Effect of dilution gas composition on the evolution of graphite electrode characteristics in the spark gap switch

As the widely implemented electrode material, graphite has the characteristic of sublimation by the thermal shock of the switching arc, and the produced carbon vapor is easy to condense into carbon powders and deposit in the switch. The impact of the type of dilution gas in a mixture of 20% oxygen and 80% dilution gas on the sublimation and oxidation characteristics of the graphite electrode is investigated. It is found that when nitrogen dilution gas was replaced by argon, the heat flux to the electrodes decreased, which led to a 63% reduction of graphite sublimation. At the same time, the cooling rate of the arc was slower in argon, which promotes oxidation of the carbon vapor. The residual solid carbon can be reduced by 70%–85% by using argon as the dilution gas. Consequently, it is demonstrated that the stability and working life of the switch could be increased by appropriate selection of the dilution gas.