Electrical Machines
A 240 V dc series motor takes 40 A when giving its rated output at 1500 rpm. Its resistance is 0.3 Ω. The value of resistance which must be added to obtain rated torque at 1000 rpm is

 1.9 Ω
 5.7 Ω
 6 Ω
 2.2 Ω

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Electrical Machines
In a synchronous motor when the rotor speed exceeds the synchronous speed during hunting

  the damper bars develop synchronous motor torque.
  negative sequence currents are generated.
  the damper bars develop induction motor torque.
  the damper bars develop induction generator torque.

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