Influence of the semiconductive material on space charge build-up in extruded HVDC cables

The paper discuss means to reduce the space charge accumulation in polymeric HVDC cables by optimising the composition of the semiconductive material used in the conductor and insulation screens. A semiconductive material contains a polymer, sufficient content of conductive carbon black to attain electrical conductivity, an antioxidant for retardation of the thermo-oxidative degradation and finally a peroxide to allow crosslinking to gain improved mechanical properties. We are reporting that the semiconductive screens will significantly influence the accumulation of space charges in the insulating layer. The effect of the various components of the semiconductive material is carefully studied. The main conclusion is that both the type of polymer and type of carbon black are important for the electrical properties. It is revealed that superior space charge properties are obtained by the use of acetylene carbon black instead of conventional furnace carbon black, and, above all, by the use of a non-polar polymer instead of a conventional copolymer-based polymer. The study has been conducted on press-moulded plaques with semiconductive electrodes on both sides. The space charge profiles have been obtained using a PEA (pulsed-electro-acoustic) system.