Electrical Machines
A 3- phase synchronous motor can operate over a wide range of power factors i.e. from lagging to leading power factor. This is achieved by

 varying the applied voltage.
 changing the field excitation.
 changing the load.
 varying the speed.

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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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