Abstract: “Power systems are exposed to various faults, such as phase-phase, phase-ground, 3-phase-ground during their operations. Due to fault type and location, some part of the system cannot be supplied when a fault occurs. Moreover, this issue not only reduces power quality parameters but also increases total energy cost of the system. Overcurrent relays are widely used tools for detecting and clearing fault in power systems. In addition to this, relays must be operated in a harmony whilst fault occurs. The coordination among relays can be quarantined by arranging their characteristics through adjusting their parameters. In conventional approach, operation characteristics of relays depend on two variables namely, pick up current (Ip) and time multiplier settings (TMS). In recent decades, several studies about optimization of relay coordination problem have been done. Since relay coordination problem is a non-convex optimization problem, most of studies has been used heuristic optimization tec”

Keywords: relay coordination, power systems, optimization, genetic algorithm, linear programming, hybrid, distributed generation