Deterioration of Water-Immersed Polyethylene-Coated Wire by Treeing

Although some reports of the water-resisting life of polyethylene-insulated wires have been made, studies of mechanism of the deterioration phenomenon have been scarcely reported. In this paper, it is pointed out that a major cause of the deterioration of polyethylene-coated wire in water is the occurrence of the "treeing" phenomena. An accelerated deterioration test through the use of high-frequency voltage has been developed. Using this accelerated test, experiments were conducted on the deterioration phenomenon of insulating wires under various conditions. The causes of tree generation were elucidated and a new type of insulating wires was developed. It has been discovered that when the polyethylene-insulated wire is immersed in water and voltage is applied (as occurs in a submersible pump) treeing will occur at extremely low voltages and is sensitive to the copper in the conductor. A metal barrier over the conductor greatly increases the insulation life owing to the effect of double layers.