Analysis of Ion Flow Field Considering Dielectric Film Under HVDC Overhead Transmission Lines

Dielectric films are widely used in agricultural greenhouses. If the greenhouse is near the high-voltage direct current (HVDC) transmission lines, the space charges generated by the corona discharge of the lines will accumulate on the surface of the dielectric film. The surface charges will severly distort the ground-level electric field. In this article, the ion flow field under the HVDC line including the effect of the dielectric film is computed by the Upstream finite-element method (Upstream FEM). The charge accumulation algorithm is proposed to deal with the dielectric film's effect on electric field and space charges. In this algorithm, the adsorption effect of the dielectric film on space charges is equivalent to the accumulation of space charges that move to the film surface nodes, and the film surface charges are corrected according to the tangential component of the electric field on the surface in every iteration. Therefore, the ion flow field near the film can be predicted. To verify the computational method, an experimental platform is set up, and the measured electric field on the ground is consistent with the calculated results. On the basis of the aforementioned algorithm, the influence of the dielectric film under the +800 kV HVDC transmission line on the electric field is analyzed, which is helpful to design the HVDC overhead lines in the vicinity of greenhouses.