West of Mehedeby in Sweden, there is a point where the HVDC powerline "Fenno-Skan 2," which runs from Finnböle in Sweden to Rauma in Finland crosses the 220 kV three phase AC powerline Gävle-Mehedeby and the parallel-running 132 kV single phase AC powerline Tierp-Gävle. This place is unique as it is the only spot in the entire world where lines of all modes used for power transmission come together.
While powerlines for three phase AC exist in almost every site on the globe, lines for single phase AC and DC are very rare. Powerlines for single phase AC exist only in areas where electric trains are powered using that method, such as Germany, Austria, Switzerland, Sweden, Norway, and some parts in the Northeast United States.
DC powerlines are only used for very long overhead lines. With short lines, expensive converters are required.
In Austria and Switzerland, there are no overhead DC lines. And in Germany, there are only underground DC cables. In the United States, there is an overhead DC line coming from Canada, but it ends north of the area where railway operation with single phase AC takes place. Also, the only overhead DC line in Norway does not cross any single phase AC lines.
- Wikipedia: Fenno Skan: http://en.wikipedia.org/wiki/Fenno%E2%80%93Skan