Electrical Machines
The compensating winding in a DC machine

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

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Electrical Machines
The 3 - Φ induction motors are, by a very considerable margin, the most widely used AC motors as

  they have very good speed regulation.
  they have maximum efficiency and maximum starting torque.
  these are cheaper in cost, simple and rugged in construction.
  they are capable of operation under range of leading and lagging pf.

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