FTIR microspectroscopy and dielectric analysis of watertrees in XLPE

The phenomenon of watertreeing is investigated by microscopic, IR-spectroscopic and dielectric techniques. Unaged material of the cable has been used for comparison. Several microscopy techniques enabled local observations of unstrained watertrees. Possible chemical changes in parts of the watertrees have been analyzed by FTIR-microspectroscopy. Using the dielectric sensitivity to polar groups, it appears possible to enhance the contribution of watertrees by taking very thin samples. Preceding the dielectric experiments, mechanical and calorimetric thermal analyses have been carried out on samples of the same part of the cable. All samples used in the experiment have been taken from the same 20/12 kV cable. A part of this cable has been kept aside for comparison with the aged samples. Under laboratory conditions watertrees were grown during 24000 hours, the applied electric field strength being ~6 kV/mm, 50 Hz