Investigate on the Electromagnetic and Loss Characteristics of NI HTS Multi-Pancake Coil During Charging Process

Non-insulated (NI) high-temperature superconducting (HTS) coil has become the core component of superconducting equipment in many high-tech applications because of its excellent electrothermal stability and self-protection characteristics. Due to the absence of turn-to-turn insulation, the electromagnetic behavior of the NI HTS coil during charging is very different from that of a traditional insulated (INS) coil. Many of its problems in engineering applications have not been fully studied. Therefore, the electromagnetic and loss characteristics of the NI HTS multi-pancake coil wound with (RE)Ba2Cu3Ox (REBCO) conductors during the charging process are studied in this article. A lumped equivalent circuit model (LECM) of NI HTS multi-pancake coil is combined with a finite element model (FEM) based on H-formulation. The LECM is used to calculate the current distribution and turn-to-turn loss, and the FEM is used to calculate the magnetization loss of the superconducting layer. The results show that after increasing the difference of the resistance or inductance in the multi-pancake coil, some coils will produce reverse circumferential current and the reflux phenomenon only exists in the early stage of charging. Increasing the number of coil layers will extend the coil charging time. Increasing the charging rate will significantly increase the rising rate and peak value of the coil radial current, making the coil quench risk greater. For the charging loss, the total loss of the multi-pancake coil is several times that of the single-pancake coil. Compared to the INS multi-pancake coil, the NI multi-pancake coil has a smaller magnetization loss rise rate but a larger total charging loss under the same conditions. Therefore, more attention should be paid to the NI multi-pancake coil in the application of superconducting devices.