Section A Pre-reading Electrical machines,transformers,and daily life Some common electrical machines and electrical equipment are shown in the An electrical machine is a device that following pictures and their names have can convert either mechanical energy to been given.Match the pictures with electrical energy or electrical energy to their corresponding names. mechanical energy.When such a device transformer contactor switch is used to convert mechanical energy to electric generator electric motor electrical energy,it is called a generator. relay When it converts electrical energy to mechanical energy,it is called a motor Since any given electrical machine can convert power in either direction,any machine can be used as either a generator ⊙ or a motor.Almost all practical motors and generators convert energy from one form to another through the action of a magnetic field.The transformer is an electrical device that is closely related to electrical machines.Since transformers operate on the same principles as generators and motors,depending on the action of a magnetic field to accomplish the change in voltage level,they are usually studied together with generators 2Discuss the following questions with your partner. and motors.These three types of electric devices are ubiquitous in modern daily 1.What is the function of an electrical machine?Tell the class the types life.Electric motors in the home run refrigerators,freezers,vacuum cleaners, of electrical machines and their applications that you know. blenders,air conditioners,fans,and many 2.How do you define electrical similar appliances.In the workplace. equipment?List some cases of the motors provide the motive power for use of electrical equipment in our daily life. 24 电气工程英语
I SectionA I Pre-reading Some common electrical machines and electrical equipment are shown in the following pictures and their names have been given. Match the pictures with their corresponding names. transformer contactor switch electric generator electric motor relay - 必， ', Discuss the following questions with your partner. 2 4 1. What is the function of an electrical machine? Tell the class the types of electrical machines and their applications that you know. 2. How do you define electrical equipment? List some cases of the use of electrical equipment in our daily life. 电气工程英语 Electrical machines, transformers, and daily life 1 An electrical machine is a device that can convert either mechanical energy to electrical energy or electrical energy to mechanical energy. When such a device is used to convert mechanical energy to electrical energy, it is called a generator. When it converts electrical energy to mechanical energy, it is called a motor. Since any given electrical machine can convert power in either direction , any mac ne can be used as either a generator or a motor. Almost all practical motors and generators convert energy from one form to another through the action of a magnetic field. The transformer is an electrical device that is closely related to electrical machines. Since transformers operate on the same principles as generators and motors, depending on the action of a magnetic field to accomplish the change in voltage level, they are usually stu ed together with generators and motors. These three types of electric devices are ubiquitous in modern daily life. Electric motors in the home run refrigerators , freezers, vacuum cleaners, blenders, air conditioners , fans, and many similar appliances . In the workplace , motors provide the motive power for
An Introduction to Text A Electric Machinery almost all tools.Of course,generators are necessary to supply the power used by all these motors. Transformers 2 A transformer is a device that changes AC electric power at one voltage level to AC electric power 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 present within the core. In a modem power system,electric power is generated at voltages of 12 to25 kV.Transformers step up the voltage to between 110 kV and nearly 1000 kV for transmission over long distances at very low losses.Transformers then step down the voltage to the 12-to 34.5-kV range for local distribution and finally permit the power to be used safely in homes,offices,and factories at voltages as low as 120 V. AC machinery fundamentals 4AC machines are generators that convert mechanical energy to AC electrical energy and motors that convert AC electrical energy to mechanical energy.The fundamental principles of AC machines are very simple,but unfortunately, they are somewhat obscured by the complicated construction of real machines There are two major classes of AC machines-synchronous machines and induction machines.Synchronous machines are motors and generators whose magnetic field current is supplied by a separate DCpower source,while Unit 2 Electric Machinery and Electrical Equipment 25
An Introduction to Electric Machinery almost all tools. Of course, generators are necessary to supply the power used by all these motors. Transformers 2 A transforn is a device that changes AC electric power at one voltage level to AC electric power at another voltage level through the action of a magnetic field. It consists of two or more coils of wrapped around a common ferromagnetic core. These coils are (usually) not directly connected The only connection between the coils is the common magnetic flux present within the core. 3 In a modem power system, electric power is generated at voltages of 12 to 25 kV. Transformers step up the voltage to between 110 kV and nearly 1000 kV for transmission over long distances at very low losses. Transformers then step down the voltage to the 12- to 34.5-kV range for local distribution and finally perm.it the power to be used safely in homes, offices, and factories at voltages as low as 120 V. AC machinery fundamentals 4 AC machines are generators that convert mechanical energy to AC electrical energy and motors that convert AC electrical energy to mechanical energy. The fundamental principles of AC machines are very simple, but unfortunately , they are somewhat obscured by the complicated construction of real machines. There are two major classes of AC machines - synchronous machines and induction mac es. Synchronous machines are motors and generators whose magnetic field current is supplied by a separate DC power source, while Unit 2 Electric Machinery and Electrical Equipment 25
induction machines are motors and generators whose field current is supplied by magnetic induction(transformer action)into their field windings.The field circuits of most synchronous and induction machines are located on their rotors. In a synchronous generator,a DC current is applied to the rotor winding.which produces a rotor magnetic field.The rotor of the generator is then turned by a prime mover,producing a rotating magnetic field within the machine.This rotating magnetic field induces a three-phase set of voltages within the stator windings of the generator.The term synchronous refers to the fact that this machine's electrical frequency is locked in or synchronized with its mechanical rate of shaft rotation.The synchronous generator is used to produce the vast majority of electric power used throughout the world. Synchronous motors are synchronous machines used to convert electrical power to mechanical power.A synchronous motor is the same physical machine as a synchronous generator,except that the direction of real power flow is reversed. Since synchronous motors are usually connected to power systems containing generators much larger than the motors,the frequency and terminal voltage of a synchronous motor are fixed (i.e.the power system looks like an infinite bus to the motor). Induction motors In induction machines,the rotor voltage(which produces the rotor current and the rotor magnetic field)is induced in the rotor windings rather than being physically connected by wires.The distinguishing feature of an induction motor is that no DC field current is required to run the machine Although it is possible to use an induction machine as either a motor or a generator, it has many disadvantages as a generator and so is rarely used in that manner.For this reason,induction machines are usually referred to as induction motors. 26电气工程英语
26 induction machines are motors and generators whose field current is supplied by magnetic induction (transformer action) into their:field ndings The field cuits of most synchronous and induction machin.es are located on their rotors. s In a synchronous generator , a DC current is applied to the rotor winding , which produces a rotor magnetic field. The rotor of the generator is then turned by a prime mover, producing a rotating magnetic field within the machine. This rotating magnetic field induces a three-phase set of voltages the stator windings of the generator. The term synchronous refers to the fact that this machine's electrical frequency is locked in or synchronized with its mechanical rate of shaft rotation. The synchronous generator is used to produce the vast majority of electric power used throughout the world 6 Synchronous motors are synchronous machines used to convert electrical power to mechanical power. A synchronous motor is the same physical machine as a synchronous generator, except that the direction of real power flow is reversed. Since synclrronous motors are usually connected to power systems containing generators much larger than the motors, the frequency and terminal voltage of a synchronous motor are fixed (i.e. the power system looks like an infinite bus to the motor). Induction motors 1 In induction machines, the rotor voltage (which produces the rotor current and the rotor magnetic field) is induced in the rotor windings rather than being physically connected by es. The stinguis feature of ai1 induction motor is that no DC field rent is required to run the machine. s Although it is possible to use an induction machine as either a motor or a generator, it has many disadvantages as a generator and so is rarely used in that manner. For this reason, induction machines are usually referred to as induction motors. 气工程英语
.The induction motor is the most popular type of AC motor because of its simplicity and ease of operation.An induction motor does not have a separate field circuit:instead,it depends on transformer action to induce voltages and currents in its field circuit.In fact,an induction motor is basically a rotating transformer.Its equivalent circuit is similar to that of a transformer,except for the effects of varying speed. DC machinery fundamentals DC machines are generators that convert mechanical energy to DC electric energy and motors that convert DC electric energy to mechanical energy.Most DC machines are like AC machines in that they have AC voltages and currents within them-DC machines have a DC output only because a mechanism exists that converts the interal AC voltages to DC voltages at their terminals. Since this mechanism is called commutator,DC machinery is also known as commutating machinery. DC motors and generators DC motors are DC machines used as motors,and DC generators are DC machines used as generators.The same physical machine can operate as eithe a motor or a generator-it is simply a question of the direction of the power flow through it. There are several types of DC motors,differing in the manner in which their field fluxes are derived.These types of motors are separately excited,self- excited and permanent magnet.The manner in which the flux is derived affects the way it varies with the load,which in turn affects the motor's overall torque- speed characteristic. DC generators are DC machines used as generators.There are several different types of DC generators,differing in the manner in which their field fluxes are Unit 2 Electric Machinery and Electrical Equipment 27
9 The induction motor is the most popular type of AC motor because of its simplicity and ease of operation. An induction motor does not have a separate field circuit; instead, it depends on transformer action to induce voltages and currents in its field circuit. In fact, an induction motor is basically a rotating transformer. Its equivalent circuit is sim ar to that of a transformer, except for the effects of varying speed. DC machinery fundamentals 10 DC machines are generators that convert mechanical energy tone electric energy and motors that convert DC electric energy to mechanical energy. Most 1 DC machines are lik~ AC mac nes in that they have AC voltages and currents wit them - DC machines have a DC output only because a mechanism exists that converts the internal AC voltages to DC voltages at their terminals. Since this mechanism is called commutator, DC machinery is also known as commutating machinery. DC motors and generators 11 DC motors are DC machines used as motors, and DC generators are DC machines used as generators. The same physical mac can operate as either a motor or a generator - it is simply a question of the ection of the power flow through it. 12 There are several types of DC motors, diffe in the manner in which their field fluxes are derived. These types of motors are separately excited, selfexcited and pem nent magnet. The manner in which the flux is derived affects the way it varies with the load, which in turn affects the motor's overall torquespeed characteristic. 13 DC generators are DC machines used as generators. There are several different types of DC generators, differing in the manner in hich their field fluxes are Unit 2 Electric Machinery and Electrical Equipment 27
derived.These methods affect the output characteristics of the different types of generators.The common DC generator types are separately excited,shunt, series,cumulatively compounded,and differentially compounded. Today,DC generators have been replaced in many applications by AC power sources and solid-state electronic components.This is true even in the automobile,which is one of the most common users of DC power. 28电气工程英语
28 derived. These methods affect the output characteristics of the different types of generators. The common DC generator types are separately excited, shunt, series, cumulatively compounded, and differentially compounded. 14 Today, DC generators have been replaced in many applications by AC power sources and solid-state electronic components. This is true even in the automobile, which is one of the most common users of DC power. 电气工程英语
New words and expressions convert /kan'v3:t/vt. rotor /'rauta(r)/n. to change or make sth.change from one form, a part of a machine that turns around a central point purpose,system,ctc.to another(使)转变；转换： (机器的)转子；转动部件 转化 commutator/'komju:teita(r)/n. ubiquitous/ju:'bikwitas/adj. a device for changing the direction in which seeming to be everywhere or in several places at electricity flows(电流)换向器：整流器 the same time普遍存在的；无所不在的 commutate/'komju:teit/vt. ferromagnetic /,feraumaeg'netik/adj. to regulate or reverse the direction of(an electric having the kind of magnetism which iron has铁磁 current),especially to make it a direct current 的：铁磁体的 (交流电)的方向；将（交流电）整流（尤指变交 flux /flAks/n. 流电为直流电) a flow or an act of flowing通量；流动 load /laud/n. synchronous /'sinkranas/adj. the power output of a generator or power plant happening or existing at the same time同时发生 电量 (或存在)的：同步的：共时的 torque /to:k/n. induction /in'dakfan/n. a twisting force that causes machinery,etc.to rotate the production of electricity in one object by (使机器等旋转的)转矩 another that already has electrical or magnetic cumulatively /'kju:mjolotivli/adv. power电磁感应 in a cumulative manner累积地；新增地 three-phase/Orii'feIz/aj.三相的 differentially /,difa'renfali/adv. stator /'sterto(r)/n. in a differential manner区别地 a mechanical device consisting of the stationary magnetic flux磁通量 part of a motor or generator in or around which the field winding励磁绕组：磁体绕组 rotor revolves(发电机的)定子 stator winding定子绕组 shaft∫a:ft/m a metal bar that joins parts of a machine or an engine together,enabling power and movement to be passed from one part to another(机器的)轴： 传动轴 Unit 2 Electric Machinery and Electrical Equipment 29
INewwordsand expressions| com·ert /kan'v3:t/ vt. to change or make sth. change from one form, purpose , system, etc. to another 转变；转换； 转化 ubiquitous /ju:'bikWJtas / adj. seeming to be everywhere or in several places at the same time 普遍存在的；无所不在的 ferromagnetic /,feraum g'net1k/ adj having the kind of magnetism wb.icb iron bas 铁磁 的；铁磁体的 flu /flAks/ n. a flow or an act of flowing ；流动 synchronous /'SIJJkranas/ adj. happening or ex.is at the same time 同时发生 （或存在 的；同 的； 时的 inductio n /rn'd n/ n. the production of electricity in one object by another that already bas electrical or magnetic power 电磁感应 three-phase /'0ri:'fe1zJ adj. 相的 stator /1ste1ta(r)/ n. a mechanical device consisting of the stationary part of a motor or generator in or around which the rotor revolves 发电机的 shaft /Ja:ft/ n. a metal bar that joins parts of a machine or an engine together, enabling power and movement to be passed from one part to another 机器的 轴； 传动轴 rotor /'rnut:;,(r)/ 11. a part of a machine that turns around a central point 机器的 子； 转动部件 commutator /'komju:te (r)/ n. a device for changing the direction in which electricity flows 电流 换向器；整流器 commutate /'komju:tert / vt. to regulate or reverse the direction of (an electric current), especially to make it a direct current 转换 交流电 的方向；将 交流电 整流 尤指变交 流电为直流电 load /I~ud/ n. the power output of a generator or power plant 电量 torque /t::,:k/ n. a twisting force that causes machinery, etc. to rotate 使机器 旋转的 转矩 cumulatively /'kju:mjul:;,t1vli/ adv. in a cumulative manner 累积地；渐增地 differential!) /,d1fa'renJali/ adv. in a differential manner 区别地 magnetic flu, 磁通 field winding 励磁绕组；磁体绕组 stator winding 定子绕组 Unit 2 Electric Machinery and Electrical Equipment 29