Influence of cable processing on the insulation impurity content

One of the principal cause of the initiation and growth of water trees in extruded cable insulation is impurities. This paper presents results on a comparison between impurity content of various insulation and semiconducting shield materials before and after extruded cable processing. Three types of insulation resin, including one conventional crosslinked polyethylene (XLPE) and two water tree retardant XLPE (WTRXLPE), and also two types of conductor shield and insulation shield resins were considered. The cables are of the 28 kV class with aluminum conductor, and one of them with a strandfill material. The measurements were performed by neutron activation on many samples taken from several batch resins and along the cables, and for several elements. The results indicate that the overall resin impurity content is lower than the respective cable component ones, which reveals that the manufacturing process has an influence on the insulation impurity content.