Working Principle of Three-Phase AC Induction Motor

A three-phase AC asynchronous motor is a type of motor powered by simultaneously connecting to a 380V three-phase AC current (with a phase difference of 120 degrees). Since the rotor of a three-phase asynchronous motor rotates in the same direction as the stator's rotating magnetic field but at a different speed, a slip rate exists, hence the name "three-phase asynchronous motor." The rotor speed of a three-phase asynchronous motor is lower than that of the rotating magnetic field. Due to the relative motion between the rotor windings and the magnetic field, an electromotive force and current are generated, which interact with the magnetic field to produce electromagnetic torque, enabling energy conversion.

When symmetrical three-phase alternating current is applied to the stator windings of a three-phase AC asynchronous motor, a rotating magnetic field is generated that moves clockwise along the inner circumference of the stator and rotor at synchronous speed n1.  Since the rotating magnetic field spins at speed n1 while the rotor conductors are initially stationary, the conductors cut through the stator's rotating magnetic field, inducing an electromotive force (EMF) (the direction of which is determined by the right-hand rule).  With the rotor conductors short-circuited by end rings, the induced EMF causes currents to flow in the conductors, generally aligned with the direction of the EMF. The current-carrying conductors in the rotor experience electromagnetic force (determined by the left-hand rule) within the stator's magnetic field.  This electromagnetic force generates torque on the rotor shaft, driving the rotor to rotate in the same direction as the rotating magnetic field.

Based on the above analysis, the working principle of the motor can be summarized as follows: When three-phase stator windings (each phase differing by 120 electrical degrees) are supplied with balanced three-phase AC power, a rotating magnetic field is generated. This rotating magnetic field cuts through the rotor windings, inducing current in them (as the rotor windings form a closed circuit). The current-carrying rotor conductors then experience electromagnetic forces under the influence of the stator's rotating magnetic field, resulting in electromagnetic torque on the motor shaft. This torque drives the motor to rotate, with the direction of rotation aligning with that of the rotating magnetic field.