The ongoing debate on climate change and emission restrictions for greenhouse gases also forces the search for SF6 alternatives (sulphur hexafluoride) in the energy transmission and distribution sector. Hence several challenges for the asset manufactures result as changing the insulating medium implies a redesign of the switchgear and its components. Here one effect in gas insulated switchgear is the reduction of the dielectric strength in case of contamination of the gas compartments with metal particles. In this paper the dielectric strength of the promising SF6 substitute CO2 (carbon dioxide) and its mixtures with non-toxic gases under particle contamination is investigated. For this purpose an arrangement designed according to a real gas insulated switchgear is used. From the comparison of the experimental investigations results a statement on the dielectric strength of CO2 under non-uniform field conditions and on the enhancement of this dielectric strength by the admixture of additional gaseous components. These results can serve as a means for the dielectric design of a SF6-free gas insulated switchgear.

Method for diagnosing a switch puffer (1), wherein the method comprises: - triggering a switching switch puffer (1) to trigger a pressure wave in a gas filling switch puffer ( 1), - detecting a pressure development (41, 42; 51, 52; 56, 57; 61-64) time dependent on at least one switch area puffer (1) in response to the switching process, and - determining a state of a nozzle erosion (11) switch puffer (1), which erodes in a switching under load for blowing an arc switching with the filling gas, in which state erosion nozzle (11) is determined by the development of pressure (41, 42; 51, 52; 56, 57; 61-64) time dependent.

Since many years the development of gas circuit breakers is surrounded by computational fluid dynamics simulations. The physical models of these simulations are often crosschecked by experiments. One of the aspects related to the interruption capability of the circuit breaker is the spatial arc resistance distribution of the arc. However, it could not yet be determined by experiments as all known methods have either an influence on the arc and the gas flow or can only be applied at special conditions. The aim of the ongoing research project is the development of a new method to determine the spatial arc resistance distribution of a quenched switching arc.

The most common filling gas of self-blast circuit breakers is SF6. If one wants to replace it by a substitute it has to be investigated whether the physical models which have been derived and proofed for SF6-filled circuit breakers are valid for non-SF6 breakers as well. Here the influence of the pressure of the blowing gas on the thermal interruption capability is of interest. First a non-SF6 self-blast circuit breaker model is designed by means of CFD-Simulations. Second this circuit breaker model is used to determine the thermal interruption capability at different blow gas pressures. From these results the validity of the relationship between the blow gas pressure and the thermal interruption capability can be derived.

In self-blast circuit breakers the material ablating from cylindrically shaped nozzles causes a pressure build-up inside a heating volume. Shortly before current zero the decreasing pressure inside the insulating nozzles leads to a backflow of gas from the heating volume which cools the arc. Circuit breaker prototypes are used to focus on the main influencing parameters as for example the pressure build-up and the amount of ablated nozzle material. In this paper the influence of alternative nozzle geometries on the switching behaviour of a circuit breaker prototype is investigated. The focus is on nozzle geometries with an additional ablation element. The results are compared to the results of previous investigations with conventionally shaped nozzles as well as to the results of CFD-simulations (computational fluid dynamics).

Circuit breakers are important elements of the electric power supply system. Due to the contact separation during the switch-off process an electric arc is ignited within the circuit breaker. A forced flow of the insulating quenching gas medium is used to cool the arc influencing its conductivity. Only if the power dissipation due to cooling exceeds the electrical power input by ohmic heating, the arc is extinguished and the current is successfully interrupted in its natural zero crossing (CZ). As the impact of the cooling by the quenching gas on the resistance of the arc is considered crucial for the success of the switch-off process, the spatial distribution of the resistance is of high importance for the assessment of a circuit breakers performance. Research and development projects related to circuit breakers more and more often use computational fluid dynamics (CFD) simulations. The implemented simulation models have to be be verified by adequate experiments. This paper deals with the influence of the simulation model on the simulated spatial arc resistance distribution near current zero. Different approaches for modelling the chaotic and turbulent phenomena of the arc are introduced and their results are compared with values measured in experiments. Here the turbulence model is of main interest. On the one hand the investigations show a good agreement between simulative and experimental results for the total arcing voltage when using adequate models. On the other hand these turbulence models lead to differences in the calculated spatial arc resistance distributions – which cannot be verified by experiments so far.

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.