Electrical Machines
Commutators in DC machines have a role of which converts

 AC to DC.
 Both AC to DC and DC to AC.
 none of these.
 high voltage DC to low voltage DC.

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Electrical Machines
In a star - delta starting of an IM

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

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Electrical Machines
Two of supply terminals to a 3 - Φ induction motor get interchanged during re-connection after normal maintenance. When switched on the supply, the motor will

  rotate in the same direction as before maintenance.
  not start at all.
  rotate in direction opposite to that before maintenance.
  get heated and damaged.

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