Seismic evaluation of Gas Insulated Lines (GIL) based on a newly defined key control metric and a simplified theoretical model

With the increasing deployment of Gas Insulated Lines (GIL) in ultra-high voltage (UHV) substations located in high seismic intensity areas, there is an urgent need to assess its seismic performance. However, the unique coaxial structure and internal electrical connections of GIL prevent the direct application of conventional seismic performance indicators to effectively characterize its potential failure modes. This study first identifies two primary failure modes of GIL—outer shell strength failure and inner conductor pull-out failure—through nonlinear time-history analysis, concentrated at the corner junctions of high-height-difference vertical sections. Based on these findings, the Inter-segment Drift Ratio (IDR) is proposed as a key control parameter for quantitatively evaluating the seismic performance of GIL. A simplified theoretical model is then developed to investigate the influence of support stiffness configuration on GIL’s seismic performance through parametric analysis. The results demonstrate that the simplified theoretical model, based on IDR, provides high accuracy, with a deviation of only ±5 % compared to finite element analysis results, making it more suitable for practical engineering design with minimal computational cost. Furthermore, adjusting the support stiffness on both sides of the height-difference section can significantly improve the overall seismic performance of GIL. In conclusion, this study introduces an innovative approach for evaluating the seismic performance of GIL, offering a practical framework for enhancing its resilience in seismic-prone UHV substations.