Real time simulation of new adaptive overcurrent technique for microgrid protection

In this paper, an adaptive overcurrent coordination technique for the microgrid having both rotating and inverter based distributed generation systems (DGs) is considered. During a fault, the magnitude and direction of fault current contributed by both the DGs vary differently with respect to the prefault current. Moreover, the fault current contributed by the inverter based DGs is clamped within 2 p.u of the rated current due to the thermal limit of the inverter present within it. Further, the fault current phasors during the islanded and grid-connected modes of operation vary to different values and lead towards false trip by overcurrent relays. This situation leads to the miscoordination between the primary and backup relays used to protect the feeders of the microgrid system. This work proposes an adaptive overcurrent relaying technique which uses the positive sequence and negative sequence components of fault current to coordinate the primary and backup overcurrent relays. A 12.47 kV, 50 Hz, 3 bus system is simulated using the real time digital simulator (RTDS) and performance of the proposed approach is tested for various fault scenarios.