Editing Autotransformer (section)

===Railways===
{{Main|25 kV AC railway electrification}}
In railway applications, it is common to power the trains at 25&nbsp;kV AC. To increase the distance between electricity Grid feeder points, they can be arranged to supply a split-phase 25–0–25&nbsp;kV feed with the third wire (opposite phase) out of reach of the train's overhead collector pantograph. The 0&nbsp;V point of the supply is connected to the rail while one 25&nbsp;kV point is connected to the overhead contact wire. At frequent (about 10&nbsp;km) intervals, an autotransformer links the contact wire to rail and to the second (antiphase) supply conductor. This system increases usable transmission distance, reduces induced interference into external equipment and reduces cost. A variant is occasionally seen where the supply conductor is at a different voltage to the contact wire with the autotransformer ratio modified to suit.<ref>{{cite book |title=Fahrleitungen elektrischer Bahnen |language=de |trans-title=Contact Lines for Electric Railways |publisher=BG Teubner-Verlag |location=Stuttgart |page=672 |date=1997 |isbn=9783519061779}} An English edition "Contact Lines for Electric Railways" appears to be out of print. This industry standard text describes the various European electrification principles. See the website of the UIC in Paris{{cn|date=December 2024}} for the relevant international rail standards, in English. No comparable publications seem to exist for American railways, probably due to the paucity of electrified installations there.{{or|date=December 2024}}</ref>