Excitation Temperature Imaging of Vacuum Arc Based on Two-Line Radiance Method

The excitation temperature of the high-current vacuum arc was measured based on the intensity ratio of two Cu I spectra of 510.6 and 515.3 nm. Diffuse mode vacuum arcs with the peak current of 2 kA, igniting between 5-mm gap, 10-mm phi electrodes, Cu100, Cu80Cr20, and Cu50Cr50 wt.% contacts were measured by a multiple-imaging optical system and high-speed video camera. It turns out that the excitation temperature was almost evenly distributed in the gap. The excitation temperature at the current peak depended on the electrode material and took higher in the order of Cu100, Cu80Cr20, and Cu50Cr50. The excitation temperature was also measured by a spectroscopic approach, and it showed the same tendencies as the measurement using multiple-imaging optical systems and a high-speed video camera. The current decreasing phase of dc interruption was simulated by using semiconductor switches at the peak of ac 50-Hz current, and as a result, the current zero with a decreasing ratio of 30 A/ $\mu \text{s}$ was realized. The excitation temperature for the Cu100 electrode decreased with the decreasing current, whereas those for Cu80Cr20 and Cu50Cr50 increased. This difference suggests that developing direct current vacuum circuit breakers needs the optimization of the electrode materials, current waveform, and plasma parameters in the gap.