Mechanisms causing nonlinear dielectric response of water treed XLPE cables

The nonlinear dielectric response of water tree degraded XLPE power cable insulation has been found to be an important additional diagnostic criterion. It has been experimentally shown that in case of long water trees the dielectric response increase more than proportional with increasing test voltage above a certain voltage level. In this paper we present possible explanations for the formation of nonlinear dielectric response based upon the mechanical damage theory of water treeing. In order to verify the proposed hypothesis, we have performed electric field computations, water content and microscopy treeing analysis.