Electrical Machines
Commutator in DC generator is used for

 reduce losses
 collecting of current
 convert AC armature current in to DC
 increase efficiency

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Electrical Machines
The damper windings also called the squirrel cage windings or damper grids

  consists of short-circuited copper bars embedded in the field pole faces.
  are provided on the stator for improving power factor.
  are provided in a synchronous motor to make it self starting.
  both (A) and (B).

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