DC Interruption Performance of Vacuum Interrupters in a Quench Protection Switch Based on Forced Current Zero

In a superconducting Tokamak, superconducting coils play crucial roles in generating desired magnetic field profile and confining high-temperature plasma. When quench occurs inside superconducting magnet, tremendous energy stored in the coil has to be dissipated in time before any damage to the magnet caused by heat or electric stress. In this paper, a quench protection switch (QPS) based on forced current zero is investigated experimentally. The first current commutation process from the bypass switch (BPS) to the main circuit breaker (MCB) is presented. The second current commutation process from the MCB to the discharging resistor is mainly studied. In this stage, experimental current in the MCB, which uses vacuum interrupter (VI), is forced to zero by a high-frequency countercurrent, which is a typical approach of DC interruption. The interruption performance and influence of contacts structure, countercurrent frequency and contacts stroke are discussed. The evolution of vacuum arc in this process is investigated as well.