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True or false: commutation becomes easier as the machine speed increases.

  • A.True, provided the load current stays constant
  • B.False, since the commutation period lengthens with speed
  • C.False, since the commutation period shortens and the reactance voltage grows
  • D.True, since the coil has less time in which to spark

Answer: C

A shorter period means a faster current reversal and therefore a larger emf of self-induction to overcome. That is one reason high-speed dc machines are limited in size and why the commutator eventually sets the ceiling.

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