D.C. voltage transformation in high tension systems

A multiphase converter station comprising:

• a plurality of converter bridges, constituting at least two groups being disposed differently to ground, the A.C. sides of said bridges being connected in parallel to a three-phase current network, each bridge having a converter transformer, said converter bridges being connected in series between a first and a second terminal of a first high voltage D.C. network, each of said groups being provided with a D.C. tap between the outer and next to the outer converter bridges, to which taps a first and a second terminal of a second high voltage D.C. network with lower potential than the first network are connected, at least one of those bridges being disposed between said first terminal of said first network and said first terminal of said second network being a rectifier-type bridge and at least one of those bridges being disposed between said second terminal of said first network and said second terminal of said second network also being a rectifier-type bridge, the remaining bridges being disposed between said first and second terminals of said second network to ground being inverter-type bridges, wherein the rectifier-type bridges direct current in the same direction as the voltage drop from the first to second terminals of the second network and the inverter-type bridges direct current in the opposite direction.