Electric Field and Ion Current Environment of HVdc Transmission Lines: Comparison of Calculations and Measurements

The electric field and ion current environment under HVdc transmission lines is an important design consideration. The flux tracing method (FTM) for calculating the ground-level electric field and ion current density distributions is reviewed and the possible errors caused by the use of Deutsch´s assumption in the FTM are estimated. Experimental data obtained under one dc test line and three operating dc transmission lines are compared with calculations made with the FTM. The results show that the most important factor influencing the electric field and ion current distributions is the corona onset gradient of the conductors, or indirectly, the conductor surface roughness factor. The results also show that for practical dc transmission-line configurations, any errors caused by Deutsch´s assumption are quite small compared with the observed variations in experimental data.