Spectroscopic measurements of electrical breakdown in various dielectric liquids

This article concerns the comparative analysis of spectrum of electrical breakdown in three various commercial dielectric liquids: mineral oil, natural ester and synthetic ester. Spectroscopic measurements were performed for breakdown arc initiated in point-plane electrode setup of 10 mm gap distance. A voltage waveform used for discharge initiation was a standard lightning impulse with 1.2 μs rise time and 50 μs fall time. The obtained results indicated that for all three liquids a clearly separate wavelength is 656 nm, which is connected with emission from hydrogen atoms (H_α Balmer line). However only for mineral oil this wavelength is dominant in breakdown arc spectrum. For natural ester similar intensity to the intensity from hydrogen atoms was observed for continuum around 510-515 nm. Moreover, for synthetic ester such continuum was noticed for the range from 440 to 500 nm and its intensity was higher than peak concerning H_α Balmer line.