Basic investigations of the performance of droplets on electrically stressed polymer surfaces

This paper deals with the influence of water-droplets at the surface of HV-insulators on the distribution of the electrical field. As compared with the electrostatic field under dry conditions an essential local field enhancement may occur and may trigger low energy micro surface discharges. These discharges are supposed to be a main source of early surface ageing. Little is known about the basic phenomena in the so-called “early” stage of ageing. Investigations were carried out by using model insulators with a-more or less-homogenous droplet layer at the surface. Experiments showed correlations between the characteristics of the droplets such as their distance and shape, the insulating surface conditions (stage of hydrophobicity) and the electrical stress parameters such as the electric field between the droplets, the local field strength and the correlated forces. Factors responsible for the actual shape of a droplet are the relevant electrical field strength and the stage of surface hydrophobicity. Until now only few systematical investigations determining the influence of the field distribution between single droplets are known or published. This paper presents a contribution to this fundamental problem and shows the advantage of applying careful numeric simulations as well as experimental studies