A motor connected to a 240V, 50Hz power supply draws 5A at a lagging power factor of 0.5. To improve the power factor to 0.9, a capacitor of 3.1A is needed with a VAR rating sufficient to compensate for the reactive power at the improved power factor.

1. Example 1
A motor connected to a 240V 50Hz supply
takes a current of 5A at a lagging power factor
of 0.5.
(a)What is the value of the capacitor needed to
improve the power factor to 0.9 (lagging)?
(b)What must its VAR rating be?

2. pf = cos Φ
Φ = cos¯¹ λ
Φ1 = cos¯¹ λ
= cos¯¹ 0.5
= 60⁰
Φ2 = cos¯¹ λ
= cos¯¹ 0.9
= 26⁰

8. (3.1 A)