Sustainable electrification in critical infrastructure: Variable characteristics for overcurrent protection considering DG stability

Abstract

Low inertia time constant of synchronous generator-based distributed energy resources (SGBDERs) makes them more susceptible to faults. Therefore, fast-response protection is of crucial importance to prevent unintentional disconnection of SGBDERs in active distribution networks (DNs) and hence, non-stop electrification in critical infrastructures. To overcome this challenge, the present study aims at devising a new protection coordination strategy (PCS) for directional overcurrent relays (DOCRs) based on numerical relays. In this regard, this paper unveils that time-current characteristics (TCCs) with gentle and steep slopes are suitable for the lines with huge and small differences in fault currents at near-end and far-end fault points, respectively. These characteristics cannot be followed by the conventional approach. Accordingly, some coefficients in the operation function of DOCRs are included in the variables set to present TCCs with steep slopes and some supplementary variables are employed to present TCCs with gentle slopes. Furthermore, to cope with the effect of increment in the number of variables, some controlling parameters are introduced to steer TCCs toward proper slopes. Finally, to provide more flexibility in meeting distributed generation (DG) stability, instantaneous functions are also included in the proposed PCS. Detailed simulation studies are conducted to assess performance of the proposed approach.