Electrical Machines
Commutator in DC generator is used for

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

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Electrical Machines
Skewing of the rotor in a 3 - Φ squirrel cage induction motor reduces

  noise, parasitic and starting torque, but increase pull out torque.
  noise and parasitic torque, but increase starting and pull-out torque.
  noise and pullout torque, but increase parasitic and starting torque.
  noise, parasitic torque, starting torque and pull out torque.

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Electrical Machines
Flashing of DC generator means

  creation of residual magnetism by a DC source.
  increasing flux density by providing extra ampere-turns in field.
None of these
 neutralization of residual magnetism.

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