Thermal grading around overhead transmission line under various environments and its influence to load capacity

The transmission capacity of overhead transmission lines is limited largely by its operation temperature, which is determined by the competition between the heat generation by load current and the heat dissipation into the environment. The ohmic heat generation is a function of the conductor resistivity, which is a function of its temperature and current distribution inside the conductor, taking the skin effect into account. The heat dissipation is influenced by the temperature of the conductor and the air, the surface condition of the conductor, the wind, the sunshine, and the humidity of air, etc. Finite Element Analyses are carried out in this paper to calculate the thermal dynamics by coupling the thermal field and the fluid mechanical models. The results show the temperature distribution and the evolution history in the conductor - air system under various environment conditions. Thus the maximal load level can be defined accordingly. The calculation also gives the time required for the conductor to reach equilibrium with load and environment changing. This information can help the grid operators to decide how to dispatch the loads among multiple transmission lines, either as a temporary routing or as a steady state solution.