Supergrid or local network reinforcements, and the value of controllability — An analytical approach

In this paper, an analytical approach is developed to address network planning questions for meshed AC networks. First, relationships are derived to compare the effectiveness of expansion measures, such as the building of long lines in the form of overlay grids, or local reinforcements along the transmission path in the existing grid. Results show that overlay networks are preferable, transferring more power for the same line-kilometers and line capacity. Second, upper bounds for the maximum utilization of long AC lines over a meshed network are extracted. The derived bounds prove to be significantly limiting in a highly meshed network. This stresses the need for controllable power flows. The obtained relationships are confirmed on the two-area RTS-96 system and through simulations on a single-node per country European network, based on real network data. Controllable flows, through the installation of HVDC lines, can save up to 8 billion Euros/year in comparison with the non-controllable AC technologies.