Adaptive Overcurrent Protection of Distribution Substations with Definite-Time Characteristics

The increasing penetration of distributed energy resources (DERs) introduces new challenges for the operation and protection of power systems. The main challenges for protection systems arise from varying power flows and short-circuit current levels, which may prevent conventional protection schemes from fulfilling the fundamental protection requirements under certain operating conditions. Therefore, the aim of this study is to develop an adaptive protection method that enables the protection of distribution substations to be adjusted to the integration of DERs. The proposed adaptive protection method consists of defining a classification index for ranking operating conditions, grouping operating conditions, and determining optimal protection function settings. The method employs non-directional or directional overcurrent protection with definite-time (DT) characteristics. The developed method is implemented on a simulation model based on the actual SS Mikanovci 35/20 kV distribution substation case study. The classification index is determined based on the relationships between protection devices and the probabilities of occurrence of individual operating conditions. The k-means algorithm is employed for operating-condition clustering, while the optimal protection settings are determined by considering the minimum required coordination time interval between primary and backup relays, as well as the constraints imposed by the surrounding network and the capabilities of the protection devices.