Capacitor bank for Fast Discharge Unit of iter facility

Superconductive magnetic systems capable of storing energy up to tens of gigajoules are used in modern electrophysical facilities. Protection of such systems is provided by Fast Discharge Units (FDU). In case of failure, in particular quench in a superconducting coil, rather fast and safe energy discharge from the magnetic system is provided by FDU, which breaks the coil supply loop and provides energy dissipation in high energy resistors. The ITER FDU should interrupt currents up to 70 kA with a voltage up to 10 kV. The FDU includes a two-stage switch consisting of a ByPass Switch (BPS, contactor with a pneumatic drive) and a fast vacuum circuit breaker (VCB). The other important part of FDU is a capacitor bank for generating the counter current pulse. The closed BPS carries a steady-state current up to 70 kA. Once the BPS opens, current passes into closed contacts of VCB. Shortly after, the VCB opens and the capacitor bank generates a counter current pulse, which compensates the current in VCB. In such a way the arcless current commutation is provided in the FDU. This paper studies the transients during FDU electrical switch-off. Peculiarities of the capacitor bank operation are considered. Capacitive storage rated for 5 kV, 70 kA is described. The tests results of capacitor bank are presented.