Analysis of the insulation characteristics of c-C₄F₈ and N₂ gas mixtures by Boltzmann equation method

Department of Electrical Engineering, Shanghai Jiao Tong University, No. 1954 Huashan Road, Shanghai 200030, P.R. China

^a e-mail: dmxiao@sjtu.edu.cn

Received: 28 September 2011
Revised: 25 November 2011
Accepted: 2 December 2011
Published online: 5 January 2012

Abstract

The present paper concerns itself with the insulation characteristics of c-C₄F₈/N₂ gas mixtures and studies the possibility of applying in the gas insulation of power equipments. We aim to use the theoretical framework of the Boltzmann equation to calculate the density-normalized effective ionization coefficients (α–ƞ)/N and transport parameters of c-C₄F₈/N₂ gas mixtures for E/N values from 180 to 550 Td (1 Td = 10⁻¹⁷ V cm²) in the condition of steady-state Townsend (SST) experiment. From the variation curve of (α–ƞ)/N with the c-C₄F₈ mixture ratio k, the limiting field strength (E/N)_lim of the gas mixtures at different gas content is determined. In order to confirm the validity of the results obtained, comparisons with Monte Carlo simulation and experimental data have been performed. It is found that the insulation properties of c-C₄F₈ and N₂ gas mixtures are much better than those of SF₆ and N₂ mixtures for applying in the high voltage apparatus as an insulation medium, especially if we take the global warming potential into account.