Evaluation of 3rd Order Harmonics in Microgrids

The implementation of distributed generation sources with islanding microgrid capabilities can introduce new challenges for engineers integrating new large generators to existing power systems. The generator interconnection transformer winding configuration and the generator winding pitch greatly impacts the flow of circulating currents and can result in unexpected generator heating, as well as high grounding resistor operating temperatures. This presentation presents a case study of the flow of 3rd order harmonic currents in a microgrid power system, and how EMTP was used to design equipment modifications necessary to reduce the current. A review of generators and how they can lead to 3rd order harmonic current generatio, along with additional options for correcting this condition will be presented.