Tracking failure process of XLPE-silicon rubber interface under impulse voltage

XLPE-silicon rubber interface is the weakest part of cable system. Dielectric breakdown called tracking failure of the interface often occurs. The failure endangers the reliability of power delivery. Massive application of power electronics easily causes over voltage or high electric field of impulse in power system, and leads to discharge or tracking failure of the interface. Therefore, it is very important to investigate the effect of impulse voltage on the tracking failure. In this paper, interface was set up by pressing together a slice of XLPE and a slice of transparent silicon rubber. High impulse voltage was applied on a pair of needle-plate electrodes which was sandwiched at the interface with their insulation distance of 10 mm. The discharge light and carbonization from discharge to the failure were recorded with a digital video recorder and then analyzed. As comparison of impulse voltage, tracking failure under AC voltage was also tested. The comparison results show that impulse over voltage leads to a short time of electric discharge of interface and produces lees heat energy. Tracking failure occurs difficultly. However, AC voltage has a longer time of over voltage in each cycle, which easily leads to arc discharge and produces a large amount of heat energy and easily causes tracking failure. It is supposed that once impulse over voltage initiates interface discharge when AC voltage is applied, interface tracking failure easily occurs. This result is important for operation of XLPE cable joint.