Computation of corona fields associated with unipolar HVDC transmission lines.

摘要

Corona performance is a topic of major significance in the design and operation of overhead hvdc transmission lines. This includes corona power loss and possible environmental effects associated with the corona generated space charge. There exists a need to develop and improve analytical and computational tools that can be used for analyzing and assessing the performance of existing as well as proposed lines.; Previous approaches towards the ionized field solution associated with hvdc corona have usually incorporated assumptions regarding the interaction between the space charge and the resulting electric field, and are thus approximate. The most commonly used simplifications are the Deutsch and Kaptzov assumptions. While the former states that only the magnitude and not the direction of the electric field intensity is affected by corona, the latter assumes that the electric field intensity at the coronating conductor surface is always constant at the onset value.; In this work, analytical and computational methods, in which these assumptions are waived, are developed. The results, thus, obtained would provide the means for assessment of the influence of such assumptions on unipolar dc corona analysis.; An improved analytical method for determination of the unipolar corona voltage-current characteristics is developed. The method is applied initially to the coaxial cylindrical configuration; then extended to the two dimensional geometry of both smooth and stranded conductors above ground. Modified expressions are derived which can be used for accurate assessment of the right-of-way ground level current density profiles.; The solution of the unipolar corona equations is carried out computationally using the finite element method. An iterative algorithm has been developed and applied successfully to the coaxial cylinder as well as the single conductor above ground geometries. The influence of Kaptzov's assumption is studied through computations of the corona power loss and spacial distributions of the field quantities at the conductor surface and over the ground plane and compared with available experimental data. The computational aspects regarding the accuracy and the efficiency of the iterative algorithm are also presented. Finally, conclusions and areas for future research are outlined.