Nozzle Material Impact on Medium Voltage Load Current Interruption in Air and in a Fluoroketone Air Mixture

Due to its high global warming potential, 25200 times that of CO $_{2}$ , SF $_{6}$ is to be phased out of high voltage equipment. Finding low global warming potential alternative dielectric mediums that can replace it, is therefore imperative. Such an alternative, a mixture of technical air and the fluoroketone C $_{5}$ F $_{10}$ O has already been used to replace SF $_{6}$ in some applications. The advantage of the fluoroketone, in addition to its low global warming potential of about one, is its high dielectric withstand voltage. Previous studies, related to the medium voltage switchgear, have explored the differences in air and the fluoroketone mixture for free-burning and low ablative configurations. In load break switchgear, however, the switching arc will form and burn inside a polymer nozzle, and therefore, understanding interactions between the gaseous dielectric medium and nozzle material during current interruption, is key to developing alternative solutions. In this paper, interactions between two gaseous dielectric mediums (air and air mixture with $7.5 \%$ fluoroketone) at $1.3 \,\text{bar}$ and nozzles made of PTFE, PP, PE, PEEK and POM-C, at two different current levels of $300 \,\text{A}$ and $600 \,\text{A}$ have been investigated. It was found that PEEK is an unsuitable nozzle material as it burns and flakes when exposed to an arc, that the pressure development and power dissipated in PTFE nozzles is lower than for the other materials and that POM-C performed best overall when it came to interruption rates and pressure development.