The economic feasibility of four-phase AC overhead connections

The goal of this paper is assessing the economic feasibility of four-phase AC overhead connections, i.e. the real chance that such lines have of being competitive with commonly-used solutions for power transmission. For this reason, the paper illustrates an economical comparison among innovative 325 kV four-phase ac lines, traditional 400 kV three-phase ac lines and increasingly-popular 500 kV HVDC lines. These systems are considered firstly in single-circuit and secondly in double-circuit overhead arrangement. The comparison is based on the main cost items that characterize these lines, namely investment costs, energy losses costs and reliability-related costs. The uncertainty of the relevant parameters, particularly significant as far as innovative four-phase ac lines are concerned, is also discussed.