OIL DUCTS AND SOLID INSULATION IN BARRIER SYSTEMS AT HVDC STRESSES

HVDC-transmission is getting more and more important in the global development of remote hydro plants and other energy sources. Yet still there are engineering challenges in terms of specific characteristics of the HVDC insulation. These challenges arise from the fact that the electric AC field distributions are determined by permittivities, DC fields predominantly by conductivities which are inaccurately known and difficult to control. The paper reports on polarity reversal measurements, measurements of conductivities and polarization processes related to materials (Transformerboard, RIP and oil) and HVDC insulation test models consisting of two or three materials. Advanced material models for solid and liquid insulation are derived. Simulations with the new models give good agreement with measurements. Results also show how charge carriers move in oil and influence currents and field strengths. Calculations of transient field strengths require the application of advanced material models, traditional permittivity/conductivity models are not sufficient.