Fundamental Investigation on Dielectric Recovery Characteristics of Copper Butt Electrode Space for Different Voltage Application Timings during Arc Decay Process

In this paper, we investigated the dielectric recovery characteristics of copper butt electrode in a vacuum circuit breaker (VCB) by constructing an experimental circuit that can apply a quasi-transient recovery voltage (TRV) with a delay time of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$t_{\mathrm{d}}$</tex> after the current decay. A vacuum arc occurs between the electrodes when the VCB opens the contacts to interrupt current, sustained by metal vapor from the melting and evaporation of the electrodes. The behavior of vacuum arcs with this metal vapor as the medium is extremely complex, making it difficult to fully elucidate solely through experimental observations. Therefore, both experimental and numerical approaches are essential to investigate the behavior of vacuum arcs for improving the performance of VCBs. Our experimental results revealed that dielectric recovery between the copper butt electrodes after the current down takes about 1.6 ms. This is due to incomplete diffusion of metal vapor within a few tens of microseconds. We further discussed the results above from the numerical simulation, uniquely constructed with combination of particle method and finite volume method. The simulation result showed a decrease in heavy particle density and the electrical conductivity between the electrodes during the current decay process. This dual approach enabled a comprehensive discussion of the dielectric recovery characteristics between the electrodes.