A Novel Differential Fault Detection Strategy for Smart AC Microgrid Incorporating Tapped Loads

The differential protection scheme offers better selectivity and performance than other protection schemes in addressing protection challenges introduced by integrating ac microgrid into conventional distribution system. However, the presence of tapped load causes differences in electrical parameters (at line ends) during steady-state, system transients, and external faults, thereby reducing the selectivity and sensitivity of the differential scheme. Therefore, this work employs superimposed negative sequence current magnitude and superimposed phase current magnitude, provided to different AND logic Gates (with a 1.5 cycle delay) to identify fault and faulty phases in both operating modes of ac microgrid under different network configurations. The superimposed negative sequence current magnitude effectively distinguishes unsymmetrical faults from different switching transients, including tapped load switching, while superimposed phase current magnitude differentiates symmetrical faults from balanced tapped load switching. The proposed differential scheme is implemented in MATLAB simulation and demonstrates high sensitivity by detecting faults up to 600 Ω in grid mode and 500 Ω in islanded mode. It achieves high selectivity by effectively distinguishing faults from balanced/unbalanced tapped load switching and different system transients, with fast fault detection (within 2 cycles). Moreover, it is compared with recent differential schemes to highlight its high selectivity and sensitivity. The scheme is further validated on laboratory-level hardware-in-loop setup using OPAL-RT 4512 controller and GE P40 MiCOM relay for generating trip signal using IEC 61850 GOOSE protocol.