What is Power Factor and why is it important?

In the electrical power system, the power factor is a very important parameter that defines how efficiently electrical power is being utilized by the connected load. It is a unit less quantity. The power factor of the system depends on the type of load connected, whether resistive, inductive, or capacitive.

In this article, We are going to discuss: what is power factor and why it is important in the electrical system. Also, what is the physical significance of the power factor in the power system? But before that, we have to understand the basic concepts of Electrical power and a brief analysis of Active, Reactive, and Apparent Power, so that it will be easy to understand the concepts of the Power Factor.

Because the concepts of power factor are derived from Electrical power concepts. We have already discussed the concepts of Electrical power (Active, Reactive, and Apparent Power) in our previous Article. So please follow my previous Article about Electrical Power titled: Electrical Power- Active, Reactive, and Apparent Power.

Well, now come to our main topic which has mainly two parts. First, what is the power factor? And another is why it is important. So let’s discuss it one by one in detail so that it will be easy to understand.

What is Power Factor?

Power factor is simply the measure of evaluating how effectively the incoming electrical power is being utilized in our electrical system. If the power factor is high, then we can say that more effectively the electric power is being used in an electrical system. A load with a power factor of 1 (maximum) results most efficient loading of the system. But if the power factor is poor (say less than 0.8), then the effectiveness of usage of electrical power reduces, which results in higher losses in the supply system and a higher bill for consumers.

The power factor represents the fraction of the total power that is used to do the useful work. The other fraction of electrical power is stored in the form of magnetic energy in an inductor or electrostatic energy in the capacitor. A high power factor benefits consumers and Power Company both. Whereas a Low power factor indicates poor utilization of Electrical Power and it penalizes consumers.

In Electrical Engineering, the concept of power factor is only discussed in AC circuits. Whereas there are no power factor concepts in the case of a DC circuit due to its Zero frequency. Its value becomes 1 (unity) for the DC Circuit. But in the case of an AC circuit, the absolute value of the Power Factor always lies between the ranges 0 to 1(0 < Cosθ < 1).

Generally, a high and leading PF is good and preferred in the Electrical system. Ideally, the minimum and maximum value for PF becomes 0 and 1 respectively. But in Practice, it is difficult to achieve unity (1) power factor. A low power factor is generally the result of inductive loads such as Induction motors, Power transformers, ballast in the luminaire, a welding set, and an induction furnace. A power factor value near 0.9 is considered satisfactory. It is calculated with the help of Power Triangle.

Power Factor Definition

There are three ways to define power factor in electrical engineering.
1. Power factor is defined as the ratio of Active Power (kW) to Apparent Power (kVA).
P.F = Active Power(kW) / Apparent Power (kVA)
2. Also, the Power factor is the cosine of the phase angle difference between voltage and current pharos.
P.F = Cosθ, Where θ is the angle between V and I.
3. One more way of defining the Power Factor is that it is the ratio between the resistance (R) and Total Impedance (Z) of an AC circuit.
PF = Resistance/Impedance = R/Z

Why Power Factor is Important?

It is very common question comes to our mind that “why the Power Factor is important in Electrical Systems?”  What is its physical significance? To understand this let’s consider an example. An Electrical machine runs at 100 kW (Working Power) and the Apparent Power supplied by Power utilities is 125 kVA. Then the first question that arises in our mind is why the working power of machines and power supplied by the Power company is different. Well, there is a concept of Power Factor behind that. So we have to understand it clearly.

Here if we find the PF, we divide 100 kW by 125 kVA (according to the definition of Power Factor), and then we get a PF of 0.8 (80%). This means that only 80% of the incoming current does useful work in the circuit and 20% is used by reactive elements in the circuit. In other words, we can say that 80% of the power is useful power which is also known as real or True Power, and the rest 20% of power is Reactive Power used by reactive elements in the circuit. Because the Electric Company must supply total apparent power (kVA) to the consumer and in return, consumers pay them only for real power (kW). Due to poor PF, the consumer pays fewer amounts to the Power company. It will be considered a loss for the power company as well as no benefit for the consumer. So power company penalizes the consumer for maintaining a poor PF. So higher PF is beneficial for both power utilities as well as consumers.

Problem with Low Power Factor

It can be observed that an increase in reactive power causes a corresponding decrease in Active Power as well as power factor. It means the power distribution system is operating less efficiently because not all the current is performing useful work in the circuit. For example, a 50 kW load with a power factor of unity (Reactive power = 0 kVAR) could be supplied by a transformer rated for 50 kVA. However, if the power factor is reduced to 0.7 (70 %), then the transformer must also supply additional power for the reactive load. So In this example, a large transformer that is capable of supplying 71.43 kVA (50/0.7) would be required. In addition to that, the size of the conductors would have to be increased to supply an increased amount of current due to low PF. So due to poor PF the cost of equipment also increased.

Types of Power Factor

There are three types of power factors in electrical science. These are the leading power factor, Lagging power factor, and Unity power factor. Let’s discuss all these types of power factors one by one in detail.
1. Leading Power Factor: A leading power factor signifies that the load in the circuit is capacitive in nature. As the load supplies reactive power to the circuit, in this case, the reactive component (Q) of Electrical power will be negative. If in the electrical circuit, there is more capacitive reactance than inductive reactance, then the PF of the circuit will be the leading power factor. In this case, the operating current will lead the voltage phasor by an angle θ. whereas in a pure capacitive circuit current leads the voltage by θ = 90 degrees.
2. Lagging Power Factor: A lagging power factor signifies that the load in the circuit is inductive. As the load will consume reactive power, in this case, the reactive component (Q) of Electrical power will be positive. If in the electrical circuit, there is more inductive reactance than capacitive reactance, then the PF of the circuit will be a lagging power factor. In this case, the operating current will lag the voltage phasor by an angle θ. Whereas in a pure inductive circuit current lags voltage by θ = 90 degrees.
3. Unity Power Factor: A unity power factor signifies that the load in the circuit is purely resistive. As the load will consume active power, therefore, in this case, the reactive component (Q) of Electrical power will be zero. Hence in case of a unity power factor, total apparent power will be utilized in the circuit. In the electrical circuit, if inductive reactance and capacitive reactance balance each other, the circuit will be in resonance condition and considered purely resistive hence PF of the circuit will be the unity power factor. In this case, the operating current will be in phase with the voltage phasor. In this case, θ will be 0 degrees.