Question

Three-phase induction motor works on the principle of ________. (Self-induction Mutual induction)

Hint:

An induction motor is conceptually a rotating transformer. The stator acts as the primary winding, and the short-circuited rotor behaves as a moving secondary winding, transferring power entirely through mutual induction.

Answer 1

Step 1: Analyzing the Induction Process:
Applying a balanced three-phase AC supply to the stator windings of an induction motor produces a rotating magnetic field (RMF) that rotates at synchronous speed ($N_s$).

Step 2: Energy Transfer Mechanism:
This rotating magnetic field crosses the air gap and sweeps past the stationary rotor conductors. As the magnetic flux cuts across the rotor circuits, it induces an electromotive force (emf) in them via Faraday's Law.

Step 3: Comparing Induction Types:

• Self-Induction: The induction of an electromotive force in a current-carrying wire when the current in the self-same wire changes (e.g., choke coils).
• Mutual Induction: The induction of an electromotive force in one circuit (rotor) by a change in magnetic flux in another separate circuit (stator).

Because energy is transferred across the air gap from the stator windings to the separate rotor circuit via electromagnetic coupling, the motor works on the principle of Mutual induction (similar to a transformer with a rotating secondary).