A Townsend’s secondary ionization coefficient estimation method for partial discharge inception voltage prediction for insulating polymers

Abstract

Paschen's law established from Townsend's theory has been widely used to compute partial discharges inception voltage (PDIV) in electrical insulation systems (EIS) using numerical models. The accuracy of PDIV calculation depends on a number of parameters such as the Townsend's secondary ionization coefficient g. The present paper aims to propose a straightforward way to obtain a first estimation of g by combining PDIV measurements and a robust experimentalsimulation approach that has been presented in a previous work to predict PDIV for aeronautical applications. In this paper, a needle-plane configuration is adopted for PDIV measurements and modeling in the case of two insulating films; a polyimide (PI) and a polytetrafluoroethylene (PTFE). The estimated value of g is determined as the value that provides the best fit with PDIV measurements for each material at 20 °C. The estimated values of g at 20 °C are 6.5x10 -4 and 10 -5 for PI and PTFE respectively, which are much lower than the traditional value found in the literature for metallic electrodes (10 -2 ). Moreover, the temperature dependence of g is investigated from 20 up to 200 °C at an atmospheric pressure of about 1 atm. It is found that the use of the literature value could lead to an error of about 30 % between simulated and measured PDIV values.