Prediction of Azeotrope System of Insulating Gas

Due to its excellent physical and chemical properties, high insulation properties, and arc quenching capability, sulfur hexafluoride <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\text{SE}_{3})$</tex> is widely used in the power industry, which has greatly promoted the development of medium voltage (MV) and high voltage (HV) equipment. However, the use of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{SF}_{6}$</tex> has also resulted in significant environmental problems. Consequently, the search for an environmentally friendly SF6 alternative gas has become a crucial task in the power industry. Extensive and in-depth research has been conducted in this field for a considerable period. Currently, the most prevalent SF6 alternative gases are categorised into four main groups. While the new fluoride insulation performance is superior to that of SF 6, the liquefaction temperature is high, rendering it unsuitable for use in equipment with minimum operating temperatures. Typically, the boiling point of the mixture is reduced by the addition of a buffer gas, which, however, affects the insulation properties of the mixture. This paper introduces the azeotropic theory of the chemical industry into the electrical industry and presents a prediction model of vapor-liquid equilibrium data constructed by combining group contribution with the equation of state. This model enables the reduction of the boiling point without affecting the insulation properties of the mixture. The method can be used to screen a large number of gases in the azeotrope system, saving time and manpower. Moreover, the method provides a theoretical foundation for the development of novel multicomponent insulating gases.