A new formulation and solving of protective relays setting and coordination problem using multi-objective optimization and fuzzy logic

This paper presents a new formulation of the overcurrent relays setting and coordination problem using the combinatory constrained multi-objective optimization. Two objective functions are selected to be minimized simultaneously namely: the minimization of the primary relays operation time as well as the minimization of the backup relays operation time. Both real and integer decision variables are considered; where the real variables are the time dial setting (TDS), as well as the pickup current (Ip), and the integer variables are the relay characteristics. To solve this constrained non linear multi-objective problem, the original algorithm of Strength Pareto Evolutionary Algorithm 2 (SPEA 2) is enhanced in order to manage both real and integer decision variables as well as to handle the constraints violation during the optimization process. A fuzzy-based mechanism is employed to aid the decision maker to choose the best compromise solution from the Pareto front. The obtained results show the efficiency of the proposed SPEA2 to solve the multi-objective optimization of overcurrent relays and capture the Pareto front. Furthermore, the proposed method is able to find values of the real (Ip, and TDS) and integer (relays characteristics) decision variables that ensure a good coordination of the relays with the satisfaction of the constraints.