Question 494Electricity & Electronics - QMED

The correct answer is A) the rotor is magnetically locked into step with the rotating magnetic field by the excitation current. In a synchronous motor, the rotor is excited by a DC current, creating a strong magnetic field. This rotor magnetic field interacts with the rotating magnetic field produced by the stator windings, causing the rotor to lock into synchronism with the rotating field. The excitation current in the rotor is what creates this magnetic locking, allowing the rotor to operate in perfect synchronism with the stator's rotating field. The other options are incorrect because: B) the amortisseur (damper) windings are used to provide starting torque, not to maintain synchronism; C) the field strength does not vary directly with rotor slip in a synchronous motor; and D) the stator flux rotates in the same direction as the rotating magnetic field, not the opposite direction.