Innovative Numerical Method for the Determination of the Corona Onset Gradient on HVDC Overhead Transmission Lines

High-voltage direct current transmission plays a central role due to the changing demands on the transmission grid resulting from the energy revolution. Especially with DC corona discharges, a measurable ion current is generated on the ground below the overhead line and can have an impact on the environment. This increases the importance of the qualification and reliable design of equipment exposed to DC voltage. Particularly in the case of bipolar transmission systems, grid operators are faced with new challenges because of the resulting corona losses. Due to the highly non-linear conditions in the simulation of bipolar corona discharges, robust and efficient numerical methods for the calculation of these phenomena are necessary because there is no analytical solution. This publication presents an efficient and generally applicable method for any overhead line configuration for the evaluation of the onset field strength. The main idea is to calculate the general integral conditions of electric discharges numerically using test particles along the electric field lines. For a meaningful analysis of the results, the results for the unipolar case are validated with the empirical Peek equation and it can be shown that the deviations are about 5%.