Question:

A DC, separately excited motor is supplied from a 240-V source. When the motor is unloaded, it draws 1A of current from the source. When the motor is loaded, it draws 25A of current and it rotates at 1560 rpm. The field current supplied to the motor remains unchanged and the armature reaction can be neglected. The motor armature resistance is equal to 0.4 Ω. Calculate the following:

a) The armature voltage of the motor under the load.

b) The amount of mechanical power developed by the motor under the load.

c) The no-load speed of the motor.

d) The amount of rotational losses of the motor.

e) The motor efficiency under the specified load if the field circuit power loss is equal to 360 W.