Electrical Machines
The field system of an alternator is usually excited

  110 / 220 V AC.
  250 / 250 V DC.
  3 - Φ, 50 Hz and 400 V.
  230 V AC.

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Electrical Machines
In a DC machine

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

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