Effects of axial tension and reduced air pressure on the radial thermal conductivity of a strained conductor

Analysis of the radial flow of heat in a multilayer stranded conductor carrying current indicates that most of the heat is conducted through the very thin air gaps at the contracts between strands in adjacent layers and through the triangular or rectangular voids between layers. The theory predicts that, with constant current, the radial temperature difference increases as the axial tension decreases, and as the air pressure decreases. To confirm these predictions, a length of 91/4.04-mm AAC conductor was tensioned within a vacuum chamber, and the temperature of each layer of wires was measured for various total currents. It was found that the radial temperature difference increased with increasing resistive power loss per unit length, with decreasing axial tension, and with decreasing air pressure. The effective radial thermal conductivity is independent of the power loss, and increases with increasing axial tension and increasing air pressure. The calculated effective gap at the contacts is 0.5 to 0.9 μm