Thermal Analysis by Conduction Convection and Radiation in a Power Cable

Abstract

Keywords: solar and wind effects, backfill material, COMSOL-MULTIPHYSICS software, moisture migration I.Introduction Power transmission through cables is much required in urban areas to reduce the outages. It is used to power all the equipments inside the buildings and houses by passing through conduits. Current flowing through the cables is based on the load connected to it. This causes losses in the conductor based on the skin, proximity effects along with the losses that occur in the insulation and the sheath. This develops the temperature which is dissipated to the surrounding to operate the cable within safety limit [1]. Heat dissipation in a cable depends upon the installation conditions, spacing between conductors and ambient temperature. Here we consider a cable which is installed in air and other one which is buried in soil. With increase in heat transfer coefficient the rate of heat dissipation increases resulting in less cable temperature [2].The ambient temperature and air velocity can influences the cables heat transfer coefficient. The maximum current carrying capacity depends on all factors that cause the variation in heat dissipation. It follows the finite element method to estimate the thermal effect on cables. When the cables are buried directly in trenches the area is filled layer by layer with the materials that are required to increase the heat dissipation rate. The bottom layer of the trench is filled with fine sand and then filled with moist soil [3]. Moisture migration takes place due to the thermal effect in the underground cable. The rate of heat dissipation is more by decreasing the thermal conductivity of bedding than that of the backfill soil [4]. Oil and gas filled cable are used to avoid the formation of voids which are filled by the pressure of the liquid or gas inside the cable. The heat generated is absorbed by the oil and it also provides electrical insulation for the cable. Sf6 gas is used because of its high dielectric strength which can be operated even at 500 kV. The heat flux distribution shown with various fillers gives appreciable results for Sf6 gas insulated cables.