Test Setup to Investigate Sparkover to Enclosure in HV Disconnector

Gas insulated switchgear (GIS) are widely used in power grids due to their compact design, high reliability even in harsh environmental conditions and their scalability up to ultra-high voltage levels beyond 1000 kV. GIS consists of many components such as circuit breakers, instrument transformers, disconnector switches, etc. For low environmental footprint SF6 alternative gases are used in modern installations, such as CO2/O2/C4-FN mixtures. These allow to maintain a compact size and high reliability. Disconnector switching as for example, bus-charging current switching (BCCS), is an important task in GIS. During BCCS typically multiple pre-strikes or re-strikes occur across its contacts which is a typical behavior of a disconnector. A possible failure mode during such switching is a ground fault which can occur due to sparkover-to-enclosure (StE). This is related to the branching behavior of the pre-strike and re-strike discharges. To investigate the branching behavior in CO2/O2/C4-FN gas mixtures, a representative test setup was built allowing changes of the background electric field. The test setup and the initial results are presented in this contribution.