Question

Calculate the compensator rating required for cos(Φ)=.7.

(a) 0.71 P.U

(b) 0.21 P.U

(c) 0.47 P.U

(d) 0.12 P.U

This question was addressed to me in an interview for internship.

My question is based upon Motors Rating and Heating in portion Rating and Heating of Motors of Electric Drives

Answer 1

The correct option is (a) 0.71 P.U

Easy explanation: The compensator rating can be calculated using the relation QP.U=√1-cos^2(∅)=√1-.49=.71. This per unit value VAR compensator is required to improve the power factor of the system.