Electrostatic performance of EHV overhead lines with asymmetrical bundles

Abstract

This study deals with the computation of the electric potential and field in the vicinity of overhead extra high voltage (EHV) power transmission lines with asymmetrical bundles. The values of the electric field at the surface of the bundles as well as at the ground wires and the ground surface will also be obtained. The computer model is based on finding the potential coefficients and then solving a set of complex equations, whose number depends on the number of subconductors per phase, number of 3-phase circuits involved and the number of existing ground wires. The method is applied to a 6-bundle, 750 KV, single circuit line with flat configuration and two ground wires, resulting in a total of 20 complex equations to be solved, in order to get the charge on each of the subconductors and ground wires. The electrostatic potential and the electric field at any point can then be readily found. A comparison of the subconductor field of both symmetrical and asymmetrical bundles is made. It will be shown that the use of asymmetrical bundles will result in a reduction of the surface gradients at the bottom subconductors. At the same time, however, the field at the surface of the other subconductors will increase. This indicates that the suggested application of these asymmetrical lines for reducing the audible noise due to the line corona activity should be investigated more critically. No general statement is possible on this issue, since the numerical values of the subconductor fields will largely depend on the particular geometrical data of the line under consideration.