Evidence theory-based seismic vulnerability assessment of ultra-high voltage converter transformers under hybrid uncertainty

The seismic vulnerability assessment of ultra-high voltage (UHV) converter transformers is a critical concern for the resilience of long-distance DC transmission systems. It represents a structural reliability problem that spans multiple damage states. However, epistemic uncertainty in structural parameters and aleatory uncertainty in ground motions are major sources of input variability. Traditional vulnerability assessment methods assume the failure threshold to be a single value, which is incompatible with the requirement for the continuity of damage states in probabilistic seismic performance analysis. To address these challenges, a seismic vulnerability assessment framework for ±800 kV converter transformers using evidence theory and a hybrid uncertainty propagation method is put forth. Aleatory uncertainty due to seismic excitation is quantified by employing multiple seismic records systematically scaled in amplitude. Moreover, an evidence theory approach is then developed to characterize epistemic uncertainty arising from ignorance in structural parameters. A hybrid uncertainty propagation method is then employed to propagate these uncertainties and to derive a robust fragility surface for UHV converter transformers. The proposed method is demonstrated via a ±800 kV converter transformer. The results show that the evidence theory-based vulnerability assessment framework effectively captures structural response uncertainties and supports the enhancement of system-level seismic resilience in UHV converter stations.