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How to improve power factor

06-07-2019 | Power quality

Power factor, simply put, is the ratio of working power to apparent power, or demand power. Power factor is an expression of energy efficiency, with a higher percentage indicating more efficient power usage and a lower percentage indicating less efficient power usage. To calculate power factor, divide working power (kW) by apparent power (kVA). While 100% efficiency may not be realistic, there are a few things that impact how power factor is improved.

Metal enclosed power factor correction capacitor bank

Power factor correction capacitors can help improve power factor in certain situations.

What is ideal power factor?

Low power factor means you’re not efficiently using the power you’re paying for. At lower power factors, more apparent power (kVA) is required to produce working power (kW). A higher power factor is more ideal than a lower one, because it means that you are using power more effectively. A common target number for power factor is 95%. Confirm with your utility what cutoff point they use—many utilities charge customers fees for having poor power factor.

Measuring and managing energy use

By measuring energy and power quality, you'll get a feel for your plant's rhythm and learn how to keep your plant running smoothly and efficiently. Strategic energy management is a key way to reduce your energy use—and your energy bill. One reason to improve your power factor is to reduce, or even eliminate, penalties and surcharges from your utility.

To do that, you need to know where your energy goes each month. First, you’ll need to measure and record energy data on your equipment and systems. The type of tool you’ll need to do this depends on your facility and needs. A multi-use tool may calculate energy loss and capture three-phase high resolution voltage and current waveforms, while another tool could provide immediate power quality health data. It is important to know the level of harmonics in your current. A total harmonic distortion (THD) measurement can help you find out whether filtering is necessary. And remember, a utility can only influence voltage quality. They can only demand that approved loads are connected and are not responsible for the current that flows because of customers’ installation.

Steps to better power factor

Motor inductance and harmonic currents are two common contributors to poor power factor. To improve power factor, you need to determine the root cause of the bad power factor.

When dealing with inductive current, adding power factor correction capacitors—energy storage devices—to your facility’s power distribution system is one common solution. Power factor correction capacitors do require regular inspection and recommended preventive maintenance, but under normal conditions, they will operate without trouble for many years.

If harmonics are causing the low power factor, then a cost-effective passive LC (inductor-capacitor) filtering is the solution.

For more complex situations, active filtering is needed. This kind of filtering compensates for reactive currents, harmonic currents, and unbalanced currents.

A common mistake is using capacitors to mitigate harmonic currents. A capacitor will behave like a short circuit for higher harmonics. Because of the internal resistance, the capacitor will heat up and have a drastically reduced lifespan because the internal electrolyte will vaporize.

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