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
In a DC machine, for the same value of φ, Z and N; which one of the following statements is correct?

  Armature emf is more with wave winding than with lap winding.
 Armature emf is same as long as the flux density in the air gap remains the same.
 Armature emf is less with wave winding than with lap winding.
 Armature emf depends on weather the machine is running as a motor or generator.

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