A 170-kA DC circuit breaker for the quench protection of the central solenoid coil of the ITER tokamak

Abstract

High current and high voltage DC circuit breakers have already been used in the field of fusion technology, in the Joint European Torus (JET) (P. Dokopulos and K. Kriechbaum, DC Circuit Breaker Arrangement 73 kA, 24 kV for the Joint European Torus, Elektrotechnische Zeitschrift A, 1976; P.L. Mondino, The JET ohmic heating circuit, 9th Symposium on Engineering Problems of Fusion Research, Chicago, US, Vol. 1, October 1981, pp. 386–389) and JT60 (R. Shimada et al., JT 60 power supplies, Fus. Eng. Des. 5 (1987) 47–68; R. Shimada et al., Development of high current DC circuit breaker for large Tokamak device, Fusion Technol. 1 (1978) 401–406) Tokamaks, with pulsed currents up to 90 kA or more, but were not able to simultaneously carry steady state currents of 60 kA and to interrupt current under high voltage. Therefore, R&D on high current (60 kA) and high voltage (20 kV) switches, especially on DC circuit breakers, has been undertaken in order to ensure the protection of the superconducting coils of the ITER Tokamak (Y. Shimomura et al., ITER Overview, 17th IAEA Fusion Energy Conference, Yokohama, Japan, October 1998; M. Huguet, The Integrated Design of the ITER Magnets and Their Auxiliary Systems, 17th IAEA Fusion Energy Conference, Yokohama, Japan, October 1998) in case of a quench (Y. Shimomura et al., ITER Overview, 17th IAEA Fusion Energy Conference, Yokohama, Japan, October 1998). For this purpose, the coil magnetic energy (in the range of several GJ) is discharged in a large resistor connected in parallel with the DC circuit breaker. Most of the coil circuits operate at 60 kA maximum DC current. Nevertheless, the Central Solenoid (CS) coil (Y. Shimomura et al., ITER Overview, 17th IAEA Fusion Energy Conference, Yokohama, Japan, October 1998) of the ITER Tokamak was designed, till the middle of 1998, to be operated at 168 kA. The assessment of such a circuit breaker concept, using parallel operation of 60 kA rated mechanical switches, will be developed in this paper. This theoretical analysis assumes the use of pure mechanical switches connected in parallel without any use of semi-conductor devices.