This article deals with the determination of leakage current and the production of thermal losses on polluted insulators under lightning stresses based on an equivalent electrical model by using Alternative Transients Program (ATP) software. The parameters are varied by thickness of
pollution, the ratio of pollution-covered length, and also the steepness of the impulse voltage. The results demonstrate that leakage currents were dramatically increased under different pollution conditions. The consequential mathematical equations show that the rate of leakage current can
be controlled by limiting the length and thickness of the pollution layer. Finally, the value of the humidity that is evaporated from the insulator surface as a result of thermal loss can be determined.