Experimental study on the effect of O2 on the discharge decomposition products of C5-PFK/N2 mixtures

Sulfur hexafluoride (SF6), the most widely used insulating medium in power equipment, is a high-greenhouse effect gas. The use of alternative eco-friendly gases as an insulating medium is of great significance to the green development of the power industry. C5 perfluoroketone (1,1,1,3,4,4,4-heptafluoro-3-(trifluoromethyl)-2butanone; C5-PFK) mixtures have remarkable potential to replace SF6 in medium-voltage (MV) grade electrical equipment. This study constructs an experimental power–frequency breakdown platform to investigate the effect of O2 on the discharge decomposition products of environment-friendly C5-PFK/N2 mixtures and address the problem of generation of solid decomposition products due to insulation breakdown during engineering application. Studies have shown that the solid decomposition products produced by the insulation breakdown of C5-PFK/N2 mixtures mainly include simple C substances, CuF2, CuO, Cu2O, and fluorocarbons. The gas decomposition products mainly include CO, CF4, C2F4, C2F6, C3F6, C3F8, C4F10 and C3F7H. Addition of O2 to C5-PFK/N2 mixtures suppresses the formation of solid and gas decomposition products, such as C2F4, C3F8, and C3F6, but promotes the accumulation of gas decomposition products, such as CO and CF4. The recommended concentration of O2 to add to engineering applications is approximately 4% of the volume fraction; such a concentration can effectively avoid the generation of solid decomposition products due to insulation breakdown, and produce as few toxic decomposition products as possible. Addition of O2 to C5-PFK/N2 mixtures can prevent solid decomposition products from occurring during electrical breakdown of the gas-insulated medium.