异步电动机起动的方法外文资料翻译

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1、 电力工程 学院 毕业设计 (论文 )外文资料翻译 原 文 题 目： INDUCTION MOTOR STARTING METHODS 原 文 来 源： ASHRAE Journal, Jan. 2009 学 生 姓 名： 学 号： 所在院 (系 )部 ： 专 业 名 称 ： 南京工程学院 1 2011 年 03 月 15 日 英文资料 ： INDUCTION MOTOR STARTING METHODS Abstract - Many methods can be used to start large AC induction motors. Choices such as full vo

2、ltage, reduced voltage either by autotransformer or Wyes - Delta, a soft starter, or usage of an adjustable speed drive can all have potential advantages and trade offs. Reduced voltage starting can lower the starting torque and help prevent damage to the load. Additionally, power factor correction

3、capacitors can be used to reduce the current, but care must be taken to size them properly. Usage of the wrong capacitors can lead to significant damage. Choosing the proper starting method for a motor will include an analysis of the power system as well as the starting load to ensure that the motor

4、 is designed to deliver the needed performance while minimizing its cost. This paper will examine the most common starting methods and their recommended applications. I. INTRODUCTION There are several general methods of starting induction motors: full voltage, reduced voltage, wyes-delta, and part w

5、inding types. The reduced voltage type can include solid state starters, adjustable frequency drives, and autotransformers. These, along with the full voltage, or across the line starting, give the purchaser a large variety of automotives when it comes to specifying the motor to be used in a given a

6、pplication. Each method has its own benefits, as well as performance trade offs. Proper selection will involve a thorough investigation of any power system constraints, the load to be accelerated and the overall cost of the equipment. In order for the load to be accelerated, the motor must generate

7、greater torque than the load requirement. In general there are three points of interest on the motors speed-torque curve. The first is locked-rotor torque (LRT) which is the minimum torque which the motor will develop at rest for all angular positions of the rotor. The second is pull-up torque (PUT)

8、 which is defined as the minimum torque developed by the motor during the period of acceleration from rest to the speed at which breakdown torque occurs. The last is the breakdown torque (BDT) which is defined as the maximum torque which the motor will develop. If any of these points are below the r

9、equired load curve, then the motor will not start. The time it takes for the motor to accelerate the load is dependent on the inertia 2 of the load and the margin between the torque of the motor and the load curve, sometimes called accelerating torque. In general, the longer the time it takes for th

10、e motor to accelerate the load, the more heat that will be generated in the rotor bars, shorting ring and the stator winding. This heat leads to additional stresses in these parts and can have an impaction motor life. II. FULL VOLTAGE The full voltage starting method, also known as across the line s

11、tarting, 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 shortes

12、t 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. If the motor is on a weak power system, the sudden high power draw can cause a temporary voltage dr

13、op, not only at the motor terminals, but the entire power bus feeding the starting motor. This voltage drop will cause a drop in the starting torque of the motor, and a drop in the torque of any other motor running on the power bus. The torque developed by an induction motor varies roughly as the sq

14、uare of the applied voltage. Therefore, depending on the amount of voltage drop, motors running on this weak power bus could stall. In addition, many control systems monitor under voltage conditions, a second potential problem that could take a running motor offline during a full voltage start. Besi

15、des electrical variation of the power bus, a potential physical disadvantage of an across the line starting is the sudden loading seen by the driven equipment. This shock loading due to transient torques which can exceed 600% of the locked rotor torque can increase the wear on the equipment, or even

16、 cause a catastrophic failure if the load can not handle the torques generated by the motor during staring. A. Capacitors and Starting Induction motors typically have very low power factor during starting and as a result have very large reactive power draw. See Fig. 2. This effect on the system can be reduced by adding capacitors to the motor during starting.