Diagnosis of XLPE insulated cables aged under conditions of multiple stresses: thermoelectric and humidity

This work summarizes the main results obtained when subjecting 15 kV XLPE insulated cables to degradation, under conditions of multiple stresses (temperature, voltage, impulses of voltage and humidity). The effect of the degradation was evaluated by analyzing the modifications that appear in the main electric properties and microscopic observations. The results show that the presence of humidity and the application of impulses constitute factors highly degrading while certain thermal cycles may collaborate in the recovery of the properties of the insulation given that the material presents certain regenerative characteristics associated with its own structure and morphology, mainly in the initial stages of the process. Additionally, it was verified that the presence of humidity in the exterior of the cables constitutes the necessary input for the development of water trees and that it leads, in a parallel way, to a reduction of the deformations in the insulation that appear by thermal expansion.