Multistress ageing of polyethylene cable insulation

Electrical properties of the polyethylene insulated power cable (LDPE) are substantially affected by moisture penetration from the environment which causes growth of water trees inside the insulation. In an experiment described in this paper, specimens are taken from LDPE insulated medium voltage power cable. The conditions of the laboratory test are similar to the service conditions of the cable system. It has been discovered that effects of moisture action on the cable insulation clearly depend on direction of water penetration. The moisture penetrating from the conductor side gives the largest change of the electrical properties of the cable. It causes the growth of water trees, decrease in the volume resistivity and the positive impulse strength of the insulation. However, it has minor effect on the time to breakdown at the AC test voltage