AbstractThe dramatic growth and development in the aviation industry contribute to huge amounts of greenhouse gas emissions in the atmosphere. Control of gas emissions from international air transport has become an emergent task to prevent further air pollution caused by carbon emission. Revolutionary design concepts for the next generation of environmentally friendly aircraft with low gas emissions and high efficiency are urgently needed. NASA has been conducting and supporting research on cutting-edge technologies in the aviation industry. Improvements in the design of aeroplane are in urgent need to enhance the performance in terms of noise, gas emissions, reliability and efficiency. A specific innovation objective involves the development of hybrid-electric aircraft, for it has potential advantages including increased fuel efficiency, reduced noise, and it is more environmental-friendly. By far, NASA has started several new projects in the aim of developing enabling technologies for the propulsion system of hybrid-electric aircraft. Boeing, collaborating with Safran, has been investing in electric or hybrid-electric propulsion systems. A 12-seat hybrid-electric commercial aircraft has been under development by U. S. ZUNUM Aero.
The ampacity of power cables used on hybrid-electric aircraft propulsion is expected to be more than several kA. Cross-section of the conventional copper cable increases with the increasing current carrying requirement, making the cable heavy and huge, which may fail to meet the improving fuel efficiency requirement of next-generation aircraft. On the contrary, superconducting cable, having a compact structure and high current carrying capacity, is a promising candidate for the propulsion system of hybrid-electric aircraft. In particular, the Conductor-on-Round-Core (CORC) cable wound with high temperature superconducting (HTS) tapes is an important cabling concept. It is advantageous for its high flexibility, high operating current, high current density, low cryogenic cost, and small bending radii. However, the complex helical geometry of CORC cable makes the understanding of its electromagnetic performance and quench behaviour challenging. This thesis presents a thorough study of HTS CORC cables mainly by numerical methods. The finite element analysis software, COMSOL Multiphysics, is used to build models for the simulation of CORC cables.
The focusing point of the thesis is to understand how the cable structure influences the electromagnetic and quench behaviour, as well as on how these influences can be reduced. The novelty of this thesis mainly lies in the use of a new T-A formulation, which is, for the first time, applied to three-dimensional (3D) modelling of CORC cables with practical geometry. The use of the new T-A formulation in FEM software COMSOL enables the research on how the winding angle and variation of transport current and magnetic field affect the electromagnetic and quench behaviour of CORC cables.
The first model proposed in this research is a 3D T-A CORC cable model. It is used to thoroughly analysing the electromagnetic behaviours of CORC cable. A good agreement is achieved between the simulation results and published experimental data, which proves the accuracy and reliability of the proposed new 3D T-A CORC cable model. A novel 2D T-A CORC cable model is then built to further shorten the computation time from days to less than an hour.
Then, quench behaviour of CORC cable is analysed using a novel 3D multi-physics T-A model to locate the potential cause of quenching during cable operation. The coupling of four modules; the T-formulation module, the A-formulation module, the heat transfer in thin shell module, and the equivalent circuit module, enables the modelling of hotspot-induced quench of CORC cables. The physical process of hotspot-induced quench is simulated and discussed in detail. The influence of uniform and non-uniform terminal contact resistances on the quench behaviours is analysed.
Finally, an HTS tri-axial CORC cable is conceptually designed for the electrical propulsion system of hybrid-electric aircraft. Two 2D T-A models are proposed in the aim of analysing how the n-th harmonic current will affect the AC loss of CORC cable and how it can be improved. The minimum quench energy of the cable during hotspot-induced quenching process is calculated.
The thesis provides efficient modelling tools for thoroughly investigating the electromagnetic and quench behaviour of CORC cables. The powerful modelling tools presented in this thesis will be valuable guidance for the next stage of design of stable-operated CORC cables with minimized AC losses for high-field and high energy conversion and transmission applications.
|Date of Award||14 Oct 2020|
|Supervisor||Xiaoze Pei (Supervisor), Manuchehr Soleimani (Supervisor), Weijia Yuan (Supervisor) & Min Zhang (Supervisor)|