Avaliação do comportamento térmico e mecânico de cabos condutores de energia em função de sua geometria e condições de escoamento

Abstract

The overhead power transmission lines are extremely important within the electric power system, since they are responsible for the link between the points of generation and consumption of energy. They convey electricity safely and at the lowest cost for end consumers and the distance from the conductor cable to the ground or to other elements along the line a factor of fundamental importance. In this context, the ampacity is an important property, because it is related to the maximum electric current that can be carried in an overhead transmission line without exceeding the maximum permissible temperature of the conductor, in light of these safety factors. With the growing demand for energy, it is needed to maximize the use of existing electricity systems because it is not always possible construction of new lines. One method is to increase the line ampacity, which can be obtained by increasing the cable heat dissipation to the environment. This document proposes the development of a numerical model that represents effectively the heat transfer phenomena and air flow on transmission line aerial cable AeroZ Linnet. The model was validated by comparison with results from tests in wind tunnel and analytical calculations proposed by technical standards in the area. It was considered a beneficial effect of the use of high emissivity coating ink and the influence of the thermal contact resistance between aluminum wires in the equivalent thermal conductivity of the cable. The validated numerical model was then used to simulate modified geometries of AeroZ Linnet cable with larger internal air space, in order to delay the heating of the steel core and the increase in the sag. This modification also allows the inclusion of elements such as optical fiber wires in these spaces. The study made possible a decrease in temperature of up to 13 % and increased ampacity of the conductor in up to 22 %, based on the use of the coating ink. The study showed that the thermal contact resistance has little effect on the equivalent thermal conductivity. The simulations indicate the new geometries as good alternatives to extend the cable utility range. The changes not only allow greater system protection against possible sudden changes in the line operation conditions, but also data transmission by optical fibers, without changing negatively the ampacity of it.