High‐Field Charge Transport Mechanisms in Crosslinked Polyethylene: The Role of Crosslinking‐Induced Structural Disorder

Abstract

Crosslinked polyethylene (XLPE) is the dominant insulation for high‐voltage direct current (HVDC) cables; however, its long‐term performance is influenced by charge transport and trapping behavior. In this work, the effect of crosslinking degree ( C GEL ) on the conduction mechanism and charge trapping characteristics of XLPE was systematically investigated by controlling the dicumyl peroxide (DCP) content from 1.4 to 2.0 phr. Gel content analysis confirmed that increasing DCP increased the C GEL from 72.4%~86.7%, while X‐ray diffraction revealed enhanced crystalline disorder and reduced crystallite size with increasing crosslinking. Current density measurements demonstrated space‐charge‐limited current (SCLC) behavior across all samples. Classical Poole‐Frenkel and Schottky analysis exhibited apparent linear relationships with electric field; however, the extracted dynamic relative permittivity ( ε r ) values were on the order of 10 6 ~10 7 , far exceeding the intrinsic dielectric constant of XLPE ( ε r  = 2.3), indicating that neither mechanism adequately describes the conduction process. In contrast, the hopping conduction model provided excellent agreement with the experimental data over a wide temperature range (30°C~90°C) and electric field range (10~60 kV/mm), confirming hopping transport as the dominant high‐field conduction mechanism. Surface potential decay reveals a strong dependence of charge trapping behavior of C GEL . The optimally crosslinked sample (XLPE‐2) exhibited the lowest trap density ( N t  = 4.48 × 10 20  eV −2  m −3 ), the shallowest trap energy level ( E t  = 0.964 eV), and the fastest charge dissipation, whereas excessive crosslinking increased trap density and depth. These findings establish a relationship between crosslinking degree, structural disorder, charge trapping characteristics, and conduction behavior, providing important guidance for the optimization of XLPE insulation for HVDC cable applications.