QUENCH PROTECTION SYSTEM USING A NOVEL DC CIRCUIT-BREAKER FOR LHD

The large helical device (LHD) has 12 superconducting coils that are s trongly coupled with each other. The rating currents of these coils ar e from 13 to 32 kA and total magnetically stored energy reached 1.6 GJ . These coils are excited by six d.c. power supplies and each coil cur rent is controlled with high accuracy to make a magnetic surface requi red-for various plasma experiments. At the same power supplies dischar ge the stored energy quickly when coil quench is detected. This paper introduces the quench protection circuit installed in the power suppli es. For this system, a 30 kA and 2 kV class d.c. current breaker using the parallel connection of a small vacuum circuit breaker (VCB) and p ower fuse is developed. Also, the best discharge resistor set, that du mps stored energy in the wide operation range of the LHD without chang ing connection, is found using numerical simulation. To confirm the re liability of quench protection and operation delay, operating tests ar e done using an actual quench protection system and power supply. In t his test, more than 400 shots for three deference power systems are fi nished without any operation failure. (C) 1998 Elsevier Science S.A. A ll rights reserved.