Dispersion of Carbon Blacks and Their Influence on the Properties of Semiconductive Materials use for High-voltage Power Cables

The cross-linked polyethylene (XLPE) extruded cables have become one of the important equipments in the high-voltage direct current (HVDC) power transmission. Recently, the semiconductive layers as the crucial materials in the XLPE cables developed rapidly. In this study, the semiconductive composites used for high-voltage cables were fabricated by melting blending method via a reciprocating single-screw extruder. The protrusions on the surface of semiconductive layer were scanned through an optical control system (OCS). The influence of carbon black and matrix characteristic as well as the extruding process on the smoothness and electrical properties of the semiconductive materials was discussed. It was found that the addition of lower concentration of carbon black particles with larger oil absorption and higher structure could easily make the formation of excellent conductive networks, which gave rise to the super-smooth surface and better electrical properties. The proper extruding process parameters including the screw configuration and speed as well as the feeding ratio played an important role on reducing the surface impurities of the materials. The prepared semiconductive materials have no protrusions larger than 50 μm and the number of protrusions (30 ~ 50) is less than 10 Num/m ² . Besides, the space charge behavior of the XLPE insulation and semiconductive materials were investigated. The results show that the prepared semiconductive materials could effectively suppress the injection and accumulation of hetero-charges in the XLPE.