Behavior of Eco-Efficient Insulation Mixtures Under Internal-Arc-Like Conditions

C5-fluoroketone (CF
₃
C(O)CF(CF
₃
)
₂
, abbreviated C5-FK) and C4-fluoronitrile [(CF
₃
)
₂
CFCN, abbreviated C4-FN] mixed with background gases such as carbon dioxide, oxygen, or air are used as alternatives to SF
₆
as the insulating and switching medium in high voltage gas insulated switchgear (GIS) due to their good switching and dielectric insulation performance and comparably low global warming potential (GWP). Like SF
₆
, C5-FK and C4-FN are chemically stable inside electrical equipment and non-flammable. Like most complex molecules, they decompose exothermically when exposed to sufficiently high temperatures and do not recombine after decomposing. In this work, we use a custom-built test device to experimentally investigate the conditions and gas compositions under which a decomposition reaction can proceed to completion in C5-FK- and C4-FN-based gas mixtures after being initiated by an electric arc. We also present the related theory. The results show that, for properly selected mixtures, even under extreme failure conditions—internal arc faults—complete decomposition of the C5-FK or C4-FN does not occur.