Comparative Analysis of Dielectric Properties at Different Radial Positions in Insulation Layer of a 330 KV XLPE Cable Before and After Type Tests

The radial non-uniformity of material properties within the insulation of electric cables can distort the electric field, significantly increasing the likelihood of cable breakdown under prolonged voltage stress and over-voltage conditions. This poses a substantial threat to the operational safety of cable systems. To assess the insulation reliability of 330 kV Cross-linked Polyethylene (XLPE) cables manufactured with domestic insulation materials, this study conducted tests and comparisons on the dielectric properties at different radial positions of the insulation layer before and after the type test. The results indicate a relatively uniform distribution of dielectric properties along the radial direction of the insulation layer. No significant variations were observed in the alternating current (AC) breakdown strength at different radial positions of the insulation layer before and after the type test, with all values exceeding <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$110 \text{kV} / \text{mm}$</tex>. Under industrial frequency conditions, the tangent values of the dielectric loss angle showed differences before and after the test, and the values of inner, middle and outer parts increased <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$15.30 \%, 12.60 \%$</tex>, and 90.04%, respectively, while the values are still small and are all on the order of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10^{-4}$</tex>. Besides, no distinct space charge accumulation was identified within the bulk of the specimens, either before or after the type tests. The results indicate the stability of the dielectric properties of the cable's insulation.