Question

For a DC generator feeding 100kW power into 230V mains, having armature resistance and field resistance equal to 0.08Ω and 115Ω resp. The value of armature current is_____

(a) 436.8 A

(b) 434.8 a

(c) 432.8 A

(d) Data insufficient

The question was asked in an online interview.

This is a very interesting question from Electromagnetic Power and Circuit Models topic in section Circuit Model, Emf and Torque of DC Machines

Answer 1

Right choice is (a) 436.8 A

Best explanation: Field current is equal to 230/115 = 2A, by Ohm’s law. When running as a generator line current IL= 100k/230= 434.8A. Since power is supplied to 230V mains, Ia=Il+If = 434.8+2 =436.8A.

For motoring mode Ia= IL- If.