Investigation of electrical treeing mechanisms in polyethylene by means of space encoded nuclear magnetic resonance (NMR) spectroscopy

The interaction of the morphology with the dielectric ageing inside polyethylene (LDPE) insulation systems has been the subject of many investigations. Spatially encoded nuclear magnetic resonance (NMR) spectroscopy offers new aspects of examining the morphology during electrical treeing which is the last phase of the dielectric ageing process. The aged specimens are investigated with NMR-techniques, which are sensitive to morphological changes in the treeing region. Neither cutting nor any other preparation of the samples is necessary so that the aged dielectric material remains unchanged. The aged LDPE samples show a significant change of the measured signal and the derived morphological parameters in the treeing region. This is a consequence of the increased local temperature caused by the partial discharges followed by an accelerated cooling compared to the production process