Identification of Unhealthy Power Systems with Non-Charateristic Harmonics

Non-characteristics harmonics including even and 3rd harmonics commonly exist in the electrical power systems 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 system, where large 3rd 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 3rd harmonics in both cases is the voltage 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 troubleshooting is always recommended in order to have a stable and reliable operation of electrical power systems.