Decomposition of SF6 Under AC and DC Corona Discharges in High-Pressure SF6 and SF6/N2 (10–90%) Mixtures

Abstract

Sulphur hexafluoride (SF6) is the gaseous dielectric the most widely used in high-voltage and very-high-voltage electrical equipment. As SF6 is a synthetic gas that is expensive and could have a non negligible impact on environment, the current trend is to reduce its quantity in electrical equipment by mixing it with natural gases such as air or N2. Such a mixture is envisaged for gas-insulated transmission lines, particularly for very high voltage network where a high power is necessary. Until now, transmission lines have been insulated with pure SF6 at a pressure of 400 kPa. They could soon be insulated with a SF6-N2 mixture with a high proportion of nitrogen (typically 90%) at pressures between 600 and 1200 kPa. These mixtures have several advantages compared to pure SF6: they are cheaper and are much more environmentally friendly1. Apart from the purely electrical problems arising from the use of such mixtures, it is important to study their chemical stability under the electrical stresses they will have to endure and especially to compare their decomposition to that of pure SF6 in identical experimental conditions.