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

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

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Electrical Machines
In a star - delta starting of an IM

  resistance is inserted in the rotor.
  line voltage is 57.7 % of stator voltage.
  reduced voltage is applied to the stator.
  applied voltage per stator phase is 57.7 % of a line volt

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Electrical Machines
When the supply terminal of a DC shunt motor are interchanged

 The direction of rotation will reverse.
 The motor will stop.
  The motor will run at its normal speed in the same direction as before.
 The motor will run much faster in the same direction.

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