Viability of Fillers in HTV Silicone Rubber in the AC and DC Inclined Plane Tests

The viability of fillers for inhibiting the dry-band arcing damage on high temperature vulcanized silicone rubber under the critical AC and the equivalent DC voltages of inclined plane test is investigated. Alumina tri-hydrate and ground silica are employed in the study as common fillers employed in silicone rubber formulation for outdoor high voltage insulation, and thermal analysis is applied in order to understand the protective mechanisms of the fillers. Filler volume effect plays a role in improving the erosion performance, and the dilution effect of water of hydration is shown advantageous for preventing progressive (directed) erosion. Dilution effect promoted with internal oxidation is found only notable at 50 wt% alumina tri-hydrate in this study. On the other hand, alumina tri-hydrate at 10 or 30 wt% may yield a porous residue, which is conducive to thermo-oxidation (combustion) and consequently erosion. The erosion suppression effects reported for the fillers in the composites employed in this study are found less viable under the equivalent DC as compared to the critical AC voltages of the inclined plane test. This study clarifies common perceptions about the viability of fillers in silicone rubber for AC and DC outdoor insulation applications.