The influence of moisture on the electrical properties of polymeric insulating materials

If organic insulating materials are used outdoors under wet conditions, moisture may diffuse into the polymer. The diffusion process normally is calculable by the second law of Fick, provided that the diffusion coefficient is independend of concentration and geometrical position, which must be proved for each material. For this, test methods are presented. The rate of water absorption depends on the kind of polymer and the environmental conditions. For insulator design the thickness of the weather shed material is a very important factor, which should be selected carefully because the time until saturation concentration is reached depends on the square of thickness.