Development of 275 KV EHV Class Gas-Insulated Power Transformer

A 275kV SF6 gas-insulated prototype transformer has been developed and is now under a long term running test for the final technical establishment. Newly developed techniques for composite insulation, liquid cooling, gas pressure regulation, on-load tap-changer, etc. are utilized together with the established ones for the 77kV class gas-vapor cooled transformers, developed in 1981 and working in service since 1982. This paper presents the feasibility examinations, newly developed techniques and performance test results of the prototype transformer.