High-voltage direct current#Back to back

An HVDC short coupling, also known as HVDC short coupling, DC coupling ( GK) or as a DC short coupling ( GKK ) denotes, in English back- to-back station with the abbreviation B2B, is to construct a high -voltage direct -current transmission, in which both converters on the same area, usually even within the same building are and the length of the DC line, therefore, is only a few meters. HVDC short couplers are used for the electrical connection of power grids, which are each operated with alternating current or three-phase alternating current.

The range of application of the coupling of networks with different network frequency between 60 Hz and 50 Hz as in Japan in the Higashi- Shimizu Frequency Converter or in Saudi Arabia at the GKK Al Fadhili. Furthermore, short HVDC coupling system with different frequency and phase number to replace Bahnstromumformerwerke used in the coupling of networks with rotating machines. Another field of application is the coupling of mutually asynchronous three-phase systems, as in the located in Russia HVDC short coupling Vyborg, which connects the Russian electricity network to the Finnish network. In the U.S. Today, close couplings are also common, as there exist nine asynchronous transmission networks. In Central Europe were to 1995/ 96, the GKK Etzenricht Duernrohr GK and GK Vienna-Southeast in operation, which have been superseded by the synchronous circuit of the Western and Eastern power grids.

In contrast to long-distance HVDC lines, the DC voltage in the intermediate circuit can be chosen lower in HVDC close couplings because of the short line length, typically a DC voltage is in the range of 70 kV to 150 kV. They always chooses so that the voltage remains as low as possible to keep the converter hall as small as possible, but always so high that the maximum transmission power parallel connection of rectifiers is necessary.