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.