3-Phase Induction Motor

 A commonly used variant of motor is three phase induction motor. It is mainly used for industrial purpose, where high power is necessity.

 Like any other induction motor it has two main parts called stator and rotor. Stator is stationary part and Rotor is the rotating part. The stator has three windings ,each for every phase. when the three phases are applied to the windings, it Produces rotating magnetic field. Actually it seems to be rotating, because the three phase which we have applied to the windings have 120 degrees of difference between them.
Firstly winding A attains maximum magnetic field, then it reduces and winding B attains maximum magnetic field, then it also reduces and winding c attains maximum magnetic field and then it reduces then A  and so on... In summation we can say that the magnetic field is rotating. The Stator and rotor are made by stamping of laminated plates of silicon steel. Silicon steel is used because it has very low hysteresis loss in it, when it is operated in an alternating magnetic field. The stamping of stator is done to prevent eddy current losses. We will discuss eddy current loss and hysteresis loss in other posts,later.
The rotor has also stamping and it also has rods between the stamping, that work as conductors during operation. they are joined together by a steel plate on both sides.the rods are insulted from the rotor because of lamination of the stamping. It is necessary because the rods will carry current and they should not touch the rotor.

 The stator is mounted on a solid base, So that it will not move during operation. The rotor is fitted in the stator, with the help of outer body or shell of the motor.
            During operation, when we apply all the three phases to the motor windings,of the stator, The stator creates a rotating magnetic field and associated rotating flux with it. Because the rotor is placed in the stator, flux produced by windings cut the rotor rods.According to Faraday's law of electro-magnetic induction,when a flux linking to a conductor changes, a current is induced in it.Thus, a  current is produced in the rods. Now according to Flemming, when a current carrying conductor is placed in a magnetic field it experiences a force.
Hence the rotor starts rotating. When no load is connected to the motor, the speed of the rotor continuously increases until it comes close to the synchronous speed of the rotating magnetic field.
But it will never equal to the synchronous speed because of friction and the loss happen due to the friction in the form of heat. So the actual speed of motor is always less then the speed of rotating magnetic field.
     I think it will give you a basic idea of construction and working of 3 phase induction motor.