Research on Difference between HVDC and HVAC Cable Shielding Materials

Abstract

As DC transmission has been used widely, HVDC and EHVDC Flexible cables are the development direction of power grid in the future. The biggest existing problem of HVDC cable is accumulation of space charges in XLPE insulation and researchers tried to suppress space charges by improving shielding layers which are directly contact with XLPE. Four kinds of HVDC and HVAC cable shielding materials from different manufacturers were selected in this paper. Transmission electron microscope (TEM), thermogravimetric analysis (TGA), volume resistivity and mechanical properties of shielding materials were measured and analyzed. Commercially available insulation material of HVDC cable was selected to prepare samples for space charge tests and the pressure wave propagation (PWP) method was adopted to study space charge injecting effects of shielding materials on XLPE insulation. The results showed that addition of conductive carbon black in HVDC cable shielding materials were lower than that in HVAC cable shielding materials, although volume resistivity of these shielding materials were almost same. Tensile strength and hot set properties of these shielding materials were almost same, but elongation at break of HVDC cable shielding materials were better. HVDC cable shielding materials had a more positive effect on suppressing space charges in XLPE insulation on the basis of lower field enhancement factor (FEF) caused by space charges.