Water trees in cables: generation and detection

The paper describes a new selective detection method for water trees develo ped in consideration of the electrophysical concept of the water treeing ph enomenon. As most of the liquid water is not chemically bound in the water trees it can move out or in, depending on the actual physical conditions su ch as the solubility of water in the surrounding polymer. An increase of th e insulation temperature finally leads to a drying out of water trees and t he water tree correlated loss tangent decreases. This change is very specif ic and characteristically different from that of cable insulations without water trees. Hence the differential variation of loss tangent and capacitan ce in dependence on the temperature can be used as a measure of water tree degradation of polymer insulated medium voltage cables.