OHLE over LU 4th rail

Kneedown · 30 Jul 2012

Many thanks for that Nym. Will have a good read of it.

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Nym · 30 Jul 2012

Kneedown said:
Many thanks for that Nym. Will have a good read of it.

Any questions or background, elaborations etc drop me a message or on here and I'll have a go at explaining it better than the paper does, there is a level of assumed knowledge on these things that is sometimes a bit high for the general non-expert audience it's supposed to be aimed it.

The search terms on Google Scholar are, "DC Tram Leakage Current Corrosion" if you want to search some more.

Kneedown · 31 Jul 2012

I think i've got the gist.
Basically the metal structures in the ground provide the path of least resistance for the stray current, thus accelerating the corrosion process?

Thought provoking stuff with the references to sewer pipes and reinforced concrete being damaged. I'd never even considered that before, but i had wondered why some of the structures around Hunts Cross look in poorer condition than elsewhere.

Thanks for taking the time to find and supply the info!

Bald Rick · 31 Jul 2012

A very real problem. The OLE structures at the south end of North London Line at Acton Central all had to be replaced 8 years ago for this very reason. We had a suspicion there was a problem, so did a pull test on one structure. Basically it came out with a big chap leaning on it. Cue hurried calls to steel manufacturers and some clever electrical engineers to figure out a permanent solution.

ole man · 1 Aug 2012

And what was the solution you came up with?.
As i stated above the NLL uses plastic insulated washers between each nut and bolt, also this is used on Thameslink around the City Thameslink area

Bald Rick · 1 Aug 2012

I'm not an engineer so can't really say. What I do remember is that it took some clever people a long time to come up with and it cost about half a million quid. This was on top of the insulation around all the anchor bolts in the foundations.

Mystic Force · 1 Aug 2012

So just to clarify, I understand that 3rd rail is not compatible with overhead AC because of issues with return currents and difference of grounding method. Except were significant infrastructure is used to mitigate this problem making it unsuitable for wide scale deployment.

However I am still unsure if the same issue was the case for 4th rail from the above discussion. So if someone who understands it could clarify this point for me I would be most grateful. And what I am referring to specifically is the use of London underground 4th rail alongside AC overhead. No 3rd rail running is being considered here.

es373 · 1 Aug 2012

Isn't this called electrosys? Not sure but maybe thinking of something else.

joeykins82 · 1 Aug 2012

apk55 said:
Therefore I would not see any problem in dual electrification on LU 4 rail systems with high voltage AC (although the signalling system would need considerable work to immunise for both systems as at lest one of the running rails would be needed as a return current path).

I think this answer is the best on here

swt_passenger · 2 Aug 2012

torquewrench said:
Isn't this called electrosys? Not sure but maybe thinking of something else.

Yes.

But spelt electrolysis - one of those awkward to remember terms. The effect is known as electrolytic corrosion.

OHLE over LU 4th rail

Kneedown

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