Electrical Machines
The compensating winding in a DC machine

 is located on commutating poles for improving commutation.
  is located on pole shoes to avoid the sparking at the brushes.
  is located on pole shoes for avoiding the flashover at the commutator.
 is located in armature slots for compensation of the armature reaction.

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Electrical Machines
In speed control of DC Series motor, speed lower than the rated speed can be obtained by

 Any of the above.
 Connecting an additional resistance in the armature circuit.
 Connecting an additional resistance in stator circuit.
 Connecting an additional resistance in the field circuit.

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