Discovery of a novel binary azeotrope with positive synergistic insulation strength as eco-friendly SF6-alternative

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Abstract Sulfur hexafluoride (SF6), as the arc extinguishing and insulating medium, is broadly applied in power equipment. While it is very essential to find an environmentally friendly substitute gas for SF6 due to its strong greenhouse effect. Although there are many potential alternatives, most have relatively high boiling points that cannot meet the minimum operating temperature of the power equipment. In the past, the liquefaction temperature of the mixture was reduced by mixing with buffer gases, such as CO2, N2, or dry air. But this method cannot take the insulation performance requirements of eco-friendly insulating gas into account. Therefore, given the current problems and challenges, a novel approach is presented to exploring new eco-friendly gases by incorporating the azeotropic theory. The liquefaction temperature of the gas mixture can be reduced simultaneously while the insulation strength is increased. In this approach, a theoretical prediction model E-PPR78 was introduced to predict the vapor-liquid equilibrium data and RC318 was found to exhibit azeotrope behavior with HFO-1336mzz(E) at 17%. Furthermore, the predicted vapor-liquid equilibrium data obtained were validated against cyclic-analytical experimental results, affirming the efficacy of the proposed model. Subsequently, to assess its insulation performance, breakdown tests were conducted under both AC and lightning impulse voltages, revealing significant positive synergistic effects in the gas mixture. The possible mechanisms of this positive synergistic effect were also discussed. This study offers an innovative way of tackling high boiling point issues plaguing eco-friendly gases. The findings may also enlighten the design of eco-friendly switchgear that utilizes HFO-1336mzz(E) mixtures to replace traditional SF6 gases.