Some aspects of water tree growth in XLPE insulation exposed to DC voltage

A preliminary study of the influence of the short exposure to DC voltage on the growth of water trees in XLPE cable insulation was performed. The DC voltage of 4U/sub 0/ (where U/sub 0/ is the rms rated voltage) was applied for the duration of 15 minutes prior to AC aging, in one set of samples, and in the middle of AC aging, in another set of identical samples. The results have shown an increase of the average length of water trees grown in samples subjected to DC voltage compared with those not exposed to DC voltage. The result was similar for accelerated aging with the liquid needle electrode method and for plain samples aged under rated voltage.