411 / 2017-04-27 09:22:15

Chromium Vapor Density Measurement by Optical Absorption Spectroscopy at Current-zero of Vacuum Arcs in Vacuum Interrupters

Vacuum arc;,Anode spot;,Optical absorption spectroscopy;

The metallic vapor density at current-zero after interrupting a sinusoidal vacuum arc in a vacuum interrupter is crucial to the dielectric recovery process. In this work, the objective is to measure the Cr metallic vapor density at current-zero of vacuum arcs between chromium butt contacts by optical absorption spectroscopy using a broadband light source. The peak current varies from 2 kA to 14 kA and the external axial magnetic field intensity varies from 0 mT to 90 mT, that lead to different vacuum arc mode from diffuse mode to anode spot mode. The results show that the metallic vapor density at current-zero increase exponentially with the increase of peak current. Moreover, the increase of external axial magnetic field intensity can dramatically decrease the metallic vapor density in the gap. When an anode spot appears, the metallic vapor density at current-zero is about 2×1019 m-3, which is sufficient for re-ignition. Therefore, the residual plasma and electrode condition at current-zero play more important roles in the post-arc breakdown process than we had expected.