Vergleich von Strahlungs- und Turbulenzmodellen zur Modellierung von Lichtbögen in SF -6-Selbstblasleistungsschaltern

摘要

High voltage circuit breakers are important elements in the transfer of energy between the power plant and the consumer. Circuit breakers of the third generation, so-called SF6-selfblast-circuit-breakers, use the energy set free by the switching arc in case of a fault to build up the pressure necessary for extinguishing the electric arc. Advancing the development and the optimization of circuit breakers requires state-of-the-art simulation tools which grasp the complex interactions between the switching arc, radiation, ablation and gas flow. In the present thesis a model is presented which – due to its physics-based modeling – can be used to answer a wider range of different questions about SF6-arcs in comparison with preceding papers, in which the experiment-based two-zone-model for ablation-controlled electric arcs and selfblast-circuit-breakers was deduced and used. The electric arc is modelled by Ohmic heat, convection, heat conduction and radiation included in the energy balance equation and represents a control circuit which controls its temperature profile by specifying only the current. The development of this model is based on a comparison of different radiation models and on the simulation of a SF6-model circuit breaker with experimental data. The choice of a suitable radiation model is the essential goal of this thesis. For the simulation of ablation controlled electric arcs both the radiation losses in the arc as well as the radiation flow on the surface of the nozzle, which is necessary for the PTFE ablation, must be established. It turns out that within the given framework the P1 model, which requires solving additional differential equations, is clearly better suited for a CFD simulation than the method of the partial characteristics or the Monte Carlo model, which require a beam-pursuing process in the solution space, or the net emissions coefficient, which requires the use of correction factors. The electric arc model was validated with the simulation of wall-stabilized electric arcs, for which the core temperatures can be calculated in good agreement with the experiment. Experimental data for electric arcs in a PTFE nozzle are used to investigate ablation-controlled arcs. Here, not only the pressure build-up is compared, but also the structure of the arc. A suitable turbulence model is chosen with the help of an axially blasted arc for different amperages and by comparing temperature profiles. It turns out that the measured temperature profiles can only be calculated with a reasonable degree of exactness with the help of the SST model. The entire model is validated by virtue of measurements at a model circuit breaker, and the limits of the model are shown.