Development of 77 KV 40 MVA Gas-Vapor Cooled Transformer

A 77 KV 40 MVA gas-vapor cooled transformer has been developed as a prototype of substation transformers, which is directed to nonflammable and lightweight properties. To examine the operating reliability of the transformer, the reliability test has continued since July, 1981 at the Hokusetsu substation of KEPCO (Kansai Electric Power Co., Inc.). This report will cover the development work on thermal stability of materials, electrical fault test, insulation characteristics, cooling of model transformer, flow-induced static electrification, protection system and the prototype unit which is being built based upon these developments.