Short-Line Fault Interruption Performance Comparison of SF₆ Alternatives

Measurements of the interruption performance of SF₆ and its alternatives including air, CO₂, and its mixtures with O₂, C₄F₇N, and C₅F₁₀O were performed under short-line fault like conditions. The measurements were conducted with an experimental puffer-type circuit breaker in which the same upstream pressure and the same contact separation at the current zero instant were ensured for every gas. At p = 5. 8 bar, the interruption limit of SF₆ was found to be 12. 39 A/ s. In the CO₂-based alternatives at the same pressure, the thermal interruption limit was found to range from 9. 01 A/ s\, to\, 9. 46 A/ s, while in air an interruption limit of 4. 17 A/ s was identified. Despite the similar thermal performance among CO₂ based mixtures, it was found that in those mixtures without fluorinated additives, the overall interruption limit is lowered by the occurrence of hot dielectric failures. Limit values of the arc conductance decay, G200 and G500, were found to be 1. 44 mS and 3. 83 mS respectively in SF₆, while in the alternatives these limit values ranged from two to six times lower. Arc voltage extinction peak was also evaluated, with SF₆ found to have the lowest limit value at 628 V, and air found to have the highest at 1535 V. Post-arc current was also measured, and found to not exceed 350 mA in any gas, with a duration limited to 9\; s or less. Gas analysis of two fluorinated CO₂ mixtures (CO₂/C₄F₇N and CO₂/O₂/C₄F₇N) showed no significant influence of oxygen on the creation of byproducts.