Non-destructive diagnostic testing of service aged MV XLPE cables

In this paper, results from diagnostic measurements performed on service aged 12 and 24 kV XLPE cables are reported. The main purpose of this work has been to test two non-destructive diagnostic test methods based upon measurements of return voltage and depolarisation current. The actual condition of the cables was determined by laboratory AC breakdown tests and water tree examinations. Both methods detected bad cables containing high density of long vented water trees. However, additional measurements of polarisation currents are needed to detect water trees bridging the insulation. The evaluation criteria need to be further developed, in order to reliably assess the condition of cables with very few but long vented water trees.