Electrical Testing
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Tip of the Week: Power Quality, Part 4

Before you resort to buying equipment to address a harmonics problem, check the electrical distribution system voltage.

The subject of power quality is much wider than many people assume. Power quality is not about harmonics, though if you have excess harmonics, you have one type of power quality problem.

Before going out and buying fancy equipment aimed at handling a harmonics problem, do the following:

Check the electrical distribution system voltage. There are four voltages you should check before looking at anything else.

  1. Line-to-line RMS voltage for a balanced condition. Where you find voltage imbalances, you will need to plan for correction as soon as you have the downtime to do so.
  2. Line-to-ground RMS voltage for a balanced condition. Correct as soon as you can.
  3. Line-to-line voltage transients greater than twice rated or nominal RMS input line voltage. This indicates a need for TVSS and surge device system engineering.
  4. Line-to-ground voltage transients greater than three times the rated or nominal RMS voltage with a time duration greater than 1 millisecond.

Next, review your system to see if it is adequate for the demands being placed upon it. Correcting inadequacies at this point typically corrects one or more power quality problems. For example, changes since construction have resulted in several overloaded transformers. As a consequence, the waveforms are chopped.

Review all transformers, panels, wiring, and breakers to determine if they are sufficient for the loads that have been added since these devices were installed.

Review single-phase loads (lighting, computers) to determine what level of harmonics already exists on a system before adding more non-linear loads.

Suppose you complete this work and harmonics are reduced, but you still have high rates of equipment failure? Is that the time to buy harmonics mitigation equipment?

It may be that you actually have more serious power quality problems than the harmonics. For example, you might have grossly distorted waveforms on several branch circuits.

This is where you should probably call in a firm qualified to conduct a power quality analysis. Ask them what drawings and other documents they will need, and have those ready before the first site visit.

Once they’ve performed the analysis, they can advise you on what measures to take to fix the problems. That might include harmonics mitigation equipment or it might not.


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