Page 19 - September October 2014

IT JUST AIN’T PROTOTYPICAL
Third Rail Electric Pick-up on City Streets Nick Prior
A streetcar system using an electric third rail on city streets is about to be introduced in Washington, DC using a safe working system pioneered in France, in the city of Bordeaux.
By the turn of the 20th century electric street tramways had become popular, but even then local objections were made to the unsightly poles and overhead wires for aesthetic reasons. Several inventors in Europe tried to solve this problem with limited success. In the UK, Wolverhampton District Company cars were modified with Lorain stud contact system equipment and on 15 October 1906 began working between Dudley and Wolverhampton.
This system, and the similar Dolter system introduced the following year on the streets of Torquay and Hastings, used electrically live elements under the road surface which were lifted into contact with a pick-up ski on the underside of a tram as it passed over. In both systems the tram had a powerful magnet on the underside to perform this lifting movement. In the Dolter system a permanently live stud was lifted by the magnet through a hole in the road surface into contact with the ski as the tram passed above. The studs were spaced apart by a distance slightly less than the length of the ski. After the tram had passed the stud was retracted by a return spring. In the slightly different Lorain system the magnet raised a live element into contact with the underside of a metal plate in the road surface and the metal plate was contacted by the ski. In this case also the live element was retracted by a spring once the tram had passed.
These systems worked well in theory but in practice were beset by mechanical gremlins. Sometimes the live elements did not lift, causing the tram to stop. Of more concern, they did not always retract after the tram had passed. In both Wolverhampton and Torquay, horses died when they stepped on un-retracted live elements. There were no reports of human fatalities, but perhaps the innate caution of local pedestrians prevented them from stepping on the elements at all. The systems were aban-
doned quickly, mostly by 1909, and nothing more happened for over a century, with the exception of the adoption of conduit systems with their own problems for narrow-tyred cars and cyclists. Remember the film Genevieve?
By the beginning of the 21st century improved electronic con- trol systems and better manufacturing tolerances had led to the city of Bordeaux reintroducing the live third-rail system on city streets using the Alimentation Par le Sol (APS) in 2003.
In the APS system a third rail for electrical pick-up is arranged between the running rails. It is divided electrically into 8-metre segments with 3-metre neutral segments in between. The trams have continuous articulated cars and are about 40 metres long. Each tram has two power collection skis and next to each ski is an antenna that sends radio signals to energise controllers associated with each electric rail segment to render the segments live as the ski passes over. As soon as the antenna has passed over an electric rail segment and the controller is deactivated, the rail segment loses power and becomes safe to touch. At any one time, there are no more than two adjacent rail segments under the tram that are live. Thus except where the tram is over the third rail, the latter is electrically neutral and no danger to pedestrians.
The safety of the system is ensured by the arrangement by which the controller providing power to a rail segment is only activated when it receives a signal from an antenna and no tram means no signal.
Having been to Bordeaux and experienced the weird sensation of stepping on the third rail just after a tram has passed, I can attest to the safety of the system. More particularly, in the ten years during which the system has been operating throughout the centre of Bordeaux there have not been any safety issues.
Other cities are now adopting the system, including Washington mentioned above, and it seems likely that third-rail pick-up will become standard in city-centre tram systems due to its great aesthetic benefits.
Above: Track with APS under construction, Bordeaux Above: Bordeaux Tram Photos: Nick Prior
STOP PRESS – WESTERN UNION
Monthly meets will now take place at the premises of the 1st Crownhill Scout Group in Plymouth at PL6 5DX, in a clean, dry and well-lit hall that is in all ways superior to Hilltop, other than being a few feet shorter in length. The rest of the previously- arranged Hilltop dates for 2014 are hopefully being transferred to the new venue, which is less than a minute’s drive once you leave the Tavistock interchange on the A38. Take the same turn-off from the main Tavistock Road that you did for Hilltop, but instead of going through the roundabout to Tamerton Foliot, take the first exit to skirt the Police Station, and immediately after you pass the Police main driveway on the left, indicate right and turn off into the side road just a few yards onward on the other side of the road. Follow the road around and past some garages, and through a double metal-fenced gate. For further information, contact: Mike Ruby, 17 Coombe Way, St Budeaux, Plymouth PL5 2HA
Tel: 01752 369068; Email: mike.ruby@talktalk.net.
NB Only those arriving by 8.30 a.m. to help set up, and staying to dismantle the layout, will be allowed to run trains!
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