A system for high power transmission on an installation comprising a first part (1, 11) and a second part (2, 12) rotating relative to each other characterized in that the system further comprising a rotary three-phase transformer having primary (U1, V1, W1) and secondary (U2, V2, W2) windings, the first part being provided with one of said primary (U1, V1, W1) or secondary (U2, V2, W2) windings, the second part being provided with the remaining winding of said primary (U1, V1, W1) or secondary (U2, V2, W2) windings, said primary (U1, V1, W1) and secondary (U2, V2, W2) windings are arranged to face each other, and an air gap (6) is provided between the primary (U1, V1, W1) and secondary (U2, V2, W2) windings and their corresponding parts of the transformer cores.