Directional overcurrent relays are used to protect interconnected power systems and looped distribution systems. The problem is modeled as a constrained nonlinear optimization problem in which the decision variables are the devices that control the act of isolation of faulty lines from the system without disturbing the healthy lines. Time dial setting (TDS) and plug setting (PS) are considered as optimal parameters. IEEE 3-bus model and IEEE 4-bus model are two models of this problem. This paper presents a new efficient and reliable approach based on a constrained harmony search algorithm (HSA) to solve the problems.  The authors’ proposed technique is called Box-Muller harmony search (BMHS) algorithm. BMHS has been tested by applying it to two models. The simulation result of this technique is compared with those reported in the literature. The outcome is very encouraging and proves that the new technique outperforms them in terms of reaching a more optimal solution and speed.

Key words: BMHS, Box–Muller transform, coordination, directional overcurrent relay, HSA, power system.