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Comparative Evaluation of DC Fault-Mitigation Techniques in Large PV Systems

Over the past five years, the industry has learned that photovoltaic (PV) system fault protection must be refined to include additional fault protection not provided in most existing PV system installations. Using a failure mode and effects analysis scoring system, this study evaluated the risk associated with 13 faults that could be missed by typical PV System fault protection and the effectiveness of 20 different solutions in containing these faults. Based on the analysis in this study, the ground fault protection in all new PV systems should be capable of detecting any ground fault with 50 mA or more of fault current to address the highest risk faults. For resistively grounded systems, both high- and low-risk faults can be prevented by using a combination of combiner box arc-fault circuit interrupt (AFCI) protection and either continuous isolation monitoring or inverter input differential current protection. For solidly grounded systems, combiner box AFCI protection should be paired with either higher sensitivity current detectors in the ground bond or inverter input differential current protection.