AC induction machines are popular due to their simplicity, reliability, and direct operation from an AC line voltage. ACIMs are asynchronous machines and always have a lower mechanical rotor speed than the power line frequency.
The principle of operation for an ACIM is based on the voltage induction from the stator to the rotor. When the stator winding is fed by a three-phase supply voltage, the current flows in the winding and the stator rotating magnetic field is generated. Induced voltage in the rotor windings will create the rotor current and the rotor magnetic field. The interaction between two magnetic fields creates the mechanical torque needed to turn the rotor.