Experimental evaluation of liquid “glass-like” coatings to improve tracking and erosion resistance of insulators for outdoor applications

Coatings made of ldquoglass-likerdquo materials, such as water-glass (soluble sodium silicate) and a silane-based sol-gel material (a densely cross-linked network obtained after the removal of the solvent), on cycloaliphatic epoxy (CEP) were investigated to evaluate their potential to improve the outdoor performance of the epoxy. For this purpose, an inclined-plane tracking and erosion test - as defined in IEC 60587 ed. May 2007 - was used to evaluate the tracking and erosion resistance of coated and uncoated samples. The test found that water-glass coatings on CEP did not improve tracking and erosion resistance because of an affinity of cross-linked sodium silicates with water, atmospheric moisture and the wetting agents used in the test. On the other hand, thin sol-gel, chemically cross-linked coatings demonstrated improved tracking and erosion resistance. In accordance with IEC 60587, CEP samples coated with the sol-gel material were successfully tested for six hours at 3.5 and 4.5 kV_rms, and while uncoated CEP samples passed the 3.5 kV test but systematically failed the 4.5 kV_rms test. CEP coated and uncoated insulators were then tested in the harsh outdoor environment of the Koeberg Insulator Pollution Test Station (KIPTS) in South Africa for six months. This field test has visually proven that the sol-gel coated CEP insulator coped much better in such an environment than its uncoated counterpart.