Electrical Machines
Flashing the field of DC generator means

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

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Electrical Machines
For an ideal transformer the winding should have

 no ohmic resistance on either side
 maximum resistance on primary side and least resistance on secondary side
 minimum resistance on primary side and maximum resistance on secondary side
 equal resistance on primary and secondary side

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