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Working Principle of Three Phase Induction Motor

An electrical motor is such an electromechanical device which converts electrical energy into a mechanical energy. In case of three phase AC operation, most widely used motor is Three phase induction motor as this type of motor does not require any starting device or we can say they are self-starting induction motors. For better understanding, the principle of three phase induction motor, the essential constructional feature of this motor must be known to us. This Motor consists of two major parts:

Stator of Motor

Stator of three phase induction motor is made up of numbers of slots to construct a 3 phase winding circuit which is connected to 3 phase AC source. The three-phase winding is arranged in such a manner in the slots that they produce a rotating magnetic field when three-phase AC supply is given to them.Stator of  Motor

Rotor of Motor

Rotor of three phase induction motor consists of cylindrical laminated core with parallel slots that can carry conductors. The conductors are heavy copper or aluminium bars which fit in each slot, and they are short-circuited by the end rings. The slots are not exactly made parallel to the axis of the shaft but are slotted a little skewed because this arrangement reduces magnetic humming noise and can avoid stalling of the motor. squirrel cage rotor

Working of Three Phase Induction Motor

Production of Rotating Magnetic Field

The stator of the motor consists of overlapping winding offset by an electrical angle of 120o. 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.

Secrets Behind the Rotation: 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 be observed that the rotor speed should not reach the synchronous speed produced by the stator. If the speeds become equal, there would be no such relative speed, so no emf induced in the rotor, and no current would be flowing, and therefore no torque would be generated. Consequently, the rotor cannot 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.

Thus the three phase induction motor is:

Working Principle of Three Phase Induction Motor - Video



PPATRICK commented on 24/05/2018
Thank you, its a good explanation
NNITIN CHAURASIA commented on 20/05/2018
Thank you
EERAM commented on 24/04/2018
This is really a good explanation. Very helpful
DDHRUV JOSHI commented on 20/04/2018
Superb technical explanation great job keep it up
VVICTOR OPIAZA commented on 06/04/2018
Good explanation and I am very satisfied.
SSHIV commented on 15/03/2018
Easy and lucid way explained. Nice
Comments

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