Optimal Coordination of Directional Overcurrent Relays Using Biogeography-Based Optimization Algorithms

Optimal coordination of directional overcurrent relays (DOCRs) is a highly constrained and nonlinear optimization problem. The operating time of each relay depends on two independent variables called plug setting and time multiplier setting. As the network becomes larger and more complex, the number of relays will increase and, thus, finding the optimal solution becomes very hard. In this paper, a new population-based evolutionary algorithm called biogeography-based optimization (BBO) is proposed and the performance of ten types of constraint-handling techniques is evaluated. In addition, a new hybrid BBO with linear programming (BBO-LP) is proposed to enhance the performance of the conventional BBO algorithm. The performance of the proposed BBO-based algorithms is evaluated by using five test systems. The results show the effectiveness and superiority of the proposed algorithms compared with the performance of the other optimization methods presented in the literature.