Breakdown and flashover phenomena related to the presence of high absolute water contents in clean and carbonized transformer oil

This paper reports on experimental investigations dealing with the impact of dissolved and disperse water on the breakdown strength of open oil gaps and the flashover behavior of solid/liquid interfaces in a uniform electrical AC field using clean as well as carbonized transformer oils. The measurements reveal that in technically clean oil with disperse water at small gap distances the breakdown strength can for subsequent voltage stresses be significantly higher after the first initiation of a breakdown than during the first readings while for larger gap spacings this effect cannot be noticed. Moreover, it is shown in this contribution that especially for practically relevant long gap distances carbonized oils can exhibit a better electrical strength in the presence of high absolute water contents than clean oil. This finding applies to the breakdown voltage of open oil gaps as well as to the flashover behavior of solid/liquid interfaces.