Power Factor Correction Systems

Some utility electricity bills can include a some for Reactive Power charges. Not all utilities charge for Reactive Power in the same way and some provide a threshold level below which no charge is made. When a site does incur Reactive Power charges, the costs can be eliminated through the installation of an appropriately sized power factor correction (PFC) system.

What is Reactive Power?

Reactive power is a measure of ‘unproductive’ power and in an electrical circuit arises from the creation of the electro-magnetic field required by motors and transformers to generate their output. The field impedes the flow of electrical current, leading to the need for Reactive Power. The unit of measure for Reactive Power is kVArh.

A typical analogy and example involves a horse pulling a barge along a canal towpath. The horse cannot walk directly in front of the barge and pulls at an angle to the barge itself. The force in the towrope exerted by the horse consists of two elements: a force to pull the barge forward (useful) and a sideways force to tow the barge towards the canal bank (not useful). The sideways force is unproductive and ‘reactive’.

Utility operators charge for Reactive Power as more current must be drawn by a site operating system generating electro-magnetic fields to provide the same output of work as one that is not. The higher current demand leads to increasing costs for the Distribution Network Operator (DNO).

For sites that do not have Reactive Power metering, the DNO may apply estimated charges. The lack of metered data could be dye to a poorly configured meter or the wrong type of meter installed.

How Power Factor Correction Works

A power factor correction system uses AC (Alternating Current) capacitors that store electrical energy when charged (from a mains power supply) and act as Reactive Power generators in order to reduce the current drawn from the mains power supply for loads that require an electro-magnetic field to operate.

A PFC system is typically housed within a metal cabinet installed in parallel to the mains power supply at the building incomer. PFC components can also be built-into LV switchboards. The benefits of power factor correction include:

  • Remove or reduce reactive power charges on electricity bills
  • Optimise the performance and working life of industrial plant and machinery
  • Lower power line and distribution transformer loses
  • Reduce voltage line drop and power pollution from upstream loads

Current distortion and harmonics can be generated into the mains power supply by non-linear loads including inverters, welding machines, saturated transformers, rectifiers and IT server/ computer-type loads using Switch Mode Power Supplies (SMPS). These types of power problem can cause affect the operation of:

  • Rotating machinery: generate Eddy currents and consequent vibrations leading to a weakened mechanical structure, overheating and isolation damage.
  • Transformers: increase core and winding losses with potential for damage to the primary and secondary windings. The presence of a DC voltage or current can saturate the magnetic core of the transformer and increase the magnetising current.
  • Capacitors: reduce life expectancy from overheating and exposure to higher voltages.

The AC capacitors used within a power factor correction system will require replacement towards the end of their working life to maintain their effectiveness. A power factor correction system should be inspected annually as part of a routine electrical maintenance contract.

Synchronised Power provides testing and maintenance contracts for existing power factor correction systems including capacitor replacement and their eco-friendly disposal and recycling. New systems can be designed and installed following a site survey to assess the size of system required and a desktop review of utility bills for Reactive Power charges.

For a power factor correction system site survey or existing system health check please contact our power engineering and energy efficiency team.