Understanding Power Factor - Reasons for Low Power Factor (2024)

It is usually assumed that a low power factor implieslow power consumed, and consequently a low electricity bill which ismisleading. This blog might help break down the concept of power factor.

How much of the electricity drawn by electric/electronic devices is used for performing actual work, like heating up coils to toast bread in a toaster or run a water purifier to purify water by passing it through various filters etc, is called Active/ Real Power (kW). Now, in some cases, power is utilized not to produce some useful output, but consumed by the device itself. For example, in the electric motor (part of booster pump) of a water purifier, some portion of the power drawn is utilized to set up a magnetic field, required for the operation of the motor. This is seen as no useful work from the outside by the end consumer, but electricity is still utilized.This is called Reactive Power (kVAR) . A vector sum of Active and Reactive Power gives Apparent Power (kVA).

Now, power factor is simply the ratio of Real Powerand Apparent Power and ranges between 0 and 1. If the power factor is low(close to zero), it implies that very little power out of the total drawn powerby a device is used to perform actual, useful work.

PF= KW / KVA

Power factor is a way to find out how effectively you are using your electrical power. A high-power factor indicates effective utilization of electrical power, whereas low power factor signifies inefficient use of electrical power. The device is considered to be very efficient if the power factor is close to 1.

The analogy below can be used to explain the components of power. The chips we eat represents the real power. The air (nitrogen) in the packet represents the reactive power. We however pay for the entire packet, even though we consume only some portion of it. The nitrogen in the packet is to prevent the chips from going stale and any damage during transit, so it has to be present in the packet. Similarly, the reactive power maintains the system voltage. It helps establish and maintain the magnetic and electric fields required by the system. Thus, like nitrogen, reactive power is necessary. If the reactive power increases beyond a threshold, the system becomes unstable and tends to draw more current from the source, or essentially a low power factor.

Reasons for low power factor

(Note that allthese issues result in a change of reactive/ real power)

• Inductive loading – 90% of the industrial load consists of induction machines (single and three phase). Such machines draw magnetizing current to produce the magnetic field and hence work at low power factor.
• Variations in power loading – When the system is loaded lightly, the voltage increases and the current drawn by the machines also increases. This results in a low power factor.
• Harmonic currents
• A condition known as 3 phase power imbalance occurs, due to improper wiring or electrical accidents. This results in low power factor too.

Reactive power is utilized by giving rise to no useful work. Thus, we pay for the apparent power, but utilize only the real power. When you have a low power factor, you are not fully employing the electrical power you are paying for. Utilities often penalize customers for low power factor as an incentive to compensate for this inefficiency.

Why do utilities levy a power factor penalty?

In India, if thepower factor of the consumer drops below 0.85, they will be charged heavily.When the power factor is low, power and energy losses in power lines andtransformers increase and the utilities include these costs in the electricitybill in the form of power factor penalty.

Power factor correction

Consumers canavoid power factor penalties by installing devices for power factor correction,

• Install capacitorsin the distribution system. While capacitor banksimprove the overall system’s power factor, the individual machines which causeda drop in power factor would still remain the same. These machines can beserviced or improved into more energy efficient versions, to maintain a healthyelectrical system.
• Minimize operationof idling or lightly loaded motors
• Install variablefrequency drive (VFD) systems to lightly loaded induction motors
• Install new motorsthat will be operated near their rated capacity
• Replace lightlyloaded motors with motors sized to be operated near their rated capacity
• Avoid operation ofequipment above its rated voltage.

(Source: Improving power factor to reduce energy demand charges, increasecapacity)

Thus, it is important to pay attention to the power factor of your machines and your system as a whole, and utilize most of the power bought from the utilities to perform actual work. Maintain a healthy electrical system and avoid power factor penalties by staying informed about the electrical parameters of your place, with the help of energy monitoring devices like ones provided by Energyly and check out their pricingplans.