Hi Aussiesteve
Quote:
Originally Posted by aussiesteve
G'day electric traction boffins,
I have seen brief old BnW footage of third rail emu operation in the UK.
I don't remember the location, if detailed, and it would take a while to scan through my collection of DVDs.
There was a fourth rail, in the middle of the four-foot.
And sparks seemed to emanate occasionally when trains passed over gaps in this rail.
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Sounds like the UK underground system (which of course runs on the surface for some of the time) and has four rails.
According to Wonkypedia the outer rail carries +420V DC and the inner -210V DC, giving 630V in all. This is to reduce corrosion in the cast iron tunnel linings.
Linky to uk traction current supply here..
https://en.wikipedia.org/wiki/Railwa..._Great_Britain
We also have a Third rail system above ground for high -intensity commuter lines over much of the south eastern/south central part of the country which carries 750V DC. This can also occasionally have an apparent fourth centre rail, but is for an additional earth route in 'electrically difficult' areas. This rail does not contact the train, but is bonded to the running rails - which are the normal return route in third rail systems. One such place where this occurs is at Farringdon in the centre of London where EMUs used to be limited to 15mph whilst hauling themselves up a steep incline out of a wet tunnel.
And yes, I prefer Overhead traction current supply for two reasons.
1) There's no risk of electrocuting yourself if you put your feet down clumsily or take a tumble.
2) If your train has an electrical fire or fault, you will be told to isolate it from the traction supply. On the DC you have to go round the train and manually lift every shoe off the rail with a paddle (and it always seems to be raining or snowing at the time). A friend of mine was nastily burnt during a rain shower once when the last shoe flashed and his nylon trousers burnt away.
Whereas on the AC you just press the Pan Down button on your desk - and all the 25kV of scary electrickery goes away.
Best wishes. BW