Power Factor


Power Factor is a measure of how efficiently your plant and equipment converts the electricity you receive from the electricity network to useful output - such as heat, light or mechanical motion. In some cases, the amount of electricity you receive is more than you actually use.

The concept is expressed as a numerical value between zero and one.  A power factor of 1.0 is perfect. A power factor greater than 0.96 is both achievable and desirable.

The higher the power factor, the more effectively your electrical equipment is being used. For example, a power factor of 0.8 means the useful work being done is 80% of what could be done with the same power and a perfect power factor.

If your power factor is low, you may also be paying power factor penalties.

The simplest way to improve a low power factor is to install a Power Factor Correction Unit.

Correcting a poor Power Factor could save you money and it also improves the network’s efficiency by releasing capacity from the network so it can be used at other times.

Power Factor in more detail

The electrical power used by motors (such as those used in air conditioners, elevators, pumps, chillers, and ventilation systems) and fluorescent lighting ballasts has two components:

  • Working Power – which is converted into useful work such as turning motors or producing light.  This power is also referred to as “Active” or “Real” power. It is measured in kilowatts (kW).
  • Non-working Power – which doesn’t do useful work and is only used to “energise” the magnetic or electrostatic properties of the equipment. This power is also referred to as “Reactive” power. It is measured in kilovolt-amperes-reactive (kVAr).

These two types of power combine to create the “Total” or “Apparent” Power, which is measured in kilovoltamperes (kVA) and is what the distribution network supplies.

Non-working power still has to be produced and transmitted to you over the electricity network. Producing and transmitting the non-working power creates costs for electricity companies which may be passed on to you as power factor penalties or surcharges.

Power factor is the ratio of Working Power (kW) to Total Power (kVA).

The Beer Analogy

A commonly used analogy is a typical glass of beer, comprising both beer and froth.

The total content of the glass - beer and froth – represents the Total Power.

The froth, representing Non-working Power, does nothing to quench your thirst.

The beer, representing Working Power, does quench your thirst.

To get maximum value for money from the glass of beer it needs to be full of beer with no froth.


Last Updated: 
Thu 06/06/2013

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