Application of characteristic curves appropriate for relay coordination in adaptive protection networks containing distributed generation facilities

The integration of distributed generation (DG) facilities into power grids improves energy supply but introduces significant complexity, particularly with respect to protection coordination. Since power output from most DG facilities depends on variable conditions such as wind speed and solar irradiance, the magnitude of short-circuit currents that arise during faults also varies continuously. This variability causes deterioration of overcurrent relay coordination and selectivity, potentially leading to unnecessary power outages and equipment damage. To address this challenge, this study proposes an adaptive protection algorithm that selects the most appropriate relay time-current characteristic curve based on the real-time connection status of DG facilities to the network. The algorithm distinguishes among eight operating modes defined by the on/off states of three DG units and assigns either the standard inverse or extremely inverse characteristic curve accordingly. The proposed method was implemented and validated in a MATLAB/Simulink environment using a modified IEEE 4-bus test system integrated with three squirrel-cage induction generator-based wind turbines. Performance was evaluated across 24 scenarios comprising 8 operating modes and 3 fault locations. Simulation results demonstrate that the proposed algorithm reduces the tripping time of backup relays in 20 out of 24 cases, with improvements ranging from 29.11% to 90.98% compared to conventional adaptive protection. These findings confirm that the proposed method significantly enhances relay coordination, selectivity, and system protection in DG-integrated networks.