Time-Resolved Analysis of SF6 Arc Plasmas in a Laboratory Model Chamber for Circuit Breaker

Abstract

This article presents time-resolved analysis of SF6 arc plasma generated in a laboratory-scale model chamber prepared for studying the characteristics of a circuit breaker. During the arc discharge, the optical emission spectra are measured by a high-speed spectrometer under various operating conditions. The time-resolved electron temperature and density values are determined using the well-known Boltzmann plot and Stark broadening methods, respectively, for the measured Cu I, S II, and F I emission lines. Moreover, the temporal evolution of the electrical conductivity of the arc plasma is deduced from the measured electron temperature and density values, depending on the operating conditions. In our experimental conditions, it is revealed that the electrical conductivity of arc plasmas is mainly determined by Coulomb (electron-ion) collisions as opposed to electron-neutral collisions due to the much higher Coulomb collision frequency compared to the electron-neutral collision frequency. Both the electron temperature and density were found to increase when the discharge current is increased at a fixed gas pressure, resulting in an increase of the electrical conductivity. When the gas pressure inside the model chamber is increased, the electron density is increased as well, but the electrical conductivity does not change significantly due to the slight change in the electron temperature. The present study will be helpful for investigating the performance capabilities of circuit breakers because the electrical conductivity, the most important parameter to guarantee successful circuit breaking at points near the current-zero, is determined by the temperature and density of the electrons.