Self-blast Current Interruption and Adaption to Medium Voltage Load Current Switching

Abstract

Ablation-assisted current interruption is a candidate for improving interruption capability in medium voltage switchgear. In high voltage switchgear, ablation is utilized to achieve high pressures in self-blast circuit breakers. Self-blast switch technology adapted to medium voltage could represent an attractive alternative to SF 6 technology in load current interruption. However, the arc energies involved would be much lower than in fault current interruption, where self-blast technology is traditionally employed, and to achieve sufficient pressure buildup, this must be compensated for. Higher pressure could be achieved by reducing the radius or increasing the length of the nozzle throat, reducing the heating volume size, changing or increasing the amount of ablative material, or restricting the outward gas flow. Interruption experiments in air have been performed on four different model switch designs that are meant to highlight the possibilities and challenges of adapting self-blast technology to medium voltage load current interruption. The results show that typical load currents can be interrupted at 24 kV, but below a certain critical current, in the present case 200 A, interruptions fail. Self-blast technology could prove useful in medium voltage load current interruption in the future, provided a method for interrupting the lowest currents can be found.