Radiative Properties and Numerical Modeling of C4F7N-CO2-O2 Thermal Plasma

Abstract

C<sub>4</sub>F<sub>7</sub>N and C<sub>4</sub>F<sub>7</sub>N-CO<sub>2</sub> mixtures are considered as alternatives to SF<sub>6</sub> for use in medium voltage gas insulated switchgear applications (GIS), due to the low global warming potential and good dielectric properties of C<sub>4</sub>F<sub>7</sub>N. Current work is focused on the calculation of radiative properties (absorption coefficients) of C<sub>4</sub>F<sub>7</sub>N-CO<sub>2</sub> thermal plasma and computational fluid dynamics (CFD) simulations of free burning C<sub>4</sub>F<sub>7</sub>N-CO<sub>2</sub> arcs that are stabilized by natural convection. Absorption coefficients of C<sub>4</sub>F<sub>7</sub>N-CO<sub>2</sub> plasma used in the CFD model are derived from spectral absorption coefficients by Planck averaging. An optimization procedure has been applied to find the optimal number of spectral bands as well as spectral band interval boundaries. Radiation and flow model results for C<sub>4</sub>F<sub>7</sub>N-CO<sub>2</sub> in comparison to SF<sub>6</sub> and air are provided and discussed.

Transport and radiation properties of C4F7N-CO2 gas mixtures with added oxygen

“…In these advanced models, the radiation transfer equation is solved for a limited number of bands, which provides reasonable accuracy while drastically reducing the overall computational effort. Our earlier work [19] provided further details regarding the calculation of the optimized band-averaged values of the Planck mean absorption coefficients. The divergence of the radiative flux (DRF) is a part of the arc plasma energy balance, expressed here as power per volume per body angle.…”

“…According to the IEC 62271-200 standard, the maximum allowable absolute pressure within an MV-GIS is 4 bars. We have presented a few preliminary results for C 4 F 7 N-CO 2 mixtures at 1 bar in our earlier work [18,19]. These properties are necessary for performing thermal plasma modeling of SF 6 alternative gas mixtures in both simple academic geometries and complicated GIS switchgear.…”

“…(1) The LTE assumption might not be strictly valid close to the electrode walls and arc fringes, and (2) the accuracy of the model results are dependent on the accuracy of thermodynamic, transport and radiation properties. We would again refer the readers to our previous works [19,66] for additional CFD model related details.…”