Electrical Machines
Short circuiting is caused in the armature winding due to

  any of above.
 failure of insulation between two commutator bars.
  failure of insulation between two turns of coil.
  grounding of two or more turns of the same coil.

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

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