Test Setup and Methodology for Characterization of Water Trees in Insulation of Extruded MV Cables

Paper in proceeding, 2026

Water treeing degradation is one of the main causes of premature failures in mechanically stressed high voltage polymeric cables. Existing research on water trees has primarily focused on the fundamental performance of raw polymeric materials following the procedures outlined in ASTM D6097 standard. There are scarce research and limited studies focusing on evaluations of actual, manufactured, cable insulation and its resistance to water tree growth. Such investigations are crucial for elucidating changes in material structure and properties throughout cable lifetime. In this work, the developed setup and methodology for the characterization of water trees in insulation samples of real cables are described. The setup included a test cell accommodating up to eight samples, which were simultaneously exposed to the test voltage recommended in the existing guides. In the validation experiments, samples from XLPE and water tree retardant XLPE cables were used. After a subsequent period of testing, the samples were taken out from the test cell for analysis and were treated according to the standard procedure. The patterns and characteristics of water trees were analyzed using an optical microscope. Clear differences in trees properties were observed in the samples corresponding to different cables. The results confirm that the presented test procedure is suitable for assessment of water tree growth in samples taken from real cables.