Three-rail trams.
The video:- http://www.youtube.com/watch?v=ui63-Zjbcvo
shows (IMO) London trams operating without overhead wires with a third rail visible between the tracks. I'd never heard of this system before (though I am not a tram enthusiast). A search on Googoo revealed a new third-rail system being installed in Boulogne in 2004 (though there is a sophisticated modern-technology safety system):- Quote:
Another overhead-wire-free system is described here:- http://www.railwaygazette.com/news_v...tion_tram.html Sections of the Braunschweig system are also three-rail:- http://www.railway-technology.com/pr.../braunschweig/ but these are all modern schemes. Did London really have three-rail trams in the 1930s? It seems so:- Quote:
More on ground-level supply:- http://en.wikipedia.org/wiki/Ground-level_power_supply and conduit-collection:- http://en.wikipedia.org/wiki/Conduit_current_collection Quote:
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You may have read or seen this elswhere but the lodon authorities at the time did not allow overhead wires inside a particular area . The London trams had a thing called a (like a knife blade ) plough which collected the current and returned it through the rails( Earth) . Frinstance if a tram arrived from the east end of London at say somewhere like Walthamstow a changer man would attach the plough under the tram and pull down the trolley pole for the journey on into the centre. The reverse would apply on the return journey........... Regards Alan
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Thanks. Until I saw the video - and did my research - I'd never heard about such a system.
I'd like to see drawings of the system (and see how they maintained contact with both 'rails' - or was it 'earth return' though the rails?). Are (were) overhead wire systems 'earth return'? |
Have a look here I have drawings some where and books the actual part that went into the ground looked like an upturned horseshoe with the current collector at the bottom .It was dc current and failsafe all the metal was at zero potential, live at the single pole or plough..Did you know that most tramways found it difficult to compete with other transport forms as most tram companies had to pay for the upkeep of the roadway for about 1yd(mtr) each side of the trackway..then there was lack of investment ie maximise profit,...fiddle with this link as found a couple of dead Links Regards Alan
http://dewi.ca/trains/conduit/ploughs.html |
I had heard of the "3-Rail Tram System", which I knew as the "Trough and Plough", but I was always under the impression that the trough had a moving cable in it! As an engineer, I find it incredible that live electricity would be in a trough! It would be easy for the trough to fill up with everyday rubbish, but the biggest bugbear must have been water. If it rained, or there was a nearby mains leak, the trough would have filled with water. Surely any pedestrian in close proximity to the trough would have been electrocuted, or am I missing something?
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And don't even contemplate ice . . .
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I may have got it exactly right for I now notice the 2 cables emitting from the top of the plough and contacts each side of the base. However most must have used earth rail return as they only had one roof pole(pickup) in London that is there are photos of the system under the road ao another page of the afore mentioned wed site......Alan
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When running on the overhead wire, the trams used an earth return via the wheels and rails. (in fact in event of a derailment where the trolley pole still beon the wire, the crew were instructed to jump from car to the ground rather than create an earth when dismounting!)
When running on the conduit the system supplied both positive and negative. Two subsurface 'T rails' were contacted by the plough which took the current via the busbars to the tram's circuits. As previously mentioned the system arose to avoid the unsightly overhead wires, but it was expensive to build and maintain and outer sections were wired instead. A sectional diagram of the plough and T rail arrangement can be found at http://londonmodeltramways.webs.com/ a website that describes my two 1/76 scale model tram layouts based on London's Kingsway Subway and Dog Kennel Hill. |
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But as you say the return is through wheels to the rail. When I was active on the museum/vintage/commercial tram traffic with old trams we learned exactly what you said. Jump of without touching the tram and then pull down the pantograph (or pull it down from inside the tram if possible) with the wire. Then mount the "växelspett" (metal bar with narrow end and a handle used for turning the point to change track) to the coupling and to the rail. Then pull up the panthograph again and drive off from what isolates the tram. Of course, if you have derailed you don't need to drive away from there. Let the recovery crew take care of that. But two axle trams (not bogies) can be isolated if there is a lot of sand or other isolating material on the rails. |
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