Atsushi Kudo - Mitsubishi Electric Corporation Ako Works, Japan
Tsuneo Nishitani - Mitsubishi Electric Corporation Ako Works, Japan
Thoru Yoshikawa - Mitsubishi Electric Corporation Ako Works, Japan

In recent several years,the demand of SF6 gas insulated transformer is increasing very rapidly in Japan, Hongkong and the other densely populated urban areas. The background of this demand increase is mainly based on the social trend or requirements of non- flammable transformers to realize the nonflammability as a whole of substation with the other electrical apparatus of SF6 gas insulation. This paper describes the development of the world's first 275KV gas-cooled type gas *insulated transformer, together with the general ideas/conceptions, technical details and advantages of gas insulated transformer.