电气工程及其自动化-专业英语课程论文.docx

重庆邮电大学移通学院电气工程及其自动化专业英语课程论文 年 级 2012 专 业 电气工程与自动化 姓 名 孙猜胜 学 号 Three-phase asynchronous motorAbstract: The three-phase asynchronous motor is motors one kind.Compared with single phase asynchronous motor, three-phase asynchronous motor operating performance is good, and can save various materials.Has the structure to be simple, the manufacture is easy, firm durable, the service is convenient, cost inexpensive ,drag the ability is good,and so on a series of merits. thus becomes in each kind of electrical machinery the output to be biggest utilizes the broadest one kind of electric motor.Key words: Moror Motor starting Star delta StartingThree-phase asynchronous motor principle: When the stator winding through into the three-phase ac three-phase symmetric arises when a synchronous speed n1 along the stator and rotor round for space in a clockwise rotation magnetic field. Because of a rotating magnetic field rotating speed to n1, rotor conductor of the static beginning, so the rotor conductor will cut the stator and produce a rotating magnetic field induction emf (induction emf direction DingZe judge with the right hand). Because the child is short circuit loop ends conductor short meet, in the role of the induced emf, will produce the rotor conductor with induction emf direction basic consistent induced current. The rotor current-carrying conductor at stator magnetic field is the role of the electromagnetic force (the direction of the force with the left hand DingZe judge). The electromagnetic force of the rotor axis electromagnetic torque, drive along the rotor rotating magnetic field rotation direction.1Through the above analysis can be summed up the motor principle: when the three-phase motor stator winding (each differ 120 KWH Angle), ventilation with three-phase ac, will produce a rotating magnetic field, the rotating magnetic field cutting rotor winding, and thus to the rotor winding induced current (rotor winding is closed access), load flow of rotor stator conductor under the action of a rotating magnetic field will produce the electromagnetic force, thus in the motor shaft formed on the electromagnetic torque, driving motor rotation, and motor rotation direction and the rotating magnetic field in the same direction. Thestructureofthree-phaseasynchronousmotor:Types of three-phase asynchronous motor, but all kinds of three-phase asynchronous motor is the same basic structure, they are the stator and rotor of these two basic components, the stator and rotor has a certain air gap between. In addition, end caps, bearings, cable boxes, rings and other accessories,1).Statorpart Stator is used to generate the rotating magnetic field.Stator Three-phase motors generally shell, stator core, stator windings and other parts.a.ShellThree-phase motor casing including base,end caps,bearing caps,rings,such as junction boxes and comp onentsb. Stator Core Induction motor stator core is part of the motor circuit from 0.35mm 0.5mm thick coated with a thin insulating paint from silicon,c.Thestatorwindings Three-phase motor stator windings are part of the circuit,there are three-phase three-phase motor windings,summetrical three-phase current access,it will have a rotating magnetic field.Three-phase winding consists of three separate components of the winding, and each has a number of coil windings connected.Is a phase of each winding, each winding in the space angle difference between the 120 electrical2.2). Rotor part a. Rotor Core With 0.5 mm thick steel from, set in the shaft, the role and the same stator core, on the one hand, as part of the motor magnetic circuit, on the one hand to place the rotor windings.b. Rotor windings The rotor winding induction motor winding is divided into two kinds of cage-shaped and which is divided into winding rotor asynchronous motor with cage induction motor. 3). Other parts ofOther parts including the cover, fans, etc.Induction motor starting methods:There are several general methods of starting induction motors: full voltage, reduced voltage,wyes-delta,and part winding types.The reduced voltage type can include solid state starters, adjustable frequency drives, and autotransformers.The following is the most common method.1).Full voltageThe full voltage starting method, also known as across the line starting, is the easiest method to employ, has the lowest equipment costs, and is the most reliable. This method utilizes a control to close a contactor and apply full line voltage to the motor terminals. This method will allow the motor to generate its highest starting torque and provide the shortest acceleration times.This method also puts the highest strain on the power system due to the high starting currents that can be typically six to seven times the normal full load current of the motor.2).Autotransformer The motor leads are connected to the lower voltage side of the transformer. The most common taps that are used are 80%, 65%, and 50%. At 50% voltage the current on the primary is 25% of the full voltage locked rotor amps. The motor is started with this reduced voltage, and then after a pre-set condition is reached the connection is switched to line voltage. This condition could be a preset time, current level, bus volts, or motor speed. The change over can be done in either a closed circuit transition, or an open circuit transition method. In the open circuit method the connection to the voltage is severed as it is changed from the reduced voltage to the line level. Care should be used to make sure that there will not be problems from transients due to the switching. This potential problem can be eliminated by using the closed circuit transition. With the closed circuit method there is a continuous Voltage applied to the motor. Another benefit with the autotransformer starting is in possible lower vibration and noise levels during starting.3).Star delta Starting This approach started with the induction motor,the structure of each phase of the terminal are placed in the motor teminal box ,This allows the motor star connection in the initial start up,and then re-connected into a triangle run.The initial start time when the voltage is reduced to the original star connection,the starting current and starting torque by 2/3. Depending on the application on,the motor switch to the triangle in the rotational speed of between 50% and the maximum speed.Must be noted that the same problems,including the previously mentioned switch method ,if the open circuit method,the transition may be a transient problem.This method is often used in lesst than 600V motor,the rated voltage 2.3KV and higher are not suitable for star delta motor start method.34).Series Resistor or Reactor Starting This method is to use a series resistance or place in the