Optimal communication-free protection of meshed microgrids using non-standard overcurrent relay characteristics considering different operation modes and configurations based on N-1 contingency

Smart grids (SGs), meshed active distribution networks (ADNs), and microgrids (MGs) frequently experience reconfigurations and changes in their operation modes (grid-connected and islanded), which leads to protection miscoordination and speed challenges. Several research works have studied the protection of MGs/SGs, considering different configurations. On the other hand, non -standard relay characteristics provide some flexibility in protection design. However, the literature review shows that less attention has been paid to the optimal protection of MGs/SGs, incorporating non -standard relay curves and consideration of N-1 contingency configurations and operation modes. This paper aims to respond to this research gap. Also, the slow tripping of backup relays, a common drawback of recent works, is concerned with a modified objective function (OF). The presented coordination optimization problem (COP) is formulated in a mixed-integer nonlinear programming-linear programming (MINLP-LP) form and solved using hybrid heuristic-linear programming algorithms: Genetic algorithm-particle swarm optimization-linear programming (GA-PSO-LP) and water cycle algorithm-moth flame optimization-linear programming (WCA-MFO-LP). The introduced research is applied to the distribution portion of the IEEE-14 test system. The analysis and discussions emphasize that the proposed protection scheme speed is improved by over 36 % compared to available ones. Also, there is no coordination violation under different system configurations.