Insulation Deterioration of Cables as the Downlead for Unibody Composite Pylons Under Lightning Dielectric Barrier Discharge

Cables are suitable as downleads of a composite pylon to provide the ground potential for the shielding wires. However, the impact of lightning-induced plasma on the cross-linked polyethylene (XLPE) layer remains unclear when lightning current passes through the cable downlead. To explore the deterioration mechanism of the cable layer under lightning striking, the XLPE samples are treated with high-frequency plasma for different durations. Subsequently, surface morphology and molecular bonds are characterized, and electrical properties such as dielectric spectroscopy, surface potential decay, trap density, conductivity, and breakdown strength are evaluated. Additionally, a 2-D axisymmetric model of the pylon is developed to analyze the electric field distribution using the finite element method (FEM). The findings demonstrate that thermo-oxidative induced by high-frequency DBD breaks the XLPE chains, resulting in increased dielectric constant and conductivity, shallower traps, and reduced breakdown strength. Moreover, high-frequency DBD not only deteriorates the downlead cable’s insulation properties but also deforms the material and roughens the surface, consequently amplifying the electric field distortion at the cable-air interface and lowering the partial discharge inception voltage on the cable surface. This study elucidates the degradation mechanism of downlead cables under lightning plasma and offers insights into selecting appropriate cable insulation materials.