Answer / iamdon

When a 3 phase balanced supply is given to the 3 phase
balalced sator winding,a rotating magnetic field of
constant amplitude is produced.

Rotating field cuts the stationary rotor conductor.So emf
induced in conductor according to Faraday's laws.The rotor
conductors are short circuited.So current starts flowing in
conductor according to Lenz law.

As we know the EFFECT will always OPPOSE THE CAUSE.Here the
EFFECT IS THE CURRENT INDUCED and the CAUSE IS RELATIVE
MOTION between rotating magnetic field and stationary
conductor on rotor.So the torque acting on the rotor
conductor is in such a way that it will oppose the cause.So
rotor starts rotating in the SAME DIRECTION as that of
rotating magnetic field as long as there is relative motion
between two.Rotor will never catch the field so it continue
to run.Due to this reason Induction Motor is self starting.

This principle is similer to transformer.Hence Induction
motor is also called as Rotating Transformer.

Author:arbelectbit@yahoo.com

Answer / jain c

The three phase induction motor is a self starting one as
the three phase supply produces the rotating magnetic field.

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