Power transmission systems are called upon to play a crucial role in the future decarbonized, electrified and digital energy sectors, as they constitute the most effective way of distributing vast amounts of electricity from renewable energy sources to faraway locations. This paper aims at critically reviewing worldwide the regional visions, as well as existing and newer technologies involved in the development and upgrading of bulk transmission systems. The main emphasis is put on the major challenges and boundary conditions arising during the paradigm change that electric energy systems will undergo over the next half century. Recent research and pilot projects on this subject are revised, embracing effective combinations of AC and DC technologies, such as high-voltage AC transmission systems, phase-shifting transformers, flexible AC transmission systems and point-topoint and multi-terminal high-voltage DC systems. The challenges faced by this transition involve technical, economical, environmental, regulatory and social factors that will finally determine the preference for one or another technology in particular regions of the world. General recommendations and guidelines are proposed to increase the probability of success of future transmission projects, regardless of the type of technology, geographic location or particular external conditions. Several somewhat competing architectures are envisioned in this more volatile context, all together offering great possibilities to increase transmission capability while loop flows are prevented and system stability is preserved or enhanced.
