Fundamental insulation characteristics of air; N2, CO2, N2/O2, and SF6/N2 mixed gases

Abstract

SF6 gas has excellent dielectric strength and interruption performance. For these reasons, it has been widely used for gas-insulated switchgear (GIS). However, use of SF6 gas has become regulated under agreements set at the 1997 COP3. Presently, development of a gas circuit breaker (GCB) using CO2 gas and development of a high-voltage vacuum circuit breaker (VCB) are being pursued. GIS consists of disconnectors (DS), earthing switches (ES), and buses (BUS) in addition to GCB. Since the interruption performance is not an important requirement for DS, ES, and BUS, use of a gas with high dielectric strength is better than use of a gas with good interruption performance. Air and N2 are not greenhouse gases, and their dielectric strengths are higher than those of other SF6 alternative gases, but only about one-third of the dielectric strength of SF6 gas. This paper deals with a suitable insulation gas which has no greenhouse effect as an SF6 alternative gas. The N2/O2 mixed gas was investigated by changing the ratio of O2. Moreover, the effect of an insulation coating was investigated and compared with the dielectric strength of SF6/N2 mixed gas. The dielectric strength of air under the coating condition was equal to that of 10% SF6/N2 mixed gas. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(3): 9–17, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20348