Improved Coupled Ion-Flow Field Calculation Method for AC/DC Hybrid Overhead Power Lines

The conversion of multicircuit ac transmission lines to hybrid ac/dc lines is a promising way of substantially increasing transmission capacities in areas where it is difficult to obtain new rights of way. Critical questions related to such a conversion include the impact on the electric fields and ion currents at the ground level, as well as the dc current coupling into the ac phases. In this paper, a new procedure based on the method of characteristics is proposed for solving the fully coupled ion-flow problem. The method does not make the Deutsch assumption and is fast and stable even for high assumed wind speeds. A hybrid tower is simulated with different voltages and wind speeds. The results show the influence of the onset gradient, the dc line voltage, and the wind speed on the current coupling as well as the electric field and ion current density at the ground level. It is shown that the new proposed method can serve as the tool for dimensioning real hybrid towers.