Identification of Unhealthy Power Systems with Non-Charateristic Harmonics

Non-characteristics harmonics including even and 3 rd harmonics commonly exist in the electrical power sys- tems but in small amount which are usually below IEEE Std 519-1992 limits. However, in some cases significant amount of non-characteristic harmonics might be present in an industrial facility, which could be an indication of unhealthy power systems. Two case studies are performed in this paper. Case study 1 is about an even harmonic issue in a large mining sys- tem, where large 3 rd harmonic currents are also present. Case study 2 is a triplen harmonic issue at the input of multiple variable frequency drives experienced in an oil field distribution system. The root cause for even harmonics in Case 1 is the malfunction of two large rectifiers in the mining facility, while the root cause for 3 rd harmonics in both cases is the vol- tage unbalance issue from the utility side. The two case studies verify that non-characteristic harmonics can serve as an indication for unhealthy power systems. When they are detected in unusually large amounts, an analysis and troubleshoot- ing is always recommended in order to have a stable and reliable operation of electrical power systems.