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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.
137 --- Bordeaux trams run without overhead wires
138 --- Track with APS under construction in Place Paul Doumer, Bordeaux
139 --- A section of APS track showing the neutral sections at the end of the powered segments plus one of the insulating joint boxes which mechanically and electrically join the APS rail segments
140 --- Bordeaux tram using APS on route B near the Roustaing tramstop
141 --- The channel of Stream system at Trieste
Ground-level power supply is used, primarily for aesthetic reasons, as an alternative to overhead lines. It is different from the conduit current collection system which was one of the first ways of supplying power to a tram system by burying a third and fourth rail in an underground conduit ('vault') between the running rails. Conduit current collection was used in historic tram systems in Washington, Manhattan, Paris, Berlin, Marseilles, Budapest, Prague, and London. It fell into disuse because overhead wires proved much less expensive and troublesome for street railways and because in Manhattan, Paris, Washington and West Berlin all trams were replaced by buses for reasons unrelated to the power supply issue.
Unlike the track-side third rail used by most metro trains and some main-line railways, APS does not pose a danger to people or animals and so can be used in pedestrian areas and city streets.
APS uses a third rail placed between the running rails, divided electrically into eight meter segments with three-meter neutral sections between. Each tram has two power collection skates, next to which are antennae that send radio signals to energize 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.
Use in Bordeaux
Modern ground-level current collection was pioneered by the recent Bordeaux tramway in France, E.U.. The public had assumed that the new system would use a traditional conduit system, like that of the Bordeaux trams which ran prior to 1958 and objected when they learned that it was not considered safe and that overhead wires were to be used instead. Facing complaints both from the public and the French Ministry of Culture, planners developed APS as a modern way of replicating the conduit system.
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 43.3 km as of 2008.
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 drain quickly enough after heavy rain.
In other cities:
In summer 2006, it was announced that two new French tram systems would be using APS over part of their networks. These will be Tramway d'Angers and Tramway de Reims, with both systems expected to open in 2011. A couple of months later, another French city was added to the list, this being Orléans, which will use APS on a section of its second tram line. The planned Al Sufouh Tramway in Dubai will use APS. Another French City will use APS and that City is Tours.
Other cities to propose the use of APS include:
The predecessors of APS (known as Stud contact systems) were developed around 1900, and used on several tramway companies in Paris and in England. Associated with these systems were the inventors Dolter and Diatto.
There were two main differences from APS:
- Power was supplied not from rails but from studs, set in the road at intervals
- Switching in of the contacts was done by strong electromagnets beneath each car.
Each contact contained a fuse, which would be blown by an earthed safety shoe on the rear of the tram should the contact not have switched out. This proved to be unsatisfactory, because the strong currents melted down the switch contacts, resulting in contacts frequently remaining 'live'.
Another system of ground-level power supply was used by Budapest trams from 1887.
Overhead lines were considered an eyesore, so builder Siemens developed the following system: on the inner side of one rail, a powered third rail is hidden underground in a half covered ditch, with a narrow slit opening upwards, through which a trolley pole reaches downward from the trams. The Budapest system was generally safe and water-protected.
However, there was no defense against snow and ice, dirt filled up the ditches and trolley poles suffered intense wear. Overhead wire replaced the " Budapest system" everywhere by the 1920s.
Conduit current collection has the power supply carried in a channel under the roadway, between and underneath the running rails, much in the same fashion as the cable for cable cars.
Stream is an Acronym that stood for TRasporto Elettrico ad Attrazione Magnetica" dell'allora ("System of Transport Electric by Magnetic Attraction"). The channel made of composite material was thus insulating the vehicle equipped with a special shoe on the passing magnetic channel raised the band allowing contact with the copper strip and then the electrical connection.