Dielectric constant of gas in compartment

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

$0.974\cdot p_{gas}$ for 20/80% mix
$1.228\cdot p_{gas}$ for 50/50% mix

with $p_{gas}$ being the gas pressure.

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.

Symbol

$\epsilon_{gas}$

Choices

Id	Gas	Dielectric constant	Dielectric strength
Air	dry air	1.000536	1.0
N2	N₂	1.00058	1.15
SF6	SF₆	1.002	2.5
CO2	CO₂	1.000921	0.95
O2	O₂	1.000495	0.85