Advertorial - Mitigating harmonics in critical applications
Variable speed drives are known culprits for the increasingly widespread problem of harmonics. However, according to ABB’s Chris Plumb, HVAC Drives Key Account Manager UK, new innovations in drive technology have now made them part of the solution.
Harmonics are a growing problem in the HVAC industry. They are distortions of current and voltage waveforms caused by introducing non-linear loads to the grid. These can include switched-mode power supplies, LED lighting, photocopiers, computers and televisions, as well as solar inverters and EV chargers. Introduce too many of these devices, and their cumulative effect will affect power quality and disrupt equipment operation, resulting in overheating and nuisance trips. For critical applications such as hospital operating theatres, data centres or airports, this can have serious implications for system stability and safety.
Imagine a pint of beer with a frothy head. In this analogy, the head represents reactive power, measured in volt-amperes reactive (VAR) and, as with the head on a pint of beer, is essentially waste. The beer itself, i.e. the useful bit, is the actual real power, measured in kW, while the head and the beer combined represent total apparent power, measured in kVA. Dividing the kW and kVA values gives you the power factor of your system. A system with 100% beer and 0% head is what we call “unity”, which means less energy is wasted and is what any system should be aiming for.
Any switching device can cause harmonics, including variable speed drives, and traditionally a solution would be to add additional harmonic filters. However, new developments in drive technology mean that harmonics can now be mitigated by the drive itself. Active front end (AFE) drives have an active supply unit and integrated line filter, which can help to reduce harmonic content produced by the drive by up to 90 percent. No other commonly used switching device has in-built mitigation, and in practice removing drive harmonics can make a vast difference to the harmonic content on the network overall. Furthermore, only one AFE drive is needed for the critical application that you’re looking to protect; there’s no need to replace everything all at once.
Active front end drives have a higher upfront cost compared to conventional drives, but they save money in other ways. They allow the use of a smaller transformer, and smaller cables, while removing the need for any additional harmonic filters. On the whole, an active front end solution will typically come out cheaper than a conventional drive, while also drastically reducing the risk of disruption caused by harmonic content, while also and improving the overall system efficiency.
For more information about mitigating harmonics in HVAC applications, download ABB’s application guide: https://search.abb.com/library/Download.aspx?DocumentID=3AUA0000230021&LanguageCode=en&DocumentPartId=&Action=Launch