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%.

 82.5%
 72.5%
 67.5%
 78.5%

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Electrical Machines
If the frequency of input voltage of a transformer is increased keeping the magnitude of voltage unchanged, then

 Ph will decrease but Pe will remain same
 both hysteresis loss(Ph) and eddy current loss(Pe) will increase
 Ph will increase but Pe will decrease
 Pe will increase but Ph will decrease

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