Hydrophobic cycloaliphatic epoxy (HCEP) has been used as outdoor insulation material to maintain good electrical performances under multiple stresses, in which acidic attack to this kind of materials has been causing concern in recent years. To study the performances of HCEPs under acid rain, a new acid fog test method has been established and an acid fog chamber was constructed. During the 1000 h acidic rain test, contact angles of the HCEPs decreased and the less hydrophobic samples had higher leakage currents. Increase of the surface roughness and diameters of the micro holes have been observed by AFM and SEM, and oxidation of surface groups was analyzed by FTIR. Resistance to tracking and erosion remained good after the 1000 h test. The results showed that HCEPs exhibited good outdoor insulation performances in acidic fog under DC stress.

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Coatings made of 'glass-like' materials, such as waterglass (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.