Jargon Buster: Power factor correction

So what exactly is power factor?

Simply put: it’s all about efficiency. Technically, power factor is the ratio of the true power (kW) that is used to do work in electrical equipment and the apparent power (kVA) that is supplied to the circuit.

If you’re scratching your head right now, all this means is that the power that goes in one end doesn’t necessarily match the power that comes out the other. So power factor is a measure of how efficiently electrical power is being converted into useful output.

Power factor is presented in a value that ranges from 0 (bad power factor) to 1 (good power factor). In the real world of industry and commerce, you’re not going to get a power factor of 1 because equipment such as electric motors, welding sets, and fluorescent and high bay lighting create something called an “inductive load”, which in turn causes the amps in the supply to lag the volts. The resulting lag is power factor.

So why does it need to be corrected?

With energy prices seeming to go up at each bill, we all want to make the most of the power we’re paying for. So the most common reason to install power factor correction is to maximise the electrical supply into your building. By using power factor correction equipment, you will be able to run more machines and do more work on the same amount of electrical supply.

The bad news is that power factor correction equipment reduces kVA not kW and the majority of your electrical bill is based on the kW you use. However, you may save on any reactive charges on your electricity bill from your supplier, as some suppliers will charge you for having a poor power factor. You may also be able to reduce your ‘authorised supply capacity’: this is the agreed maximum power you are allowed to use at any time.

The other benefit is that you’ll improve your equipment service life, since the amount of heat generated within cables, switchgear, transformers and other equipment is reduced at an improved power factor.

How is a poor power factor corrected?

Installing a capacitive load (capacitor) into the circuit cancels out the effects of the inductive load and therefore improves the power factor. This process is known as power factor correction.
Power factor correction capacitors are sold in kVAR ratings, usually in a trio of three capacitors, which may or may not be packaged in a single enclosure. The equipment needs to be sized and specified correctly as the installation of the wrong power factor correction equipment can cause more harm than good – one of the many reasons you need to hire the right electrical company for the job.

Capacitor boxes often contain some surge suppression circuitry. This is important as although experts widely agree that surge suppression saves virtually no energy, it may be highly beneficial in protecting valuable equipment if there are any serious voltage spikes on the circuit.

Things to consider

Two things to bear in mind…
1. If you are looking to have power factor correction equipment fitted it needs to be the correct type for your installation, otherwise the existing equipment on your site may interact with standard power factor correction equipment and give you grief.
2. Remember that power factor correction equipment needs to be serviced to maintain optimum performance; it is recommended this is carried out every 12 months.

Any questions, give us a call on 01924 283737 and one of our trained staff will be happy to help.