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Abstract In medium voltage and high voltage polymeric insulated power cables, operating in a wet environment, a degradation process known as water treeing may occur. Water treeing phenomenon causes the creation of structures called water trees, which are dielectrically weakened areas, in polymer insulation. This phenomenon was first detected in 1969. Research on understanding the mechanism of formation of water trees and means of preventing treeing was initiated worldwide. In spite of the vast amount of literature on this subject, the phenomenon remains unexplained. Presently, water treeing is considered responsible for the majority of failures in underground distribution cables. Water treeing occurs at moderate fields and needs the presence of at least moisture and electric field. Because of the formation and growth of water trees the breakdown strength of the cable insulation is reduced below the rated service voltage. Although many cable manufacturers reduce this problem by a proper cable design, e.g. water tight shields, the uncertainty in the cable lifetime prediction remains. |