Working Principle of Three Phase Induction Motor
The stator of
the motor consists of overlapping winding offset by an electrical angle of
120°. When the primary winding or the stator is connected to a 3 phase AC
source, it establishes a rotating magnetic field which rotates at the synchronous
speed.
According to Faraday’s law an
emf induced in any circuit is due to the rate of change of magnetic flux linkage through the circuit.
As the rotor winding in an induction
motor are either closed through an external resistance or directly shorted by end
ring, and cut the stator rotating magnetic field, an emf is induced in the rotor
copper bar and due to this emf a current
flows through the rotor conductor. Here the relative speed between the rotating
flux and static rotor conductor is the cause of current
generation; hence as per Lenz's law the
rotor will rotate in the same direction to reduce the cause i.e. the relative
velocity.
Thus from the
working principle of three phase induction motor it may observed that the rotor
speed should not reach the synchronous speed produced by the stator. If the
speeds equals, there would be no such relative speed, so no emf induced in the
rotor, & no current
would be flowing, and therefore no torque would be generated. Consequently the
rotor can not reach the synchronous speed. The difference between the stator
(synchronous speed) and rotor speeds is called the slip. The rotation of the magnetic field in an induction
motor has the advantage that no electrical connections need to be
made to the rotor.
No comments:
Post a Comment