cable insulation with a DC voltage with superimposed
transients. The effect these transients have on the
performance of the polymeric cable insulation is yet not
clear. The main purpose of this work has been to
investigate the effect of such transients on XLPE cable
insulation when exposed to moisture.
Laboratory experiments were performed on Rogowski
shaped test objects with an insulation thickness of 1.3
mm. At one of the semi-conductors, 20 sodium chloride
(NaCl) particles were placed in order to facilitate
initiation of vented water trees. The test objects were
conditioned with water at 20 °C for two months
ensuring saturation of water inside the insulation system
The test objects were aged with an AC voltage
simulating the transients from a HVDC converter.
Experiments were performed using the AC voltage with
and without DC stress to investigate the influence of the
DC level on the water tree growth.
The ageing was done at 30 °C.
Test objects were taken out and inspected for water tree
growth regularly. The results show a rapid ageing
caused by water treeing when exposed to the DC
voltage overlaid AC voltage with a frequency of 5 kHz
and a pure AC voltage stress.