A dc, separately excited motor has a load torque of 140 Nm and a frictional torque of 10 Nm. The motor is rated at 240 V. The armature resistance of the motor is 1 ?. The motor speed at the given load is 600 rpm. Ignore the field losses and calculate the motor efficiency.

What will be an ideal response?


Separately excited motor:



The developed power,



Solving for Ia gives Ia = 49.46 A or 190.54 A

The higher value gives lower efficiency, so the lower value is selected.

Hence, the input power to the motor is





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