Understanding the effects of condensation on electrical discharge phenomena in next generation more-electric and hybrid aircraft

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Decarbonisation of the transport sector is a major priority, both nationally and globally. It is estimated that the domestic and international aviation sectors constitute 2% of the global CO2 emissions arising from human activity. The member states of the UN International Civil Aviation Organisation are committed to offset any increases in emissions beyond 2020 which, combined with the drive for increasing fuel efficiency, will stimulate aircraft weight reduction beyond that already achieved through the adoption of composite airframe materials.The more-electric aircraft concept permits higher system efficiencies to be realised through electrification of traditional mechanical and hydraulic aircraft subsystems. It can also be considered a stepping stone to realising a commercial hybrid and all-electric aircraft. Both types of aircraft will be equipped with more diverse and safety-critical subsystems, based on high density power electronic converters and system ratings in excess of 1000 Volts. The increased stress experienced by cable insulation, connectors and other equipment, combined with extreme and dynamic environmental conditions experienced in flight, presents a number of technical challenges.The uprating of electrical power systems requires the aircraft design engineer to control for electrostatic phenomena which will arise within the normal operating regime of the aircraft, and there are a number of factors that must be taken into account when assessing the performance of such systems:- The increased use of switched dc and its influence on insulation stress.- The increase in the system voltage, and its effect on the frequency and severity of temporary over-voltage events.- Changes in altitude and atmospheric conditions (temperature, pressure and humidity) and other effects such as the formation of condensation and ice crystals on cable insulation. - Indirect effects induced by lightning strikes.There is to date very little published work concerned with dynamic atmospheric effects during ascent and descent, or the implications of short term system- and atmospherically-induced over voltages. A fundamental understanding of these parameters in medium-voltage dc systems is critical to the increasing electrification of airborne power distribution, and places renewed emphasis on insulation coordination and the mitigation of partial discharges. The following unknowns have been identified as limitations of the scientific understanding in the up-rating of airborne electrical systems:- Validity of the Paschen for specifying minimum conductor segregation.- Validity of steady-state atmospheric correction factors.- Influence of condensation on electrostatic discharge phenomena.- Dependence of partial discharge inception on the applied voltage wave shape.This research project proposes to quantify the effect of atmospheric conditions on the partial discharge thresholds on the more- and all-electric aircraft. A purpose-built test facility will be established to replicate the dynamic atmospheric conditions to which aircraft systems are subjected in service. Simulations will be performed to determine the appropriate test conditions, which will then be applied to standard test samples to study the mechanisms and thresholds of partial discharge activity, with particular focus on the influence of condensation and icing. The findings will be used to inform a set of correction factors that system designers may use in the robust design of future airborne electrical systems.