Induction Motor as a Transformer

Both induction motor and transformer works under the principle of Electromagnetic induction. In transformer, primary winding and secondary winding are magnetically coupled. Whereas in induction motor, the stator and rotor are magnetically coupled.

A transformer is said to be alternating flux transformer because alternating flux is used to induce the mutually induced emf in the secondary side. Whereas a induction motor is said to rotating flux transformer because rotating flux is used to induce the mutually induced emf in the rotor of the motor In a alternating flux transformer the frequency of induced emf and current in primary and secondary is always same. However in the induction motor frequency of emf and current on the stator side remains same but frequency of rotor emf and current depends on the slip, where slip depends on load on the motor, so we have a variable frequency on the rotor of the motor. During starting of induction motor, the slip (S = 1) which means the frequency of supply to the stator and of induced emf in the rotor are same at starting. In alternating flux transformer, the entire energy present in the secondary circuit is in the form as electrical form. Whereas, in rotating flux transformer, the entire energy present in the secondary circuit is in the form as Mechanical form.