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
 1, 2, and 3
 1, 2 and 4
 2, 3 and 4

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Electrical Machines
In synchronous generator, inverted V curve is drawn between

 field current on X-axis and power factor on Y-axis
 field current on Y-axis and power factor on X-axis
 field current on X-axis and armature current on Y-axis
 field current on Y-axis and armature current on X-axis

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