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During induction starting of a synchronous motor, the field winding is

  • A.left open circuited so that no current can flow in it
  • B.excited at full value from the beginning of the start
  • C.disconnected physically from its exciter and earthed
  • D.short circuited through a discharge resistance

Answer: D

Correct answer: short circuited through a discharge resistance

Left open, the field winding would have a very large voltage induced across it during the induction start, since it has many turns and the field is sweeping past at slip frequency. Closing it through a resistance limits that voltage while still allowing the winding to contribute a little starting torque.

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