Space-Time Pattern of Ion Flow Under AC/DC Hybrid Overhead Lines and Its Application

Building HVdc and HVac transmission lines in the same corridor or even on the same tower is an attractive way to extend electricity transport capacity where getting the new right of way is difficult. The resulting hybrid lines produce a new corona performance, such as ground-level hybrid electric field and ion current density, which are quite different from those of pure ac or dc lines. In this paper, inherent space-time pattern and characteristics of the information propagation in Lagrangian description are presented for the ion transport problem, that is, the ion density at a certain point has a direct relationship with its drift time. Based on this, the theoretical explanation is provided for the decoupling algorithm, by which the ground-level dc component can be solved with the ac conductors assumed to be at zero potential and vice versa. The simulation results show that the sinusoidal ac field has negligible influence on the dc ion drift time from conductor surface to ground, whereas stationary electric field generated by the grounded ac lines has a dominant effect. Therefore, ac energization has a rather low impact on ground-level quantities and the simplification of grounded ac conductors is quite reasonable.