Breakdown probability of SF6 due to voltage transients [GIS applications]

SF₆ gas has nowadays established itself as a reliable insulating medium for gas-insulated switchgear (GIS). In GIS, however, different kinds of defects may occur, such as protrusions fixed to the conductors. Such defects locally enhance the electric field, which can result in partial discharge (PD) activity or even breakdown. For the application of condition based maintenance (CBM) on GIS, it is important to be able to assess its insulation condition. Aspects which have to be taken into account are sensitive detection of partial discharge activity, identification and location of the discharging source and probability of breakdown. In this paper, the criticality of fixed defects has been investigated. For this purpose, AC voltages have been applied to study the breakdown probabilities under pure AC conditions. Secondly, the defects have been tested with standard lightning impulses (LI) and switching impulses (SI) and finally a bias-test was performed.