Study on water treeing retardant XLPE insulations

Water-tree-retardant XLPE was evaluated using two types of polyethylene: a polymer-blend XLPE containing blends of ethylene copolymer having a polar group, and VLDPE (very low density polyethylene), which is a novel grade of polyethylene. While the polymer blend XLPE permitted cable extrusion under the same conditions as in the case of conventional XLPE because its base material is conventional XLPE, the VLDPE was so difficult to extrude that the extruding conditions had to be modified. The water-tree acceleration test (10 kV, 1 kHz, conductor and inside of jacket poured with water, 90°C heat cycle) using the cable samples (insulation thickness of 3 mm) demonstrated a water-tree retardant effect in favor of the polymer blend XLPE, that is, about 1/30 of the water-tree (bow-tie tree) generation and 1/2 of the maximum length of the water tree as compared with conventional XLPE. Furthermore, the test revealed no generation of bow-tie trees in the VLDPE, demonstrating an almost complete water-tree retardant effect