Electrical Machines
Which of the following factors improve commutation in a dc machine ? 1. High contact resistance of brushes 2. High inductance of the coils undergoing commutation 3. Shifting of brushes in the direction of rotation for a generator and in the opposite direction For a motor 4. Narrow width for the commutation bars Select the correct answer using the codes given below : Codes :

 1, 2 and 4
 2, 3 and 4
 1, 2, and 3
 1 and 3

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Electrical Machines
Skewing of the rotor in a 3 - Φ squirrel cage induction motor reduces

  noise and pullout torque, but increase parasitic and starting torque.
  noise, parasitic torque, starting torque and pull out torque.
  noise, parasitic and starting torque, but increase pull out torque.
  noise and parasitic torque, but increase starting and pull-out torque.

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