Developing Superconducting Fault Current Limiters (SFCLs) for Distributed Electric Propulsion Aircraft

Distributed electric propulsion aircraft have been proposed by leading players in the aviation industry as a disruptive technology to address the environmental impact of air travel. Electric propulsion offers flexibility to distribute the electric power within the aircraft and better integration of distributed propulsion with airframe, leading to significant fuel saving, emission and noise reduction. The NASA N3-X concept aircraft for example has great potential to deliver 70% fuel saving relative to 2000 baseline. Superconducting fault current limiters (SFCLs) are critically required to achieve reliability and safety of the distributed electric propulsion power system under different fault conditions. Resistive superconducting fault current limiter (SFCL) is the simplest and most compact design making use of the intrinsic superconductor material behaviour of quenching at high current levels and transitioning from negligible resistance to a high resistance to limit the fault current.
Previous and ongoing SFCL research have been undertaken mainly for land-based power system. Resistive SFCLs have been successfully developed and demonstrated reliable operation in AC live-grids. Straight samples and small coils of 2G HTS conductors have been investigated for DC application. However, up to now there is no SFCL specially designed for aeroplane application. Compared with the land-based power system, the key challenges to design SFCL for aeroplane application is efficiency improvement and weight reduction in order to deliver minimum weight penalty. Therefore, there is a timely requirement to develop high efficiency and lightweight AC and DC SFCLs using both numerical and experimental methods to enable future development of large-scale electric propulsion aircraft.
This project will meet this requirement by delivering 1) an AC SFCL with minimised AC losses, and 2) a DC SFCL with minimised HTS materials required. This will be achieved by determining the optimum combination of novel winding strategy and candidate HTS lamination material. Firstly, we will develop a new multi-physics finite element model coupling analysis of electromagnetic and thermal behaviour of the 2G HTS SFCL coil. The combination of novel winding strategies and HTS lamination materials which deliver optimum AC and DC SFCL coils will be investigated using the finite element model. Secondly, we will construct and characterise representative small helical coil for the AC SFCL. A 1 kA demonstration AC SFCL coil will also be built using the optimum combination identified and characterised in a wide range of operation temperature between 50 K and 77 K. Thirdly, we will construct and characterise a 1 kA DC SFCL demonstration coil and determine the optimum operating temperature in terms of minimum overall system weight. And finally, we will validate the multi-physics SFCL model and examine fundamental physics limitation based on the experimental results. We will also determine the pathway to scale up laboratory demonstrators to industry prototype. This will provide a vital step towards the realisation of high efficiency and lightweight SFCLs for aeroplane application. This work will be carried out in close collaboration with Airbus and Oxford Instruments, and will provide specific recommendations to scale up laboratory demonstrators to industry prototype.

The European Commission's "Flightpath 2050" has set a long-term target for the aviation industry to achieve a 75% cut in CO2 emission, 90% cut in NOx emission and 65% reduction in noise based on the 2000 standards. The distributed electric propulsion system has great potential to achieve less fuel burn, emissions and noise, which presents unique opportunities for the aviation industry to accommodate the ever-increasing air travel demands and achieve long-term sustainability. The proposed research will be of great help to the government to achieve this emission and noise reduction plan by 2050. The fault current management using superconducting fault current limiters will ensure the reliability and safety of the distributed electric propulsion power system, which is the primary concern for the aircraft application. It will also be of great benefit to the industrial and academic community who are active in the study of and uses for distributed electric network and applied superconductivity.
The aviation industry of the UK is the fourth-largest national aviation industry in the world and the third largest in Europe, with an annual turnover of over £60 billion in 2015. There are a wide range of companies in the aviation industry interested in this technology including Airbus and Oxford Instruments. They will act as industry advisors giving their requirements and expert advice on how the laboratory demonstrator can be scaled up and adopted by industry partners in the future. This monitoring and feedback process will go on throughout the project, thereby giving confidence in investigating the pathway to scale up the laboratory demonstrator to an industry prototype.
This project will also produce a significant impact on the academic and industry community of applied superconductivity. After 30 years since the discovery of high-temperature superconductivity, the conductor technology is on the edge of penetration into the large-scale applications market. The proposed project will significantly broaden the application area of superconducting fault current limiter by extending the technology for the first time to the market of electric aircraft system, thereby increasing the profile and attracting vital industry stake holders. It will also give specific recommendations to superconductor manufacturers for further developing their materials to be more suitable for electrical power applications. Further improvement on the technology will accelerate the penetration of high-temperature superconductors into the electrical power industry.
As an integral part of the project management, the industrial partners will be invited to attend the project meetings held in Bath every six months. Interested collaborators (the industrial sponsor and other relevant commercial and government bodies) will be supplied with the technical reports about research findings. Informal meetings with potential sponsors to seek a follow-on support of the project will also be held.