Electrochemical degradation or water treeing
In the early 1970s, cable life was significantly shorter than the desired lifetime of 30 years. The service experience in North America was worse than that in Europe - the poor performance being attributed to electrochemical degradation, more commonly known as water treeing. South Africa also experienced a problem with first generation XLPE in the early 1980s. Current experience around the world, and in South Africa, is significantly better. The information in this article is based on several papers presented at the Jicable Conferences held in France.
- There is no test regime which can accurately predict service performance, but a wide range of test methods can be used to compare deterioration by water treeing.
- Any early generation XLPE cables should be scheduled for replacement rather than repair.
- Modern XLPE (after 1986) in South Africa appears to be quite stable. This is largely due to material and process cleanliness.
- Review of current designs could offer some marginal life improvement.
- Rather perform no test than a dc test on aged XLPE cables.
- Water trees are not a problem to utilities. Cable life expectancy is.
- Early generation XLPE cables should be replaced rather than repaired.
- Post 1986, XLPE cable in South Africa has been found to be reliable, this due largely to improvements in materials and manufacturing processes.
‘Jicable’ is the international conference on Insulated Power Cables, that has been hosted in Versailles, France, since 1984.
Tracking the evolution of XLPE and water trees: Jicable, 1984 – 2011
By K Leeburn, CBI-electric: african cables, South Africa
Electricity+Control June 2012 (pgs 4 – 10)