Comparative optimization of overcurrent relay coordination in DG-integrated distribution networks: water cycle algorithm versus genetic algorithm and big bang-big crunch.

The increasing penetration of distributed generation (DG) has significantly complicated protection coordination in modern distribution networks by introducing bidirectional power flows and variable fault current levels. These challenges become more pronounced under different operating modes, particularly in islanded operation, where reduced fault current levels place severe constraints on overcurrent relay (OCR) coordination. This paper presents a comparative assessment of metaheuristic optimization techniques for coordinating overcurrent protection in DG-integrated distribution networks. Two distribution systems with different topological characteristics are examined. A radial 9-bus system is analyzed under three operating modes: conventional grid-connected operation without DG, DG-integrated grid-connected operation, and islanded operation. In contrast, a meshed 30-bus distribution system is evaluated exclusively under islanded operation to represent the most demanding coordination conditions, where fault current support is limited to inverter-based DG sources. Relay coordination is formulated as a constrained optimization problem aimed at minimizing total relay operating time while satisfying coordination time interval (CTI) requirements. Three metaheuristic optimization algorithms are applied under identical protection models and fault conditions: the Genetic Algorithm (GA) as a conventional reference approach, and the Water Cycle Algorithm (WCA) and Big Bang-Big Crunch (BB-BC) algorithm as more recent techniques. Short-circuit calculations are performed for three-phase faults in accordance with IEC 60909 standards. The results indicate that all investigated algorithms successfully achieve coordinated relay settings under the examined operating modes.