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Question

# A 60 kW, 250 V shunt motor takes 16 A when running at 1440 rpm. The resistance of the armature and field are 0.2 Ω and 125 Ω respectively. The efficiency of the motor when taking 152 A is

A
77.73%
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B
85.17%
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C
87.17%
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D
81.45%
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Solution

## The correct option is A 77.73%Field current, If=250125=2 A No load armature current, Ia0=16−2=14 A Constant losses, PK=(250×14−(14)2×0.2)+250×2=3960.8 W Ia=152−2=150 A PL=Ia 2Ra+PK=(150)2×0.2+3960.8 =8.461 kW Pin=250×152=38 kW ∴ Efficiency, η=38−8.46138×100=77.73%

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