Influence factors analysis of ionized field characteristics of Zhangbei ±500kV flexible direct current transmission lines

The ionized field should be controlled in order to insure the environmental friendliness of high voltage direct current (HVDC) transmission lines. Different with traditional HVDC transmission lines, the metal return lines is first employed in Zhangbei ±500kV flexible HVDC lines. In this paper, the characteristics of ionized field with and without metal return lines are calculated on the basis of numerical method with Deutsch’s assumption. The influence factors, i.e. roughness coefficient, distance between metal return line and height of the metal return line, are analysed in detail. The results show that the metal return lines will have a shield effect on the ionized field on the ground. The distribution of ionized field is nearly independent on the height of metal return line. The shielding effect of the metal return line mainly contributes to the projection position of the metal return line. The presented results can give instructions for the design and control of the ionized field level of flexible HVDC lines with metal return lines.