Abstract
Reducing greenhouse gases, saving energy resources and mass optimization require technological changes towards increasingly electric vehicles. At the same time, performance improvement of semiconductor and dielectric materials further promotes electronic components confinement, resulting in a significant increase of embedded power densities. In the particular case of future hybrid propulsion aircrafts, electrical power that intended to supply reactors would be converted through power electronics components mounted on power busbars and insulated by solid dielectrics materials. These dielectrics materials have to respond to various electrical constraints of use (HVDC), in spite of environment change of aircraft parameters such as low pressure, temperature and thermal cycles, humidity... Unfortunately, partial discharges phenomenon is the most problem within electrical insulation system (EIS). Based on a topological model of power busbars designed for power converters dedicated to hybrid aircraft, partial discharge studies were conducted by simulation in various charging conditions of a PTFE insulator. Simulation results, which focus on electric field thresholds criteria of partial discharge inception voltage in air, reveal a net sensitivity of a space charge accumulation and distribution on dielectrics behaviour even for low space charge density, depending on their location in dielectrics. Compared to the behaviour observed with implanted homocharges, when by increasing homocharges density from 0.5 C/m3 to 2 C/m3 we observe a decrease of electric field by 450%, simulation results show a highest risk of partial discharge inception when heterocharges are accumulated inside dielectrics. Their accumulation increases the electric field in triple points beyond electric field thresholds of partial discharge inception in air. The simulated electric field reaching 22 kV/mm with only 2 C/m3 of heterocharges density accumulated in dielectric/busbars interfaces.
Highlights
Increase environmental impact of greenhouse gas emissions induced by air transport requires substituting pollutant fuel propulsion by cleanest propulsion systems
Compared to the behaviour observed with implanted homocharges, when by increasing homocharges density from 0.5 C/m3 to 2 C/m3 we observe a decrease of electric field by 450%, simulation results show a highest risk of partial discharge inception when heterocharges are accumulated inside dielectrics
Polarization in busbars configuration presented in this power circuit topology would not permit direct injection of heterocharges, prediction of their accumulation at busbar/insulator interface would require to carefully rethink industrial chain of insulators design dedicated to power converters intended to hybrid aircraft, in order to prevent partial discharge risks as highlighted by this study. These simulations are a contribution to the study of partial discharge appearance, through analyse of space charges impact in a solid dielectric (PTFE) used for insulation of power busbars dedicated to hybrid aeronautical systems
Summary
Increase environmental impact of greenhouse gas emissions induced by air transport requires substituting pollutant fuel propulsion by cleanest propulsion systems. For surface charging cases induced by secondary electron avalanche [4] [6] If these important studies had already highlighted many aspects of electric field enhancement at triple points, its impact in regard of partial discharge risks at triple junction points remains a big question for electronics power designers since this region constitutes the weak point of insulation system, due to the mismatch between solid and gas permittivities [7]. For this reason, beside experimental measurements, more and more theoretical studies are performed to propose various analytical solutions of electric field distribution at triple point under conduction [8] [9] or geometrical effects [10] in triple point
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