: Existing EMS applications resort to static network models built upon constant
resistances whose values are specified beforehand. However, the steady-state thermal balance of
overhead conductors requires that ohmic losses be dissipated by convection and radiation heat,
leading to conductor resistances being a function both of environmental factors and transmitted
current. Each term of the equation involved in the thermal balance of overhead conductors is
analysed allowing the influence of conductor current on conductor temperature to be separated
from that corresponding to environmental factors. As a result, three approximate thermal models
are elaborated, which are compared on the Spanish transmission system. Test cases are included
showing that the influence of the selected model on transmission losses may be significant enough,
particularly when the transmission system spans areas with diverse loading levels and weather
conditions
