The Norwegian railway network consists of of electrified railway lines, constituting 62% of the Norwegian National Rail Administration's of line. In 2008, electric traction accounted for 90% of the passenger kilometers, 93% of the tonne kilometers and 74% of the energy consumption of all trains running in Norway, with the rest being accounted for by diesel traction. History Early schemes Technology for electric railways was demonstrated in Germany in 1879; the first revenue line took electric traction into use in 1881. The first electric industrial railway in Norway opened in 1892 at Skotfos Bruk near Skien. Two years later, parts of the Oslo Tramway were electrified. The first alternating current (AC) line became operational in 1892, while the first line to use a single-phase, single overhead wire power supply opened in Germany in 1903. In 1912, all German railway agreed to use the standard, which was later adopted first by Sweden and then by NSB. Several of the private lines that preceded NBS's electrification chose different standards. Sydvaranger chose to install the only mainline direct current (DC) and third rail system. Mainline systems The first three mainline systems to be electrified were private ore-hauling lines. The Thamshavn Line opened in 1909, and remained in revenue use until 1973, after which it was converted to a heritage railway. It is the world's oldest remaining alternating-current railway and the only narrow gauge railway in the country to have been electrified. It was followed by Norsk Transport's Rjukan and Tinnos Lines two years later, and Sydvaranger's Kirkenes–Bjørnevatn Line in 1922. The Norwegian State Railways' (NSB) first electrification was parts of the Drammen Line in 1922 and the ore-hauling Ofoten Line in 1923, which connects to the Ore Line in Sweden. The use of El 1 locomotives on the Drammen Line proved a large cost-saver over steam locomotives, and NSB started electrifying other lines around Oslo; from 1927 to 1930, the remainder of the Drammen Line, and the continuation along the Randsfjord and Sørland Lines to Kongsvinger were converted, along with the first section of the Trunk Line. In 1935, the Hardanger Line became the first section of new NSB track to be electrified. From 1936 to 1940, NSB electrified the Østfold Line as well as more of the Sørland Line and the Bratsberg Line, connecting all electric lines west of Oslo. The 1940s onwards During the 1940s, NSB electrified the Sørland Line, although