Research on the Reignition Problem and Interruption Characteristics of Series Connected Vacuum Interrupters

When vacuum interrupters are connected in series, some merits of this structure will be seen and a lot of improvements are expected. This paper describes our investigations on the reignition problem and interruption characteristics of series connected vacuum interrupters. In vacuum interrupters, CuCr (Cr: 25%) is not sufficient at the voltage level ${>}{\rm 120}~{\rm kV}$ because of saturation of material. Thus, we should add some material or use completely new material to replace it. By connecting two interrupters in series, the reignition problem sufficiently reduced. Simultaneously, compared with spiral electrode, axial magnetic field has an advantage on voltage sharing because it has a smaller fluctuation of postarc current. In addition, this was confirmed by the experiments with practical ac vacuum interrupters and nuclear fusion experiment dc interrupters. For dc circuit breakers (CBs), because of special characteristic, insulation recovers instantly, and this can be used for dc current breaker for subway and Tokamak nuclear experimental devices. For the application of ac CBs, as with series connection, no reignition happens, and it can be used in the Japanese market for the section separator in super express train.