Optimal dual characteristics for enhancing coordination index in protecting forward and reverse fault currents

Satisfying coordination constraints among protective devices is a challenging task in the protection system of electrical grids. On the other hand, increasing interest on the distributed generations (DGs) jeopardizes the selectivity among overcurrent relays in active distribution networks. Therefore, sustainable electrification requires enhancing the protection coordination index (PCI) in order to increase DG penetration in these networks. In this paper, time-current-voltage​ characteristics and dual-setting directional overcurrent relays (DOCRs) are jointly employed to improve PCI in interconnected distribution networks. Dual-setting relays can operate in forward and reverse directions with individual settings in both directions which help to provide more flexibility in improving PCI. Moreover, the time-current-voltage​ characteristics have the voltage parameter in operation time of relays which can simplify the optimization process to yield higher flexibility in the coordination process. Furthermore, the proposed protection scheme is extended by user-defined time-current-voltage​ characteristics to improve PCI as much as possible. The proposed scheme is formulated as a nonlinear programming model that is solved by the genetic algorithm (GA). The proposed scheme is tested on IEEE 14-bus and 30-bus testbed. Results show a remarkable improvement.