Research Of Multi-stage Vacuum Insulator Stack Flashover Probability Analysis Methods

In this dissertation, the background and the significance of multi-stage vacuum insulator stack(VIS) flashover probability analysis research were outlined, and an overview about VIS research in the world was stated.The three primary factors which affect the whole stack flashover probability were: multi-stage, azimuthal transit-time and nonuniform-grading. The calculation of VIS flashover probability must consider simultaneously above factors, so the flashover probability analysis method under this condition was particular. In this dissertation, two different analysis methods, the method based on JCM flashover relation and the method based on statistical model, were developed. The advantages and disadvantages of two methods were compared. Validated by a series small VIS experiments and operation data of Z machine of America, the method based on statistical model was applied to actual VIS(VIS of PTS device) design.Firstly, the dissertation summarized theoretic and experimental research status of standard 45 degree vacuum insulator interface and a few factors which affect the flashover stress. Based on two basic surface flashover theoretic models(SEE model and EPTR model), advanced a creationary theory, that the experimental phenomena of 45 degree vacuum insulator interface is a balance state of anode-initiated flashover model and cathode-initiated flashover model. A set of vacuum insulator flashover experiment device was established, and a number of experiments of standard 45 degree frustum of several kinds of materials(PMMA and Rexolite etc.) was operated. Utilized the experimental data which was gained under similar working conditions to actual VIS(t_eff≈100ns), the key factors of two flashover relations(JCM relation and statistical relation) was known.Based on above two flashover relations, two different analysis methods, the method based on JCM flashover relation and the method based on statistical model, were developed. In calculation of whole stack flashover probability, the effects of azimuthal transit-time and nonuniform-grading were considered respectively, the detailed mathematical expressions and its physical connotation were also given. Especially in discussion of method based on statistical model, some possible approaches of improving the flashover performance of a stack were advanced. In research of flashover probability analysis, a few creationary calculation methods were invented, they were static-electromagnetic method to calculate the overvoltage-factor, equivalent permittivity method to calculate the azimuthal transit-time, linearized subsection method to calculate the effective pulse width(t_eff), and an analytic expression of whole stack flashover probability and its corresponding C language program.Two aspects of validation of above two different analysis methods were carried on: validate...