Optical Emission Spectroscopy in Self-Blast Gas Circuit Breaker at Large Current Condition

Arc temperature measurement by optical emission spectroscopy in a gas circuit breaker (GCB) has been of great interest to improve the interruption performance. In this article, emission spectra were observed by using the actual self-blast GCB apparatus. Under the large current condition of 50-kA root-mean-square (rms), a strong continuous spectrum was observed. On the contrary, S
⁺
line emission spectra, which have been widely used for arc temperature evaluation, were not observed under the large current condition. Thus, the gas temperature was evaluated by assuming that the continuous spectrum was a black-body radiation spectrum. The gas temperature at the stagnation point decreased gradually, while that at the nozzle throat decreased suddenly by about 1 ms before current zero. Absorption spectra of the C
₂
radical generated by the ablation of a nozzle material were also observed in the continuous spectrum. Then, the C
₂
density was roughly evaluated by the intensity of C
₂
absorption spectra. It was confirmed that the gas temperature decreased with a decrease of C
₂
density, which indicates that SF
₆
gas blow to the arc plasma reduces the gas temperature.