A testing method with steep impact voltage inspecting the internal defects in EMU roof cable termination

A high‐voltage cable terminal on the roof of a high‐speed electric multiple unit operates in an intermittent impact load environment. The internal defects of the cable terminal are accelerated and are likely to cause insulation failure. Therefore, in this study, a steep impact voltage method is proposed to identify defective cable termination and establish a thermal and electric field model of the cable termination to analyse the defect development process. The results demonstrated that the interface performance of the cable terminal decreased after operation, and the internal insulation broke down under a steep‐wave impulse voltage. Under the operating voltage, there was an electric field concentration at the interface between the stress layer and the insulation layer of the cable terminal that can cause partial discharge within the defect located in this part. The thermal field distortion at the cable terminal joint was obvious, and the resulting air gap reduced the interface performance. Field distortion aggravates the insulation damage under frequent thermal shock and causes insulation accidents. This study provides an experimental reference and theoretical basis for the design and operation of cable terminations.