Three phase asynchronous motor is a type of induction motor that is powered by simultaneously connecting 380V three-phase AC current (phase difference of 120 degrees). Due to the fact that the rotor and stator of a three-phase asynchronous motor rotate in the same direction but at different speeds, there is a slip rate, so it is called a three-phase asynchronous motor. The speed of the rotor of a three-phase asynchronous motor is lower than that of the rotating magnetic field. The rotor winding generates electromotive force and current due to relative motion with the magnetic field, and interacts with the magnetic field to produce electromagnetic torque, achieving energy conversion.

Compared with single-phase asynchronous motors, three-phase asynchronous motors have better operating performance and can save various materials. According to the different rotor structures, three-phase asynchronous motors can be divided into cage type and wound type. The asynchronous motor with cage rotor has a simple structure, reliable operation, light weight, and low price, and has been widely used. Its main disadvantage is the difficulty in speed regulation. The rotor and stator of a wound three-phase asynchronous motor are also equipped with three-phase windings and connected to external resistors through slip rings and brushes. Adjusting the resistance of the variable resistor can improve the starting performance of the motor and regulate its speed.