Electromagnetic-Thermal Behaviors of HTS Noninsulation Closed-Loop Coil During Quench Process

Although the high-temperature superconducting closed-loop coil operating in persistent current mode can eliminate the huge heat leakage from current leads, application of the noninsulation (NI) winding technique further improves its thermal stability and self-protection ability. Therefore, the NI closed-loop coils are preferred in certain applications, where safe operation, thermal stability, weight, and size of the magnetic are strictly demanded, e.g., electrodynamic suspension system. It is noticeable that the magnetic field stored in the closed-loop coil exhibits a reduction when a heat disturbance occurs, because the power supply is eliminated. Unfortunately, the quench behaviors of the NI closed-loop coils have not been systematically studied. In this article, an electromagnetic-thermal coupling model was established to study the electromagnetic-thermal behaviors during quench process. It is demonstrated that when the heat triggered quench occurs in one turn of the coil, the current at quench location flows to the turn-to-turn, which reduces the local heating. Because the traditional minimum quench energy was not suitable as a quench characteristic criterion for the NI closed-loop coils, the concept of final remained magnetic field retention ratio (FRMFR) was proposed for the first time. The FRMFR is determined by the ratio of the remained magnetic field to the original magnetic field, when the magnetic field of the coil returns to natural decay, indicating that the coil returns to steady-state operation. Based on the simulation model, the effect of turn-to-turn resistivity on the FRMFR was clearly explained. In addition, the influences of heat quench energy, quench location, and local insulation on the quench characteristics of the coil were studied systematically.