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Armature reaction in a dc machine

  • A.distorts the main field and can worsen commutation
  • B.increases the main field flux and so raises the torque developed
  • C.has no effect on the operation of the machine at any load
  • D.reverses the direction of rotation at heavy load

Answer: A

The armature current sets up its own field that shifts and distorts the main one, which is why interpoles and compensating windings are fitted on larger machines. Poor commutation shows as brush sparking and shortens brush life.

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