Working Principle of 3 Phase Induction Motor:
When a short circuited coil is placed in a rotating magnetic field, a current is set up in the coil and tends to move due to electro-magnetic induction. When a three-phase supply is fed to the stator winding of the three induction motor which producing a rotating magnetic field. It revolving at a synchronous speed. As the rotating magnetic field cuts the short circuited copper bars of the squirrel cage induction motor rotor winding. Then a high current flows in the rotor bar and creating another field.
Now this rotor field oppose the main rotating field. As the rotor is designed to free moving. It tends to follow the rotating field in the same direction of rotations. Now, the rotor starts and picks up the speed until it approaches the synchronous speed. The rotor never reaches the synchronous speed and runs always just below the synchronous speed.