Influence of oxygen on dielectric and decomposition properties of C4F7N-N2-O2 mixture

We investigated the influence of oxygen on insulation and decomposition characteristics of C4F7N-N2-O2 gas mixture. The power frequency breakdown voltage, self-recovery characteristics, discharge dispersity as well as the decomposition properties of C4F7N-N2-O2 gas mixture under different O2 content conditions were tested and analyzed. It is found that the breakdown voltage of C4F7N-N2-O2 gas mixture increases with the O2 content (0%~8%). The addition of O2 could effectively suppress the precipitation of solid by-product on the electrodes surface and reduce the discharge dispersity. The decomposition of C4F7N-N2 gas mixture after breakdown mainly produces CF4, C2F6, C3F8, CF3CN, C2F4, C2F5CN, (CN)2 and C3F6. Another by-product CF2O is found and amount of CF4 is detected after the addition of O2. The self-recovery characteristics of the gas mixture is promoted firstly and then reduced as the oxygen content increases. It is recommended to add 4%-6% O2 in the C4F7N-N2 gas mixture for engineering application to improve the insulation performance and suppress the precipitation of solid by-products.