Electric power consumption, has been increasing uninterruptedly, being this increase specially accelerated in the last years. New power generators are been built, the installed power increases each year, thus it is necessary a way to transmit the bulk energy. Nowadays electric lines are saturated, they are reaching critical values of ampacity and sag. Therefore building new lines is necessary to provide the ever increasing consumption. The difficulty to find corridors to construct new overhead lines is increasing in industrialised countries and in many cases it is simply impossible. It is not easy to obtain the rights of way for new transmission lines. The construction of new overhead electric lines is increasing difficulty, thus there is a need to look at alternatives that increases the power transfer capacity of the existing right of ways. This circumstance is forcing the use of the existing lines, which represents a cheaper solution than making an underground transmission.