Optimal design of combined AC-DC transmission lines

In the paper an optimal procedure is proposed in order to face with power upgrading of transmission line of a double circuit line. The methodology is quite general, allowing to take properly into account all the technical constraints which have to be satisfied for a line acceptable behaviour. This procedure is based upon an optimal power flow which maximizes the power line capability, ensuring that the original line structure is not altered. The results of the optimal power flow could be of great interest being a powerful mean for the designers aligned with the recent tendency towards the exploitation of the existing structures, avoiding the construction of new transmission lines. In the last part of the paper relevant numerical applications are reported in order to demonstrate the feasibility of the proposed approach.