Electrical salt-fog performance of XLPE insulation with different levels of CaCO3

This paper presents a study of the electrical performance of crosslinked polyethylene (XLPE) in salt fog conditions. Specimens of XLPE having 0, 15 and 25% calcium carbonate (CaCO₃) filler, a fixed concentration of 2% carbon black and an additional ultraviolet stabilizer were used. The leakage current and the current pulse counts were monitored as a function of time of exposure to combined electrical stress and salt-fog. Both leakage current and current pulse count were found to increase with increasing test time and with increasing filler concentration. The time to failure of the specimens as a function of the filler concentration was found to increase with increasing filler level. The contact angle decreased, and the surface roughness increased with increasing test time in energized salt fog. A SEM study showed that the surface roughness increased with increasing filler levels, giving an independent confirmation of the results obtained from the surface roughness tester. The EDAX study showed that the intensity count of X-ray of calcium on the surface increased after salt-fog test, indicating that CaCO₃ was not removed from the surface. Both the SEM and EDAX studies confirmed that the number of CaCO₃ particles on the surface increased with increasing filler level. It is suggested this was responsible for the observed larger roughness of the surface, higher resistance to arcing erosion and longer lifetime of XLPE polymer with increasing level of CaCO₃ filler