Active De-Excitation System Using Magnetically Coupled Secondary Coil and Charged Capacitor for Fault Protection of Superconducting Coils.

Coils excited for high magnetic fields have large discharging time constants owing to high inductance and low resistance for large operating currents. This type of coil requires a de-excitation system to reduce the current as quickly as possible when a fault occurs and to minimize the damage caused by Ohmic heating. This paper introduces a new de-excitation system that rapidly reduces the current discharged through the dump resistor by using the active current of the secondary coil. To verify the performance of the proposed method, a de-excitation system utilizing the primary superconducting coil and secondary copper coil was constructed and discharging tests were performed. Good agreement was obtained between the circuit simulation and test results. The performance of the proposed system was compared with those of other de-excitation systems, and it was confirmed that the proposed approach provides a feasible and powerful means of reducing the fault energy load and that it reduces this load more than the other systems considered. In addition, the effects of the charging voltage, coupling coefficient, capacitor bank configuration, and diode on the performance of the de-excitation system were analyzed and information about the secondary Section that most effectively reduces the current was obtained.