Ground-level power supply, also known as surface current collection and Alimentation par Sol (APS) is a modern method of third-rail electrical pick-up for street trams. It was invented for the Bordeaux tramway, which was constructed from 2000 and opened in 2003. Currently this is the only place it is used, but there were and are proposals to install it elsewhere:
APS uses a third rail placed between the running rails, divided electrically into eight-metre segments with three metre neutral sections between. Each tram has two power collection skates, next to which are antennas that send radio signals to energise the power rail segments as the tram passes over them. At any one time no more than two consecutive segments under the tram should actually be live.
APS was developed by Innorail, a subsidiary of Spie Enertrans, but was sold to Alstom when Spie was acquired by Amec.
There are 12 km of APS tramway in the three-line network of 21.3 km total length, expected to be 40 km by 2007. Sources suggest that APS adds about €100,000 to the cost of the trams, whilst the infrastructure is about 300% more expensive than overhead wires. Bordeaux Citadis trams use pantographs and electric overhead lines in outlying areas.
Before use in Bordeaux, APS was tested and proved viable on a short section of reserved-track tramway in the French city of Marseilles. Nevertheless, Bordeaux has experienced problems, with APS being so temperamental that at one stage the Mayor issued an ultimatum that if reliability could not be guaranteed, it would have to be replaced with overhead wires. Although things have improved, in October 2005 it was announced that 1 km of APS tramway is to be converted to overhead wires.
Problems have included water-logging, when the water does not disperse or flow away quickly enough after heavy rain.
There were two main differences from APS:
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