Emissivity-temperature dependence of Cu and Al conductors up to about 250°C and its effects

Accurate thermal-electric models of power line conductors and busbars require knowledge of surface emissivity and absorptivity, especially when operating at temperatures significantly different from ambient temperatures. Although emissivity tends to increase with conductor temperature, this temperature dependence is often overlooked in conductor models. This paper focuses on measuring this dependence by using two solid copper and aluminum rods with a round cross-section. The rods are heated by passing an alternating current of a known magnitude through them under controlled laboratory conditions. The results show an evident increase in emissivity with temperature, though it differs for copper and aluminum due to their inherent differences and different oxidation behaviors. The data presented show a significant increase in emissivity for aluminum and copper when the temperature ranges from 50°C to over 200°C. This paper also shows the impact of varying emissivity values on the final temperature of the conductors. These results can be useful for accurately modeling electrical conductors and can be directly applied to dynamic line rating (DLR) applications. • Emissivity critically influences the final equilibrium temperature of conductors. • The emissivity of conductor materials changes with temperature. • The nature of this change depends on material's properties and oxidation mechanisms. • It is shown that Al shows a linear increase in emissivity below 300°C. • However, the behavior of Cu is more complex due to the formation of Cu₂O and CuO.