Optimal coordination of dual-setting directional over-current relays in multi-source meshed active distribution networks considering transient stability

Sustainable electrification calls the need for more efficient protection schemes. Synchronous-based distributed generations (SBDGs) are more susceptible to power grid faults owing to their low inertia time constants. Accordingly, fault elimination faster than the associated critical clearing time (CCT) is required to prevent unintentional disconnection of SBDGs, which inevitably makes the coordination of directional over-current relays (DOCRs) complicated than before, especially in meshed structure distribution networks (DNs). This study proposes communication assisted dual-setting DOCRs as effective solutions for providing fast-response protection in order to meet transient stability constraints of SBDGs in meshed active DNs. Dual-setting DOCRs are capable of operating in both forward and reverse directions with individual settings for each direction and thus providing flexibility in the coordination process. In this regard, time domain simulation as a reliable method is conducted to calculate CCTs. Afterwards, coupled with selectivity constraints associated with dual-setting DOCRs, transient stability constraints are all together accommodated in the optimisation process. Moreover, dual-setting DOCRs are allowed to follow user-defined time-inverse characteristics which help to alleviate clearing time of faults. The approach reveals a non-linear programming model which is tackled by seeker algorithm. Detailed numerical studies are carried out to validate the performance of the proposed approach.