Electrical properties of oven aged cable insulations based on XLPE and EPR

Sections of EPR and XLPE insulated electric power cables were oven aged at 175°C for a period of eight weeks. After 2, 4 and 8 weeks of aging, pieces of each cable were removed and samples were prepared for measurements of D.C. resistivity, dielectric constant, dielectric loss and A.C. breakdown strength. In each measurement, ASTM procedures, respectively D257, D150 and D149, were followed. All measurements were made at room temperature. Only the dielectric loss and D.C. resistivity changed with this aging. The loss tangent of the EPR remained unchanged at 6.9 × 10⁻³, whereas the loss tangent of the XLPE increased by about an. order of magnitude from its initial value of 2 × 10⁻⁴. The volume D.C. resistivity of the EPR remained nearly unchanged whereas the volume D.C. resistivity of the XLPE decreased by about a factor of six. For both insulations the surface resistivities decreased markedly (by about two orders of magnitude for the XLPE and by a factor of 40 for the EPR).