Role of semiconducting compounds in the premature aging of XLPE cable insulation

A clean, crosslinked polyethylene insulating material was sandwiched between two parallel layers of semiconducting shield compound in test cells which simulated extruded medium-voltage cables. Four commercial and four experimental semiconducting compounds were used. Cells were aged at 60 Hz, with a stress of 2.6 kV/mm (65 V/mil) or 3.4 kV/mm (85 V/mil), with one shielding layer exposed to air and the other exposed to distilled, deionized water. The effects of water soluble impurities in the semiconducting compounds on the number, size, and location of water trees developed in the insulation, at the semiconducting shield interfaces, are discussed. The movement of soluble impurities is also addressed.<>