OPTIMAL DESIGN OF ELECTRICAL INTERCONNECTION SYSTEMS IN FUTURE ELECTRIC AIRCRAFT

Abstract

Future aircraft will use more electrical energy to replace the traditional energy sources as electrical systems are more reliable, environmentally friendly and have lower maintenance costs. Increasing electric power levels result in increasing voltage and current levels, putting more electrical and thermal stresses on electrical interconnection systems (the cables and connectors that run across the aircraft). This thesis focuses on research into high voltage interconnection systems in future aircraft. It aims to investigate current carrying capacity and safe operating voltage related to electrical interconnection systems considering several key operating factors such as temperature, pressure and frequency. The performance of novel busbars and screened cables are compared with conventional aircraft cabling to investigate the advantages they could provide in an aerospace environment. A thermal model for the determination of current carrying capacity of rods (simulating round cables) and busbars was developed and validated by experimental results under various geometries and operating conditions. Busbars showed a higher current carrying capacity when compared with rods under the same cross-section area and operating condition. The phenomenon was clearer when the busbar aspect ratios were increased. The effect of insulation thickness and frequency on current carrying capacity was also investigated, something not considered in the current standards. The increasing frequency led to a lower current carrying capacity due to skin effect, whilst increasing insulation thickness led to either increasing or decreasing current carrying capacity, depending on the geometry and operating conditions. The safe operating voltage of unscreened cables and busbars was investigated based on electric field simulations and the streamer criterion method. The results showed that safe operating voltage was determined by the minimum partial discharge inception voltage (PDIV) of the phase-phase geometry. The increasing conductor diameter led to a decrease in the safe operating voltage of unscreened cable, with its effect on the safe operating voltage of unscreened busbars being negligible. For both unscreened cable and busbars, increasing the relative permittivity of insulation resulted in a lower PDIV. However, due to the limited range of permittivity values, its sensitivity was not as large as the insulation thickness, especially under low pressures. Insulation thickness is the most important parameter to determine the PDIV. The PDIV for cable termination with and without a stress grading system was also measured. The results showed that stress grading material increased the PDIV regardless of operating condition. Frequency had no effect on the PDIV for cable termination without stress grading material. The PDIV decreased with the increasing frequency when stress grading material was applied but was overall higher than the values measured without a stress grading system. The electric field simulation results for the stress grading system showed that the partial discharge inception electric field decreased with decreasing pressure under a fixed frequency, while the partial discharge inception electric field increased and then saturated around 500 Hz under a fixed pressure. Based on the investigation of parameters controlling the electric field distribution of the stress grading material, the effect of stress grading material properties on electric field distribution along the cable termination surface was analysed. The power carrying capacity and power/weight ratio of unscreened cable, unscreened busbar and screened cable were calculated and compared based on their current carrying capacity and safe operating voltage. The effect of conductor size and insulation thickness on power/weight ratio was analysed. Increasing conductor size and insulation thickness increased power carrying capacity but did not provide the maximum power/weight ratio.

Date of Award	31 Dec 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Ian Cotton (Supervisor) & Tony Chen (Supervisor)