An efficient method to include the effect of radial feeders on optimal coordination of directional overcurrent protections

Abstract This short article shows an efficient way to include the effect of coordination with radial feeders on the optimal coordination of directional overcurrent protections. This effect can be important, but it has been seldom considered. The proposed method is based on the inclusion of constraints related to coordination with radial feeders as simple increments of lower limits of the time multiplier settings of upstream directional protections. Although the overcurrent protections of radial feeders usually have inverse-type curves, the fault currents for the coordination are known and, consequently, their operation times can be directly computed. Therefore, these known operation times can be simply summed to the time margin required for selectivity, in order to compute the lower limits of time multiplier settings of upstream directional protections. The main advantage of the proposed method is the avoiding of increments in the number of constraints of the optimization problem.