Highly insulating LDPE compounds at high temperature: the effect of electron-withdrawing PCBM on DC dielectric properties

Abstract

Low-density polyethylene (LDPE) is an excellent insulating material that ensures the safe and reliable operation of high-voltage direct current (HVDC) cables. The insulation properties of LDPE can be improved by doping with voltage stabilizers. Due to its electron-withdrawing property, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) has the potential to be used as a voltage stabilizer to improve the DC insulation performance of LDPE, especially the high temperature insulation performance of cable insulation. Therefore, the impact of PCBM on carrier trap characteristics and micro charge transport at high temperatures and high fields requires further study. LDPE is used as the matrix material to prepare composites with concentrations of 0.5 and 1wt%. The experimental results show that the Weibull characteristic breakdown strength can be increased by 10.5% and the DC electrical conductivity can be reduced by 73.6% at 90 °C, when the PCBM doping concentration is 0.5wt%. These results can be explained by trap characteristics and molecular chain displacement. It reveals that the introduction of PCBM can effectively increase the trap density, which can capture more charge carriers, resulting in a decrease in carrier mobility and electrical conductivity. Quantum chemical calculations indicate that owing to the high electron affinity and low ionization potential of PCBM, it is more prone to attracting and capturing electrons, thereby efficiently absorbing high-energy electron energy. Moreover, PCBM makes the amorphous region more tightly ordered, which manifests as an improvement in crystallinity. It also enhances the friction coefficient of the molecular chain and suppresses the molecular chain displacement in LDPE, which is verified by charge transport and molecular displacement modulated model simulations. This study provides a new method for improving the properties of cable insulation materials.