Question

The given variable losses are 5kW fr a 500 KVA, 11 kV, 3-phase star connected alternator having armature resistance of 4 ohms. Calculate the current at which maximum efficiency occurs?

(a) 20.4A

(b) 10.2A

(c) 40A

(d) 26A

This question was posed to me in an interview for job.

I would like to ask this question from Efficiency of Synchronous Machines topic in portion Efficiency and Regulation of Electrical Machines

Answer 1

Right option is (a) 20.4A

To explain I would say: I^2=5000/3*4

             I = 20.4 A.