Enhancing overcurrent relay performance in distributed generation networks: A novel non-standard time-current characteristic approach

Abstract

High-speed operation of protection relays to isolate faulted systems is critical for active distribution networks. The overcurrent relay with standard time-current characteristics is vulnerable to delayed operation or loss of sensitivity due to fault current contribution from distributed generation. The non-standard time current characteristics (NSTCCs) have been proposed in the literature to make the relay operation steadfast but it breach the relay operation time minimum constraint. In this paper, a novel non-standard time current characteristics has been proposed with a logarithm function to achieve the fast relay operation time (ROT) and rehabilitate the sensitivity of the backup relay at a lower fault current magnitude. Further, a new auxiliary variable is introduced to provide the additional time delay to avoid the oversensitive behavior of NSTCC or offset in ROT to make it faster regardless of the fault current. The stringent criteria are defined to set the boundary limits of the auxiliary variable. The proposed scheme is validated on IEEE-9, IEEE-33, and meshed IEEE-8 bus systems using ETAP and MATLAB. For the IEEE-9 bus system, it reduced ROT by 31.55% and 23.34% compared to NSTCC and STCC, respectively, while for the IEEE-33 bus system, it achieved reductions of 55.66% and 25.16%. While other schemes violated relay operation time and coordination time interval constraints, the proposed scheme met all constraints, demonstrating superior performance and reliability.