Influence of thick epoxy nanocomposite coatings on lightning impulse breakdown behavior in air

The design constraints of gas insulated switchgear(GIS) are changing due to an increasing power demand and decreasing available floor space for substations. Ideally, new GIS should operate at a higher nominal voltage with a minimal or no increase in size. Another ongoing development in the power industry is the desire to replace SF₆ by an environmentally friendly gas which is preferably readily available and has relatively low production costs. Unfortunately these gases show a breakdown strength which is significantly lower than SF₆. Coatings can prove to be a possible solution to this problem. The breakdown strength of GIS can be improved with the application of a dielectric coating on the electrode surfaces. In this paper, the influence of thick coatings on the breakdown strength of GIS is evaluated with negative lightning impulse breakdown tests. The tests are performed on a rod-plane electrode arrangement in which the rod electrode is coated. The coatings consist of a 10mm thick layer of epoxy or an epoxy based nanocomposite.