The influence of electrode materials on the emission spectrum in SF6 under AC corona discharge

Sulfur hexafluoride (SF6) has excellent insulation and arc extinguishing performance. However, SF6 is sensitive to the non-uniformity of electric field. The increasing electric field will lead to the insulation deterioration of SF6 and further develop into insulation failures. Therefore, it is necessary to find an effective way to monitor and detect partial discharge. In recent years, optical methods have proven to be effective in identifying the insulation status of electrical equipment. In this paper, the needle-plate electrodes with different materials (copper, 316 stainless steel and aluminum) were used to simulate corona discharge of the extremely non-uniform electric field under 50Hz AC voltage. Then, the corona discharge emission spectra of SF6 were measured by a spectrometer. And then the characteristic bands of SF6 gas corona discharge were identified, that is, the band near 309nm and the band of 420-510nm. The former is the spectrum of OH radicals (A(2)Sigma(+) -> X-2 Pi,Delta nu = 0) produced by the inevitable presence of a small amount of water vapor during experiments. The latter is produced by the radiation of SF6 molecule itself. The materials of needle electrode have little effect on the spectral distribution, but an obvious effect on the spectral intensity. Both the work function of the electrode materials and the local electric field strength have significant influence on the spectral intensity. In the range of 420-510nm, the 316 stainless-needle electrode has the highest spectral intensity, followed by the aluminum needle electrode, and the copper needle electrode is the weakest. The experimental results can provide a reference for the optical method to detect partial discharge in SF6 insulated electrical equipment.