绕线式异步电机四象限运行

三相异步电动机电力拖动系统的特性分析

2010年11月27日 15:44 本站整理作者：佚名用户评论（0）

关键字：电动机(177)

教学目标

掌握分析三相异步电动机的机械特性;

掌握三相异步电动机的各种起动方法；

掌握三相异步电动机的回馈、反接、能耗制动运行状态。

3.1 Speed /Torque Curves

Vocabulary

1. power distribution

2. electromagnetical torque

3. breakdown torque=stalling torque

4. asymptotic

5. abscissae

6. skew

7. full-pitch coil

Example

A three-phase,230V,60Hz,12kW,4 pole wound induction motor has the following parameters expressed in Ω /phase.

R1=0.095 x1=0.68

x2=0.672 xm=18.7

Using MATLAB, plot the electromechanical torque Tmech as a function of rotor speed in r/min for rotor resistances of r2=0.1,0.2,0.5,1.0 and 1.5 Ω.

3.2 Starting of Induction Motors

Vocabulary

ball mill, crusher, compressor

terminal, a deep-bar cage

installation, maintenance

aperiodic component

resultant flux , stationary

inrush current , residual magnetisation

qualitative , inertia , parabola , kinetic

direct connection to the line

autotransformer

starting by star-delta switching

m.m.f = magnetomotive force 磁动势

rotating field 旋转磁场

ampere-turns 安匝

stator, rotor, primary (secondary) winding 定、转子初（次）级绕组

slip 转差，滑差

lamination 冲片，叠片；薄片

periphery 圆周

counterclockwise 反时针方向的

phase-sequence 相序

It is interesting to note that this expression could have been written down directly by applying the general theorem for maximum power transfer in such a series circuit; i.e. the load resistance must be equal to the impedance modulus of the remaining circuit components.

The starting torque can be increased up to the maximum figure merely by inserting an external resistance to bring r 2 up to (substitute s=1 in eqn. (2.7)), this value is much higher than the natural rotor resistance

In a number of industries motors must satisfy very strict speed characteristic requirements, both in respect to range and smoothness of control and also in respect to economical operation. From the point of view of speed-control characteristics, induction motors are inferior to d.c. motors, the shortcoming being the greater the wider the range of control.

1. State in which quadrants a machine operates

a. As a brake

b. As a motor

c. As a generator

2. Under what circumstances is reduced voltage starting required ?

3. Name four types of circuit diagrams and describe the purpose of each. o 转子串电阻分级起动

作图法计算起动电阻：

先画固有机械特性；

确定最大起动转矩 T 1 及切换转矩 T 2 ；

作第一级起动机械特性；

作第二级起动机械特性；

作第三级起动机械特性；

完成作图。

解析法计算起动电阻

3.3 三相异步电动机的制动

能耗制动

基本原理