Power Factor Correction: What is it? (Formula, Circuit And Capacitor Banks)

What is Power Factor Correction?

Power factor correction (also known as PFC or Power Factor Improvement) is defined as a technique used to improve the power factor of AC circuits by reducing the reactive power present in the circuit. Power factor correction techniques aim to increase the efficiency of the circuit and reduce the current drawn by the load.

Generally, capacitors and synchronous motors are used in circuits to reduce the inductive elements (and hence the reactive power). These techniques are not used to increase the amount of true power, only to decrease the apparent power.

In other words, it reduces the phase shift between voltage and current. So, it tries to keep the power factor near to the unity. The most economical value of the power factor is between 0.9 to 0.95.

Now the question arises, why the economical value of the power factor is 0.95 instead of the unity power factor? Is there any disadvantage of the unity power factor?

NO. There is not a single disadvantage of the unity power factor. But it is difficult and costly to install unity PFC equipment.

Therefore, utility and power supply companies try to make a power factor in a range of 0.9 to 0.95 to make an economic system. And this range is good enough for a power system.

If the AC circuit has a high inductive load, the power factor may lie below 0.8. And it draws more current from the source.

The power factor correction equipment reduces inductive elements and current drawn from the source. It results in an efficient system and prevents the loss of electrical energy.

Why Power Factor Correction is Needed?

In DC circuits, the power dissipated by a load is simply calculated by multiplying voltage and current. And the current is proportional to an applied voltage. Therefore, the power dissipation by the resistive load is linear.

In AC circuits, voltage and current are sinusoidal waves. Hence, the magnitude and direction change continuously. At the particular instant of time, the power dissipated is a multiplication of voltage and current at that instant.

If an AC circuit having inductive loads like; winding, chowk coils, solenoid, transformer; the current is out of phase with the voltage. In this condition, actual power dissipated is less than the product of voltage and current.

Due to non-linear elements in AC circuits, it contains both resistance and reactance. Therefore, in this condition, the phase difference of current and voltage is important while calculating the power.

For pure resistive load, the voltage and currents are in phase. But for inductive load, the current lags behind the voltage. And it creates inductive reactance.

In this condition, the power factor correction is most needed to reduce the effect of the inductive element and improve the power factor to increase the efficiency of the system.

Power Factor Correction Formula

Consider an inductive load is connected with the system and operates at power factor cosф1. To improve the power factor, we need to connect power factor correction equipment in parallel with the load.

The circuit diagram of this arrangement is shown below figure.

The capacitor supplies leading reactive component and reduce the effect of lagging reactive component. Before connecting capacitor, the load current is IL.

The capacitor takes IC current that leads voltage by 90˚. And the resultant current of the system is Ir. Angle between voltage V and IR is decreased compared to angle between V and IL. Therefore, the power factor cosф2 is improved.

Power Factor Correction Phasor Diagram

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