Power Factor

The power factor of an AC electric power system is defined as the ratio of the real power flowing to the load to the apparent power, and is a dimensionless number between 0 and 1 (frequently expressed as a percentage, e.g. 0.5 PF = 50% PF).

The real power is the actual power utilized by the load such as TV, Fridge, Fan, Bulb etc. And the real power is measured in watts (W).

The Apparent power is the power consumed by the power supply unit to supply real power to actual load. Apparent power is measured in Volt-Amperes (VA).

So apparent power is the sum of the real power supplied to load, and the reactive power wastage in reactive components such as capacitor or inductor. Reactive power, the nonworking power caused by the magnetizing current, required to operate the device. This reactive power will be dissipated as heat in power supply unit.

Why Improve Your Power Factor?

If apparent power is much higher than real power, then the power supply unit is said to be inefficient.

In an electric power system, a load with low power factor draws more current than a load with a high power factor for the same amount of useful power transferred.

If you buy an inverter with 500VA rating, it will not drive a load of 500W. Based on the power factor of the inverter, you can calculate the real power it can deliver to load.

For example an inverter is rated with 1000VA, and is designed for a power factor of 0.8. Then the inverter can handle loads upto 800W.

You pay electricity bill for the reactive power dissipated in the power supply unit or electrical cables. you may have noticed advertisements for power supply units that claims to reduce your monthly home electricity bills. The advertising literature states that you are paying for the added electricity that must flow when power factor (PF) is less than “unity” within your house.

To make use of entire apparent power to convert into real power, the power supply unit shall be designed with power factor approaching unity.

Power Factor Correction (PFC)

Power factor of the load/device can be corrected with the use power factor correction circuits built with passive and/or active components.

Power factor correction brings the power factor of an AC power circuit closer to 1 by supplying reactive power of opposite sign, adding capacitors or inductors which act to cancel the inductive or capacitive effects of the load, respectively.

Linear loads with low power factor (such as induction motors) can be corrected with a passive network of capacitors or inductors. Non-linear loads, such as rectifiers, distort the current drawn from the system. In such cases, active or passive power factor correction may be used to counteract the distortion and raise power factor.

Power Factor Correction (PFC) Devices

Power factor can be corrected or improved with the use of either passive devices or active devices

  • Passive PFC devices
    • Capacitor
    • Inductor
    • Passive filters with various combinations of capacitor and inductor
  • Active PFC devices
    • Boost Converter
    • Buck Converter
    • Buck-Boost Converter

Benefits of power factor correction

By optimizing your energy use you can:

  • Reduce electricity costs by eliminating power factor surcharges
  • Enhance equipment operation by improving voltage
  • Improve energy efficiency
  • Reduce line losses
  • Delay costly upgrades
  • Free up transformer and distribution system capacity