Coordination of directional overcurrent relays that uses an ant colony optimization algorithm for mixed-variable optimization problems

In this paper, the coordination of directional over-current relays (DOCRs) using an ant colony optimization (ACO) algorithm is presented. The ACO performed is an extension of the ACOR algorithm for continuous optimization to tackle mixed-variable optimization problems, reduced in two types of variables both continuous and categorical. The DOCRs problem is a non-linear programming problem (NLP), usually solved with a linear programing technique (LP) only considering the time dial setting (TDS) as a decision variable, without dealing with the non-linear problem of plus setting (PS), or solving the PS component using a heuristic technique. In this work, both TDS and PS are decision variables, TDS is considered continuous and PS categorical. Parameters are adjusted according to literature to guarantee performance. The ACO algorithm has proved high probability of solving a problem when a high number of function evaluations exist. For testing this methodology two transmission systems (3 and 8 Bus accordingly) were evaluated to compare with the literature demonstrating effectiveness of the algorithm.