A crucial remark on the importance of considering transient configurations on the optimal coordination of directional overcurrent relays in power systems with high penetration of inverter-based generation resources

Since 1988, several papers have been written on the topic of optimal coordination of directional overcurrent protections (DOCP). Nevertheless, a fundamental deficiency can be highlighted in the vast majority of these contributions, and in particular, in the optimization formulations used to solve the problem: the constraints associated with the selectivity criteria do not consider the dynamic changes in the network topology that appear during the fault clearing process. In this paper, we analyze the severe negative technical consequences of discarding this important aspect in the formulation of the optimization problem in the context of smart grid applications based on the integration of inverter-based generation resources in interconnected power systems. It is shown that the above-mentioned simplification leads to an important loss of selectivity and, therefore, to a miscoordinated relay operation. Three illustrative examples are presented and discussed, showing that the omission of the correspondent constraints jeopardizes the security and resiliency of the system in real-world conditions. Protection system selectivity is crucial to providing adequate reliability in the case of meshed networks with high penetration of distributed energy resources.