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Residual life assessment of MV & HV cable systems
What is the cost of replacing a cable system prematurely?
The technical service life of high voltage cables is estimated to be 30 years. Nevertheless, the experience figures show that a large proportion of the cable systems have a significantly longer service life. Results from various studies indicate that one can expect a lifespan somewhere between 40 and 80 years.
Every cable system is exposed to a number of different environmental and operational stressors that can accelerate aging. In other words, there will be large variations in the actual service life on various facilities.
A non-destructive cable diagnosis provides a good overview of the technical condition of the cable system. With this knowledge, the cable system can be completely recovered or reveal that segments of the cable, joints or terminations should be replaced to avoid breakdowns.
XLPE cable from 1984 buried in a very wet environment showed no signs of watertreeing
Neka recently carried out a non-destructive cable diagnosis on a 1.3 km long 22 kV cable from 1984. The cable route ran along a river and considering the cable type's water tree issues, there was great voltage to the condition of the cable.
The cable diagnosis consists of:
(1) Offline PD measurement: Detects weak points in cable insulation, joints or terminations
(2) Offline TD measurement: Detects insulation aging and water tree aging.
The results from the cable diagnosis indicate no insulation failure and low insulation aging. Based on this, there is nothing to indicate that the cable in question should be replaced even if it has passed the technical service life.
