Investigation Of Enclosure Burn-Through In Hv Gis Circuit-Breakers Due To Internal Arcing

Modelling of internal arc faults in GIS is a complex and challenging task due to a large number of mutually dependent and highly variable factors, which influence the whole process. This is especially the case in GIS circuit-breakers with high rated short circuit currents, where the risk of internal arcing is much higher due to the presence of the switching arc and contamination of SF₆ gas caused by the arc and by the products of material evaporation. Severe conditions resulting from internal arcing ultimately determine its design limits and must therefore be carefully investigated. This paper focuses on one of the main effects of internal arcing, the enclosure burn-through, and presents a novel analytical approach to the estimation of the enclosure burn-through time, as a result of the combined thermal impact of the arc root, arc motion and mechanical stress due to pressure rise, establishing a relation between the thermodynamic and transport gas characteristics in the arcing chamber, and the time to enclosure burn-through. In order to achieve this, this model was implemented within an enhanced internal arc simulation model, derived from the work of the CIGRÉ working group A3.24. Validation of calculation results of the implemented model was conducted using internal arc withstand tests and available measurements of time to enclosure burn-through.