Power System - Fault Clearance with Limited Fault Current

Abstract

Abstract The integration of renewable energy sources like wind and solar power into the grid, typically through converter interfaces, has introduced significant technical challenges, particularly in fault current management. This thesis explores the evolving challenges and solutions in power system protection as the share of converter interfaced generators continues to grow in response to global ambitions for reducing greenhouse gas emissions. Traditional synchronous generators provide predictable and substantial fault currents that are essential for the reliable operation of existing protection schemes. However, converter interfaced generators, governed by converter controllers, produce fault currents that are not only lower in magnitude but also less predictable, creating a need to reassess and adapt current protection systems. This research investigates the impact of high converter interfaced generators penetration on short-circuit capacity and the preparedness of transmission system operators to manage these changes. The study highlights the limitations of conventional protection schemes, such as overcurrent and distance protections, where they exhibit under-reaching of distance relays and delayed tripping of overcurrent relays. These issues arise when fault currents are significantly reduced and exhibit varying characteristics, including diminished negative sequence currents and a wider range of phase angles. The research also examines the potential of new protection technologies and contingency strategies, such as grid forming converters, synchronous condensers, adaptive protections, and advanced methods like traveling wave-based protection, in addressing these challenges. Despite promising developments, the thesis identifies several obstacles to the widespread implementation of these new technologies, including high costs, complex performance evaluations, communication and cybersecurity concerns, and a lack of standardization, which hinders interoperability among different equipment vendors. Furthermore, evolving grid codes and new requirements for fault ride through and reactive power control demonstrate the ongoing efforts to mandate better fault management characteristics for converter interfaced generators.The reliability of overcurrent protection in distribution system and distance protection in transmission system can be significantly compromised in the evolving grid. There has been significant progress in adapting protection systems to accommodate more renewable resources, but further research and development are crucial to overcoming the remaining challenges and ensuring reliable fault detection and clearing in the modern power systems.