new kind of an equivalent circuit of the two-winding autotransformer with a clear distinction between flows of electric and electromagnetic power has been discovered. It is shown that the presented model has important methodological significance as it allows to clearly display triangles of each power flow in all modes of operation of the autotransformer on vector diagrams along with the currents and voltages. Completeness of vector diagrams is achieved by separately displaying on them the magnetic fluxes in steel, thicker windings and the gap between them. We have obtained a high degree of clarity in explaining the overstimulation of certain parts of the steel in a short-circuited autotransformer and in deriving the formula for determining super- and anti -fluxes (compared to idling fluxes) in this mode directly from the vector diagram. The presented equivalent circuit serves the step-up and to the step-down autotrans formers at the same time, and is responsive to the saturation of their magnetic system in steady and transient processes.