Abstract: This paper addresses the issue of equipment alarms and thyristor breakdown caused by discharge from the RC damping circuit high-voltage conductors to the damping capacitor casing in the high-voltage end valve group of Pole I at the CS converter station. It aims to analyse the root causes of the incident and propose targeted solutions. By reconstructing the entire incident sequence, integrating high-voltage conductor parameter characteristics and thyristor-level potential distribution calculations, and analysing the discharge mechanism based on Paschen's Law, a fault failure chain model is established. Research indicates that the direct cause of the incident was insufficient clearance between the high-voltage conductor and capacitor housing, leading to insulation failure. The core contributing factor was the conductor insulation's inability to withstand the actual potential difference, with equipment vibration causing conductor displacement serving as an indirect cause. Through existing equipment inspections, new construction project verification, and optimised maintenance procedures, such discharge hazards have been effectively mitigated. The proposed four-tier prevention and control system alongside technical modification solutions provide practical guidance for the safe operation and maintenance of similar converter station equipment, holding significant importance for enhancing the reliability of ultra-high voltage direct current transmission systems.