Calculation of pressure rise in electrical installations due to internal arcs considering SF 6-air mixtures and arc energy absorbers

摘要

Internal arcs cause sudden temperature and thus pressure increase in electrical installations, which may endanger personnel, installation rooms or buildings as well as the security of power supply. Overpressure can be controlled by e.g. relief openings. The proof of internal arc withstand is usually performed by tests in high power laboratories or by pressure calculations especially in cases, where tests are impractical. Nowadays, there exist reliable pressure calculation methods, which are able to determine pressure rise due to internal arcing. For practical applications, two methods are of importance, the CFD calculation method, which provides spatially resolved results, and the standard calculation method providing spatially averaged results. However, the application range of these methods is limited. This is especially true if SF6-air mixtures have to be considered (SF6-insulated switchgear) or if arc energy absorbers are installed. In this thesis, both effects, which are important for pressure rise in the case of internal arcing, are treated. The key point of modelling SF6-air mixture flows of changing composition is the generation and treatment of reliable gas data. A further main focus is the modelling of arc energy absorbers. For this purpose, heat absorption and flow resistance are considered first of all separately. In order to describe both effects simultaneously, existing and improved model approaches are evaluated and appropriate model combinations are proposed. SF6-air mixtures and the effect of arc absorbers are implemented in both calculation methods for the first time with reliable gas data. Special care is taken on data handling and modification of the equation systems. The inclusion of the effect of absorbers is achieved by considering heat sinks and friction forces. Based on the standard calculation method, a versatile improved software tool (Improved Standard Calculation Method) for the determination of pressure developments is developed, which is fast, easy to handle, able to treat SF6-air mixtures and absorbers based on reliable gas data, platform independent and including any number of rooms and openings. Both calculation methods are validated by comparing measurements in different arrangements with calculation results.