Stress induced electrochemical degradation of the inner semicon layer of XLPE-insulated cables and model samples

A degradation phenomenon of the inner semicon layer of extruded cable insulation occasionally has been observed in different service aged as well as in laboratory aged polymer insulated cables. To investigate this effect, accelerated aging tests on XLPE-insulated cable cores as well as on a new type of model sample (aluminum wires, semicon and XLPE insulation layer) were performed. It is shown that under the influence of an electrolyte and mechanical strain, channel-like structures develop in the semicon of both test objects, and that vented trees are initiated when these structures reach the interface to the insulation. Thus, this type of degradation also is of particular importance for the long time aging behavior and testing procedures of polymer insulated cables. It is demonstrated that the newly developed model sample test arrangement is a valuable tool for the study of aging of insulation systems.