The ac induction motor is one of the most widely used motors with greatest demand. Among machines with electricity as power in every country, there are about 90% of the ac induction motor, in which, small ac induction motor accounts for more than 70%.
In the total load of the power system, the ac induction motor electricity accounts for a large proportion. In China, the electricity consumption of ac induction motor accounts for more than 60% of the total load.
The basic characteristic of ac induction motor is that the rotor windings doesn’t need to connect to other power, and the stator current can be taken directly from the AC power system; Compared with other motors, the ac induction motor has simple structure, easy manufacture, use, maintenance, high reliability, light weight and low cost. The ac three-phase induction motors, for example, compared with a dc motor with the same power and speed, has only half weight of the latter and only one-third cost.
The ac induction motor also is easy to derive a variety of products according to different environmental requirements.
It also has load characteristics of early constant speed, meeting most of the requirements of industrial and agricultural production machinery dragging. Its limitation is that its speed and its synchronous speed of the rotating magnetic field has a fixed slip, thus its speed performance is poor, and it can’t be economical and convenient like the dc motor in usage scenarios demanding for a more smooth wide speed range (such as mill drive , winches, large-scale machine tools, etc.). In addition, when the ac induction motor is running, it will draw reactive power from the power system in the field, which causes deterioration of the power factor of the power system. Therefore, in the high-power, low-speed applications (such as dragging a ball mill, compressors, etc.), using synchronous motors is more reasonable.
As the ac induction motor with big production capacity and a wide surface required the number of varieties, specifications and all kinds of machinery and equipment, thus in design and production of ac induction motor, particular attentions should be paid to standardization, serialization, universal.