Discussion
A synchronous motor is not self-starting because
Answer: D
Correct answer: at standstill the stator field sweeps past the rotor too quickly
Switched on to a fixed supply at rest, the stator field rotates at synchronous speed past a stationary rotor. In the first half-cycle the torque acts one way and in the next the other, and the rotor’s inertia is far too great for it to follow, so the average torque over a cycle is zero and the machine simply hums. Starting requires either a damper winding to bring it up as an induction motor, or a converter whose frequency is raised gradually from zero.
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