Third Rail - How does it work?!

[New Haven Neil]

4 minutes ago, Compound2632 said:

Trollybuses. Now I understood that they were a cheap way of continuing to use tram infrastructure without going to the expense of replacing worn out rails. So if the trams were returning through the rails, how did a trollybus, with its insulated wheels, work? 

 

Ours were a two wire system - but the power supply was as used by the Tramways - mercury-vapour rectifiers etc.  Which went on to power the NCB Westoe/Harton railway incidentally, replacing the rotary converters (which also remained in situ and operable).

Edited May 6, 2019 by New Haven Neil
spelling

[Compound2632]

Just now, uax6 said:

Through a negative return wire strung in the overhead.... or by dragging a skate on one of the rails behind the bus....

 

Andy G

 

Thanks - I'd just found that out. But the second method sounds a bit fishy...

[Mike Storey]

3 minutes ago, Compound2632 said:

Trollybuses. Now I understood that they were a cheap way of continuing to use tram infrastructure without going to the expense of replacing worn out rails. So if the trams were returning through the rails, how did a trollybus, with its insulated wheels, work? 

 

A trolleybus almost always uses two wires at height, one for feed and one for return, whereas a tram or train, has one overhead wire, and usually uses one or both running rails for the return or earth.

 

[melmerby]

32 minutes ago, Nearholmer said:

I’ve found a copy of the BoT Regulations governing leakage from traction return (not on-line, it’s an Appendix in an old textbook), and the version as amended up to 1912 requires:

 

- potential difference return to Earth not to exceed 3V;

 

- leakage not to exceed 2A per single track mile;

 

- potential difference between any two points in the return circuit not to exceed 7V.

 

It is mostly aimed at street tramways, where the risk of leakage is far greater than on a railway, and the title makes clear that one of the big concerns was electrolytic corrosion of gas and water mains by return currents choosing that path.

With the universal change to plastic service pipes on renewal that will diminish in the future (probably already has)

[uax6]

But used quite a bit for buses gaining access to depots that where once tram depots, but haden't had their wiring modded, or for the testing of new busses before the tramway was abandoned...

 

Andy G

[melmerby]

duplicated by save!

Edited May 6, 2019 by melmerby
two posts whilst trying to save

[Compound2632]

There's a family tale that my grandmother was nervous of treading on the tram tracks for fear of getting an electric shock. She once asked a tram conductor about this, he said, only if you put your other foot on the overhead wire. That didn't go down to well - apart from anything else, she wasn't by any means a tall woman.

[melmerby]

1 minute ago, Compound2632 said:

 

Thanks - I'd just found that out. But the second method sounds a bit fishy...

Used when trolleybuses needed to traverse a section wired  only for trams.

Birmingham did on some depot moves during normal service and not for the reason as quoted above

[uax6]

3 minutes ago, melmerby said:

With the universal change to plastic service pipes on renewal that will diminish in the future (probably already has)

 

Probably not actually. Its going to take a very long time to replace all water and gas mains, and then you have the telecom ducts, and they can produce some interesting effects to speech!

 

Then there is the effect on other buried metal objects that happen to be used in any sort of electric circuit...

 

Andy G

[Nearholmer]

On interference with early telegraph systems, another of my ancient electric railway textbooks has this to say:

 

"In the early days a certain amount of trouble was experienced with telegraph instruments due to the earth currents; this was effectively eliminated by inserting resistance in circuit with the instruments, and increasing the battery power for working the telegraphs."

 

The text goes on to blame noise on telephone lines caused by DC traction systems on poor quality insulation on the telephone circuits, which seems fair to me, as a heavy current chap, but may not seem fair to telephone engineers!

 

If you'd like to see the world's first trolleybus, and how it collected current, there is an animation here https://new.siemens.com/global/de/unternehmen/ueber-uns/geschichte/news/mit-strom-auf-die-strasse.html

Edited May 6, 2019 by Nearholmer

[melmerby]

9 minutes ago, uax6 said:

 

Probably not actually. Its going to take a very long time to replace all water and gas mains, and then you have the telecom ducts, and they can produce some interesting effects to speech!

 

Then there is the effect on other buried metal objects that happen to be used in any sort of electric circuit...

 

Andy G

All the ones in Brum being disturbed by the tram works seem to be fibre in plastic

[Nearholmer]

Compound

 

Your grandmother might have enjoyed the the first practical, as opposed to purely demonstration, electric railway in the world, that built by Siemens & Halske at Gross Lichterfelde in 1881, because, in common with a number of other pioneering efforts, it used two-rail electrification, just like most people's toy trains (I use the more advanced third-rail electrification system). 

 

I've read a contemporary French account of it that talks about thrill-seekers deliberately giving themselves shocks by touching both rails simultaneously, and women getting shocks while crossing the track due to their trailing skirts, which the author (rather unchivalrously) blames on them for not paying more attention because they are too busy fiddling with their make-up!

 

Kevin

 

 

Edited May 6, 2019 by Nearholmer

[Compound2632]

Probably not, as she was born in 1899, by which time, I read, it had been converted to overhead. Not that it sounds much more dangerous than my maternal grandfather's youthful and very Irish hobby of turning sixpences into ha'pennies with the assistance of the DSER at Arklow. (That would have been in the years immediately leading up to and maybe during the Great War - he was born in 1905.)

Edited May 6, 2019 by Compound2632

[298]

57 minutes ago, Compound2632 said:

 

Thanks - I'd just found that out. But the second method sounds a bit fishy...

 

A Trolleybus has run at Crich, with a small 4w Trolley towed behind for current return.

[Edwin_m]

2 hours ago, Nearholmer said:

They do, except in the case of trolleybus systems, some odd three-phase systems like people-movers at airports, and very early Siemens DC tramway/railway systems which had two overhead slotted-tube conductors.

 

There are/were also probably other oddities that I’m ignorant of.

I seem to remember the conduit system used in London and some other places had two power rails in the conduit, so the running rails were presumably not used for return current. 

1 hour ago, Compound2632 said:

There's a family tale that my grandmother was nervous of treading on the tram tracks for fear of getting an electric shock. She once asked a tram conductor about this, he said, only if you put your other foot on the overhead wire. That didn't go down to well - apart from anything else, she wasn't by any means a tall woman.

Pretty sure that was actually a cartoon in Punch magazine. 

[melmerby]

1 hour ago, Nearholmer said:

 

The text goes on to blame noise on telephone lines caused by DC traction systems on poor quality insulation on the telephone circuits, which seems fair to me, as a heavy current chap, but may not seem fair to telephone engineers!

 

 

I'm not surprised, as insulation on telecom cables, before the advent of plastics, was pretty crude as paper was still a common insulator in multi-core cables, even when I joined the GPO.

The slightest bit of moisture seeping in and......... well you can guess!

[johnofwessex]

I read that the Tyers Tabley Apparatus at Bath Junction suffered a 'wrong side' failure as a result of interference from Tram Cables under the Bellotts Road bridge

[melmerby]

9 minutes ago, Edwin_m said:

I seem to remember the conduit system used in London and some other places had two power rails in the conduit, so the running rails were presumably not used for return current. 

 

Correct

London even had plough entry and exit points on the system where they changed over to trolley pole:

https://dewi.ca/trains/conduit/ploughs.html

 

Blackpool started with conduit but constant wind blown sand made the system unreliable and they soon changed to O/H wiring.

[melmerby]

1 hour ago, Nearholmer said:

I use the more advanced third-rail electrification system

Kevin

 

AC of course, fed directly from the 240v by a rheostat

[Nearholmer]

Very tempted, there being a good few locos still around which were designed for that system, but probably not the best idea to apply in a modern domestic setting.

 

What I do really fancy creating is miniature generating station, and I'm always on the look out for an old open-frame DC machine of about 24V to use as a dynamo, and a very small gas engine. Both are now surprisingly difficult to find, collectors hang on to what they've got, whereas even fifty years ago there were a few still about - forty years ago, I created a 5hp rotary-convertor set, mains 415V AC to 24V DC, obtaining the DC machine from an old battery-operated mobile crane.

 

The ultimate would be to recreate this marvellous model railway, which was used by Professors Ayrton and Perry to demonstrate the automatic control of trains (well single car trams) in the early 1880s https://www.gettyimages.ca/detail/news-photo/professirs-ayrton-and-perrys-new-electric-railway-a-gas-news-photo/455698621 This set-up is largely forgotten, but was hugely important, because it was the first time that anyone had used relays to control power flow, rather than just as repeaters in telegraphy, and it led directly to automatic lifts (elevators), and through them to multiple-unit control of trains.

Edited May 7, 2019 by Nearholmer

[Joseph_Pestell]

13 hours ago, Compound2632 said:

Probably not, as she was born in 1899, by which time, I read, it had been converted to overhead. Not that it sounds much more dangerous than my maternal grandfather's youthful and very Irish hobby of turning sixpences into ha'pennies with the assistance of the DSER at Arklow. (That would have been in the years immediately leading up to and maybe during the Great War - he was born in 1905.)

 

Converted sixpences into halfpennies. Did he ever consider becoming Chancellor of the Exchequer?

[Mark Saunders]

39 minutes ago, Joseph_Pestell said:

 

Converted sixpences into halfpennies. Did he ever consider becoming Chancellor of the Exchequer?

 

The Bank of England was set up on a better model, you gave them your money and in return they gave you a promissory note, they just keep reprinting them!

[Compound2632]

6 hours ago, Joseph_Pestell said:

 

Converted sixpences into halfpennies. Did he ever consider becoming Chancellor of the Exchequer?

 

No. He had a much more useful career as foreman of a council house maintenance team, in the days when council housing meant something worthwhile.

[ess1uk]

So the ECRO doesn’t have a big control and adjust the voltage up and down to change the trains speed? 

[Nearholmer]

On the former Post Office Railway, that was pretty much how things worked, except that it was done by automated relay control, rather than a bod, with a big knob(!).

 

 

Edited May 12, 2019 by Nearholmer