Electrical Machines
In dc machines, the field system has to be provided on stator unlike synchronous machines Where in it could be on any member, because

 it gives more uniform air-gap flux distribution
 it reduces field structure iron losses
 commutator action is not possible otherwise
 dc machines are comparatively low rating machines.

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Electrical Machines
In a star - delta starting of an IM

  applied voltage per stator phase is 57.7 % of a line volt
  line voltage is 57.7 % of stator voltage.
  resistance is inserted in the rotor.
  reduced voltage is applied to the stator.

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