Light emission from corona discharge in SF₆ and SF₆/N₂ gas mixtures at high pressure

¹ LEMD/CNRS, 25 rue des Martyrs, BP 166, 38042 Grenoble Cedex 9, France
² Laboratoire de Génie Électrique, Université de Guelma, BP 401, 24000 Guelma, Algeria

Corresponding authors: lemzadmi@yahoo.fr andre.denat@grenoble.cnrs.fr

Received: 8 February 2005
Revised: 17 October 2005
Accepted: 20 December 2005
Published online: 4 April 2006

Abstract

A spectroscopic investigation of corona discharges in SF₆/N₂ 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 μm. Spectra are measured for high pressures ranging from 0.2 MPa up to 1.4 MPa and for different concentrations of SF₆ 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 SF₆ emits in the region of 420 nm to 510 nm in positive and negative polarities, although in negative polarity the emission is weaker. For SF₆/N₂ mixtures, the main source of light emission is from N₂. The resultant spectra are used to evaluate the rotational T_r and vibrational T_v temperatures of excited N₂, 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 N₂ 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 SF₆. In all conditions, we found and T_v is less sensitive to the variation of the current.