Quench protection system for KSTAR superconducting coil

This paper presents two-stage high-power mechanical-thyristor switches developed as 40 kA DC circuit breakers for the superconducting coil quench protection system. An advanced switching system used in the quench protection should allow multi-shot mode of operation without maintenance and long lifetime with arcless DC current commutation.. The system is designed to combine the advantages of the both mechanical and thyristor switches. The mechanical stage is to conduct DC current for normal superconducting coil operation and the thyristor stage is to provide fast arcless DC current interruption for quench protection. Compared with the all solid-state switches and vacuum interrupters with equal capabilities the proposed switch is much cheaper than the DC breakers and has lower power dissipation in switch on state. Also, it is much faster than the vacuum interrupters. The system is designed to break 40 kA DC current within 150 ms.