Electrical Machines
In a DC generator, the armature reaction results in

 demagnetization of centers of poles.
  magnetization of inter poles.
 magnetization of leading and demagnetization of trailing pole tip.
  demagnetization of leading & magnetization of trailing pole tip.

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Electrical Machines
Flashing the field of DC generator means

  creating residual magnetism by a DC source.
  neutralising residual magnetism.
 increasing flux density by adding extra turns of winding.
  making the magnetic losses forces parallel.

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