We investigated the space charge characteristics in sheet samples under AC field which have water trees developed by using various kinds of electrolytes. The results show that: homo charge was formed around the tip of water trees independent of the electrolyte species; the amount of space charge varied with electrolyte species (among the electrolytes used, ferrous sulfate induced the largest space charge in spite of water tree growth being relatively small); the space charge induced by water trees changes the internal field distribution in the insulation; the harmfulness of specific ions with regard to electrical breakdown cannot be explained simply by the change in the field distribution.
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