Protection coordination in microgrid using fault current limiters

Abstract

To ensure the seamless working of the microgrid, another Smart Grid tool- the Fault current limiter (FCL) has been proposed to suppress the fault currents to the level such that the requisite protection coordination is possible. The FCL suppresses the fault currents from the utility grid and acts as a solution to the directional overcurrent relay coordination problem within the microgrid. The FCLs are unique in the way that they are 'invisible' during the normal unfaulted operation of the power system but come into picture at the time of fault. The contributing reactance from the FCL is instrumental in reducing the fault currents flowing inside the microgrid from the incoming transmission feeder during the time of fault. In this paper reactance FCLs are only being used for coordination of directional overcurrent relay (DOCR) settings. Symmetrical three phase faults are considered for relay coordination. The distributed generation (DG) considered here is the conventional synchronous generator directly connected to the medium voltage networks. The proposed solution is tested on a radial distribution system (the benchmark Canadian distribution system model) of 9 bus which is adequately connected to DGs within the microgrid. Further investigation of the proposed method has been carried out for three configurations i.e grid connected, islanded and dual. It is observed from the simulation results that the operating times of relays in the grid connected configuration are similar to the operating times of the relays in the islanded mode when the optimal settings are done for the dual configuration mode and the optimizer is unable to find out any setting for both configurations without the help of FCL in the incoming feeder within the given range of relay settings.