Einfluss des Elektrodenabbrandes auf das Schaltverhalten eines SF 6-Selbstblasschalters
Due to the fact that high voltage circuit breakers are able to work under short current conditions, too, they are the important security elements in electrical power systems. During the switching operation an electrical arc exists between the switching contacts. The operation method of all circuit breakers is to quench this electrical arc. In SF6 self blast circuit breakers, which present the newest generation of high voltage circuit breakers, the arc burns within the insulating nozzles. The high temperature of the arc leads to an ablation of the nozzle material and to a resulting gas flow on the one hand in the direction of an outlet and on the other hand into a pressure chamber. This gas flow causes a pressure rise in the pressure chamber. Close to current zero the energy input in the insulating nozzle decreases, and thus the ablation decreases too. The stored gas in the pressure chamber is now able to flow backwards towards the arc into the outlet volume. Due to the fact of this intensive gas flow the arc cools down, and the current can be successfully interrupted. A successful interruption in a SF6 circuit breaker does not only depend on the blow gas pressure, but also on the quenching gas composition. During the interrupting process the high temperature of the arc yields to an ablation of the switching contacts, too. This electrode ablation material can also be distributed to the pressure chamber of a SF6 self blast circuit breaker and thereby influences the interrupting behaviour in a negative way. The aim of this thesis is to systematically investigate the influence of the ablated electrode material on the interrupting limits of SF6 self blast circuit breakers. For that purpose a model breaker arrangement is developed to reproduce the behaviour of a self blast circuit breaker. For testing the model breaker arrangement with current densities of real circuit breakers, an appropriate test setup is designed. The investigation method allows measuring the ablation behaviour of the insulating nozzle and of the electrodes, the pressure build up in the pressure chamber and the interrupting behaviour of the model breaker. The concentration of ablated electrode material in the pressure chamber is provided by CFD-simulations, which includes a new electrode erosion model. The electrode vapour contamination of the quenching gas yields to a reduction of the interrupting limit of the model breaker. Compared to the unaffected case, already a relative contamination of around 0.9% reduces the interrupting limit by approximately 20%. This depends not only on the contamination of the quenching gas, but also on the presence of electrode material in the arc zone. Therefore, a more intensive arc cooling by an existing electrode ablation contamination is required. It is demonstrated that the influence of the ablation of the electrodes on the interrupting behaviour can be reduced by an appropriately balanced proportion of the electrode surface to the insulation nozzle surface.
info:eu-repo/classification/ddc/530, Physik, Elektrische Energietechnik, Energietechnik, Schalter, Elektrodenspannung, Abbrand, Schwefelhexafluorid, Selbstblasschalter, Elektrodenabbrand
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