An actual XLPE cable was degraded thermally by conductor current heating to simulate its operational condition. Chemical changes of insulating materials for XLPE cable were analyzed in order to investigate degradation mechanism and degradation diagnosis method on an XLPE cable with water-barrier design. DSC, XRD, and FT-IR measurements were applied to the new and the thermal aged cable insulations. From the viewpoint of remaining antioxidant content of insulation, DSC measurement was carried out under oxygen atmosphere to obtain the initial oxidation temperature (IOT). From the result of IOT measurement, remaining antioxidant content of the new cable insulator gradually decreased from outer to inner of the insulator (Fig). After thermal degradation of cable insulator, IOT of the insulating layer decreased although the decreasing behavior of IOT was not same in radial position. XRD and FT-IR were also applied to obtain the crystallinity and changes in the chemical bonding of insulations, respectively. The crystallinity difference between outer and inner parts of the insulator was found in the new cable and decreased with the increasing of crystallinity in the thermally aged cable. Although the antioxidant still remained in the new cable insulator, the evidence of carbonyl bond was found at the FT-IR spectrum of the inner part of new cable insulator. This result would lead the difficulty of quantitative analysis for oxidation of XLPE cable insulators by FT-IR measurement. From these investigations, it was suggested that the chemical changes of actual XLPE cable insulator after thermal degradation should be compared with the radially same position of insulator.

Estimation of chemical changes of actual XLPE cable insulator thermally aged by conductor current

2019 Spring National Meeting

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