How can you determine you have a harmonic problem by identifying symptoms and sources of harmonics?

Can you help me identify if I have a harmonics problem? And what we typically would ask is — What makes you think that you have a harmonics problem? Because there's a lot of things that can happen on a power system that are power quality related, that aren't necessarily harmonics problems.

To clearly identify if the problem is truly harmonics related or not, you have to think about the symptoms of the problem. A transient problem could be the result of a lightning strike or type of surge event. Equipment can sometimes blow up despite our control and although that is unrelated to harmonics, there could be a harmonic resonant problem that could blow up capacitors.

Voltage sags are a very common problem. If your equipment is dropping out, it's likely a voltage sag or an interruption or recloser event, but that doesn't necessarily mean there isn't something that's harmonics related as well. Some equipment may not be operating properly because of harmonic voltage distortion. 

Identifying the symptoms of the problem is very important. Symptoms such as long-term overheating, intermittent operation, equipment not working properly and PLCs locking up could indicate harmonics issues.

Insulation deterioration can be a result of a harmonics or transience issue. If the insulation looks burned or baked in an oven for a long period of time, then there is most likely a harmonics problem. If there is a single pinpoint failure on a pretty new looking varnish, then that is probably indicative of a transience issue.

Audible noise can also be an indicator of harmonics issues. A lot of times we get audible noise from equipment that is not supposed to make a noise. For example, you may hear a tuning fork type of sound—that is basically 2nd, 3rd and 4th harmonics. Although that sound is short term, it's actually harmonics. The kinds of noises that you hear coming from equipment may or may not give an indication of harmonics issues.

Finally, with resonance, it is super important to understand really how resonance plays into harmonics, especially when power factor correction capacitors are added.

The following are four brief summaries of actual case studies that showed symptoms of harmonics. 

An automobile manufacturer had to recall minivans because of poor welds on the tailgates. There was significant voltage notching so the welds were not substantial. Instead of being 20 cycles long (20 electrical cycles) there were only eight.

In a data center, a couple of generators could not be paralleled. One was loaded and one was unloaded. Because of harmonic distortion, there were issues with the transfer switch and relay scheme that was used in doing the paralleling. 

In regard to a steel mill, a third of a 30 megavar capacitor bank failed because of harmonic resonance.

Lastly, in a commercial building, as more and more fluorescent lights were added, it turned out that those lights were self-infecting, causing them to flicker. The symptoms showed a harmonics issue but whether the harmonics should be filtered or the lights be replaced is what needed to be determined.