Electrical Machines
The rotor of a 3 - Φ wound induction motor is provided with

  single phase winding.
  heavy short-circuited end rings.
  three phase winding.
  heavy copper or aluminium bars placed in rotor slots.

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Electrical Machines
In a DC machine

 current and emf at the terminals are alternating.
 current and emf in armature are alternating.
 current and emf in armature are unidirectional
 emf in armature conductors and at the terminals is alternating.

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