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.

Simulation methods are routinely applied in the design and development process of power distribution devices. Arcing phenomena that occur during switching operations or fault events are modeled to optimize device performance and gain deeper insights into the behavior that testing cannot easily provide. In this contribution, some applications are presented in detail. The first example describes the distribution of debris that is generated inside a molded case circuit breaker (MCCB) during short-circuit interruption. A model is used to analyze the debris transport and to derive a solution to address issues caused by the debris. Second application example is a cooling device for hot plasma gases vented by circuit breakers. A model driven design process helps to define the device dimensions to achieve a safe temperature level of the exhaust gases. The third example deals with short-circuit behavior of a hollow core high voltage surge arrester, comparing model and experimental results.

<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>