Red Seal Electrician Practice
Motor controlsQuestion 1209 of 1506

How is a large industrial synchronous motor normally started on a 60 Hz supply?

  1. Rotor cage bars start it like an induction motor, then the rotor field is energized.
  2. The rotor field is energized first, then the stator is put on the line.
  3. A small permanent magnet rotor pulls the main rotor up to speed before the field is used.
  4. The motor is turned by hand until the rotor locks to the line frequency.
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Correct answer: Rotor cage bars start it like an induction motor, then the rotor field is energized.

The cage in the rotor brings it near synchronous speed. Only then is the rotor electromagnet energized.

Source: Lessons in Electric Circuits II: AC (Kuphaldt), 13.2: Synchronous Motors

Practice motor controls

Questions last reviewed: 18 October 2026