Ground Directional Protection Assessment in Inverter Dominated Distribution Networks

Inverter-Based Resources (IBRs) are challenging traditional line protection systems, that have been designed and developed over the years considering the fault characteristics of synchronous generator dominated power systems. The response of IBRs under faults is mainly driven by the inverter control design that can vary across different manufacturers. This study focuses in assessing the performance of negative and zero sequence voltage polarized ground directional elements in a Medium Voltage (MV) distribution grid with increased penetration of Photovoltaic (PV) systems. A system has been developed, modelling a part of a distribution grid and utilizing detailed Electro Magnetic Transient (EMT) models to emulate the behavior of IBRs. The design of the substation protection scheme includes an 11 kV blocking scheme employing ground directional elements. The system is simulated in a real time environment and Hardware In the Loop (HIL) tests are performed with actual protection relays utilizing the industry standard IEC 61850 protocol for the communications. The performance of the blocking scheme is examined under different configuration scenarios, with the results indicating that under certain conditions, with heavy IBR fault contributions, the protection scheme is impacted negatively.