Quench protection system for the superconducting coil of the KSTAR Tokamak

This paper presents two-stage high-power mechanical-thyristor switches developed as 40-kA direct current (de) circuit breakers for the superconducting coil energy dump system of Korea superconducting Tokamak advanced research (KSTAR). An advanced switching system used in the quench protection should allow multishot 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 solid-state power 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 (QP). Compared with the all solid-state switches and vacuum interrupters of equal capabilities the proposed switch is much cheaper than the dc breakers and has lower power dissipation in current conducting state "Kuchinski et aL in Proc. Power Ele., 899-903, 1995;" "Benfatto et aL IEEE Power Del., Vol. 3, No. 4, pp. 1372-1376, Oct. 1998." Also, it is much faster than the vacuum interrupters. The system is designed to break 40-kA dc current within 200 ms. Also, KSTAR device, a configuration of the energy dump system and coil power supplies are presented.