Experimental Investigation on Insulation Performance of SO₂/CO₂ Gas Mixtures

In an effort to replace the use of SF₆ gas in high-voltage equipment, research has been conducted on more environmentally favorable alternative gases to this potent greenhouse gas. In the present study, the SO₂–CO₂ gas mixture is selected among all alternatives, including SF₆, with the requirement to meet features such as reducing ozone depletion potential, global warming potential, being chemically stable, non-toxic, and having a having a boiling point of − 15 °C. Furthermore, aspects like material compatibility-based electrical properties such as dielectric constant, cost, and environmental impacts were taken into consideration. Consequently, a gas mixture of 30% SO₂ and 70% CO₂ was finally chosen. In this paper, power frequency breakdown voltage was experimentally measured under a quasi-uniform field while varying gas pressure from 0.2 to 2 bar for 5 mm and 10 mm of electrode gap, respectively. Subsequently, a synergistic coefficient is calculated for this mixture. The obtained results of PFBDV and synergism coefficient for a 30% SO₂ and 70% CO₂ gas mixture were compared with mixtures like SF₆/N₂, CF₃I/N₂/CO₂, C₃F₈/CO₂, C₄F₇N/CO₂, R12/air/N₂, and c-C₄F₈O/CO₂/N₂. Consequently, it emerged that the insulating characteristics of 30% SO₂ and 70% CO₂ are better than most of the other alternatives, along with considerable advantages like negligible environmental impact, low cost, better material compatibility, and low toxicity. These systematic investigations predominantly indicate that a gas mixture containing 30% SO₂ and 70% CO₂ can be employed as a substitute for SF₆ in high-voltage gas-insulated equipment.