THE OPENING PROCESS OF THERMAL PLASMA CONTACTS IN A POST-ARC CHANNEL AFTER CURRENT ZERO IN A FLAT-TYPE SF6 GAS-BLAST QUENCHING CHAMBER

摘要

The electrical resistivity rho(res) of a post-are channel after current zero was measured along the nozzle axis in a flat-type SF6 gas-blast quenching chamber. In the chamber, iron electrodes were intentionally adopted, since Fe spectral lines at wavelengths of 426 and 443 nm have much higher radiation intensities than those of S+, F or Cu at temperatures below 5000 K. Observation of the two Fe spectral lines permitted determination of temperature T and iron vapour concentration X(Fe) in the post-are channel up to 100 mu s after current zero, On the other hand, rho(res) of SF6 gas contaminated with iron vapour was theoretically calculated on the basis of the simplified first Chapman-Enskog approximation, Use of this calculation result made it possible to estimate rho(res) Of the post-are channel from the measured T and X(Fe). The estimation result revealed that rho(res) increased more dramatically at the nozzle throat than at other axial locations, reaching 4.3 Omega m at 100 mu s after current zero, Furthermore, on the basis of the axial distribution of rho(res), the concept of 'thermal plasma contacts' was developed to interpret behaviour of the post-are channel. [References: 29]