New Overcurrent Relay Coordination Method Through Time Intervals to Enhance Microgrid Protection

This paper presents a method to protect microgrids (MGs) through coordination of directional overcurrent relays (DOCRs). The new formulation is subjected to restrictions of pre-established time intervals to guarantee the primary and backup functions of each relay. Traditional DOCR coordination is made according to the time operation sequence for the primary and backup functions, resulting in a functional dependence between the relays. Thus, slow relays affect the neighbor relays, increasing the operating time. The new coordination method has advantages over the conventional coordination because functional independence between the relays is achieved. It is only necessary to update the setting in the relays affected by contingencies, topological changes, or during the formation of islands. The use of non-conventional curves is considered to give the flexibility necessary to meet the time intervals at each required location. Based on the results, the proposed coordination method reduces the operation time of the relays compared with that under the conventional coordination method in the power systems studied. Further simplification in the relay adjustment process under the different contingencies studied was obtained, which improved under the various operating conditions in the test systems.