Air Pressure Impact on the Avalanche Size for Turn-to-Turn Insulation of Inverter-Fed Motors
Hadi Naderiallaf, Yatai Ji, Paolo Giangrande, Michael Galea
Abstract
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, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${K}$ </tex-math></inline-formula> , 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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N} _{\text {c}}$ </tex-math></inline-formula> ) increase with air pressure reduction. Different SIPs such as critical field line length (CFLL), effective ionization coefficient of air ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha _{\text {eff}}$ </tex-math></inline-formula> ), PD inception field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E} _{\text {inc}}$ </tex-math></inline-formula> ), firing voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {firing}}$ </tex-math></inline-formula> ) across the critical field line (CFL), and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${K}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N} _{\text {c}}$ </tex-math></inline-formula> are analyzed extensively as a function of air pressure. In light of the findings of this contribution, it is demonstrated that the derived <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${K}$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${K}$ </tex-math></inline-formula> 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.