Key technologies for relay protection of bulk renewable energy transmission lines

This paper examines the declining adaptability of conventional relay protection systems caused by large-scale renewable energy integration. A systematic review is conducted on fault characteristics of different renewable energy sources and corresponding protection improvement strategies. Through comparative analysis of dynamic characteristics between renewable energy systems （wind/photovoltaic） and conventional synchronous generators， the study identifies key challenges introduced by power electronic devices： limited fault current amplitude， controlled phase response， and increased harmonic complexity. Building upon existing research achievements， this paper conducts an in-depth exploration of renewable energy equivalent modeling and its application value in fault characteristic research， while systematically analyzing the causes behind the degraded adaptability of conventional protection schemes such as pilot differential protection and distance protection in renewable energy scenarios. The analysis reveals that although existing improved solutions have enhanced protection performance through innovative principles including transient voltage-based phase selection， bilateral fault information similarity， and transient energy differential， they remain fundamentally constrained by technical limitations： the strong coupling with control strategies， complexity operating conditions， and difficulties in reclosing coordination. Future reasearch needs to further explore： 1） The intrinsic relationship between renewable energy control strategies and transient fault characteristics； 2） The establishment of a multi-dimensional fault feature extraction system； 3） Theoretical breakthroughs through integration of control links with conventional protection. The paper concludes with technical prospects for protection technology development， providing references for secure opeation of modern power systems.