Effect of Interfacial Pressure on Electrical Tree between XLPE and Silicone Rubber

XLPE and silicone rubber (SIR) have been widely used in power cables and accessories for their excellent mechanical and electrical performance. However, the interface between them in accessories remains one of the weakest parts in the cable system. Electrical treeing is an important destructive factor for HV insulation structures, and it always leads to final breakdown. Therefore, it is essential to investigate the effects of interfacial pressure on electrical tree. In this paper, tests were carried out by pressing XLPE and SIR samples together under different interfacial pressures with a specific pressing device. AC voltage was applied on a pair of pin-plane electrodes placed at the interface. The pin-plane distance was 2 mm. The needle diameter was 0.25 mm and the tip curvature radius was (10 +/- 1) mu m. Under different interfacial pressures, the voltages for electrical trees to initiate were recorded and statistically analyzed. Meanwhile, the tree morphology and breakdown channel were also captured by using a digital micro-imaging system. The results show that at a low interfacial pressure of 50 kPa, no electrical trees can be observed. Instead, discharge light can be seen at the interface. As the interfacial pressure increases, electrical tree begins to appear. It is found that at 75 kPa, electrical tree initiates and grows, which finally leads to a severe breakdown along the interface. While at pressures above 100 kPa, electrical tree tends to grow into SIR side, and the breakdown channel is slender, only observed in the SIR. Besides, the electrical tree initiation voltage increases with the increase of the interfacial pressure. It indicates that a high interfacial pressure can effectively delay the initiation of electrical trees, and for the two materials that constitute the interface, XLPE seems to have a better electrical treeing endurance than the SIR.