| A topic of great significance in design and operation of overhead DC transmission lines is the phenomenon of corona. This encompasses such traditional, yet continually important aspects as power loss and interference caused by corona, as well as more recent questions regarding distributions of corona-generated ions (resulting from ionization processes), and of electric field intensities and current densities at ground level.; Analytical and numerical approaches to the solution of the corona problem on overhead HVDC lines have invariably relied upon a variety of simplifying assumptions regarding natural (equilibrium) conditions and interactions prevailing between corona-produced space charge and resulting electric field. As an outcome, answers obtained have been only approximate.; One of the simplifications most commonly employed, referred to in this thesis as Deutsch's assumption, states that only the magnitude, but not the direction, of the electric field intensity vector is influenced by corona. In this thesis, this approximation, as well as others appearing in literature, is waived. Hence, a true picture of the interaction between space charge and field, is derived. The thrust of the work is concentrated on the case of unipolar DC corona on a single conductor above ground.; Solution to the corona problem, carried out in this thesis, consists of several steps. Physical and mathematical aspects of unipolar DC ionized fields are presented. Simplified solution methods, developed and published since the early work of Townsend in 1914, are reviewed and placed in perspective of their inherent approximations. The mathematical models of corona are discussed in detail, both with regard to computational (numerical) features, and in terms of physical insight into, and interpretation of the ionized-field equations. This leads to construction of computational Algorithms for solution of the unipolar DC corona problem. Most importantly, simplifying assumptions, with respect to spacial distributions of charge and electric field, are not employed.; The approach to solving the second-order differential equations comprising the mathematical models of corona, is the Variational Finite Element Method (VFEM). The VFEM is described and some difficulties discovered, of numerical nature only and peculiar to certain details of the VFEM, are discussed. Computational procedures proposed, developed originally for coaxial cylinders, are successfully applied to the geometry of a conductor above ground.; The main results of the thesis, for reduced-scale lines, are presented as equipotential maps of the electric field, as graphs of distributions of field quantities and as computations of power loss. The influence of corona upon equipotential curves, hence upon the electric field intensity vector, is made clearly evident. This permits, for the first time, proper interpretation and evaluation of Deutsch's and other assumptions, and better insight into the phenomenon of ionized fields.; The conclusions of the thesis state that, for purposes of engineering analysis and design of overhead unipolar DC transmission lines, approximate approaches--particularly those combining in good proportion the simplicity and the accuracy--should be quite adequate. |
