Abstract: The power supply reliability of the auxiliary converter is directly related to the operational safety of the train. As a key component in the design and application of the auxiliary converter, the stability of the AC filter reactor directly affects the power quality of the auxiliary converter. By analyzing the burnout problem of the reactor, it is ultimately determined that inter-turn short circuit is the core cause of the reactor burnout. Based on the analysis results, on the one hand, the production process of the reactor is optimized to enhance the reliability of the product from the source; on the other hand, logical protection is added to build a current overload protection mechanism under all working conditions to ensure the reliable operation of the auxiliary converter under various working conditions.