Finite Element Simulation of Ion Currents from Coronating Hvdc Overhead Lines

Abstract: Today's need for transmission capacity is continuously growing. As it is difficult to obtain new rights-of-way, options such as replacing existing ACby DC-lines to maximize the power capability of existing corridors are required. So as to limit land use, overhead transmission lines have been built as multi-circuit AClines on the same structure in many countries. Changing one AC circuit to DC results in transmission lines with AC/DC hybrid towers in such situations. With practically no hybrid AC/DC-line realized worldwide so far, questions concerning the mutual interaction of the different circuits arise, such as superimposed ACand DC-fields intensified with coronagenerated space-charges. In contrast to such hybrid lines, the problem of calculating the ion flow fields of HVDClines has been widely addressed in literature; undoubtedly it can be numerically solved very precisely. However, great uncertainty exists about the boundary conditions, i.e. the amount of ions produced by corona. In the work presented here, the numerical calculation of ion-currents and electric fields of DC-lines by means of a finite-element-method software is reproduced. The novelty is the time-dependence of the simulation, needed for the case of hybrid lines, and boundary conditions yielding results in closer accordance with experimental data found in literature.