High Impedance Fault Detection and Isolation in DC Microgrids

Faults in dc microgrids require quick interruption than in traditional ac power systems. This is due to the reduced stiffness of dc microgrids being powered by low inertia DERs interfaced to through power converters. For a high impedance fault, the limited magnitude of the fault current poses additional challenges in identification and locating the faults in the system, with difficulty in distinguishing the fault condition from the normal operating condition. This paper focuses on designing a cost-effective protection system for fast identification, selective isolation of high impedance faults and system restoration in such dc microgrids through proper coordination of source converters with sectionalizers, and with no solid state circuit breakers in action. The high impedance faults are identified through multi resolution analysis of the locally measured current signals with discrete wavelet transform and K-nearest neighbor based classifier at each source converter and contactor. The selectivity is achieved through adaptive resistance time curves set by the controllers installed at each contactor in the system.