# Why Induction Motor is called Asynchronous Motor?

An induction motor is called asynchronous motor because the actual speed of the motor is not equal to the synchronous speed of the motor. The synchronous speed of the motor is always more than the actual speed of the motor. If the actual speed of the motor(N) is equal to the synchronous speed (Ns), then no torque will be produced and motoring function not possible.

That is why an induction motor is called asynchronous motor. Let us understand what is synchronous speed of the motor? The synchronous speed is the speed of rotating magnetic field which is produced when the three phase supply is fed to the stator of the motor. The rotor conductors of an induction motor is short circuited at the end rings. The magnetic filed acts on the rotor. When the magnetic field gets linked to the rotor conductor the voltage is induced in the rotor conductor. The underlying principle is electromagnetic induction, similar to transformer.

However, if the rotating magnetic field and  rotor rotates at the same synchronous speed, the EMF induced in the rotor is zero because the field will be constant with respect to rotor. The voltage will be induced in the rotor if rate of change of flux  exist.

The motor rotation happens when there is slip between the rotor and the stator. The slip is the difference between the speed of rotational magnetic field and the actual speed of the rotor. The inability of the rotor to catch up the speed of the rotating magnetic field is called the slip of motor. Thus, an induction motor working is possible if slip exist  between rotating magnetic field and the actual speed of the rotor. As the load is increased on the motor its slip gets increased.

That is why an induction motor is called asynchronous motor.

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