Enhanced Symbiotic Organisms Search for Optimal Overcurrent Relay Coordination Under Thermal Constraints in DG-Integrated Distribution Networks

This paper introduces Symbiotic Organisms Search Featuring Comprehensive Opposition and Adaptive Parasitism (SOSCAP), an enhanced symbiotic organisms search algorithm that integrates comprehensive opposition and adaptive parasitism strategies to balance exploration and exploitation and prevent premature convergence. The proposed algorithm is applied to the optimal coordination of overcurrent relays in a 20 kV, 16-bus test distribution network with integrated distributed generation, accounting for conductor thermal capacity. A hybrid assignment of relay curves, combining normal inverse, very inverse, and extremely inverse characteristics, is introduced to improve optimization performance. Three scenarios are simulated to evaluate the algorithm under varying characteristic assignments. Simulation results indicate that SOSCAP outperforms the original symbiotic organisms search algorithm and its variants in solution quality. In the hybrid scenario, SOSCAP achieves a best fitness value of 8.92 s, representing a 68 percent reduction compared to the baseline scenario, while ensuring that all relay tripping times remain below one second. The improvements achieved demonstrate SOSCAP’s suitability for practical deployment in modern distribution systems.