Periodic Reporting for period 1 - NI HTS machine (Developing novel high temperature superconductor rotor windings for electric aircraft propulsion machines)
Periodo di rendicontazione: 2018-06-04 al 2020-06-03
This project is to apply the No-insulation high temperature superconductor (HTS) coil technique on the rotor windings of HTS machine in electrical aircraft propulsion, so that the thermal stability, reliability and safety of the HTS machine can be enhanced significantly. As a new winding technique, the key idea of NI HTS coil is to remove the turn-to-turn insulation of traditional insulated HTS coils. When a quench happens, the transport current can bypass the local hot spot automatically through the turn-to-turn metallic contacts, so that the thermal stability of the HTS coil can be enhanced. Now, it is absolutely unclear about the electromagnetic and quench behaviour of NI HTS windings under machine environment, which has never been studied so far.
The aerospace sector is actively pursuing revolutionary design concepts toward hybrid-electric aircraft to further improve the environmental impact of air travel. The United Nations’ International Civil Aviation Organization plans to cut carbon emissions from airplanes by more than 650 million tons between 2020 and 2040. The EU plans to have more than 75 % reduction in CO2 and NOx emissions by 2050. These regulations are the key drive for the aviation manufacturers to design more efficient electric-hybrid aircraft, which can help to shift the industry to electric or turboelectric propulsion. The advancements of hybrid or electric power to improve automobiles serve as the base technology being applied toward aircraft. However, electric aircraft propulsion requires very high power density which cannot be achieved by conventional electric machines. High temperature superconductors (HTS) offer a transformative opportunity to develop electrical machines with high power densities, because their current-carrying capability is more than twenty times that of copper.
This project will remove the largest challenge of the HTS machine, low thermal stability during quench, by applying the NI HTS winding technique. The HTS motor technique is one of the most promising propulsion design for electrical aircraft, which can match the demand of high power density. This project can make a considerable progress on the development of passenger electrical aircraft.
The overall objective of this project is to develop a robust HTS winding technique with high thermal stability and enough safety for the future electrical aircraft motor/generator. This project will investigate the practicability and reliability of the NI HTS machine design, and the electromagnetic and quench behaviour of the NI HTS coils are studied in machine environment by a series of models and experiments.
The aerospace sector is actively pursuing revolutionary design concepts toward hybrid-electric aircraft to further improve the environmental impact of air travel. The United Nations’ International Civil Aviation Organization plans to cut carbon emissions from airplanes by more than 650 million tons between 2020 and 2040. The EU plans to have more than 75 % reduction in CO2 and NOx emissions by 2050. These regulations are the key drive for the aviation manufacturers to design more efficient electric-hybrid aircraft, which can help to shift the industry to electric or turboelectric propulsion. The advancements of hybrid or electric power to improve automobiles serve as the base technology being applied toward aircraft. However, electric aircraft propulsion requires very high power density which cannot be achieved by conventional electric machines. High temperature superconductors (HTS) offer a transformative opportunity to develop electrical machines with high power densities, because their current-carrying capability is more than twenty times that of copper.
This project will remove the largest challenge of the HTS machine, low thermal stability during quench, by applying the NI HTS winding technique. The HTS motor technique is one of the most promising propulsion design for electrical aircraft, which can match the demand of high power density. This project can make a considerable progress on the development of passenger electrical aircraft.
The overall objective of this project is to develop a robust HTS winding technique with high thermal stability and enough safety for the future electrical aircraft motor/generator. This project will investigate the practicability and reliability of the NI HTS machine design, and the electromagnetic and quench behaviour of the NI HTS coils are studied in machine environment by a series of models and experiments.
1. A multi-physics model is developed for the NI HTS coil in machine environment. This model is based on an equivalent circuit network model, and it couples a magnetic field model and thermal model. The equivalent circuit model is developed to study the distribution of the induced eddy current as well as turn-to-turn loss in the NI HTS coil. The effects of stator windings on the NI rotor windings is replaced by equivalent virtual coils in this network model, which can generate same ripple magnetic field on the rotor windings. Then the influence of the stator windings can be represented by coupling through the mutual inductance between NI arc elements and this virtual coils. A magnetic field model is coupled to calculate the magnetic field induced by the current in the NI HTS coils. A solid heat transfer model is also coupled to calculate the temperature distribution.
2. Study on the charging delay of the NI HTS coil for HTS machines. Two NI HTS coils with different turn-to-turn resistivity are wound by different REBCO tapes, and an insulated HTS coil is also wound for comparison. The NI coils is wound by tape from SuNAM, South Korea. The results show that the charging delay of normal NI HTS coils are too long to be practical for HTS machines. The NI coil wound by tape with stainless steel has much less charging delay, which is more suitable for HTS machines..
3. The thermal stability of the NI HTS coil under machine environment are also studied by simulation and experiments. A copper solenoid coil is wound to generate an AC magnetic field, which is to simulate the ripple background fields on the rotor windings. Two HTS pancake coils are wound by REBCO tapes. One is NI coil and the other one is traditional insulated HTS coil for comparison. Hot-spot induced quench test are performed on the two coils. The results validated the enhanced thermal stability of the NI HTS coil under machine environment.
4. The effect of ripple magnetic fields generated by stator windings are studied by both measurements and simulations. The AC losses of the three HTS coils exposed to AC external magnetic fields are measured by the calibration free method. The measurement shows that the AC loss of the NI HTS coils under ripple magnetic fields is 50 times higher than that of its insulated counterpart. The simulation results also show the same results. Results from simulation also obtain similar results, and it also find that most of eddy current accumulates on the outer turns of the NI HTS coil, and a very small external ripple field may induce a very high eddy current on outermost turns. Therefore, AC loss may be challenging for the efficiency of HTS machines, when the NI coil is applied in machine environment with ripple fields. A grading turn-to-turn resistivity technique is proposed to solve this problem successfully.
2. Study on the charging delay of the NI HTS coil for HTS machines. Two NI HTS coils with different turn-to-turn resistivity are wound by different REBCO tapes, and an insulated HTS coil is also wound for comparison. The NI coils is wound by tape from SuNAM, South Korea. The results show that the charging delay of normal NI HTS coils are too long to be practical for HTS machines. The NI coil wound by tape with stainless steel has much less charging delay, which is more suitable for HTS machines..
3. The thermal stability of the NI HTS coil under machine environment are also studied by simulation and experiments. A copper solenoid coil is wound to generate an AC magnetic field, which is to simulate the ripple background fields on the rotor windings. Two HTS pancake coils are wound by REBCO tapes. One is NI coil and the other one is traditional insulated HTS coil for comparison. Hot-spot induced quench test are performed on the two coils. The results validated the enhanced thermal stability of the NI HTS coil under machine environment.
4. The effect of ripple magnetic fields generated by stator windings are studied by both measurements and simulations. The AC losses of the three HTS coils exposed to AC external magnetic fields are measured by the calibration free method. The measurement shows that the AC loss of the NI HTS coils under ripple magnetic fields is 50 times higher than that of its insulated counterpart. The simulation results also show the same results. Results from simulation also obtain similar results, and it also find that most of eddy current accumulates on the outer turns of the NI HTS coil, and a very small external ripple field may induce a very high eddy current on outermost turns. Therefore, AC loss may be challenging for the efficiency of HTS machines, when the NI coil is applied in machine environment with ripple fields. A grading turn-to-turn resistivity technique is proposed to solve this problem successfully.
This project successfully applies the NI HTS winding technique on the HTS machine of electrical aircraft. It validates the practicability and reliability of the NI HTS machine concept, which makes a significant progress on the electrical passenger-aircraft. The eddy loss NI HTS rotor windings induced by the ripple magnetic fields is the greatest challenge of the NI HTS machine design. we proposed a grading turn-to-turn resistivity technique to reduce this eddy loss, which is beyond the expectation of this project. It can significantly enhance the thermal stability of the NI HTS coil exposed to ripple magnetic fields.
The results of this research have generated a wide and great reputation among the international researchers. The applicant has been invited to do oral presentations on several international conferences: the HTS modelling workshop 2018, The Applied Superconductivity Conference 2018, the EUCAS2019, the Applied Superconductivity Conference 2020. Part of the results has been published on the most reputable journal on electrical transportation, IEEE transactions on electrification transportation. More publications will be published in the near future. The NI HTS machine design abstracts a great interest on industry companies. The CRRC has applied the NI HTS machine technique on their future HTS maglev design, and a test model is being built.
The results of this research have generated a wide and great reputation among the international researchers. The applicant has been invited to do oral presentations on several international conferences: the HTS modelling workshop 2018, The Applied Superconductivity Conference 2018, the EUCAS2019, the Applied Superconductivity Conference 2020. Part of the results has been published on the most reputable journal on electrical transportation, IEEE transactions on electrification transportation. More publications will be published in the near future. The NI HTS machine design abstracts a great interest on industry companies. The CRRC has applied the NI HTS machine technique on their future HTS maglev design, and a test model is being built.