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 :

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

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Electrical Machines
Cogging and crawling are phenomena associated with

 any of the above.
 the former at a fraction of its rate speed and the latter during starting.
 cage induction machines and they are essentially the same.
 the former during starting and the latter at a fraction of its rated speed.

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