List_of_installations_for_15_kV_AC_railway_electrification_in_Sweden
Electric railways in Sweden are powered from a single-phase AC supply of 15 kV at 16+2⁄3 Hz, as used in Germany, Austria and Switzerland. Unlike these countries, the 132 kV traction current grid covers only part of the country, approximately north of Stockholm. This grid is fed by frequency converters and has no generation nor transmission lines from Norway, which uses the same traction current system. Formerly, the Porjus Hydroelectric Power Station provided electric power to the traction network. In the future the Älvkarleby Hydroelectric Power Station may be connected to the traction network, as this would increase stability of the power grid of the railway system. Separate from the 132 kV grid is a 30 kV line connection between Mon and Varp substation north of Gothenburg.
Also the overhead wire system has some differences. It is common, that the pylons for the overhead wire also carry a three phase AC system. In order to reduce counts of substations, the voltage at the substations for the overhead wire is 32 kV at some lines (AT-System). However trains require 16 kV and therefore auto transformers are used, which have a central connection connected with the grounded railway, while the other connections are connected to the 32 kV output. The voltage between this central connection to the phase is 16 kV. The other pole to ground is also 16 kV, but with opposite polarity and runs along the track on the overhead wires until separation section. Other lines are fed directly with 16 kV from the substations. However differential transformers are used for feeding, in order to eliminate jamming signals.