Switching performance of alternative gaseous mixtures in high-voltage circuit breakers

Summary

For decades, sulfur hexafluoride (SF6) has been used as the main gas for insulation and switching in gas-insulated high-voltage equipment because of its heat dissipation properties, insulation properties and excellent arc quenching capability. However, SF6 is a strong greenhouse gas with a high global warming potential (GWP) that is about 23’500 times higher than that of carbon dioxide (CO2) over a 100-year time horizon. Therefore electrical equipment manufacturers are now exploring new gases (with significantly lower GWP) and approaches that could be developed as alternatives to SF6 for electrical insulation and current interruption. For high-voltage circuit breaker applications, the most frequently mentioned gases in the context of SF6 alternatives to date are CO2, and its mixtures with either the C5 perfluoroketone (C5-PFK, C5F10O), or the C4 perfluoronitrile (C4-PFN, C4F7N). In this contribution, we report on measurements of the switching performance of three gas mixtures that have been proposed as low-GWP alternatives to SF6: CO2+O2, CO2+O2+C5-PFK, and CO2+O2+C4-PFN. In a first series of tests, the thermal interruption performance of each mixture was assessed by measuring the maximum slope of the current around current zero (di/dt) for which the breaker could interrupt when used with each of the three different mixtures. Our results show that the maximum interruptible di/dt is not significantly affected by the addition of fluorinated components like C5-PFK or C4-PFN to a CO2+O2 mixture. Further tests were carried out to assess the dielectric recovery after arcing with currents corresponding to the 10 % and 30 % current levels of a short-circuit current rating of 31.5 kA. These tests demonstrate that the presence of the fluorinated components C5-PFK or C4-PFN in the gas leads to a significantly faster recovery of the dielectric withstand after current zero than the one seen in CO2+O2 mixtures. Results of gas analysis after arcing are also presented.

Additional informations

Authors

HIGASHIYAMA, Bartylak, ARAVIND, KAMARAJU, LIAO

Keywords

SF6-free gas circuit breaker, C5 fluoroketone, CO2, hot dielectric recovery