CIGRE WG 13.06 studies on the reliability of single pressure SF6-gas high-voltage circuit-breakers

The f inal results of the CIGRE second international enquiry on the reliability of high voltage circuitbreakers in service are presented. In the seventhies the first international enquiry, that covered all technology circuit-breakers, was conducted. The second international enquiry (from 1.1.88 to 31.12.91) was limited to single pressure SF6 gas circuit-breakers, thus showing the improvements due to this technology.The main conclusion is that the reliability concerning Major Failures has increased considerably and that the maintainability of modern SF6 circuit-breakers is much better than the older technology circuit-breakers. Also the conclusions from several other studies, based on the results of the enquiries, are presented. The publication of this paper, as a result of an international effort by CIGRE SC 13, is sponsored here by the IEEE Switchgear Committee in order to support this valuable contribution to the industry and to continue the cooperation between the two organizations.