Power Quality » Understanding PFC
Are you considering a power factor correction unit, but would like to know more? We’ll cover power factor basics and then provide some recommendations to help you decide as well as some maintenance and troubleshooting advice for your unit.
Power Factor Correction Overview
Power factor correction (PFC) units are quite common across medium and large commercial sites. In this article we’ll first summarise power factor and then share some recommendations for power factor correction to help you decide what’s best and how to troubleshoot issues.
Power Factor Summary
Power Factor (PF) is the ratio between 0 and 1 of real power (kW) to apparent power (kVA). A low PF can be introduced by a large quantity of reactive power loads on site such as air conditioning, pumps, or industrial equipment.
In an analogy for apparent power, a latte is made up of two parts: coffee and froth. While a bit of froth is ok, when there’s too much you’re getting less coffee, in the same way that you could be paying too much for your apparent power when the site’s reactive power is too high. The larger the reactive power, the lower the power factor.
A low PF can have an impact on the capacity portion of your electricity bills, leading to higher charges than may be necessary. It also is a form of site inefficiency that affects the electricity network and your on-site equipment. For more detail on what PF is, as well as why and when it’s important, please read through our Power Factor Overview Article.
Power Factor Correction Benefits
A PFC unit is designed to help offset the reactive power loads that are on site. In a physical sense, it is basically a bank of capacitors that acts as a buffer between your site’s equipment and the electricity grid, sitting in the main switchroom when there’s space.
- When tariff appropriate, saves money off your electricity invoices
- Helps to reduce strain on the network’s physical infrastructure
- Reduces equipment failure issues with improved power quality
- Improves voltage stability to eliminate operational difficulties with processing equipment
Should I Get a PFC Unit?
If you answer yes to many of these questions, then it is worth looking into.
- Is your network tariff appropriate? Yes, if KVA appears on your electricity invoices.
- Do you have a low PF? Yes, if your PF is often less than 0.85 during peak periods.
- Is your site’s electricity demand large enough? Yes, if your demand is often > 150 kW during peak periods.
- Do you have much reactive power equipment on site? Yes, if plenty of inductive equipment.
- Do you frequently experience electrical or mechanical equipment failure?
Joining the PFC Club
Make sure to choose a reputable supplier and installer. There’s nothing worse than having a problem with your unit 14 months in, only to discover that the company has gone under. Some grid networks have a register of installers (see section below) or offer PFC services themselves. Also, ask peers in your industry for recommendations.
The supplier and installer will be able to provide you with a quote on the right sized unit for your site. They should also provide you with an expected payback timeframe based on the conservative savings. Within a few years is typically a good timeframe for payback. Units are rated based on reactive power needs (kVAr).
Estimated costs are usually around $70/kVAr for low voltage and $150/kVAr for high voltage. Costs can increase for added requirements such as limited switchroom space, enclosure cooling, and harmonic filtering. Features such as controllers to scale capacitors with the varying site power demand will increase costs compared with static PFC capacitors. Similarly, to cope with non-linear loads (e.g. computers and variable speed drives) that exceed 15% of site totals, a de-tuned PFC will double costs over a standard PFC.
Looking After Your PFC Unit
Annual servicing for units is typical, or six-monthly if located in a hot or dusty location. Ongoing testing and maintenance ensures that units continue to operate effectively, provide the right level of correction, and facilitates budgeting for expected future component replacement. This also helps to uncover issues ahead of incidents that could inadvertently affect the capacity charges that you pay.
Is My PFC Unit Performing Properly?
Since you’ve made a significant investment in the hardware to improve your PF, it makes sense to validate that it’s working from time to time. Fortunately, you can use EnergyLink to view your site’s power factor performance during peak times of equipment operation. Naturally, when the inductive loads are switched off, the PF will typically return closer to 1.
Below are two examples of sites with poor PF during daytime peak periods, despite having PFC units on site.
Resolving PFC Issues
If your PFC unit doesn’t seem to be operating optimally, get in touch with your supplier/installer for advice.
It might be time for testing and servicing, which may lead to uncovering control issues or worn out components needing replacement.
Your site’s electricity demand may have outgrown the capacity of the unit. To address this, the capacitor bank may need to be expanded or additional demand management options, as in references, could be explored.