Transformer, comprising: - a primary circuit with a primary inductor (Lprim), - a first secondary circuit with a first secondary inductor (Ls1.1) that is galvanically isolated from the primary inductor (Lprim) and coupled to the primary inductor (Lprim), - a second secondary circuit with a second secondary inductor (Ls2.1) that is galvanically isolated from the primary inductor and coupled to the primary inductor, wherein the second secondary inductor (Ls2.1) is implemented redundantly with respect to the first secondary inductor (Ls1.1), wherein the first and second secondary inductors (Ls1.1, LS2.1) are connected to one, or each to one, DC voltage source (V, V1, V2) as well as each to a test circuit with a tapping point for tapping off a test voltage (TRCHK1.1, TRCHK2.1), a third secondary circuit with a third secondary inductor (Ls1.2) that is galvanically isolated from the primary inductor (Lprim) and coupled to the primary inductor (Lprim), a fourth secondary circuit with a fourth secondary inductor (Ls2.2) that is galvanically isolated from the primary inductor (Lprim) and coupled to the primary inductor (Lprim), wherein the fourth secondary inductor (Ls2.2) is implemented redundantly with respect to the third secondary inductor (Ls1.2), wherein the third and fourth secondary inductors (Ls1.2, Ls2.2) are each connected to a DC voltage source (V3, V4) or to the DC voltage source of the first and second secondary inductors (Ls1.1, Ls2.1), as well as each to a test circuit with a tapping point for tapping off a test voltage (TRCHK1.2, TRCHK2.2), wherein the secondary inductors (Ls1.1, Ls2.1, Ls1.2, Ls2.2) each comprise their own earth connection and each comprise a galvanic isolation from the earth connection. - a primary circuit with a primary inductor (Lprim), - a first secondary circuit with a first secondary inductor (Ls1.1) that is galvanically isolated from the primary inductor (Lprim) and coupled to the primary inductor (Lprim), - a second secondary circuit with a second secondary inductor (Ls2.1) that is galvanically isolated from the primary inductor and coupled to the primary inductor, wherein the second secondary inductor (Ls2.1) is implemented redundantly with respect to the first secondary inductor (Ls1.1), wherein the first and second secondary inductors (Ls1.1, LS2.1) are connected to one, or each to one, DC voltage source (V, V1, V2) as well as each to a test circuit with a tapping point for tapping off a test voltage (TRCHK1.1, TRCHK2.1), a third secondary circuit with a third secondary inductor (Ls1.2) that is galvanically isolated from the primary inductor (Lprim) and coupled to the primary inductor (Lprim), a fourth secondary circuit with a fourth secondary inductor (Ls2.2) that is galvanically isolated from the primary inductor (Lprim) and coupled to the primary inductor (Lprim), wherein the fourth secondary inductor (Ls2.2) is implemented redundantly with respect to the third secondary inductor (Ls1.2), wherein the third and fourth secondary inductors (Ls1.2, Ls2.2) are each connected to a DC voltage source (V3, V4) or to the DC voltage source of the first and second secondary inductors (Ls1.1, Ls2.1), as well as each to a test circuit with a tapping point for tapping off a test voltage (TRCHK1.2, TRCHK2.2), wherein the secondary inductors (Ls1.1, Ls2.1, Ls1.2, Ls2.2) each comprise their own earth connection and each comprise a galvanic isolation from the earth connection.