Power Factor Improvement

If the power factor is low or poor, it is necessary to improve or correct it. It may be improved by injecting a leading current into the circuit so as to neutralize the effect of lagging current. The power factor may be improved by using static capacitors or synchronous motors.

Power factor correction by static capacitors

Consider an inductive load consisting of a resistor R and an inductor L connected to an AC supply. The circuit and phasor diagrams are shown in the figure.

Let,

V – supply voltage.
I₁ –  load current
φ₁ – phase angle by which the current I₁ lags behind the voltage
cosφ1 – original power factor

Let the capacitor C be placed in parallel with the load. It will take a leading current  I_c  from the supply. The circuit and phasor diagrams are shown in the figure.

The total I₂ drawn from the supply will be equal to the phasor sum of I₁ and I_c that is

Conclusions

• The phase angle of I₂ is φ₂. It is seen from the phasor diagram that the φ₂  is less than φ₁, and hence, cosφ₂ is greater than cosφ₁. In other words, the power is improved from cosφ₁ to cosφ₂.
• The new current supply from the supply is less than the load current I₁, i.e., I₂> I₁. The new current is given by the equation

• By connecting a capacitor in parallel with an inductive load, the power factor is improved, and the current from the supply is reduced without altering either current or power taken by the load.

This relation shows that the power taken from the supply has not altered.