Why is the actual speed of the asynchronous motor lower than the synchronous speed?

Looking at the parameter table of various three-phase asynchronous motors, the synchronous speed of the 2-pole motor is 3000r/min, the synchronous speed of the 4-pole motor is 1500r/min, the synchronous speed of the 6-pole motor is 1000r/min, and the synchronization of the 8-pole motor. The speed is 750r/min. . . The actual speeds of the various types of motors are different, and slightly lower than the synchronous speed of the motor. Why is the actual speed of the asynchronous motor lower than the synchronous speed ? Why is it called an "asynchronous" motor? "Asynchronous" means that the motor windings use three sets of coils that are mutually different from each other by 120 electrical angles. The load is a three-phase power supply; the rotor speed of the motor is slightly lower than the rotational magnetic field speed generated by the stator windings, and the two rotational speeds are not synchronized. asynchronous. Another point of asynchronous is that the motor can be reversed, that is, changing any two fire lines during normal operation can change the direction of rotation.

(1) At start-up, the rotor is stationary, the rotating magnetic field of the stator is synchronous, the rotor cuts the stator magnetic field to generate an induced potential, and an induced current is generated in the short-circuit winding. The rotor current is subjected to electromagnetic torque in the stator magnetic field to cause rotation.

(2) During the rotation process, if the rotor reaches the synchronous speed, it is relatively stationary with the rotating magnetic field of the stator. The rotor does not cut the stator magnetic field to generate the induced potential and the induced current, and the rotor is not affected by the electromagnetic torque of the stator magnetic field. The rotor will slow down.