When the energy sustainability of the future is sought by modifying the synchronous generator whose efficiency values ​​very easily exceed 90% even at relatively low nominal powers and there are synchronous generators in commercial exploitation with 98.5 and 99% efficiency (Siemens SGen 2000P), it is worth questioning whether scientifically to insist on the synchronous generator is right or not, but when the experimental results show non-negligible savings (5–15%), practice is always the criterion of objective truth and knowing that the Law of Conservation of Energy unobjectionably governs all energy processes, there is only one logical possibility: the way in which efficiency is being evaluated is incomplete and energy efficiency is actually inferior to those beautiful numbers of excellence. Making a new magnetic circuit in the synchronous generator as a way of sustainable savings is therefore a double scientific challenge: the physical challenge of achieving the result and the theoretical challenge of coherently explaining the energy conversion process in the synchronous generator, the latter being the objective of this article.