Effects of interfacial pressure on tracking failure between XLPE and silicon rubber

XLPE power cables are increasingly used in power distribution system for their excellent mechanical and electrical performance. However, interface between XLPE and silicon rubber in cable joint remains one of the weakest part of the cable system, because aging and relaxation of silicon rubber may reduce the interfacial pressure and then cause interfacial discharge and tracking failure. Therefore, this paper investigates the effects of interfacial pressure on interface discharge and tracking failure at the interface. Test samples were made by pressing a piece of XLPE and silicon rubber together under different interfacial pressures. AC voltage was applied on a pair of needle-plate electrodes at the interface with the insulation distance of 10 mm. Both the initial discharge voltage and the time to tracking failure were recorded with variation of the interfacial pressure and the applied voltage. Meanwhile, the discharge light and the carbonized configuration were also captured by using a high-speed camera. In order to quantify the light and the carbonization, the methods of image processing and fractal dimension (FD) were employed to establish the relationship between the quantitative characteristics of tracking process and the interfacial pressures. The results show that both the initial discharge voltage and the time to tracking failure increase with the increase of interfacial pressure. With increasing the interfacial pressure, the FDs of discharge light and carbonization path show the decreasing tendency, which indicates that the higher interfacial pressure can effectively delay the interfacial discharges and the tracking failure.