The breakdown electrical field for SF6+N2 mixtures was studied in 'A Study on Dielectric Strength and Insulation Property of SF6/N2 Mixtures for GIS' by Su-Youl Woo et al. (2012). They came up with the formulas for breakdown E-field (p.u.) being
The dielectric strength is relative to air with dry air having a dielectric strength of 3 kV/mm and SF6 one of < 8 kV/mm.
|Id||Gas||Dielectric constant||Dielectric strength|