Question

Refer the diagram; a single-phase supply of 100V, 50Hz is fed to the step-up transformer having primary impedance of 1 ohms and secondary impedance 20 ohms. What is the power consumed by the load of 5 ohms?

(a) 20 W

(b) 40 W

(c) 10 W

(d) 100 W

I got this question during an online interview.

The above asked question is from Machine Ratings topic in division Rating and Loss Dissipation of Electrical Machines

Answer 1

The correct option is (a) 20 W

For explanation I would say: The referred resistance to the secondary, Z2=1*(5^2) = 25 ohms

                  Total resistance at secondary = 25+20 = 45 ohms

    Total resistance seen by source = 45+5 = 50 ohms

    Hence, current in secondary = 100/50 = 2 A

    Power consumed by the load = I^2 *R = 4*5 = 20 W.