C₄F₇N and C₄F₇N-CO₂ mixtures are considered as alternatives to SF₆ for use in medium voltage gas insulated switchgear applications (GIS), due to the low global warming potential and good dielectric properties of C₄F₇N. Current work is focused on the calculation of radiative properties (absorption coefficients) of C₄F₇N-CO₂ thermal plasma and computational fluid dynamics (CFD) simulations of free burning C₄F₇N-CO₂ arcs that are stabilized by natural convection. Absorption coefficients of C₄F₇N-CO₂ 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 C₄F₇N-CO₂ in comparison to SF₆ and air are provided and discussed.

<p>Gas mixtures containing fluoro-nitriles C&lt;sub&gt;4&lt;/sub&gt;F&lt;sub&gt;7&lt;/sub&gt;N or fluoro-ketones C&lt;sub&gt;5&lt;/sub&gt;F&lt;sub&gt;10&lt;/sub&gt;O as minority components (&lt;20%) have been identified as promising alternatives to SF&lt;sub&gt;6&lt;/sub&gt; in medium voltage gas-insulated switchgear (GIS) applications, because of their low Global Warming Potential together with their dielectric strength values being comparable to SF&lt;sub&gt;6&lt;/sub&gt;. The buffer gases in such fluoro-nitrile or fluoro-ketone based gas mixtures are usually N&lt;sub&gt;2&lt;/sub&gt;, O&lt;sub&gt;2&lt;/sub&gt;, CO&lt;sub&gt;2&lt;/sub&gt;, or air. In this contribution, we provide calculation results of transport properties, assuming local thermodynamic equilibrium (LTE), of thermal plasma containing following gas mixtures: C&lt;sub&gt;4&lt;/sub&gt;F&lt;sub&gt;7&lt;/sub&gt;N-CO&lt;sub&gt;2&lt;/sub&gt; and C&lt;sub&gt;4&lt;/sub&gt;F&lt;sub&gt;7&lt;/sub&gt;N-CO&lt;sub&gt;2&lt;/sub&gt;-O&lt;sub&gt;2&lt;/sub&gt;. The modifications in the thermodynamic and transport properties upon the addition of oxygen to the C&lt;sub&gt;4&lt;/sub&gt;F&lt;sub&gt;7&lt;/sub&gt;N-CO&lt;sub&gt;2&lt;/sub&gt; mixtures in the temperature range 300&amp;thinsp;K-30&amp;thinsp;kK at 1&amp;thinsp;bar are provided and discussed. These properties have been utilized to calculate the plasma temperature profile for a free-burning arc in a companion paper.</p>

Abstract. Radiative heat transfer is a major heat loss mechanism in thermal plasmas generated during arc flashes/faults in switchgear applications or during high current interruption in low voltage circuit breakers. A common way to calculate the radiation balance is by means of approximate non-gray radiation models like P1 or discrete ordinates (DOM), where the frequency dependent absorption and emission are described in a number of frequency intervals (bands) using a constant absorption coefficient in each band. Current work is focused on finding the optimal number of bands as well as band interval boundaries that provide a reasonable level of accuracy in comparison to a full spectral solution. An optimization procedure has been applied to different SF 6 and copper vapor gas mixtures for an assumed temperature profile. Radiation model results using optimized band averaged absorption coefficients as well as spectral values are provided and discussed for the exemplary temperature profile.

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