Question

Calculate the active power in a 19 F capacitor.

(a) 7.8 W

(b) 0 W

(c) 5.4 W

(d) 1.5 W

The question was posed to me at a job interview.

The question is from DC Motors topic in chapter Characteristics of DC & AC Motors of Electric Drives

Answer 1

Correct choice is (b) 0 W

For explanation I would say: The capacitor is a linear element. It only absorbs reactive power and stores it in the form of oscillating energy. The voltage and current are 90° in phase in case of the capacitor so the angle between V & I is 90°. P = VIcos90 = 0 W. Current leads the voltage in case of the capacitor.