Electrical Machines
The armature mmf of a DC machine has

  trapezoidal space distribution and is stationary in space.
  triangular space distribution and is stationary in space.
 stepped distribution and rotates at the speed of armature.
  triangular space distribution and rotates at the speed of armature.

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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 3
 2, 3 and 4
 1, 2 and 4
 1 and 3

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