A new approach to anti-fog design for polymeric insulators

Electric field strength and leakage current density in the shank region of a polluted polymeric insulator may cause local dry-banding, with a risk of long-term degradation from partial-arc discharges. In a novel approach to dry-band control, the characteristics of silicone rubber surfaces with a textured finish are investigated and, depending on the geometry chosen for the texture, two useful objectives can be achieved. First, the increase of surface area can both reduce the leakage current density in the vulnerable shank region, and also increase the longitudinal creepage distance. Secondly, the damage arising from surface discharges can be mitigated. The principles of the proposed anti-fog design are described in detail. While complete prototype insulators are now being specified for fabrication, this paper reports preliminary results from tests using rectangular samples, which show an improvement in performance. The tests are of two kinds: a) inclined-plane, to assess erosion and tracking on rectangular samples of insulation materials. Such samples have been prepared both with a conventional plane surface and with a textured surface for comparative tests; b) clean-fog tests that use an initially dry pollution layer of known salinity. Here, plane and textured samples have been used for comparative tests, where leakage current and discharge activity are monitored during the generation of the fog.