Impact of Thickness on Electrical Breakdown Characteristics and Mechanical Properties of XLPE Insulation

This study systematically investigates how insulation thickness affects the electrical and mechanical properties of cross-linked polyethylene (XLPE). We prepared XLPE samples ranging from 30 to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1000 \mu \mathrm{m}$</tex> thick and tested them. The results demonstrate that the short-time breakdown strength exhibits a nonlinear relationship with thickness. Below <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$300 \mu \mathrm{m}$</tex>, the breakdown strength decreases sharply from 212.2 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{kV} / \text{mm}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$67.2 \text{kV} / \text{mm}$</tex>. Above this threshold, the decrease becomes linear and eventually stabilizes. Field simulations of typical defects further indicate that thicker insulation leads to higher defect density and more pronounced local electric field distortion. Mechanically, tensile tests reveal that both fracture strength and elongation at break significantly improve within the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$30-200 \mu \mathrm{m}$</tex> range. However, above <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$200 \mu \mathrm{m}$</tex>, the rate of improvement slows and stabilizes. In contrast, thermal extension tests under load show no significant thickness dependence for either maximum elongation or the permanent deformation rate after cooling. Overall, insulation thicknesses exceeding <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$300 \mu \mathrm{m}$</tex> more accurately represent the material performance observed in actual cable applications. This finding provides essential theoretical and practical guidance for selecting XLPE sample thicknesses in laboratory settings