Diffusion of blocked strand material in the insulation of extruded cables

This paper presents results on the impurity content of the insulation and shield of medium voltage extruded cables having a blocked strand material, before and after simulated field extreme thermal conditions. Cables are of the 15 and 28 kV class, with aluminum compact filled conductor, water tree retardant crosslinked polyethylene (WTRXLPE) insulated, extra-clean shields, and were made by three different cable manufacturers. Two cable conditioning were used: conductor inductive heating at 90°C constant for more than 60 days, and then cycling up to 130°C, 8 hours/ON and 16 hours/OFF, for 14 days. The impurity content measurements were performed by neutron activation analysis on ribbon samples peeled off the cables. The results indicate that the insulation and shields impurity contents are not much influenced by the presence of the block strand material in the cables after manufacturing and laboratory aging.