Transformation mechanism of electrical tree to water tree in XLPE cables

In this paper, the experimental phenomenon of transformation of electrical tree to water tree in XLPE cables is reported, the conditions and mechanism of the transformation are discussed. Electrical treeing aging experiment was used to obtain electrical trees in short XLPE cable samples, and water treeing accelerating aging experiment was performed after that, then the transformation phenomenon was discovered in samples by microscopic observation, based on the finite element simulation, and the transformation characteristics were analyzed. The study finds that electrical trees can be initiated in micro defects under the action of over-voltage in XLPE cables, because of the reduction of the electric field strength of the electrical tree tips, and along with moisture invasion, electrical trees become the beginning of water trees to grow; but the growth of water trees weaken the electric field distortion to some extent, and the development of electrical trees is inhibited; When the cables are subjected to over-voltage again, an electrical tree may be initiated at the tip of water tree and leads to the cable insulation failure finally.