Endurance testing of XLPE cable insulation at extra high AC voltages

Crosslinked polyethylene (XLPE) is used as insulation material in high voltage cables for voltages up to 275 kV. These cables are operating with an electrical field stress of approximately 10-12 kV/mm. To produce cables with an extruded insulation system for the 400-500 kV voltage range, an increase of the operating field stress to the range of 15-20 kV/mm is necessary. This is because of production line limitations, cable weight, dimension and cost. The main emphasis of this report is therefore on the capability of XLPE to operate satisfactorily for long time at extra high electric stresses. The authors focus on reduction of impulse breakdown strength, which is known to be an important measure of the lifetime reduction.