Graftable voltage stabilizer for enhancing insulation performance of crosslinked polyethylene

With the popular application of alternating current/direct current (AC/DC) hybrid power grid, ultra-high-voltage (UHV) AC/DC cables of long-distance and large-capacity transmission systems have been strongly demanded. Voltage stabilizers are widely used to resist AC electrical tree of cross-linked polyethylene (XLPE) insulation materials, but poor compatibility with polymer matrix limited improvement of DC insulation performance. In this research, the maleic anhydride-modified 2,4-dihydroxybenzophenone as a novel voltage stabilizer 4-(4-benzoyl-3-hydroxyphenoxy)-4-oxobut-2-enoic acid (MDVS) was synthesized to improve the electrical properties of XLPE. The XLPE-g-MDVS with different contents of MDVS was prepared, and both AC electrical properties and DC electrical properties were tested. The results indicate that the modified XLPE retain the characteristic of voltage stabilizer to resist AC electrical tree and improve breakdown strength, and to exhibit excellent DC insulation performance in a wide temperature range. In the comparison with the pristine XLPE, the graft of MDVS can significantly suppress space charge accumulation and decrease DC conductivity. At 70 degrees C, the maximum amount of space charge density of XLPE-g-1.2wt%MDVS is 56.2% lower than that of XLPE, and the DC conductivity decreases by nearly two orders of magnitude. Furthermore, the DC breakdown strength of XLPE-g-1.2wt%MDVS materials exhibit higher than that of the pristine XLPE. In addition to the self-excited energy dissipation of the voltage stabilizer, quantum chemical calculations demonstrated that the improvement of DC performance attributed to the deep traps introduced by MDVS.