“…The performance of the UFLS schemes, which are designed based on experience, cannot be necessarily guaranteed in the modern power system. So, several optimization methods have been extensively investigated to design UFLS schemes [3,[8][9][10][11][12][13]. To minimize the amount of shed load, both traditional optimization methods and the evolutionary algorithms have been employed to determine the UFLS relay parameters, i.e., frequency thresholds, step sizes, and time delay.…”