SOLUTIONS POWER QUALITY By Jason Axelson
How to find your missing power factor Not addressing power quality issues like low power factor and harmonics can hurt
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hat would happen if the pizza just delivered to your front door was missing a piece? You wouldn’t just let that go. You’d want to know where that piece went. Did the driver eat it on the way? Maybe someone’s elbow got stuck in it while being boxed? Who knows? Consider the power coming into your facility. You pay for that power to maximize productivity. But what if you aren’t getting what you paid for? In an industrial setting, a key parameter is “power factor:” the percentage ratio of true power, measured in kilowatts (kW), to apparent power, measured in kilovolt amperes (kVA). The apparent power is the total requirement a facility places on the utility to deliver voltage and current, Figure 1: Ensuring power factor is as close as possible to 1.0 makes good financial sense because most utilities charge a higher rate when power factor falls below a certain level, typically 90%. Courtesy: Fluke
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• March 2021
PLANT ENGINEERING
regardless of whether it does the actual work. Utilities generally charge a higher rate when power factor falls below a certain level, most often 90% (see Figure 1). True power (kW)/apparent power (kVA) = power factor • Example of good power factor: 50 kW/52 kVA 0.96 (96%) • Example of poor power factor: 50 kW/63 kVA 0.79 (79%).
The cost of energy inefficiency
When the topic is power factor, we’re really talking about energy efficiency. How well is the power delivered being used in the facility? If a circuit were 100% efficient, demand would be equal to the power available. When demand is greater than the power available, a strain is placed on the utility system. Many utilities add a demand charge to the bills of large customers to offset the differences between supply and demand (where supply is less than demand). For most utilities, demand is calculated based on the average load placed within 15 to 30 minutes. If demand is irregular, the utility must have more reserve capacity available than if the load remains constant. If a facility’s power factor is less than 97%, for example, steps can be taken to find that missing energy. The two most common contributors to poor power factor are motor inductance and harmonic currents. The first step is to measure to determine the root cause of bad power factor. By measuring energy and power quality, insight is gained into the facility’s performance patterns. Measurement will help you understand www.plantengineering.com
