Development of water tree structure in polyester resin

It is commonly accepted that water trees can be initiated and developed within insulation by the simultaneous action of moisture and alternating electric field. Despite the appreciable achievements and extensive works in the field of water treeing, there is no definite mechanism explaining its initiation and development. In this work, the results of a regular optical examination of the detailed structure of water trees are reported. Various patterns of water droplets are clearly illustrated before the initiation of water trees. The role of water absorption, as a main source of the tree, is not limited to the initial stage of tree formation but it is important for the creation of channels in the later stages. This idea is highlighted via a number of photographs, describing the main stages of the building process of water trees. New evidences on the mechanisms interpreting the development of water trees are introduced. Finally, the relationship between the obtained patterns of water filled voids and the subsequent shapes of water trees is discussed