Why does the rotor rotate when the induction motor is fed from 3 phases?
1). Rotating Magnetic Field (RMF)
When a 3-phase supply is given to the stator 3 currents flow with 120° phase difference.
These currents produce a rotating magnetic field at synchronous speed.
2). Electromagnetic Induction
The rotating magnetic field cuts the stationary rotor conductors inducing an EMF according to Faraday’s Law. This causes current to flow in the rotor.
3). Torque Generation
The interaction between the rotor current and the stator magnetic field produces a force (Lorentz force) generating torque.
4). Rotor Rotation
The rotor starts rotating in the same direction as the rotating magnetic field but never reaches synchronous speed. The difference in speed is called slip.
Formula:
Ns = (120 × f) / P
Slip = (Ns - Nr) / Ns
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