A Study of the Erosion Mechanisms of Silicone Rubber Housing Composites

Abstract

Silicone rubber insulators have been replacing conventional insulators made from toughened glass and porcelain in the power system, due to the non-wetting properties of silicone rubber insulation housing. However, silicone elastomers will eventually wet-out leading to leakage current and dry-band arcing giving rise to erosion of the silicone housing material, and eventually insulation failure. Well-established formulations of insulation housing composites have been developed and validated for erosion performance using the standard inclined plane tracking and erosion test, yet no such formulations have been developed and validated for DC. With the assumption that equivalent performance will be obtained, an adjustment to the creepage distance has been the measure taken in using the AC insulators for DC, without taking into consideration the differing aspects of the DC as compared to the AC dry-band arcing. This practice questions the existing DC insulators as an unknown entity that requires further investigation to ensure the reliability of the power supply. In addition recent demands have been raised to develop housing composites specifically for DC outdoor insulation, particularly with the increased interest in DC. It follows that developing a standard DC inclined plane tracking and erosion test is necessary for the development of more suitable materials for outdoor DC insulation applications. This thesis provides a thorough study of the DC dry-band arcing mechanism as opposed to the well understood mechanism of the AC dry-band arcing and provides a mechanistic understanding to the dry-band arcing leading to erosion as a foundation for the development of a standard DC inclined plane tracking and erosion test. To this end, the influence of inorganic fillers in silicone rubber on resisting erosion due to dry-band arcing is also presented, as an essential step towards obtaining more suitable silicone composite for DC outdoor insulation applications.