Tram
Power supply

Electric trams use various devices to collect power from overhead lines. The most common device is the pantograph, while some older systems use trolley poles or bow collectors. Ground-level power supply has become a more recent innovation. Another technology uses supercapacitors; when an insulator at a track switch cuts off power from the tram for a short distance along the line, the tram can use energy stored in a large capacitor to drive the tram past the gap in the power feed. The old tram systems in London, Manhattan (New York City), and Washington, D.C., used live rails, like those on third-rail electrified railways, but in a conduit underneath the road, from which they drew power through a plough. It was called conduit current collection. Washington's was the last of these to close, in 1962. No commercial tramway uses this system anymore. More recently, an equivalent to these systems has been developed which allows for the safe installation of a third rail on city streets, known as surface current collection or ground-level power supply; the main example of this is the new tramway in Bordeaux.
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