Working principle of AC motor

The working principle of AC motor is based on Faraday's law of electromagnetic induction and Lenz's law. The conversion of electrical energy into mechanical energy is achieved through the interaction between the rotating magnetic field generated by the AC power supply and the conductor (rotor) inside the motor. The specific process is as follows:

Generation of rotating magnetic field: When three-phase AC is passed into the stator winding, a rotating magnetic field will be generated inside the stator due to the 120° phase difference between the three-phase currents in time. The rotation speed of this magnetic field (called synchronous speed) is related to the frequency of the power supply and the number of pole pairs of the stator.

Generation of induced current: The conductor in the rotor (such as the aluminum bars of the squirrel cage rotor or the winding of the wound rotor) cuts the magnetic flux lines in the rotating magnetic field, generating an induced electromotive force, and then generating an induced current. These induced currents also form a magnetic field in the rotor, called an induced magnetic field or a rotor magnetic field.

‌The action and rotation of electromagnetic force: There will be an interaction force between the rotor magnetic field and the stator magnetic field, namely the electromagnetic force. Since the stator magnetic field is rotating and the rotor magnetic field is fixed (but moves as the rotor rotates), the direction of the electromagnetic force is constantly changing, driving the rotor to rotate. Due to the hysteresis effect of electromagnetic induction, the rotor actually lags slightly behind the rotation speed of the stator magnetic field, a phenomenon called "slip".

‌Continuous rotation‌: Since the alternating current changes periodically, the stator magnetic field will also continue to rotate, constantly driving the rotor to rotate. At the same time, the stator and rotor are powered by the same power supply, and the current direction changes are always synchronized, which ensures that the direction of the electromagnetic force is always conducive to the rotation of the rotor.