IN SEARCH OF FINAL BREAKDOWN IN WATER-TREE DEGRADED XLPE

抄録

With an objective to study the final dielectric breakdown process by which a water tree converts into an electrical tree, characterized (density, impurity and water content, water tree density, oxidation) crosslinked polyethylene (XLPE) samples taken from two 28kV field-aged cables were aged at 10kV/mm, 60Hz electric stress in the presence of 0.05 or 1M NaCl electrolyte at 22-23°C. The results indicate that water tree growth saturated as a function of test time and was only slightly. influenced by NaCI concentration. Also it was found that the length of laboratory grown water trees was not affected by the presence of field grown water trees. The AC breakdown (ACBD) strength was influenced to a certain extent by the length of laboratory grown water trees. The aging conditions have led to the growth of non-conductive water trees which have almost no electric field enhancement at their tips and subsequently with no possibility to generate pre-breakdowns or electrical trees. Other mechanisms such as surge or lightning impulses, or partial discharges at operating voltage must be considered in order to effect the conversion of water trees to electrical trees.