High Power Microwave Breakdown of C4F7N (Novec 4710) Gas Mixtures

Sulfur Hexafluoride’s (SF
6
) high dielectric strength makes it heavily relied upon as a high voltage insulating medium. However, its atmospheric lifetime of 3,200 years and overall high global warming potential has motivated a search for alternatives. One possible alternative, C
4
F
7
N (NOVEC 4710) features a dielectric strength more than twice that of SF
6
yet features an atmospheric lifetime one-hundredth that of SF
6
. Previous research concerning breakdown characteristics of C
4
F
7
N has been primarily limited to long-timescale DC and 60 Hz AC conditions. In this study, the breakdown strength of gas mixtures comprised of 5%, 10%, and 20% C
4
F
7
N in a N
2
or CO
2
background were tested under pulsed, microsecond high power microwave (HPM) conditions over a range of 16 psia to 32 psia at room temperature. To achieve this, a 3 MW S-band (2.85 GHz) high-power magnetron is used to excite a traveling-wave ring resonator, which provides a nominal effective HPM power level of ~20 MW. A stepped impedance transformer is used to further increase the electric field to approximately 160 kV/cm RMS. For comparison, the reported dielectric strength of C
4
F
7
N is compared against the dielectric strength of pure SF
6
.