Operating experience of SF6 gas-filled power transformers

The Hong Kong Electric Co. Ltd. (HEC) is supplying electricity to the Hong Kong and Lamma Islands. Many of the transmission and distribution plants and equipment are located near the vicinity of high rise commercial and domestic buildings which are very densely populated. Therefore it is very important to reduce the potential fire hazard due to electrical plants and equipment to a minimum. The use of oil insulated transformers and switchgear is one of the greatest contributions to the potential danger. Whilst most of the modern switchgear are oil free, the situation is not that obvious in case of transformer. HEC has used SF₆ gas filled distribution transformers since 1981. About 2000 units are installed in the past 10 years. In 1990 HEC also commissioned the first 275 kV/11 kV SF₆ gas transformer in the world and will continue to use SF₆ gas filled transformers for all its future zone substations. The authors summarise the development and the application of the SF₆ gas transformers in HEC. Operational experience and problems encountered are also discussed