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
An inverted V curve of synchronous motor shows variation of

 supply voltage and excitation current at constant load.
 supply voltage and field current at constant excitation.
  power factor and DC excitation at constant load.
 power factor and supply voltage during hunting.

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