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Title: Superconducting cables for electric aircraft
Author: Venuturumilli, Sriharsha
ISNI:       0000 0004 7967 8120
Awarding Body: University of Bath
Current Institution: University of Bath
Date of Award: 2019
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With the continuous increase in aircraft traffic and the resultant increase in greenhouse emissions from aircraft engines, stringent emission targets have been set by the Flightpath 2050 for the industry. Replacement of the conventional engines with electric propulsion motors is speculated to be the promising idea to compete with the reduction in emission targets by 75% CO2, 90% NOX and 65% perceived noise emission compared to those in 2000. NASA aims to realise 60% CO2 and 80% NOX emission reductions compared to its existing 2005 emission records, as a part of its N+3 subsonic fixed wing project by 2025 using hybrid electric propulsion. It is theorized that, for the technological feasibility of these electric aircrafts, use of superconducting components in the electric propulsion system is inevitable. But, there were no superconducting component models currently available, to be integrated into the system models for their technical feasibility analysis with the specific dynamic power demands of the electric aircraft. The power demand of the medium to large electric aircraft propulsion ranges from 5-50 MW and with the poor/unpredictable dielectric behaviour at high altitudes restricting the high voltage application, the ampacity of the current carrying cables was expected to reach several kA's. With the ampacity of the cables being increased, the cross sectional area of the copper conductor also increases in a linear fashion making the cable bulky, reducing the efficiency of aircraft. Superconducting cables can be one of the promising solutions in this regard, reducing the overall weight and volume of the propulsion system. Thus, to investigate the possibility of employing the superconducting cables on-board aircraft, the current thesis emphasizes on the development, evaluation and testing of the superconducting cable models for turbo electric aircraft architectures. This thesis starts by introducing the concept of electric propulsion for aircraft and its importance in increasing the efficiency of aircraft propulsion facilitating a reduction of greenhouse gas emissions. From the range of possible electric aircraft architectures put forward in the literature, turbo-electric architecture is investigated in the present thesis, considering its technological feasibility over other systems. With superconductivity being considered as the enabler of the electric propulsion concept, basics of the superconductivity are briefed and experimental characteristics are detailed both under steady state and transient state. Superconducting cables are one of the most important components of the propulsion system, thus a detailed understanding of the existing cable designs are reviewed to achieve a promising cable design for electric aircraft. With high current density, flexibility and zero heat and magnetic field emissions, coaxial high temperature superconductor (HTS) cable design was chosen as the promising design and its advantages over others were detailed. The power rating of the electric aircraft was assumed to be 8 MW and with the base structure of HTS cable being chosen, the design parameters of the cable for both AC and DC architectures were evaluated. The thermo-electric lumped models of the HTS cables were then built based on the evaluated cable design parameters. A detailed evaluation of the AC loss has been carried out and a simplified novel analytical AC loss model is presented as till date fast and accurate AC loss model has been the biggest challenge for modelling superconducting applications. This model was verified with the results from the FEM models and also from literature. Using this model, the AC losses of the harmonic AC/DC currents can also be obtained, making it a unique model for both component and system level models. With the HTS AC/DC cable models built, the conventional system level models adopting the turbo-electric architecture were built to investigate its performance using HTS cables. The initial results showed not much impact on the system performance, thus recommending their use in practical systems for better efficiency. Also, the reduction in fault current rating of the entire system was observed by using the superconducting cables, for various faults and were compared with the conventional cable. Similarly, use of superconducting fault current limiters (SFCL's) in series to the shunt capacitors and fault current limiting (FCL) HTS cables in place of normal HTS cables for limiting the rail-rail fault current magnitude in the DC architecture were investigated and a fault current tolerant DC network architecture was recommended for the effective operation of the switchgear.
Supervisor: Pei, Xiaoze ; Dunn, Roderick Sponsor: Airbus Group Innovations
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Electric Aircraft ; Superconductivity ; Electric Propulsion