Characterization of unaged extruded distribution cables

This paper presents results on a preliminary characterization of several new extruded distribution cable technologies. Most of the power cables are of the 28 kV class and were extruded with different insulation and shield materials. Five types of insulation were used: conventional crosslinked-polyethylene (XLPE); three water tree retardant XLPE (WTRXLPE); and ethylene propylene rubber (EPR). Three types of semiconductive shields were also considered. The characterization comprised water and impurity contents of both the insulation and the shields, degree of crosslinking of the XLPE insulation, thermogravimetry (TGA) to evaluate the filler concentration in EPR and AC breakdown (ACBD) measurements on cable samples. The results show principally that the new technology cable components absorb much more water and that their insulations contain more impurities and their shields less than the conventional ones. Insulation is better crosslinked nowadays. The filler is well distributed in the EPR insulation thickness. XLPE and EPR cables have greater ACBD strength than WTRXLPE ones. A temperature rise of one of the WTRXLPE cable has been observed and attributed to thermal runaway.