Empirical analysis of high pressure SF6 gas breakdown strength in a spark gap switch

It is difficult to predict or measure the breakdown strength of SF₆ gas in the high pressure range. Therefore, it is hard to find reference data of the high pressure SF₆ gas breakdown strength. This paper attempts to provide empirically a novel criterion for the estimation of SF₆ gas breakdown strength in a spark gap switch. For this purpose, J.C. Martin´s breakdown field strength of non-uniform gap in air and Kuffel et al´s breakdown field strength by exploiting streamer criterion of uniform field in SF₆ gas are adopted. The research is made for the empirical method of predicting the high pressure SF₆ breakdown strength and compared results have been ascertained with several experimental data from different investigators in a wide range of pd (pressure times distance) and field enhancement factor (FEF). For further confirmation of the empirical approach, we have designed and developed a high pressure spark gap switch to be closely coupled to a high voltage PFN-Marx system. The designed spark gap switch operates above 1 MV. Our tests have verified the prediction of the breakdown strength of the SF₆ filled spark gap switch in a pd range of 0.27-1.62 MPa . cm (2.7 to 16.2 bar.cm).