Structural fault analysis of air-core reactors under lightning impulse

In ultra-high voltage （UHV） converter stations， the encapsulation of air-core reactors may deform under lightning impulse due to electromagnetic forces， which may induce structural faults and jeopardize the safe operation of power system. To address this challenge， an electromagnetic-mechanical stress coupling simulation model is established for air-core reactors. The influence of parameters such as current peak and rise time in lightning current mathematical models on the reactor’s electromagnetic distribution and structural deformation is analyzed. Based on the probabilistic characteristics of lightning impulse， a Bayesian network-based method is proposed for fault cause analysis. This method utilizes Bayesian network to compute prior and posterior probabilities， enabling systematic fault diagnosis through forward reasoning and backward inference.The results indicate that the lightning current amplitude， combined with its rate of rise （RoR）， exhibits a strong correlation with structural faults in reactor encapsulations， making it a critical factor in such failures. A field case study from an actual converter station corroborates the validity and practical applicability of the proposed simulation model and analytical approach.