On the choice of three-to-four-phase transformers for four-phase power transmission

Four-phase transmission systems, which have been deeply investigated in several recent papers, are recognized as a possible alternative to traditional three-phase transmission lines. However, the problem of the phase transformation between the three-phase and the fourphase section, which is not a new theme in the relevant literature, exhibits some troubles especially in the choice of the most convenient typology of the needed special transformers. First of all the paper examines the underlying principles of the old Parton's theory of phase transformation. Second, according to this theory new potential solutions are derived and investigated. Hence the (double) Scott connection which, in any case, continues to be familiar to most electrical engineers, is examined and framed in the theory of phase transformation. In the last section, all the examined solutions are compared resorting to different aspects and parameters connected with the wiring connections.