The application of SF

6

gas in electric insulation equipment has already widespread. It is of great significance to calculate the critical breakdown field strength of SF

6

under various electrode configurations for the study of discharge breakdown characteristic of SF

6

. In this paper

detailed theoretical studies and calculation analysis of breakdown of SF

6

gas under various electrode configurations a

re performed. Firstly

based on the existing SF

6

breakdown process

the theory is summarized and improved;then

the step lead development model is introduced to model the discharge breakdown process of SF

6

under slight non-uniform electric field. The discharge breakdown is divided into three main stages: The first electron generation stage

the streamer inception stage and the lead development till breakdown stage. Finally

the comprehensive model for calculation of converted critical breakdown field strength of SF

6

gas at various electrode configurations is set up with combination of physical parameter of the gas and the critical breakdown field strength of SF

6

gas under multiple electrode configurations is obtained. It is shown by the study that under the same intensity of pressure condition

the critical breakdown field strength under AC voltage is lower than the converted critical breakdown field strength under lightning impulse voltage. The polarity of critical breakdown field strength under lightning impulse voltage changes with the change of electrode structure and intensity of pressure conditions. Also

due to the influence of space charge generated by the partial discharge at the electrode with large curvature and with the increase of intensity of pressure and the lengthening of the tip of a projection

the critical breakdown field strength under the positive lightning impulse voltage tends to that of applying AC voltage.