Design and Model Test of a Water-Cooled VCB for Superconducting Magnet Power Supplies

Abstract

A vacuum circuit breaker (VCB) is one of the key components that constitute a quench-protection circuit for a superconducting coil. A water-cooled VCB having a continuous high-current carrying-capacity was newly designed and its model test was conducted. The target values of its performance were determined from the viewpoint of application to quench protection for superconducting coils in fusion devices as follows: (1) continuous current-carrying capacity of 25 kA or more, and (2) current interruption rating of 50 kA or more. Since thermally critical parts of the VCB are contacting surfaces of its electrodes, a key issue of the design is how to remove the heat generated on the surfaces in the electrodes from the vacuum area. For heat removal with good efficiency, the VCB was designed to possess a short fixed rod with a large coil outside the vacuum area and a fat movable rod where a water-cooling channel can be bored. Thus the new VCB has an up-down asymmetrical structure having the coil that provides co-axial magnetic field for stabilizing the current interruption property. Thermal characteristics of the VCB were analyzed by computer simulation. In addition, a model of the VCB was fabricated and tested to evaluate the characteristics. At the test of the model VCB, it was proved that the water-cooled VCB with a current-carrying capability of about 18 kA is feasible.