Results from Danish failure statistics for medium voltage XLPE cables

In this paper is given an overall assessment of the condition of the medium voltage XLPE cable population in Denmark. The assessment is based on results from Danish failure statistics. It is concluded that there are no significant signs of an increasing failure rate for dry-cured XLPE cables after a service time of a least 30 years. It is also shown that a large part of the failures take place while the system is operated at elevated phase-to-earth voltage on sound phases due to an earth fault somewhere in the system. An analysis also shows that the systems often are operated with an earth fault in 30 minutes or more before the XLPE cable failure occurs, which is interesting when comparing to recommended test duration for power frequency testing of MV cables.