Prediction of Breakdown Field Strength for Large-Area and Multilayer Film Dielectrics

The polymer film dielectric has been widely used in high voltage equipment for bulk insulation owing to the excellent insulation performance. Martin's empirical formula for bulk breakdown is frequently used to predict the breakdown field strength of multilayer thin film with different electrode areas. In this article, based on the academic consensus that the cumulative breakdown probability of single-layer film obeys the Weibull distribution, the relationship between the cumulative breakdown probability of film dielectric under different electrode areas and the applied electrical field is deduced. Moreover, the relationship between the cumulative breakdown probability of film dielectric with various numbers of film layers and the applied electrical field is obtained and simplified. On these bases, combined with the experimental results of the average breakdown field of film dielectric with smaller electrode areas and fewer layers, a prediction model of the average breakdown field strength of film dielectric with different electrode areas and film layers is established. To obtain the solution of the prediction model concerning the number of film layer, an effective approximate solution method is proposed to solve the calculation problem with ultralarge and ultrasmall data, which significantly reduces the complexity of the solution process. A coaxial film capacitor is developed and tested to verify the prediction model with the "Chenguang" accelerator. The experimental breakdown field strength of 54 layers of 15 mu m biaxially oriented polypropylene (BOPP) film with an electrode area of 218.1 cm(2) is 355.6 V/mu m, which is comparable to the predicted result of 374 V/mu m. The prediction model presented in this article is of certain reference significance for the insulation design of film dielectrics.