The working principle of an asynchronous motor (induction motor) is to generate an induced current in the rotor through the rotating magnetic field of the stator to generate an electromagnetic torque, and the rotor does not directly generate a magnetic field. Therefore, the speed of the rotor must be less than the synchronous speed (without this difference, that is, the slip rate, there is no rotor induced current), so it is also called an asynchronous motor.
And "three-phase asynchronous motor", three-phase means that the voltage is three-phase electricity, and the power supply mode is 120° electrical angle to generate an alternating magnetic field to drive the motor to work. Three-phase means three-phase AC, and asynchronous means relative synchronization. The rotor speed is not equal to the synchronous speed to form a certain difference. The relevant parameters refer to the slip rate. The fundamental difference between synchronous and asynchronous is whether there is excitation or not. Asynchronous motors rely on electromagnetic induction to generate a potential on the rotor to form a current, and rotate under the magnetic field force formed by the stator. Therefore, the first condition is that there is slip. The magnetic field will be cut, and the force will be generated. The "asynchronous" meaning of the three-phase asynchronous motor is that the speed of the rotor is always lower than the synchronous speed in the electric working state.
The rotor speed of the three-phase asynchronous motor will not be synchronized with the rotating magnetic field, nor will it exceed the speed of the rotating magnetic field. Because the induced current in the rotor coil is due to the relative movement of the rotor conductor and the magnetic field. If the rotational speed of the rotor is equal to the rotational speed of the rotating magnetic field, then there is no relative motion between the magnetic field and the rotor, and the conductor cannot cut the magnetic field lines, so there will be no induced potential and current in the rotor coil, and the rotor conductor is in the magnetic field. It will not be affected by the electromagnetic force to make the rotor rotate. Therefore, the rotor rotation speed of the asynchronous motor cannot be the same as the rotating magnetic field, and is always less than the synchronous speed of the rotating magnetic field. However, in special operating modes (such as generator braking), the rotor speed can be greater than the synchronous speed. Because the rotor and stator rotating magnetic field of a three-phase asynchronous motor rotate in the same direction and at different speeds, it is called a three-phase asynchronous motor instead of a three-phase synchronous motor.
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