An apparatus for reducing a magnetic unidirectional flux component in the core of a transformer with at least three legs, in particular a three-phase transformer having at least one compensation winding per transformer leg, wherein the compensation windings are magnetically coupled to the core of the transformer, where two compensation windings are provided per leg, the first compensation windings of a leg are each electrically connected together in a first delta connection, in each case the second compensation windings of a leg are each electrically connected together in a second delta connection, the compensation windings of at least one leg have different numbers of windings, and where at least one switching unit is arranged in series with the compensation windings for phase angle control.