Electrical Machines
A 240 V, dc shunt motor draws 15 A while supplying the rated load at a speed of 80 rad/s. The armature resistance is 0.5 W and the field winding resistance is 80 W. The net voltage across the armature resistance at the time of plugging will be

 234 V
 240 V
 474 V
 6 V

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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, 2, and 3
 1, 2 and 4
 1 and 3
 2, 3 and 4

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Electrical Machines
Due to magnetic saturation, the flux per pole in a DC machine without brush shift

 increases in both the generators and the motors with load.
 decreases in generators and increases in motor with load.
 increases in generators but decreases in motor with load.
  decreases in both generators and the motors with load.

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