A three-phase transformer for twelve-phase thyristor rectifier comprising first and second three-phase full-wave rectifiers (3, 4), the three-phase transformer comprising: • main magnetic core composed of three columns (51, 52, 53) magnetically connected in parallel at their ends by two yokes, each of said columns receiving: - two primary windings connected in parallel; - two secondary windings, three of the secondary windings wound on separate columns being connected in a star configuration to the terminals of the three-phase transformer and being adapted to be connected to said first three-phase full-wave rectifier, the other three secondary windings being connected in a triangle configuration to the terminals of the three-phase transformer and being adapted to be connected to said second three-phase full-wave rectifier; and • a first inductive core comprising three columns, on each of the columns being wound one of said pairs of primary windings, characterised in that the three-phase transformer also comprises: • three pairs of auxiliary windings wound, between the primary and secondary windings, around each column (51, 52, 53) of the main magnetic core and of the first inductive core; • a second inductive core having three columns, each of the columns being disposed between a pair of auxiliary windings and a pair of primary windings; and • three output connectors connected with the auxiliary windings and being adapted to be connected to at least three capacitors (C1-C3) with the auxiliary windings, so as to form at least one harmonic and power factor correction filter. • main magnetic core composed of three columns (51, 52, 53) magnetically connected in parallel at their ends by two yokes, each of said columns receiving: - two primary windings connected in parallel; - two secondary windings, three of the secondary windings wound on separate columns being connected in a star configuration to the terminals of the three-phase transformer and being adapted to be connected to said first three-phase full-wave rectifier, the other three secondary windings being connected in a triangle configuration to the terminals of the three-phase transformer and being adapted to be connected to said second three-phase full-wave rectifier; and - two primary windings connected in parallel; - two secondary windings, three of the secondary windings wound on separate columns being connected in a star configuration to the terminals of the three-phase transformer and being adapted to be connected to said first three-phase full-wave rectifier, the other three secondary windings being connected in a triangle configuration to the terminals of the three-phase transformer and being adapted to be connected to said second three-phase full-wave rectifier; and • a first inductive core comprising three columns, on each of the columns being wound one of said pairs of primary windings, • three pairs of auxiliary windings wound, between the primary and secondary windings, around each column (51, 52, 53) of the main magnetic core and of the first inductive core; • a second inductive core having three columns, each of the columns being disposed between a pair of auxiliary windings and a pair of primary windings; and • three output connectors connected with the auxiliary windings and being adapted to be connected to at least three capacitors (C1-C3) with the auxiliary windings, so as to form at least one harmonic and power factor correction filter.