Investigations concerning the impact of the water content on the flashover strength of different spacer materials in transformer oil

This paper reports on experimental investigations dealing with the impact of different water contents on the electrical strength of oil gaps without and with a solid/liquid interface in a non-uniform electrical field. The measurements at AC stress reveal that an increase of the oil humidity can be combined with a marked reduction of the electrical strength which is especially pronounced for the open oil gap. For the configuration with a parallel solid/liquid interface the influence of the oil humidity on the flashover behavior depends significantly on the surface structure of the spacer material. Moreover it will be shown in the contribution that at negative lightning impulse stress a variation of the water content has a smaller impact on the electrical strength than at AC stress