Electrical Machines
Flashing the field of DC generator means

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

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Electrical Machines
In speed control of DC Series motor, speed lower than the rated speed can be obtained by

 Connecting an additional resistance in the field circuit.
 Connecting an additional resistance in the armature circuit.
 Connecting an additional resistance in stator circuit.
 Any of the above.

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