tree experiments performed on samples of commercially
available 6/10 kV XLPE insulated cables. The main purpose
of the investigation was to examine possible water tree
enhancement, due to mechanical tension of the insulation.
During water tree ageing at 50 Hz AC voltage of 14 kV
(Emax=5.2 kV/mm) the cable samples were mechanically
stretched at 1%, using both static and dynamic mechanical
load varying at 0.1 Hz. In addition thermal treatment
indicated a total residual longitudinal mechanical strains of
6% , frozen in during the manufacturing process.
Both the density and growth rate of vented and bow-tie
water trees was found to increase with increasing applied
mechanical tension. During non-strained thermal treatment
the axial length of cables was reduced by about 6%.
The low density of vented trees originating from the outer
insulation screen supports the assumption that frozen in
compressive stresses at the outer insulation surface may
balance the effect of the applied strain.