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
 1, 2, and 3
 1 and 3
 2, 3 and 4

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Electrical Machines
An ideal synchronous motor has no starting torque because

 relative velocity between the stator and rotor mmf’s is zero.
  relative velocity between stator and rotor mmf’s is not zero.
 rotor winding is highly reactive.
 rotor is made up of salient poles.

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