Question

An electrical load operates at 240 V rms. The load absorbs an average of 5 KW at lagging power factor of 0.8 The reactive power Q is:

 Select one

 a 3.75 KVAR

 b 4.50 KVAR

 c 6.00 KVAR

 d 6.75 KVAR

 e 5.25 KVAR

Answer 1

Average power, P $= 5KW$

But $P=/S/ cos \theta$

Given power factor $cos \theta=0.8$

$=sin \theta=\sqrt{1-cos^2\theta}$

$=sin \theta=\sqrt{1-0.8^2}=\sqrt{0.36=0.6}$

$P=/S/ cos \theta$

$5KW=/S/*0.8$

$/S/=\frac{5000}{0.8}=6250$

Reactive power, Q $=/S/ sin\theta$ VAR

$Q=6250(0.6)=3750$ VAR

$S=P+jQ$

$S=5000+j3750$

$S=5+j3.75$ KVA