Investigation of DC Breakdown Properties of Low GWP Gas R404a and Its Mixtures with N2/CO2 as an Alternative to SF6

Sulfur hexafluoride (SF6), an extraordinary gas insulation medium, must be replaced by environmentally friendly gas in electric equipment because of its high global warming potential (GWP). In this research work, the DC breakdown properties of R404a gas and its mixtures with N2 and CO2 are studied under a sphere–sphere electrode configuration and uniform field conditions. The GWP of R404a is 16% of SF6 and its liquefaction temperature is also in the suitable range for practical applications. Nitrogen and carbon dioxide are mixed with R404a to reduce its boiling point and GWP. Other important parameters such as the self-recoverability, liquefaction temperature, GWP, and synergistic effect of R404a/CO2 and R404a/N2 were also studied to complement the insulation performance and the results are comparable to other gas mixtures. As a result, it was found that both the mixtures containing 80% R404a and 20% N2 or 20% CO2 possess a breakdown strength of 0.83 times that of SF6. Mixtures containing an 80% concentration of R404a possess a GWP equal to only 15% of SF6. These properties make gaseous mixtures containing 80% R404a and 20% N2 or CO2 a suitable alternative to SF6 in medium-voltage gas-insulated equipment.