Short-Line Fault Interruption Performance Comparison of SF$_{6}$ Alternatives

Abstract

Measurements of the interruption performance of SF $_{6}$ and its alternatives including air, CO $_{2}$ , and its mixtures with O $_{2}$ , C $_{4}$ F $_{7}$ N, and C $_{5}$ F $_{10}$ O 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 $\Delta p = \text{5.8 bar}$ , the interruption limit of SF $_{6}$ was found to be $\text{12.39 A}/ \mu \text{s}$ . In the CO $_{2}$ -based alternatives at the same pressure, the thermal interruption limit was found to range from $\text{9.01 A}/ \mu \text{s}\,\text{to}\, \text{9.46 A}/ \mu \text{s}$ , while in air an interruption limit of $\text{4.17 A}/ \mu \text{s}$ was identified. Despite the similar thermal performance among CO $_{2}$ 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 $\text{1.44 mS}$ and $\text{3.83 mS}$ respectively in SF $_{6}$ , while in the alternatives these limit values ranged from two to six times lower. Arc voltage extinction peak was also evaluated, with SF $_{6}$ found to have the lowest limit value at $\text{628 V}$ , and air found to have the highest at $\text{1535 V}$ . Post-arc current was also measured, and found to not exceed $\text{350 mA}$ in any gas, with a duration limited to $\text{9}\; \mu \text{s}$ or less. Gas analysis of two fluorinated CO $_{2}$ mixtures (CO $_{2}$ /C $_{4}$ F $_{7}$ N and CO $_{2}$ /O $_{2}$ /C $_{4}$ F $_{7}$ N) showed no significant influence of oxygen on the creation of byproducts.