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Getting to grips with Harmonics and Harmonic Filters

08 Dec 2020

Industry insights

Harmonic filters improve the quality of your power supply. They help eliminate nuisance circuit breaker tripping, reduce stresses on electrical plant and minimize downtime caused by electrical power outages. In other words, they save time and money for any industrial business that depends on electricity to power its operations.

But, what are harmonics?

Harmonics are a distortion of a wave form; in this case, the electrical AC (alternating current) supply. They are made up of a division of the electrical wave into multiple smaller ‘sub-waves’. These “sub-waves’ are multiples of the fundamental frequency.

An easy to understand example of harmonics is found in music. A pure, clean note viewed on an oscilloscope or similar device would produce a sinewave. However, the reason musical instruments sound different to each other is because of the proportions of harmonics in their sound – it’s why musicians will spend thousands of pounds to find an individual instrument that sounds exactly the way they like.

This is most obvious with an over-driven electric guitar (say, in a heavy metal band), where a very large part of what you hear is made up of harmonics producing a ‘distorted’ sound. On the other hand, a clean sound would be made up of notes with a lower ‘harmonic content’, so the same instrument can produce a range of sounds by varying the harmonic content of the signal sent through the amplifier to the speaker.


In electrical power systems, harmonics are typically generated by non-linear power electronic devices such as variable frequency drive (VFD) speed controllers and inverters. These are commonly found in industrial and power generation applications.

Due to the way they interrupt the current flow, by changing the AC frequency sent to the motor they control, VFDs can introduce harmonic distortion to the electrical supply wave form. While a guitarist creates harmonic distortion by increasing the input to the amplifier, as a VFD reduces the speed of the motor, it increases the harmonic distortion caused in its power supply.

Read more about harmonics and how we address them with harmonic filters in the full paper – Harmonic filters (web)

Find out more on our harmonic filters and capabilities here – Harmonic Filters


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