Electrical Engineering ⇒ Topic : Calculations of Power Factor Correction

Calculations of Power Factor Correction

Consider an inductive load taking a lagging current I at a power factor cos Φ. In order to improve the power factor of this circuit, the remedy is to connect such an equipment in parallel with the load which takes a leading reactive component and partly cancels the lagging reactive component of the load. Fig. a (i) shows a capacitor connected across the load. The capacitor takes a current I_c,which leads the supply voltage V by 90°. The current I_c partly cancels the lagging reactive component of the load current as shown in the phasor diagram in Fig.a (ii). The resultant circuit current becomes I and its angle of lag is Φ₂. It is clear that Φ₂ is less than Φ₁ so that new p.f. cos Φ₂ is more than the previous p.f. cos Φ₁.

                                                                                                Figure (a)

Power triangle. The power factor correction can also be illustrated from power triangle. Thus referring to Fig. (b), the power triangle OAB is for the power factor cos Φ₁ whereas power

triangle OAC is for the improved power factor cosΦ2. It may be seen that active power (OA) does not change with power factor improvement. However, the lagging kVAR of the load is reduced by the p.f. correction equipment, thus improving the p.f. to cosΦ₂.

Leading kVAR supplied by p.f. correction equipment

                                                                                  figure (b)

Knowing the leading kVAR supplied by the p.f. correction equipment, the desired results can be obtained. The p.f. of an electric system is very important to power companies and large industries because p.f. determines how efficiently the power distribution equipment (e.g. transformer, power lines etc.) is used