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.

In gas insulated switchgear(GIS) SF6 gas is widely in use because it has good electrical insulation and arc interruption capabilities. Due to environmental constraints the desire to use alternative gases is continuously growing. This paper focuses on dry air as an alternative gas which unfortunately has a breakdown strength which is lower than the breakdown strength of SF6 at equal gas pressure. To improve the breakdown strength of dry air filled GIS, dielectric coatings can be applied to the electrodes. In this paper, the performance of GIS with thin coatings is evaluated through breakdown tests in a rod-plane electrode arrangement. Negative lightning impulse voltage is applied on the rod electrode and the gas pressure is kept constant at 0.9 MPa.