Statistical behaviour of GIS and GIL insulations

The statistical breakdown behaviour of SF/sub 6/ and N/sub 2//SF/sub 6/ insulated equipment depends on the electrode geometry, the electrode material and changing conditions at the electrode surface due to previous oxidation and breakdowns. In this context investigations were undertaken with positive lightning impulse voltage and pure SF/sub 6/ in a revolvable wheel-plane gap. Comparing these test results with previous test results without rotation the breakdown distribution function is steeper. This effect is explained by a charge accumulation on the alumina layer. The test results can be used for insulation co-ordination of GIS and GIL.