The influence of thin dielectric coatings on LI and AC breakdown strength in SF6 and dry air

Electric power consumption has increased over the years while the available space for substations has become smaller. Newly designed gas insulated switchgears (GIS) have to be smaller and have to operate at a higher system voltage. Furthermore, the urge to decrease the use of SF6 as an insulating gas in GIS is becoming larger because of the high production and handling costs and the high global warming potential. Unfortunately, the breakdown strength of alternative gases is usually lower than that of SF6. However, with the application of a coating on the electrodes in GIS the breakdown strength can be improved. In this paper, the performance of GIS with thin coatings is evaluated with breakdown tests. The test setup consists of a rodplane electrode arrangement with a coated rod electrode. The coatings vary in thickness between 40 micrometers and 2 millimeters. The breakdown tests are performed at either 50 Hz AC or lightning impulse voltage.