Partial Discharge Characterization in a Defect Subjected to HVDC Cable Operating Conditions

In this work, the role of the electric conductivity on the variations in the PD phenomenon in XLPE insulation under dc stress is investigated and demonstrated. To enable this investigation, a new experimental setup simulating the insulating layer of a cable with an embedded air void defect and subjected to a dc stress and temperature has been proposed. The setup consists of two flat specimens connected in series. One of them is heated while the other one, which contains the defect, is kept at ambient temperature. Consequently, the electric fields induced by the externally applied dc stress differ between the two specimens. In this way, a conductivity variation between two dielectric layers is obtained. To facilitate the usage of this method, a new simulation model related to the proposed experimental setup has also been developed. The model is an extension of the three-capacitor model, in which variable resistors are introduced. Both simulation and experimental results indicate that the introduced discrete thermal gradient results in higher conductivity values and enhanced PD activity.