Polarization and Depolarization Current Analysis for Field Degraded Cross Linked Polyethylene Cables

Abstract

Gradual deterioration in polymeric cable insulation system, whether due to continuous applications of high voltages or ageing mechanisms, may lead to eventual cable failure and subsequent electricity disruption. This has led to the growth in need for power utility companies to explore methods to closely monitor and assess the health of cable insulation, through condition-based monitoring (CBM) exercises. Polarization and depolarization current (PDC) analysis is a non-destructive insulation monitoring method that has been widely applied to assess the health of insulation for high voltage equipment especially power transformers. This study proposes to expand on the recent interest in PDC's assessment of cross-linked polyethylene (XLPE) cable insulation degradation. It attempts to investigate the PDC behaviour by performing experimental and simulation studies on in-service field degraded XLPE cables. Comparisons between PDC measurements and simulations for 39 field cables saw matching patterns in terms of categorization by conductivity values. Based on works done by established researchers, a five level PDC based CBM categorization for cable maintenance was proposed, ranging from healthy to moderately degraded to severely degraded cable insulation conditions. Comparison between the proposed and existing PDC based CBM table of a power utility company saw a 76.92% match, suggesting that the technique can be used to ascertain cable insulation degradation.