Upstream Fault Detection Using Second Harmonic Magnitudes in a Grid Tied Microgrid Setting

Microgrids have been introduced to integrate more renewable resources onto the utility grid. Bidirectionality and low fault current levels are issues that cause fault detection problems for microgrids in both grid-connected and islanded modes of operation. During an upstream fault condition the desired reaction for the microgrid is to island itself. This allows certain loads, such as critical loads, to remain uninterrupted during an outage on the main grid. Therefore, the maintenance crew can be safely dispatched to alleviate the problem without fear of back-feed from the microgrid side. Hence, a critical problem that still needs adequate solutions developed is the detection of upstream faults in the grid connected mode without the reliance on communication systems. A protection method to detect upstream faults through second order harmonic magnitudes is proposed in this paper. The protection solution detects faults based on voltage and current second harmonic magnitudes during a fault transient period. A microgrid system was built in computer simulation and validated against an actual operational microgrid. The effectiveness of the proposed solution was demonstrated against multiple case studies in the PSCAD/EMTDC simulation environment.