Question

For a separately excited dc machine of 25 kW, 250 V and armature resistance of 0.25 ohms, is running at 3000 rpm with supply of 255 V. The electromagnetic power produced at the armature in kilo watts is?

(a) 5

(b) 10

(c) 0.5

(d) 8

I had been asked this question in an international level competition.

The origin of the question is Machine Ratings in chapter Rating and Loss Dissipation of Electrical Machines

Answer 1

The correct option is (a) 5

The best explanation: The current in armature, Ia = 255-250/0.25 = 20 A

             Power = Eb*Ia = 250*20 = 5000 W.