Sub-Millisecond Artificial Current Zero Interruption of DC Fault Current Using a 40kV Ultra-Fast Vacuum Interrupter

Voltage Direct Current (VSC-HVDC) system is increasingly adopted for efficient power integration and long-distance power delivery. The rapid expansion of offshore wind power and multi-terminal VSC-HVDC systems has imposed stringent requirements on ultra-fast DC fault protection. This study develops a 40 kV sub-millisecond vacuum interrupter driven by a high-speed electromagnetic repulsion mechanism for DC circuit breaker applications. DC interruption based on artificial current zero under short arcing condition is systematically investigated using axial magnetic field, butt, and transverse magnetic field contacts. The effects of arcing time, contact structure, and current rate of change at current zero on interruption performance are experimentally investigated. A pronounced synergistic interaction between arcing duration and di/dt is identified as a key factor governing dielectric recovery and successful DC interruption. The results provide experimental evidence on the sub-millisecond DC interruption behaviour of vacuum interrupters and support the development of ultra-fast, high-reliability protection technologies for future HVDC grids.