Halting harmful harmonics
By J Mitchell, CP Automation
Electricity+Control, August 2014 (pages 8 – 9)
Enquiries: John Mitchell. CP Automation. Email firstname.lastname@example.org
Download the full article on Halting harmful harmonics in PDF format.
Various approaches have been used to combat harmonics over the years. This has led to many suppliers using set-ups which are not meant for harmonic mitigation, in configurations that are often unnecessarily complex, outdated, take up lots of space or are inefficient, ultimately raising costs.
When looking to combat harmonics, there is the added issue of meeting international harmonic control requirements such as IEEE-519  which limits ‘the maximum frequency voltage harmonic to 3 % of the fundamental and the voltage total harmonic distortion (THD) to 5 % for systems with a major parallel resonance at one of the injected frequencies.’ Some form of filtering is subsequently recommended.
We are fortunate in the United Kingdom (UK) to have a stiff grid, but this is not true everywhere. Developing countries often suffer from weak grids, with an unreliable supply and inadequate infrastructure. The power ratings on products are often based on calculations performed in ideal conditions. Buyers would be wise to note that these products may perform adversely in weak grids and may not perform to IEEE 519  standards in these conditions.
Active and passive solutions
Active and passive solutions can be installed in both series and parallel (shunt) configurations. Series solutions operate in line with the load, meaning that units must be sized for the full current load. Shunt units can be sized only for the harmonic disturbance. There is a clear decision to be made between series-passive, shunt-passive, series-active and shunt-active solutions to combat harmonics.
Refer to pdf article for references.
- Various approaches have been used to combat harmonics over the years.
- Although a series harmonic filter works well as a ‘catch-all’, it is grid sensitive and may lead to interaction.
- Effective harmonic mitigation does not have to be intimidating.