Effect of surface smoothness on tracking mechanism in XLPE-Si-rubber interfaces

Cable joints are the weakest part of power cable systems due to the presence of an interface between the cable insulation and the insulation of the accessory. Electrical tracking is one of the main failure mechanisms that can occur at dielectric interfaces. Therefore, this paper investigated the effect of interfacial smoothness on the tracking mechanism in XLPE-Si-Rubber interfaces. The interface was setup by slices of XLPE and silicon rubber in the experiment. The XLPE surfaces were polished into different smoothness by using abrasive papers. AC voltage was applied on a pair of flat-round electrodes at the interface with an insulation distance of 10 mm. The initial discharge voltage, the tracking failure voltage and the time to tracking failure with different interfacial smoothness were recorded and the tracking failure process at the interface was recorded with a high-speed camera. In order to quantify the discharge light and the carbonization degree, the photo patterns were analyzed with fractal dimension method. Obtained results showed that with the increase of interfacial smoothness, the initial discharge voltage, the tracking failure voltage and the time to tracking failure increased, but the fractal dimensions of the carbonization degree and the discharge light decreased.