Study on the recovery characteristics of disc-type superconducting fault current limiter coils from the perspective of boiling heat transfer and bubble behaviors

Abstract

The disc-type superconducting fault current limiter (SFCL) encapsulated by yttrium barium copper oxide (YBCO) superconducting material has broad application prospects in the current limiting field. However, the difficulty to recover quickly and safely after quench remains the bottleneck of the disc-type SFCL. Existing work on the SFCL mainly focused on the resistance recovery while the bubble behavior and distribution, which are important factors affecting the temperature distribution of the superconducting tape, are rarely noticed. In this paper, a visualization platform for the superconducting tape impulse experiment is built, and the dynamic behavior and distribution characteristics of bubble clusters are analyzed by image processing technology. Two arrangements (vertical and horizontal) disc-type coils are comparatively studied. Firstly, the huge differences in the recovery performance of the superconducting tape at different positions are observed and compared. In the vertical coil, the fastest one can recover in 1.414 s and the slowest one takes 2.426 s to recover to the superconducting state. The maximum temperature difference of superconducting tapes at different positions in the coil is up to 10.8 K. In the horizontal coil, the recovery times of the two samples are 1.497 s and 1.595 s, respectively, indicating that the recovery is significant uniform. The whole process of bubble generation, merging and detachment in the transient boiling process is comprehensively and qualitatively analyzed with the help of the high-speed camera. Secondly, it is observed a phenomenon of bubble retention is common in the vertical coil while the horizontal coil is not, which is not conducive to the safe operation of the system. Therefore, the bubble recovery is as important as the resistance and the temperature as a recovery reference. In summary, the horizontal coil is superior to the vertical coil in terms of safe recovery and uniform cooling based on the experimental results in this paper, the coupling analysis of bubble dissipation behavior and thermodynamic characteristics of superconducting tape during quench and recovery is of theoretical significance to the future research work on accelerated recovery and the SFCL structural design.