Morphology evolution and breakdown mechanism of cross-linked polyethylene(XLPE)-silicone rubber(SiR)interface induced by silicone grease diffusion

Silicone grease(SG)is used for lubrication during cable accessory installation and can penetrate into the silicone rubber(SiR),leading to properties deterioration of the SiR.In this study,the effects of SG on the breakdown characteristics of the cross-linked poly-ethylene(XLPE)-SiR interface are investigated.First,the variation of the XLPE-SiR interface breakdown voltage with SG coating time is experimentally explored.The interface breakdown voltage significantly increases after SG is applied,remains stable for coating times of up to approximately 144 h and then rapidly decreases;the minimum interface breakdown voltage is lower than that without the SG coating.Next,the effects of SG on the chemical composition and surface topography of the SiR are examined by infrared spectroscopy and optical profilometry,respectively.The SG penetration does not change the functional groups of the SiR but significantly increases its surface roughness.Finally,the interface electric-field distribution after coating with SG is analysed by finite-element simulation,revealing that the residual SG at the interface distorts the interface electric field after a long coating time.The increase in the SiR surface roughness caused by SG diffusion and the interface electric-field distortion caused by the residual SG together lead to the decrease of the interface breakdown voltage.