In a single-phase autotransformer only the difference between the circulation of the input and output currents in the common section of the winding can be found during the charging process. In this way, the section of the in-load winding can be designed with a smaller section. It should further be considered that the output power is delivered largely directly from the input side to the output side through current conduction through the common winding section. Only a reduced component can be transported by magnetic flux. Therefore, the iron core can be designed so that it is less robust.

Thus, in the case of a multi-winding transformer, all the generated power can be transported from the primary to the secondary through the magnetic field. This means that the primary and the secondary, like the iron core, must be sized so that they can appropriately transport all the energy to be transformed. The autotransformer, as well as the energy stream, is transformed from the primary to the secondary through a galvanic connection by copper, with only part of the energy being transported through the magnetic flux.