Investigation of SF6/CF4 mixtures as the insulating and cooling medium of gas insulated transformer

Rapid development of power network in overpopulated urban areas leads to a strong demand for oilless, non-flammable and nonexplosive large-capacity SF6 gas insulated transformers from the viewpoint of accident prevention and compactness of equipment. Applying gas mixtures as the insulating and cooling medium can comprehensively solve the problems of heat dissipation and liquefaction of SF6 gas. Having studied the great influence of variations of both mixed proportion and gas pressure on the dielectric and thermal properties of gas mixtures, a SF6/CF4 gas mixture is presented instead of SF6/N2 gas insulated transformers. The temperature rising distributions of coils are also theoretically calculated by applying discrete differential model when transformer is filled with SF6/CF4 gas mixtures. Calculated results show that applying SF6/CF4 gas mixtures will not excessively influence coil temperature rising compared with pure SF6 gas. The research work presents a reference basis for the development of gas insulated transformers toward both high voltage and large capacity.