The ongoing evolution of the power system to implement climate action policies is resulting in a continuous increase in the penetration of renewables and the necessity of strengthening the transmission grid to optimize the usage of those sources and contain operation costs. Reinforcing the transmission lines or building new ones is a process that is made difficult due to authorization issues related with environmental and public acceptance concerns. Developing innovative conductors for overhead lines with enhanced performances with respect to the traditional ones would bring benefits in terms of energy efficiency increases in transmission and distribution grids without requiring the substitution of the existing towers. The project CALAJOULE (the genesis of the acronym comes from the union of the Italian verb "calare"-to decrease-to the third person singular, namely "cala" i.e., decreases, and of Joule, obvious reference to the active losses), cofinanced by the Italian Ministry of Economic Development in the framework of the "Ricerca di Sistema" program, aims at proposing innovative solutions for overhead line conductors for the containment of Joule power losses. In this paper, starting from the state-of-the-art of the currently adopted conductors, the main innovative solutions resulting from the project are presented and compared with the traditional ones to evaluate the achievable reduction in Joule losses.Energies 2019, 12, 3107 2 of 21 flexibility. The above-mentioned climate action policies are resulting in an evolution of the generation park, with the gradual substitution of traditional fossil-fuelled power plants with a high number of smaller generators, the majority of which are connected to the distribution network. To accompany this change, it is of utmost importance to have a power system infrastructure capable of hosting the geographically displaced generation and the sudden changes in the power flows, containing the formation of bottlenecks, and improving the energy efficiency of the whole system. Along with innovative network management techniques [4], aiming at exploiting the presence of distributed generators and their participation to the ancillary services market [5], it will be necessary to upgrade the infrastructure of the electricity system as increasing shares of electricity production will shift from large power plants to small generators. As it is well known, active losses in electricity systems vary considerably depending on the voltage level. Typically, active losses ranging from 2% to 10% can be assumed, passing from transmission networks (high and extra-high voltage levels, HV and EHV, respectively) to distribution networks (medium and low voltage levels, MV and LV, respectively) [6][7][8][9]. For overhead lines (OHLs), the different Joule losses values are due to the r/x ratios (ratio between the resistance r and the reactance x of the positive sequence impedance) of the transmission lines being much lower than those of the distribution networks. The reduction of Joule losses in the po...
