AC breakdown characteristics of C4F7N/air mixture under different electric field structures

摘要

In order to explore the breakdown characteristics of C4F7N/air mixture under quasi uniform, slightly inhomogeneous and extremely inhomogeneous electric fields, the AC breakdown tests of C4F7N/air mixture at 0.1 to 0.7 MPa were carried out under three kinds of structures of plane-plane, sphere-plane and needle-plane electrodes. The effects of mixing ratio, pressure and electric field inhomogeneity on the breakdown voltages of C4F7N/air were analyzed and compared with SF6. The results demonstrated that the AC breakdown voltages of C4F7N/air mixture increased linearly with increasing of pressure under quasi uniform and slightly inhomogeneous electric fields, and showed synergistic effect with the content of C4F7N. Under the extremely inhomogeneous electric field, the AC breakdown voltages of C4F7N/air mixture presented a “Hump” shape with pressure. With enhancing proportion of C4F7N, the hump area expanded. According to the breakdown characteristics, the dielectric strengths of C4F7N/air mixtures with 5% and 13% of C4F7N were higher than 70% and 90% SF6 respectively. 5% to 13% of C4F7N/air mixtures showed good application prospects in the non arc extinguishing gas-insulated electrical equipment.