Self heating of insulators

The voltage distribution over the surface of an insulator in humid conditions is determined by the shape of the insulator and the surface resistivity. The latter changes very rapidly with the temperature rise caused by the Joulean heating in the surface layer. In the paper a comparison is made between computed and observed temperature distributions on a cylindrical and on a disc shaped glass insulator. The computation is based on a simple thermal model of the insulator and the known behaviour of the surface resistivity. The results demonstrates the importance of the thermal properties of the insulator in controlling the temperature and the associated voltage distribution.