Adaptive and Automated Protection Settings for Over-Current Relays in Radial Grid Configuration

In this paper, the challenges related to power system protection for medium voltage distribution grids (focus is Germany) are addressed considering a future power system with a high share of distributed energy resources, grid configuration changes, and digitization. These make the conventional protection design unselective, and thus there is the requirement for improvement. An automated adaptive non-directional over-current protection scheme using a centralized communication architecture is proposed as a solution here. Within a supervisory control and data acquisition system, both the tripping time and the threshold current settings of each relay in the grid are calculated. The unselective behavior of the existing protection scheme is first evaluated during a grid reconfiguration in different radial topologies after a fault incident, and then a smart protection design method is introduced to solve the issues of relay selectivity and sensitivity. It is shown with a few case studies in a medium-voltage distribution grid that the proposed scheme is resolving the challenges and ensuring an efficient and flexible protection operation, that will be practically useful by system operators and protection engineers.