Breakdown characteristics of CF3I-N2 gas mixtures in a needle-plate geometry

The breakdown voltages in a needle-plate geometry have been measured by 50 Hz power frequency tests for the CF3I-N2gas mixtures (5-30% CF3I) over the gas pressure from 0.1 to 0.3 MPa. The influence of different conditions on the breakdown performance is investigated. The synergistic effect of CF3I-N2gas mixtures is verified from the respect of breakdown voltage. Moreover, the behavior of the gas mixtures in highly divergent fields is characterized by a pressure range of corona stabilization, which can explain the relation of the breakdown strength to gas pressure and mixing ratio. A comparison to the theoretical breakdown voltages in uniform electric field shows that the breakdown strength reduces with the rising non-uniform coefficient of electric field at relatively short gap distance. Furthermore, the sensitivity of the insulating ability to divergent field is weakened by the increasing CF3I ratio.