Advanced Protection Concepts for MV Grids with High PV Penetration: Impacts on Relay Behavior and Future Directions

Abstract

The increasing integration of photovoltaic (PV) generation into medium-voltage (MV) power distribution networks challenges the coordination and effectiveness of traditional protection schemes. This study investigates how PV placement and penetration levels affect fault current magnitudes and tripping behavior of overcurrent and distance protection relays.

Using the Cigre Medium Size (MS) benchmark grid in DIgSILENT PowerFactory, a series of short-circuit simulations were performed under various PV scenarios, varying the connection point and infeed. In addition to steady state analysis, a custom-developed dynamic PV model was implemented to assess time-domain behavior under fault conditions, enabling the extraction of relay-measured impedance and tripping times. The modeling approach considered the inverter-based generation's contribution and its influence on relay sensitivity.

The results show that PV located upstream of the fault enhances fault current levels and accelerates relay tripping, while downstream PV reduces the fault contribution and leads to delayed protection operation. Notably, distance protection elements exhibited zone underreach in certain configurations, revealing limitations in detecting high-resistance or low-infeed faults in distributed generation contexts. These findings highlight the risk of miscoordination and delayed fault clearance in PV-rich distribution networks.

The study emphasizes the need for adaptive, data-driven protection strategies capable of adjusting to real-time system conditions. Integrating phasor measurement units (PMUs), flexible relay logic, and communication-based coordination is proposed as a pathway to enhance protection performance in future distributed energy systems.