Abstract
This work deals with a way of substituting the sulphur hexafluoride gas (SF6) used in High Voltage apparatus especially in Gas Insulated Substations (GIS). This gas has good dielectric properties but its Global Warming Potential (GWP) is estimated to 23,900 times greater than the carbon dioxide (CO2). Unfortunately, simple gases such as nitrogen (N2) present a dielectric withstand two or three times lower than SF6. To improve the system dielectric withstand, an insulating coating based on silicone and composed of a first 0.5 mm thick semi-conducting layer and a second 1.5 mm thick insulating layer is applied on the system?s conductors in order to limit or suppress the role of electrons emitted by the metal. The experimental investigations, made with Lightning Impulse Voltage and under conditions close to the industrial practice, show that with N2 the coated system dielectric withstand is controlled by the gas. Consequently, applying an insulating coating on the conductors reduces the system dielectric withstand (capacitive effect). These investigations show, however, that it is possible to improve the system dielectric withstand with the coating in case of SF6 under negative Ligthning Impulse Voltage. The gas cleanliness, the gas ionisation and most of all the charges which remain on the gas-coating interface seem to be important parameters. These charges have under certain conditions a beneficial effect. This last result gives a track for further work.