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

The electrical resistivity rho(res) of a post-are channel after curren t 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 hav e much higher radiation intensities than those of S+, F or Cu at tempe ratures below 5000 K. Observation of the two Fe spectral lines permitt ed 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 othe r hand, rho(res) of SF6 gas contaminated with iron vapour was theoreti cally calculated on the basis of the simplified first Chapman-Enskog a pproximation, Use of this calculation result made it possible to estim ate rho(res) Of the post-are channel from the measured T and X(Fe). Th e estimation result revealed that rho(res) increased more dramatically at the nozzle throat than at other axial locations, reaching 4.3 Omeg a m at 100 mu s after current zero, Furthermore, on the basis of the a xial distribution of rho(res), the concept of 'thermal plasma contacts ' was developed to interpret behaviour of the post-are channel.