We’re wrapping up our Power Quality series by giving an overview on power factor and the correction of poor power factor.
Have you missed our previous articles in the series, click below to catch up now!
You’ve probably realised by now that power factor correction saves you money? We’re taking a few steps back to give you a basic understanding on what power factor is, and what you can do to correct poor power factor.
What is Power Factor?
Power Factor (PF) is a measurement of how effectively your facility uses electricity. It is a unit-less number used in alternating current circuits.
PF is a ratio of the power used calculated by dividing true power in Kilowatts (kW) by apparent power in Kilovolt amperes (kVA).
True power and apparent power are not the same. The difference between true power and apparent power is called reactive power, and is measured in Kilovolt-Ampere Reactive (kVAr). Reactive power is the non-working power delivered to a facility.
The best way to explain the difference, is using a beer analogy…
We pay for beer by the glass. However, if there is a lot of foam and less beer, you’re not getting value for money. The glass represents apparent power (kVA). The glass is filled with beer and foam. The beer represents true power (kW) – it’s what we want and what we’re happy to pay for. The foam represents the reactive power (kVAr). The reactive power is a waste in the sense that we get no use from it - but still have to pay for it, although we do need it to be able to do the work in the first place.
The sum of true power (kW) and reactive power (kVAr) is apparent power (kVA).
Power Factor tells us how much value for our money we are getting for the power we consume.
Power Factor is therefore the ratio of true power (useful power) in kW and apparent power in kVA (the power we are charged for).
Power Factor = True Power (kW) divided by Apparent Power (kVA)
What are the causes of reactive power?
Oversized motors are often the culprit of reactive power. Oversizing is a design precaution used to ensure power is adequate for the job at hand. For example, an idling motor isn’t doing any work, but it still consumes power to keep the electrical field operating. This is reactive power. This is the cost on a utility bill that every business dreads…
Reactive power charges
In a typical residential electricity bill, you will generally see a fee for the amount of power used in kilowatt hours (kWh). As the power factor in residential electricity consumption is very low, it is not charged for. However, in a commercial or industrial electricity bill, for large buildings in particular, you may find reactive power charges.
So why is reactive power charged for?
When large consumers have bad power factors, they are increasing the current flow through the electricity grid, which causes voltage drops. These subsequently reduce the utility’s distribution capacity, which affects other users of electricity.
Moreover, electricity cables are rated to handle only a specific amount of current flowing through them. If numerous large consumers with bad power factor connect, cables could overload.
When the power of a building falls below a certain level, reactive power charges occur. This level is defined by the utility supplier, and is typically around 0.95 or less. The very ideal, but highly unlikely, power factor is 1.0 (Unity).
How do you get rid of this cost?
This cost can be reduced and even removed by implementing Power Factor Correction capacitors. These temporary storage units provide reactive power to your motor instead of receiving it from the utility. Both true power (kW) and reactive power (kVAr) come from the utility. When a capacitor is installed in your facility, it replaces the reactive power supplied by the utility. Thus, reducing the apparent power (kVA) delivered to your facility. Reduced power from the utility results in reduced cost!
How do you calculate power factor?
For commercial buildings such as offices, you’re likely to see a power factor of around 0.98 – 0.92. However, this is far from the case for industrial buildings. Industrial buildings could experience a power factor as low as 0.7.
How can you correct poor power factor and reduce reactive power charges?
There are two types of poor power factor – lagging and leading. In most cases we come across lagging power factor caused by inductive loads, but we can also come across leading power factor in a capacitive loading system.
To correct poor power factor, we can add capacitors or inductors to the circuit which will realign the current back into phase and bring the power factor closer to 1. If we have a lagging power factor caused by high inductive loads in the circuit then we add capacitors, this is most common. If we have a leading power factor caused by high capacitive loads then we add an inductive load to the circuit.
Have a power factor audit!
Optimise your power factor value by installing the right power factor correction equipment. For more information on what kind of capacitor you may need, and where it can go in your facility, contact us for an audit.
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