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A separated excited dc machine is delivering 50% rated torque at 20% rated speed. Find the...

A separated excited dc machine is delivering 50% rated torque at 20% rated speed. Find the efficiency of the motor at this operating point. The details of the machine are as follows: 1500 kW(rated output power), 600V(rated voltage), 2650A (rated current) 600rpm (rated speed), brush voltage drop = 2V, Filed power input = 50 kW, Ra=3.645 mOhm, La=0.1 mH, Machine frictional torque coefficient = 15 Nm/rad/s. Field current is constant and armature voltage is variable.

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