Diagnostic of field aged cables and accessories by time-domain dielectric spectroscopy

Dielectric Spectroscopy was used as a diagnostic tool to assess the degradation state of field-aged extruded cables retrieved from underground networks. A high voltage time-domain spectrometer was used to measure the time-domain dielectric response of unaged and field-aged cables up to 25 kV. In addition to time-domain dielectric spectroscopy (TDDS), high voltage frequency-domain dielectric spectroscopy (FDDS) was performed for the sake of comparison. Cables were characterized with respect to water content and water tree density. ACBD strength measurements were also performed on some of the cable samples in order to estimate their state of degradation. Field-aged and unaged cable accessories were also characterized with respect to their dielectric response in order to account for their effect on real line diagnostic.