Question

An alternator supplying a 600 kW load at 0.75 power factor lagging has its power factor raised to unity by means of over excited synchronous motor. At a constant armature current the reactive power supplied by the motor and the power factor of operation are respectively.

• A. 529.15 kVAR, zero p.f. lagging
• B. 630.23 kVAR, zero p.f. leading
• C. 630.23 kVAR, zero p.f. lagging
• D. 529.15 kVAR, zero p.f. leading

Answer 1

The correct option is D 529.15 kVAR, zero p.f. leading

$\text{Given, Load = 600 kW at 0.75 p.f. lagging}$

$\text{Load kVA =}\frac{600}{0.75}=800kVA$

$\text{Load kVAR= Load kVA}\times sin\varphi$

$=800\times \sqrt{1-(0.75{)}^2}$

$=529.15kVAR$

When a synchronous motor is connected to improve the power factor, it is over excited. As there is reactive power required from motor so it will operate at zero power factor leading which supplied 529.15 kVAR to load.