Analysis of the XLPE Insulation of Distribution Covered Conductors in Brazil

Cross-linked polyethylene (XLPE) has been the most common insulation applied to medium voltage covered conductors (MVCCs) in Brazil. The results of accelerated aging tests carried out at high voltage laboratory of UNIFEI (LAT-EFEI), combining the stresses of heat and voltage to ground aiming at enhancing surface corona activity assays, have identified the early failures in XLPE insulations of the Brazilian MVCCs. The observed failures indicate that complementary studies should be performed to better understand the degradation mechanisms of the MVCCs insulations manufactured in Brazil. In this paper, x-ray photoelectron spectroscopy (XPS), contact angle analysis (CA), photoacoustic spectroscopy (PAS), x-ray diffraction (XRD), and atomic force microscopy (AFM) measurements on samples of five Brazilian national/regional MVCCs are reported. XPS, CA, and PAS analysis indicated that a large variety of oxygen-containing groups associated to the oxidation of the XLPE insulations appear to be related to the manufacturing conditions. AFM analysis indicated that the average surface roughness and topography of the XLPE insulation changed significantly and depend on the selected manufacturer. XRD analysis indicates a strong heterogeneity of crystals nucleation that results into different degrees of crystallinity of the Brazilian MVCCs cables. The results of this work indicate strong evidences of manufacturing defects in the XLPE insulation of Brazilian’s MVCCs. The origin of these defects seems to be inherent to the technology used by manufacturers to the production of the MVCCs. The production-related defects are not detectable by the standard tests as partial discharges or even the standard routine—acceptance power frequency assays routinely used in dielectric compatibility tests at high voltage laboratories.

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