The Insulation Performance of Novel Refrigerant Gas as an Alternative to SF₆ for Medium Voltage Switchgear

Gas-insulated systems are widely utilized in the electric power sector to transmit and distribute electrical energy. Sulphur-hexafluoride (SF6) has dominated gas insulation in high-voltage insulation technology since the early 60s. It is a greenhouse gas with a protracted lifespan in the atmosphere. This paper proposes an economical and comparatively more environmentally friendly R507 gas alternative to SF6 for medium-voltage applications. R507 has been analyzed experimentally through power frequency breakdown and lightning impulse testing to validate the performance and theoretical concepts. R507 has a very low liquefication temperature of
$-46.7^{\circ }\text{C}$
, but it must still be mixed with buffer gases such as CO2, N2, or dry air to meet the diverse liquefaction temperature applications. Various field utilization factors under AC and lightning impulse voltages are used in the experiments, along with different electrode geometries, including sphere-to-plane and rod-to-plane (i.e., quasi-homogeneous and inhomogeneous electric field distribution). For comparison, identical experiments are conducted with pure SF6. R507 gas was found to be a promising substitute for SF6 gas, with its dielectric strength being approximately 0.95 times that of SF6 gas. A positive synergistic effect is present between R507 and CO2, along with the good self-recoverability property of the gas mixture. The current research study serves as a fundamental resource for characterizing the R507/CO2 gas mixture insulation properties to be utilized in practical applications.