Optimal coordination of directional overcurrent relays in power energy systems with emphasis on the discreteness of variables: Comprehensive comparisons.

The challenge related to the coordination of overcurrent relays in a looped network, which is a highly constrained problem, is to find a more optimum solution and at the same time there is no miscoordination. In this problem, the utilized optimization algorithm has a direct effect on finding a more optimal solution. High exploration particle swarm optimization (HEPSO) algorithm, which utilizes multi-crossover mechanism of the genetic algorithm and the bee colony mechanism to increase the exploration capability, has been selected to solve the coordination problem. To validate the HEPSO algorithm, a new algorithm called turbulent flow of water-based optimization (TFWO) is also used, and their results are compared. A new approach to discretization of variables is presented, which prevents miscoordination in the relays coordination. It is a realistic assumption for all relay types, especially digital relays, in preventing miscoordination. Also, the outage of sub-transmission transformers is considered for determining pickup current, which is a practical aspect of power systems operation. The obtained results are compared with the results of other algorithms and methods such as metaheuristic, mathematical and analytical, and hybrid methods. The efficiency of the selected algorithm is proven through comprehensive comparisons. The results show more optimum solutions while there is no miscoordination. Finally, the performance of the selected algorithm and the proposed approaches are tested on IEEE 14 and 30-bus test systems. Since these test systems are large enough, the number of problem variables will increase significantly, effectively validating the power and robustness of the selected algorithm to tackle this complex and constrained problem. The outage of transformers in determining pickup currents had been implemented in this section.