Analysis of Dielectric Recovery for SF6 Gas-Blast Arc

Abstract

In this paper, computer simulations of the physical phenomena occurring in the arc region before and after current zero were carried out to evaluate the dielectric recovery characteristics of two types of dual-flow nozzles. A commercial computational fluid dynamics (CFD) program “PHOENICS” was used for the simulation and the user-coded subroutines to consider the arcing phenomena were added to this program by the authors. The computed results were verified by comparison with the test results presented by the research group of BBC. In order to investigate the state of the arc region after current zero, the simulations were carried out in four steps, cold gas flow analysis, steady state arc simulation, transient arc simulation before current zero, and transient hot-gas flow simulation after current zero. The semi-experimental arc radiation model was adapted to consider the radiation energy transport and Prandtl's mixing length model was employed as the turbulence model. The electric field and the magnetic field were calculated with the same grid structure used for the simulation of the flow field. The streamer criterion was introduced to evaluate the dielectric recovery characteristics after current zero. Compared with the results obtained by assuming the current zero state in the former studies, it has been found that the results obtained by considering the state before current zero were more accurate.