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Large-scale integration of new renewables requires substantial increases of transmission capacity on existing transmission corridors. To limit land use, overhead transmission lines have been widely built as multicircuit lines. On these, changing one ac circuit to dc to increase transmission capacity leads to lines with hybrid ac/dc towers. Since practically no operational experience with such hybrid lines exists to date, questions such as superimposed ac and dc fields intensified by corona-generated space charges arise. In this paper, a method to simulate these ion-flow fields using the discontinuous Galerkin method is for the first time applied to hybrid towers. Ways to considerably reduce the computational effort of the problem are discussed. The results indicate that hybrid lines are feasible in reference to space-charge-related problems. Shielding the ground is possible at the expense of increased coupling between the ac and dc circuits.
Date of Publication: Jan. 2013