优质毕业设计三相异步电动机外文翻译.doc

汉字翻译
 异步电动机含有结构简单、运行可靠、价格低、维护方便等一系列优点，所以，异步电动机被广泛应用在电力拖动系统中。尤其是伴随电力电子技术发展和交流调速技术日益成熟，使得异步电动机在调速性能方面大大提升。现在，异步电动机电力拖动已被广泛地应用在各个工业电气自动化领域中。就三相异步电动机机械特征出发，关键简述电动机开启，制动、调速等技术问题。
1 三相异步电动机机械特征文 
三相异步电动机机械特征是指电动机转速n和电磁转矩Tem之间关系。因为转速n和转差率S有一定对应关系，所以机械特征也常见Tem＝f（s）形式表示。三相异步电动机电磁转矩表示式有三种形式，即物理表示式、参数表示式和实用表示式。物理表示式反应了异步电动机电磁转矩产生物理本质，说明了电磁转矩是由主磁通和转子有功电流相互作用而产生。参数表示式反应了电磁转矩和电源参数及电动机参数之间关系，利用该式能够方便地分析参数改变对电磁转矩影响和对多种人为特征影响。实用表示式简单、便于记忆，是工程计算中常采取形式。
电动机最大转矩和开启转矩是反应电动机过载能力和开启性能两个关键指标，最大转矩和开启转矩越大，则电动机过载能力越强，开启性能越好。
三相异步电动机机械特征是一条非线性曲线，通常情况下，以最大转矩（或临界转差率）为分界点，其线性段为稳定运行区，而非线性段为不稳定运行区。固有机械特征线性段属于硬特征，额定工作点转速略低于同时转速。人为机械特征曲线形状可用参数表示式分析得出，分析时关键要抓住最大转矩、临界转差率及开启转矩这三个量随参数改变规律。
2 三相异步电动机开启
小容量三相异步电动机能够采取直接开启，容量较大笼型电动机能够采取降压开启。降压开启分为定子串接电阻或电抗降压开启、Y-D降压开启和自耦变压器降压开启。定子串电阻或电机降压开启时，开启电流随电压一次方关系减小，而开启转矩随电压平方关系减小，它适适用于轻载开启。Y-D降压开启只适适用于正常运行时为三角形联结电动机，其开启电流和开启转矩均降为直接开启时1/3，它也适适用于轻载开启。自耦变压器降压开启时，开启电流和开启转矩均降为直接开启时l/k2（k为自耦变压器变比），适合带较大负载开启。
绕线转子异步电动机可采取转子串接电阻或频敏变阻器开启，其开启转矩大、开启电流小，适适用于中、大型异步电动机重载开启。
 软开启器是一个集电机软开启、软停车、轻载节能和多个保护功效于一体新型电动机控制装置，国外称为Soft Starter。它关键组成是串接于电源和被控电动机之间三相反并联晶闸管及其电子控制电路。利用串接于电源和被控电动机之间软开启器，以不一样方法，控制其内部晶闸管导通角，使电动机输入电压从零以预设函数关系逐步上升，直至开启结束，给予电动机全电压，即为软开启。在软开启过程中，电动机开启转矩逐步增加，转速也逐步增加。软开启器实际上是个调压器，用于电动机开启时，输出只改变电压并没有改变频率。
 3 三相异步电动机调速
三相异步电动机调速方法有变极调速、变频调速和变转差率调速。其中变转差率调速包含绕线转子异步电动机转子串接电阻调速、串级调速和降压调速。
变极调速是经过改变定子绕组接线方法来改变电机极数，从而实现电机转速改变。变极调速为有级调速，变极调速时定子绕组联结方法有三种：Y-YY、顺串Y-反串Y、D-YY。其中Y-YY联结方法属于恒转矩调速方法，另外两种属于恒功率调速方法。变极调速时，应同时对调定子两相接线，这么才能确保调速后电动机转向不变。
变频调速是现代交流调速技术关键方向，它可实现无级调速，适适用于恒转矩和恒功率负载。
绕线转子电动机转子串接电阻调速方法简单，易于实现，但调速是有级，不平滑，且低速时特征软，转速稳定性差，同时转子铜损耗大，电动机效率低。串级调速克服了转子串接电阻调速缺点，但设备要复杂得多。
异步电动机降压调速关键用于风机类负载场所，或高转差率电动机上，同时应采取速度负反馈闭环控制系统。
把电压和频率固定不变工频交流电变换为电压或频率可变交流电装置称作“变频器”。为了产生可变电压和频率，该设备首先要把电源交流电变换为直流电（DC），这个过程叫整流。再把直流电（DC）变换为交流电（AC），这个过程叫逆变，把直流电变换为交流电装置叫逆变器（inverter）。对于逆变为频率可调、电压可调逆变器我们称为变频器。变频器输出波形是模拟正弦波，关键用在三相异步动机调速，又叫变频调速器。 附录 二
外文原文
Asynchronous motor has a simple structure, reliable operation, low price, convenient maintenance and a series of advantages, therefore, asynchronous motor is widely used in electric drive system. Especially with the development of power electronic technology and AC drive technology becomes more mature, greatly improve the speed performance makes the asynchronous motor. At present, electric drive asynchronous motor has been widely used in various industrial electrical automation. The mechanical properties of three-phase asynchronous motor starting, the main motor starting, braking, speed control technology.
The mechanical properties of 1 three-phase asynchronous motor
Mechanical characteristics of three-phase asynchronous motor is refers to the relationship between the speed of the motor electromagnetic torque of N and Tem. Due to the speed of N and slip S have a certain relationship, so the mechanical properties are also commonly used Tem = f (s) representation. Electromagnetic torque expression of three-phase asynchronous motor has three forms, namely physical expression, parameters and practical expression. Physical expressions reflect the physical nature of electromagnetic torque of asynchronous motor, the electromagnetic torque is generated by the main flux and rotor active current interaction. Parameter expression reflects the relationship between parameters of electromagnetic torque and power supply parameters and motor, the expression can be used to influence easily analyze the influence of parameter variation on the electromagnetic torque and all kinds of human characteristics. Practical expressions in a simple, easy to remember, is often used in engineering calculation in the form of.
The maximum torque of motor and torque are two important indexes reflecting the overload capacity of the motor and starting performance, maximum torque and start torque motor overload capacity is bigger, stronger, better starting performance.
The mechanical characteristic of three-phase asynchronous motor is a nonlinear curve, under normal circumstances, with the maximal torque (or critical slip) as a cutoff point, the linear segment for the stable operation region, while the nonlinear section is not stable operating region. Hard characteristic is linear segment inherent mechanical properties, the nominal operating point speed slightly lower than the synchronous speed. Shape parameters available expressions man-made mechanical characteristic curve analysis, analysis the key to grasp the maximum torque, starting torque variation of critical slip and the three with the parameters of.
2 three-phase asynchronous motor starting
Three-phase asynchronous motor with small capacity can be used to directly start, cage motor with large capacity can adopt step-down start. Step-down start into stator resistance or reactance step-down start, Y-D step-down start and autotransformer start. The stator resistance or motor step-down start, starting current voltage relations with a reduced, and the starting torque with the square of the voltage is reduced, it is suitable for the starting load. Only applicable to motor start to normal operation for the triangle connection Y-D buck, the starting current and starting torque is reduced to direct startup 1\/3, which is also suitable for the starting load. Autotransformer start, starting current and starting torque is reduced to direct startup l\/k2 (k is the self coupling transformer), suitable for large load starting.
The wound rotor asynchronous motor with rotor series resistance or frequency sensitive rheostat starting, the starting torque, small starting current, suitable for heavy load starting, large asynchronous motor.
The soft starter is a novel control device for motor motor soft start, soft stop, light load energy saving and various protecting functions in one, called Soft Starter. The main structure is connected in series between the power supply and the controlled motor three-phase inverse parallel thyristor and its electronic control circuit. Through the series of soft starter is connected between the power supply and the controlled motor, in different ways, its internal control thyristor conduction angle, so that the motor input voltage from zero to a preset function gradually rise, until the end of the motor start, give full voltage, namely soft start. In the soft start-up process, starting torque motor speed increases gradually, gradually increasing. The soft starter is actually a regulator, for when the motor is started, the output voltage does not change the frequency change.
3 speed of three-phase asynchronous motor
Control method of the three-phase asynchronous motor with variable speed, variable speed and variable slip speed. The variable slip ratio control includes a rotor winding rotor asynchronous motor series resistance speed control, cascade control and blood pressure control.
Variable speed is by changing the stator winding connection mode to change the pole number, so as to realize the change of motor speed. Variable speed is speed-regulation, variable stator winding connection speed of three kinds: Y-YY, Y-, D-YY and Y run. The Y-YY connection is constant torque speed control mode, another two species belong to the constant power control mode. Variable pole speed, should also be on the stator two-phase wiring, so that we can guarantee the speed regulation motor steering.
Variable frequency speed control is the main direction of modern AC speed regulation technology, it can realize stepless speed regulation, suitable for constant torque and constant power load.
Wound rotor rotor motor series resistance speed control method is simple, easy to implement, but speed is not smooth, level, and low speed characteristics of soft, speed stability is poor, and the rotor copper loss, motor efficiency is low. Cascade speed control to overcome the rotor series resistance speed disadvantage, but the equipment is much more complex.
Step-down speed asynchronous motor for fan load, or high slip motor, closed-loop control system should be accompanied by negative feedback of speed.
The industrial frequency alternating current voltage and frequency of fixed to variable voltage or frequency of the alternating current.