Electrical Machines
When R2 is rotor resistance, X2 the rotor reactance at supply frequency and s the slip, then the condition for maximum torque under running condition will be

  R2 = s2X2.
  sR2 = X2.
  R2 = s2X2.
  R2 = sX2.

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Electrical Machines
Flashing the field of DC generator means

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

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