Computation of corona generated ionic current environment of unipolar UHVDC transmission lines using gas bimolecular collision theory

Abstract

Corona on UHVDC transmission line conductors initiates corona power loss and the inevitable ionic current flow environment at ground level. To limit this substantial flow of ionic current at ground levels, it is necessary to establish an appropriate line design configuration, including the diameter of the line conductor and the height level above the ground. It is a tedious and expensive process to establish this appropriate line design solely based on experimental findings. Hence, the computational based numerical analysis with the support of final experimental validation aids in arriving at a safe and optimal transmission line design dimension configuration. Thus, the ionic current flow environment of UHVDC transmission lines may be characterized by ionized space charge density, ionic current flow, and electrical field distribution. To estimate this ionic current flow, it is necessary to estimate the ionized space charge density in the ionization region, which incorporates the solution of the Poisson's equation. It is intricate to solve Poisson's equation with known boundary conditions: as ionization process depends on the atmospheric parameters also. Multiple computational techniques are developed to estimate the corona generated ionic current environment under the HVDC lines by waiving these atmospheric parameter effects and claims the lack of computational accuracy. In this paper, the unipolar corona equation, usually called Poisson's equation was solved by estimating the space charge ion density using the concept of gas bimolecular collision theory. The gas bimolecular collision theory inculcates the procedure to estimate the collisional reaction rate constant between the gas molecules at given atmospheric temperature and pressure parameters. Therefore, this paper developed a unique equation solution for the estimation of transition of the ionic current magnitudes at known atmospheric temperature and pressure ambient conditions. This unique equation solution prevents the multiple actual testing procedures offers to obtain safe and optimal line design dimension configurations. Multiple experimental studies are carried out up to ± 900 kV to compare the computed results in the outdoor and indoor climatic conditions at the ultra-high voltage laboratory, CPRI. Also, the computed results are compared with the results published in the literature. Based on the comparison of results, the developed computational technique exactly matches the experimental results and claims improved accuracy compared to other computational techniques.