Electrical Machines
In which of the following speed control of DC motor the speed obtained is below than the rated speed?

 Any of above.
 Field resistance control.
 Armature voltage control.
 Armature circuit resistance control.

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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 :

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

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