Round wires versus trapezoidal wires in ACSR and ACSS overhead power transmission conductors.

Abstract

In overhead power transmission, the greatest need is to transmit maximum power with reduced losses, minor environmental impact and minimal infrastructure degradation, at low costs. The conductor material and shape (form) are deemed to be amongst the main determinants for optimal power transfer. Various forms such as trapezoidal (TW), aero-z (Z) and round-wires (RW) have been developed for bare overhead power transmission conductors. About 80 % of power utilities around the globe, including South Africa, use Aluminium Conductor Steel reinforced (ACSR) conductors formed in RW for power transmission lines at voltages above 132 kV. Interest is also shown by some power utilities to use High Temperature Low Sag (HTLS) conductors, mostly Aluminium Conductor Steel Supported (ACSS) for short transmission lines. In this study electrical performances of ACSR and ACSS conductors in TW and RW forms were evaluated. The electrical characteristics considered are thermal ratings, power losses and magnetic fields. Particular reference was made to Eskom’s 400 kV power line, using the Power Line Systems - Computer Aided Design and Drafting (PLS-CADD) software program for the magnetic fields analysis. RateKit 5.0 software which uses both IEEE 738-2002 (IEEE) and CIGRÉ methods was used for conductor thermal rating calculations. The power losses were calculated using the resistances and the maximum allowable current on the conductor. The results showed slight differences between RW and TW in terms of the electrical performances. Most of the differences are due to the variances in resistances and diameters of the conductors resulting from the shape of the conductor.