Electrical Machines
A commutator in DC machines can 1. provide half-wave rectification 2. Provide full-wave rectification 3. convert ac to dc 4. Convert dc to ac 5. provide controlled full-wave rectification From these, the correct answer is

 2, 3, 4
 2, 3, 4, 5
 1, 2, 3
 2, 3 ,5

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Electrical Machines
The compensating winding in a DC machine

 is located in armature slots for compensation of the armature reaction.
  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 on commutating poles for improving commutation.

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