Electrical Machines
A DC shunt machine generates 250 V on open circuit at 1000 RPM. Armature resistance is 0.5 Ω, field resistance 250 Ω. When running as a motor takes 4 A at 250 V. Calculate the efficiency when running as a motor taking 40 A at 250 V. Armature reaction weakens the field by 4%.

 78.5%
 72.5%
 67.5%
 82.5%

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

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