Light emission from corona discharge in SF6and SF6/N2gas mixtures at high pressure

Abstract

A spectroscopic investigation of corona discharges in SF 6 /N 2 gas mixtures has been undertaken using an optical multichannel analyser (OMA). A point-to-plane geometry has been used with point radii varying from 3 to 10 μ m. Spectra are measured for high pressures ranging from 0.2 MPa up to 1.4 MPa and for different concentrations of SF 6 in the gas mixture. The spectra in the 200–850 nm spectral range are mainly made of molecular bands, which is indicative of a low temperature discharge. It has been noted that SF 6 emits in the region of 420 nm to 510 nm in positive and negative polarities, although in negative polarity the emission is weaker. For SF 6 /N 2 mixtures, the main source of light emission is from N 2 . The resultant spectra are used to evaluate the rotational T r and vibrational T v temperatures of excited N 2 , T r being considered, due to the high pressure, to be equal to the kinetic temperature T kin in the corona discharge. T r and T v are determined by comparing the experimental spectrum of the second positive system ( of N 2 and the simulated one, which is obtained using a convolution method. As expected, the results show that the measured rotational temperature T r increases steadily with the mean discharge current, while its increase with gas pressure is less pronounced. The values of T r are higher for the positive corona discharge than the negative and also for mixtures having higher amounts of SF 6 . In all conditions, we found and T v is less sensitive to the variation of the current.