This paper discusses the state of the art in the application of self-healing silicone-based materials for outdoor high-voltage insulation. Both the dynamic behavior of the dimethyl side groups of silicone rubber and the diffusion of a bulk siloxane to maintain low surface energy are respectively reported as intrinsic mechanisms responsible for the self-healing of silicone rubber. Localization, temporality, mobility, and the type of synthesis are the aspects defining the efficiency of the self-healing ability of silicone rubber. In addition, the deterioration of the self-healing ability with filler loaded into silicone rubber insulation housing composites is discussed. Taking the self-healing property into consideration among the other properties of silicone rubber insulators, such as tracking and erosion resistance, can be a useful design practice at the material development stage. Hydrophobicity retention, recovery, and transfer measurements are discussed as useful indicators of the self-healing ability of silicone rubber. Nevertheless, there remains a need to standardize them as design tests at the material development stage. The paper is intended to shed the light on the hydrophobicity recovery, a key material design parameter in the development of silicone rubber outdoor insulating composites, similar to the tracking and erosion resistance.

In this paper, the degradation mechanisms of unfilled polydimethylsiloxane with different molecular weights is investigated under dry-band arcing using the inclined plane tracking and erosion test and material characterization techniques. Tracks of carbonaceous residue formed as byproducts of radical-based crosslinking are prevalent over erosion as the molecular weight increases. Erosion becomes dominant with polydimethylsiloxane that undergoes mainly depolymerization during degradation at lower molecular weights. Accordingly, tracking due to a progressive carbonaceous residue formed on the surface is the degradation pattern observed under the dry-band arcing for the polydimethylsiloxane with higher molecular weights (45000 and 28000 g/mol) during the inclined plane test, whereas erosion due to depolymerization is more evident on the polydimethylsiloxane surfaces with lower molecular weights (17200 and 9400 g/mol). This study highlights the possibility to tune the tracking and erosion tendency of silicone rubber outdoor insulation by controlling the molecular weight of the organosiloxane base, without the sole reliance on fillers as commonly perceived.