Impacts and relay protection solutions for the distribution network in Huong Khe district, Ha Tinh province under high rooftop solar penetration

Abstract

The rapid integration of rooftop solar photovoltaics (PV) systems in Vietnam has transformed traditional radial distribution networks into active grids with bidirectional power flows. This transition poses significant challenges to relay protection systems designed for unidirectional power flow. This paper evaluates the technical impacts of high PV penetration on the 35 kV distribution network in Huong Khe District, Ha Tinh Province, a region characterized by large supply radii and high system impedance. Using PSS® SINCAL software to model the actual grid, the study identifies critical issues including protection "blinding," sympathetic tripping, and the breakdown of traditional fuse-recloser coordination. To mitigate these risks, the research proposes a coordinated technical solution involving the implementation of directional overcurrent protection (67/67N), adaptive setting groups, and the optimization of recloser-fuse curves through the use of extra inverse characteristics. Simulation results confirm that the proposed strategies successfully restore protection selectivity and sensitivity. The study concludes that upgrading to smart, directional, and adaptive protection systems is essential for maintaining grid reliability and safety in the context of increasing renewable energy penetration.