Electrical Testing
Pay Attention to Power Quality

Pay Attention to Power Quality

Conducting a power quality analysis can tell you if your equipment has power quality problems.

Looking for power quality issues typically is not done until such issues are suspected in a troubleshooting situation. If an area of the plant has power quality problems, but the equipment failure rates don’t seem unusually high, a typical maintenance department won’t even look at power quality.

Yes, equipment malfunctions should draw attention to power quality. Motor failures, in particular, may be caused by power quality problems. But the threshold at which power quality problems should be addressed isn’t when equipment fails. It’s when the cost of powering that equipment is considerably more than it should be. And the only way to know when that occurs is to perform a power quality analysis.

What “poor power quality” means in practical terms is that the usability of the power is diminished, so the equipment requires more power to do the same work.

Maybe someone used a harmonic analyzer and found that your total harmonic distortion (THD) falls within the range of what one standard or another shows is acceptable. What that standard isn’t going to tell you is that 300 pieces of equipment running on that “acceptable” power are all wasting energy. And it adds up.

To reduce the waste, look for the load (or a few loads) that most contribute to harmonic distortion on a particular feeder — the big switching power supply in that control cabinet, for example. Many harmonics mitigation techniques exist, so figure out the one best suited to the specific application. It might be as simple as installing a tank circuit or harmonics filter.

One easy fix if the source is an electronic motor drive is to replace that drive with one that is harmonics-corrected. Chances are good that it will also be power factor-corrected, rendering that inductive load neutral in terms of power factor. This is a productive area for energy savings, because low power factor at the load is often rampant in a given facility and typically the only power factor correction in the plant is at the service.

Power factor correction at the service enables you to avoid the utility’s low power factor penalty. But it doesn’t do anything for low power factor at large inductive loads. The uncorrected low power factor at these loads means each one will just draw more power to do the same work.

Severe power quality problems may contribute to, or cause, equipment failures. But that doesn’t mean you should consider power quality problems only when they are severe. Even seemingly minor power quality problems may cost plenty of money because all of the equipment on the affected feeder(s) will require more power and the losses multiply...every day, all year long.

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