A reliability-based approach to identify critical components in a UHVDC converter station system against earthquakes

Earthquakes pose a huge threat to the power system in seismically active regions. Ultra-High Voltage Direct Current (UHVDC) converter stations become integral to modern power grids, especially for long-distance power transmission, and thus understanding and improving their seismic reliability is essential for ensuring the robustness of the power system. This paper presents a comprehensive reliability-based approach to identify critical components within UHVDC converter stations, focusing on seismic reliability. A seismic reliability index is defined as the expected post-earthquake transmission capacity loss, considering both the earthquake probability and the derated capacity under different operation modes. The converter system's seismic reliability model is established based on divide-and-group principles, dividing it into subsystems and deriving an equivalent logical model based on their interdependency. Failure probabilities of subsystems, consisting of wire-interconnected electrical equipment, are determined through finite element models and seismic vulnerability analysis, accounting for wire interaction forces. Advanced sensitivity analysis techniques such as the Morris method and Sobol's analysis identify critical components influencing seismic reliability. A case study on a real-world ±800 kV UHVDC converter station system demonstrates the effectiveness of the proposed approach in enhancing seismic reliability efficiently.