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A synchronous motor is used to drive a large fan at constant speed principally because

  • A.its speed can be varied without a converter
  • B.it requires no mechanical coupling to the load
  • C.its efficiency and power factor are better at that rating
  • D.it develops a much larger starting torque than a cage machine

Answer: C

Correct answer: its efficiency and power factor are better at that rating

A large fan runs continuously at a fixed speed, which is exactly the duty a synchronous machine suits: the efficiency advantage is earned every hour, and the leading power factor supports the rest of the plant. Its poor starting behaviour hardly matters for a machine started once and left running.

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