Mobile traction substations for powering trains and trams

The power for an electric railway has to come from somewhere – and that place is a traction substation, a facility that convert hogh voltage electricity from the power grid to the voltage and frequency that trains or trams use. The vast majority of them are fixed in place, but a number of tramway and railway operators across Europe have mobile versions, able to be deployed wherever they are needed.

CFR railway traction substation outside the town of Azuga

Deutsche Bahn

In German a mobile substation is called a ‘Fahrbares Unterwerk‘. The first Deutsche Reichsbahn built their first two units in 1935, featuring rotary converters of 7MVA nominal power. Newer units were built in the 1960s, of 10 MVA or 15 MVA capacity, with twelve units still in service by the 1990s.
Early units

Swiss Federal Railways

The SBB operates a massive fleet of mobile traction substations – 18 in total, with 17 permanently positioned pending the construction of fixed substations, as well as a mobile spare. The usage of mobile substations commenced following the Second World War, when military planners saw the advantage of being able to relocate a substation in case of attack, or quickly replace damaged facilities.

Swedish State Railways

SJ was another rail operator worried about war, so following the Second World War they also built mobile traction substations, as well as a network of underground rock tunnels to protect them from enemy air strikes. Abandoned following the end of the Cold Car, one of these tunnels is now managed by the Norrbottens Järnvägsmuseum, along with a complete mobile substation train.

Russian Railways

Russians call their mobile substations ‘поставка передвижных подстанций’, with more than 30 in service on the Russian Railways network. Switchgear, transformers, rectifiers and control equipment are located on separate wagons.


ДАК-Энергетика photo

Austrian Federal Railways

The Austrian Federal Railways have eight mobile substations (fUW) built between 1986 and 1993. They are used to provide short-term support to the traction power supply, as a backup while equipment in stationary substations is upgraded, or as an interim step before the construction of additional stationary substations.

Trams in Vienna

The tramways of Vienna also have a long history of mobile traction substations. Known as Gleichrichterwagen or fahrbare Umformeranlagen the first unit was built in 1925, and was used to meet the demands of peak traffic on Sundays or summer public holidays.

A second unit entered service in 1928, with two more built in 1944.

The latter two units have since been upgraded with modern solid state rectifiers, and are still in service today.

Trams in Kyiv

The tramway network of Kiev once had mobile traction substations built from retired passenger tramcars.


Kyiv Museum of Electric Transportation photo

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