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
In large sized DC machines the compensating windings are provided to

 compensate for the decrease in speed due to increase of load.
  neutralize voltage induced in coil due to fluctuation of l
 reduce eddy current losses by providing local short circuits.
None of these

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Electrical Machines
A 10 kW, 230 V, dc shunt machine has four terminals brought out through four leads. For this machine

 both the windings have thin leads
 armature winding has thick leads whereas field winding has thin leads
 armature winding has thin leads whereas field winding has thick leads
 both the windings have thick leads

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