Thermal considerations in the performance and design of high voltage power line insulators

In 1967 the author with I. McCausland and S. B. Girvan ¹ offered an empirical relationship between the voltage gradient E over an insulator surface and the final steady surface resistivity ρSE attained under its influence. The relationship, found from a great number of tests on clean or uniformly contaminated rectangular or tubular glass specimens, was ρSE = ρSO (1 + A.E²)(i) where ρSO was the initial value of surface resistivity before the application of voltage and A was a constant for a given surface and humidity.