Air Pressure Impact on the Avalanche Size for Turn-to-Turn Insulation of Inverter-Fed Motors

This article endeavors to illuminate the variations of various streamer inception parameters (SIPs) with respect to air pressure based on Schumann's streamer inception criterion (SCSIC). The results based on measured partial discharge inception voltage (PDIV) values and using electric field distribution obtained via electrostatic simulations and ionization swarm parameters reveal that the Schumann constant, K, which is the natural logarithm of the threshold number of electrons determining the transition from Townsend to streamer discharge, and consequently, the critical avalanche size (Nc) increase with air pressure reduction. Different SIPs such as critical field line length (CFLL), effective ionization coefficient of air ( α eff), PD inception field (Einc), firing voltage (Vfiring) across the critical field line (CFL), and K and N c are analyzed extensively as a function of air pressure. In light of the findings of this contribution, it is demonstrated that the derived K functions as a function of air pressure can improve drastically the accuracy of PDIV prediction in particular for low air pressures rather than a single K parameter value obtained at ground level. The study's findings represent a guideline for electrical machine designers to improve the insulation design of electrical machines employed in the more electric aircraft (MEA) applications.