime movers,synchronous generators C.prime movers,asynchronous generators D.prime movers,prime movers 1.In power plants convert the primary energy to mechanical energy,and con-vert mechanical energy to electric energy.A.synchronous generators,prime movers
43、 B.prime movers,synchronous generators C.prime movers,asynchronous generators D.prime movers,prime movers 4.In U.S.A.,the voltages of the transmission system are typically .A.345kV B.500kV C.230kV and above D.115kV and above 1.The objective of the optimal economic operation of power systems is .A.to
44、 minimize the total production cost B.to maintain frequency constant C.to maintain voltages constan D.to ensure balance between generation and load 2.The frequency of a power system is determined mainly by .A.bus voltages B.active power generation C.reactive power generation D.active power generatio
45、n and consumption 3.The voltage levels at the terminals of generators are controlled mainly by .A.static var compensators B.series capacitors C.automatic voltage regulators D.shunt reactors 4.When the system frequency is changed away from the rating,must be regulated.A.system voltages B.reactive pow
46、er C.active power D.generators excitation 5.Regulation of the generators speed governor can change its output.A.reactive power B.active power C.terminal voltage D.reactive current 1.In a single machine power system,the maximum power transfer from the generator to the system is directly proportional
47、to .A.bus voltage B.the system frequency C.the machine internal voltage D.the line reactance 2.If the input mechanical torque is greater than the output electrical torque in a generator,the speed of its rotor will .A.decrease B.increase C.maintain equilibrium D.keep synchronous speed 3.If the synchr
48、onizing torque is insufficient in a disturbed system,will occur.A.voltage instability B.dynamic instability C.oscillatory instability D.non-oscillatory instability 4.If an electric power system lacking of sufficient damping torque under a certain operation state suffers a disturbance,will occur.A.vo
49、ltage instability B.dynamic instability C.oscillatory instability D.non-oscillatory instability 5.After a large disturbance,the system is sometimes stable in the first swing but becomes unstable as a result of growing oscillations as the end state is approached,this is because .A.the disturbance is
50、too severe B.the post-disturbance steady-state condition of the system is small signal unstable C.the duration time of the disturbance is too long D.the initial rotor angle is too big exciting voltage 励磁电压 laminated a.叠片的，分层的，薄片的 punching n.冲压，穿孔 bar n.线棒，导条 条，杆 slot n.槽 隙缝 lamination n.叠片，冲片 分层 薄片