Failure of Cable Accessory: Interface Breakdown Under the Effect of Moisture

Moisture at the insulation interface is the main cause for electrical breakdown and insulation failure of cable accessories. However, it is still unclear how the presence of moisture affects the discharge development and interfacial breakdown process. This paper clarifies the reasons for the breakdown failure of cable accessory insulation interfaces under the effect of moisture. First, the moisture and breakdown characteristics of faulty cable accessories in the field are presented. Second, the discharge evolution characteristics during the breakdown process of dry and wet interfaces are experimentally described. Then, the effect mechanism of moisture on the development of interfacial breakdown is explained by combining product analysis and electric field analysis. Finally, the proposed breakdown mechanism of insulation interface under the effect of moisture are verified through a field case. The experiment results show that the discharge develops in stages and generates gases during the breakdown of the insulation interface, and there exist multiple discrete arc discharges with random paths during the breakdown of the wet interface. The severe electric-field distortion and its dynamic movement caused by the gas bubble areas formed in the wet interface are the main reasons for the increase in randomness of interface discharge and the decrease in breakdown strength. Through current impulse detection and generated gas analysis, it is expected to provide new solutions for early fault detection for cable accessories.