SF(6) is the most common filling gas of self-blast circuit breakers due to its superior thermal interruption and dielectric behaviour. By reason of its high global warming potential alternative filling gases are investigated. The use of a non-SF6 filling gas leads to a decreased switching performance due to lower quenching capabilities of the gas. A new approach is evaluated to improve the quenching performance and will be presented in the paper. An additional ablation element consisting of a polymer material can influence the properties of the quenching gas. Therefore, it is implemented in the heating volume of a non-SF(6) self-blast circuit breaker model. The influence of this additional ablation element is investigated using simulation tools and experimental testing. The simulations show the temperature and the composition of the cooling gas. Using the simulation results the influence of the ablation element on the interruption capability can be estimated. These estimations are verified by experiments determining the interruption capability with and without the additional ablation element.

When the contacts of a circuit breaker are opened an electric arc is ignited. In conventional circuit breaker geometries the arc is limited by cylindrical insulating nozzles. The ablation of nozzle material causes a pressure build-up in the heating chamber. A short time before current zero the arc is cooled by the back flow of the quenching gas and the current is interrupted at its zero crossing.Those alternative geometries modify the shape of the arc within a basic test device. The new nozzle geometry is theoretically evaluated and experimentally tested. The general arc behaviour, the pressure inside the nozzle and the mass ablation of the nozzle are investigated. The results are compared with results obtained from previous investigations with conventional nozzle arrangements.

The extinction of the arc is the main process to achieve a successful interruption in self-blast circuit breakers. To attain this, the arc has to be cooled effectively around current zero to withstand the thermal and dielectric stresses. Hence, the cooling behaviour of the arc in a nozzle arrangement is of main interest and can be influenced by the nozzle geometry or shape. Current zero simulations including radiation and turbulence models are performed to evaluate the cooling behaviour of various nozzle arrangements. Using the resistance 200 ns before current zero, an estimation on the cooling performance of the nozzle arrangements is given and discussed.

By coupling of computational fluid dynamics (CFD) simulations of self-blast circuit breakers with a network simulation tool the influence of the surrounding network on the interrupting behaviour can be analysed. In this paper, as an example for possible applications, current zero simulations using a capacitance in parallel to the arcing contacts are presented. It can be observed that the capacitance leads to a decreasing current steepness around current zero. This effect is already obtainable due to the stray capacitance of the breaker itself and is intensified by an increase of capacitance values. Therefore the switching performance of circuit breakers can be improved.