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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Electrical Machines
If the frequency of input voltage of a transformer is increased keeping the magnitude of voltage unchanged, then

 both hysteresis loss(Ph) and eddy current loss(Pe) will increase
 Pe will increase but Ph will decrease
 Ph will increase but Pe will decrease
 Ph will decrease but Pe will remain same

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