Kenneth L. Lovorn, PE Lovorn Engineering Assocs., Pittsburgh

Harmonics No More

View the full story, including all images and figures, in our monthly digital edition Increased dependence on electronics—in everything from fluorescent ballasts and desktop computers to large-scale hospital radiation suites—has created a much greater awareness of harmonic distortion and the havoc it wreaks on equipment. The good news is that tools are available to help determine exactly which pieces of equipment are being affected and to what extent. Looking at the system as a whole, we can pinpoint and address the causes of harmonics, rather than just the symptoms. HARMONIC CONSEQUENCES Harmonics-related problems can occur throughout commercial, industrial, and institutional facilities and include: Operation of overcurrent devices without an overload or short-circuit condition Random component failure in electronic devices, such as printers and personal computers Operating problems with electronic devices untraceable to any identifiable component problems Interaction between multiple variable frequency drives (VFDs) so that one or more drives do not follow their control setpoints Interactions between uninterruptible power supplies (UPSs) and the emergency generator supplying power to them during extended utility power outages System power-factor reduction, with associated distribution-system capacity loss and power-factor penalties applied by the serving electrical utility Increased neutral currents, causing overheating of neutral conductors in panels, feeders, transformers, and other neutral locations Problems with capacitor operation and life, such as resonant conditions, capacitor-case expansion, and capacitor rupture. Most harmonics-related problems have one of two basic origins: current-wave distortion or voltage-wave distortion.