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Steam and overhead power lines question


mswjr

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25,000 volts sounds alot, but in static/lightening type electricity terms it isn't that much. You will get tracking across insulators that are dirty or where the glaze is breaking down, but that is just a trickle across the surface. Many years ago I used to walk past Willesden and could hear a crackling sound around one ohle post, then on a damp and dark morning I could actually see the arcing.

 

Insulators get dirty - fact. The amount of dirt they can tolerate can be offset by changing the 'Creepage distance' (the length along the surface of the insulator from live to ground). Vertical insulators will have undercut 'sheds' which allow rainwater to drip off without creating a continuous wet surface. When an insulator does become wet all over, the wet dirt provides a continuous path for leakage current. The surface wetting will not be uniform so that the leakage current will burn off patches of water in places. The leakage current then jumps across the dry band, that is the fizzing sound one can hear. Normally that current is quite low and would nt be expected to cause any deterioration of the insulator glazing. It is only when there is a flashover at traction current that temperatures hot enough to damage the glaze are generated. Leakage current cpuld be significant such that the only time to measure it, to see how big the problem was, was Christmas day when no trains were running.

 

I don't know the maths behind the static and kinetic clearances so that arcing does not happen in most wet weather conditions and with steam locos running under the wires. Some clever person does and that is why it is safe for trains hauled by steam locos are able to run safely under the wires.

 

Not much difference between static and dynamic clearances. Remember that clearances on 'open' lines are quite high, IIRC about 15 inches and much higher at some locations like level crossings where the wire can go up to about 18ft. It is only at places with restricted height clearance that the wires are brought down to the minimum clearance of 4 inches.

 

I seem to remember there was a ban on steam under the wire during the early 1980s. Possibly unofficial.

 

Brought in after one of the loco crews let the locomotive blow off whilst under the wires and damaged them. I think it was in Manchester.

 

Not sure how you can achieve an 'unofficial' ban. Neither am I sure what sort of damage could be inflicted as the contact wire is staggered to even out pantograph wear.

 

Surely they'd need to regularly clean the insulators at places like Birmingham NS if diesel exhaust was that much of an issue. Not to mention the Paddington to Heathrow bit.

 

As said above, you can put bigger insulators at places where there is considered to be any significant pollution - assuming anybody has actually considered it! In places like Warrington where you could even taste the stuff coming out of Crossfields soap factory in the 1970s, the insulators were covered in silicone grease to absorb the pollution but, yes, they still needed cleaning.

 

Humidity will affect the resistance of the air. In the case of someone peeing on a conductor rail the droplets are large and well spaced (see mythbusters for demonstration) In this case the droplets are tiny, very densely spaced, and the air is as humid as it is possible to be. It is only when the loco slips that the steam is dense enough to cause the flashover. The wire will be installed at minimum height for clearance to the infrastructure, so basically an all round worse case scenario.

 

Anybody still reading? Wires at stations would seldom be "installed at minimum height for clearance to the infrastructure", A significant part of the cost of electrification is taken up by the need to raise bridges to provide adequate clearance. It is only where the cost would be prohibitive that minimum clearance are used.

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As said above, you can put bigger insulators at places where there is considered to be any significant pollution - assuming anybody has actually considered it! In places like Warrington where you could even taste the stuff coming out of Crossfields soap factory in the 1970s, the insulators were covered in silicone grease to absorb the pollution but, yes, they still needed cleaning.

 

I have it in my head that the insulators along the sea wall at Saltcoats on the Ardrossan/ Largs line are a bit higher rated because of the nature of the location. Being a sea wall, and that. (Also proving that dawlish wouldn't be impossible).

On a related note, it certainly doesn't look like any other type of OLE that we have anywhere else that I've seen. Is that where the almost never used mk2 OLE is found?

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How, if at all , are insulators cleaned in the UK, and how regularily? I've watched it being done in France; a couple of tank wagons of water, and a van with part of its roof and top half of the sides and ends removed  to give a sort of 'verandah'. Some poor sool, clad like a deep-sea fisherman, including sou-wester, was pointing the jet from what liked a Karcher on steroids at the insulators.

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Not sure how you can achieve an 'unofficial' ban. Neither am I sure what sort of damage could be inflicted as the contact wire is staggered to even out pantograph wear.

 

 

 

Plenty of things are banned unofficially. Think of records on the BBC. They haven't physically banned it, it's just not getting played.

 

 

The whole steam ban from 1968 to 1971 was unofficial as was the Southern Region ban.

 

I think it was more a local issue rather than going to the higher echelons of BR. A case of I'm not letting any of those steam engines on my territory.

 

 

 

As I said this was in the early 1980s and occurred somewhere around Manchester. It was a loco crew letting their locomotive constantly blow off whilst stationary. So that section of OHLE was damaged.

 

 

Jason

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I am a third-rail person. No, not qualified to work on 630/750v dc equipment, but used to being near it, and occasionally stepping on it. I do not recommend peeing on it, because why would you want to? Anecdotally there have been unfortunate events of that sort, with distressing results. So don't, just in case.

 

As far as 25kv electric string is concerned, my only relevant experience is one misty evening standing on the platform at Milton Keynes, talking to the station manager. She and I were very aware of a 'pull' from the OLE through the mist. Again anecdotally, I heard of a terrible event more than 30 years ago when some drunk had indeed relieved himself off a bridge onto the OLE. He died of his injuries two days later, they said. Once again, you cannot see electricity, but you know it is there. Treat it with respect.

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Doing survey work under the OHL can be a bit disconcerting, in some places and conditions all the metal fittings on the survey staff could have such an induced current on them that if you touched them they felt like sticky tape. Looking through a level is also not much fun when you get an electric spark jumping to your eyeball every time you take a reading. Electronics also don't like the OHL I once had to do a whole survey with a rubber rail pad between the foot of the aluminium rod eye we were using and the rail, as otherwise the laser beam detector at the top of it went loopy every time the base of the rod eye touched the rail.

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I doubt they are there anymore but there used to be yellow metal "rails" at the end of the platforms at Euston that picked up quite a charge. If you ran your hands along them you could feel a distinct buzzing on them

 

Andi

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 Neither am I sure what sort of damage could be inflicted as the contact wire is staggered to even out pantograph wear.

 

Not sure what the relevance of stagger is - as the wire moves from one side to the other it will be directly above the track centre line (i.e. zero stagger) at mid span , and still close above the chimney or whatever for about 2/3 of the entire span length. Only if the loco is sitting almost directly under a registration is the wire likely to be a significant distance away due to stagger.

 

As said above, you can put bigger insulators at places where there is considered to be any significant pollution - assuming anybody has actually considered it! In places like Warrington where you could even taste the stuff coming out of Crossfields soap factory in the 1970s, the insulators were covered in silicone grease to absorb the pollution but, yes, they still needed cleaning.

 

Generally it is intended that rainwater is sufficient to wash dirt off insulators, such that cleaning is not normally required. However those under station canopies or bridges may need attention.

 

Anybody still reading? Wires at stations would seldom be "installed at minimum height for clearance to the infrastructure", A significant part of the cost of electrification is taken up by the need to raise bridges to provide adequate clearance. It is only where the cost would be prohibitive that minimum clearance are used.

 

Whilst I was talking specifically about Liverpool Street which does have a low wire height, there are many other stations which also have low wires. As the cost of raising a bridge is always expensive, it is usually the last resort - particularly at stations as track lowering is not an option! Not only that, but it is often the case that if a bridge is lifted, the less it is lifted the less expensive it will be, so it may well be lifted just enough to allow a minimum wire height through. As stations usually have a footbridge and often a road bridge adjacent, this means there are a large number of stations at or close to minimum wire height. This approach has of course recently been revised, but there are still a lot of stations out there with low wire heights.

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Doing survey work under the OHL can be a bit disconcerting, in some places and conditions all the metal fittings on the survey staff could have such an induced current on them that if you touched them they felt like sticky tape. Looking through a level is also not much fun when you get an electric spark jumping to your eyeball every time you take a reading. Electronics also don't like the OHL I once had to do a whole survey with a rubber rail pad between the foot of the aluminium rod eye we were using and the rail, as otherwise the laser beam detector at the top of it went loopy every time the base of the rod eye touched the rail.

 

I have done hundreds of OLE surveys all over the country in all weathers, using a variety of gauges (All based around a Hilti Laser gauge mind) and never had these problems. The only time the equipment struggled was in torrential rain, when the random distances it was measuring appeared to be the height of the raindrop above it when you pressed the button! Had to wait until the rain eased off and then all was well.

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There is or was video on YouTube showing a steam hauled charter train under the wires in heavy rain with an almost continuous arc from the wires through the black smoke to the funnel. Was probably from a link on this forum I saw it, but cannot find it now

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 Again anecdotally, I heard of a terrible event more than 30 years ago when some drunk had indeed relieved himself off a bridge onto the OLE. He died of his injuries two days later, they said. Once again, you cannot see electricity, but you know it is there. Treat it with respect.

An incident of this type did happen in the Birmingham area, IIRC it was at Belchers Lane between Adderley Park and Stechford.

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There is or was video on YouTube showing a steam hauled charter train under the wires in heavy rain with an almost continuous arc from the wires through the black smoke to the funnel. Was probably from a link on this forum I saw it, but cannot find it now

Was it this one? - http://www.rmweb.co.uk/community/index.php?/topic/48257-smokestack-lightning-youtube-clip/?hl=%2Bsmokestack+%2Blightning

 

(The consensus was that it was light from an open firehole door reflecting off the exhaust, not arcing.)

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Same reason they don't arc when it is misty or chucking it down with rain. Unless the water stream is continuous, the electricity is no better able to travel through it than through air. It's the same principle that if you were to urinate on a live third rail, you would not get  electrocuted up the pee stream because the stream is not a solid arc of pee.

I was reliably informed that peeing on an electric fence was very painfull! This was about 2500 volts and the scream was very loud!

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For info, first preserved steam mainline rail tour under wires was Britannia on a Pathfinder Cumbrian Mountains in Dec 94. Was due to be Union of South Afrika but was out of gauge. I was on it.

At least one Scottish A4 got a yellow stripe to show it was out of gauge for the reduced OHLE clearances from 1964

2953899735_4be2a277ef_z.jpg001-4-Perth-9-7-65-60031 by david.l.quayle, on Flickr

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Plent

 

For info, first preserved steam mainline rail tour under wires was Britannia on a Pathfinder Cumbrian Mountains in Dec 94. Was due to be Union of South Afrika but was out of gauge. I was on it.

 

Plenty of preserved steam railtours under the wires before that, here is Mallard under the wires at Carlisle...

 

https://youtu.be/UvlFeE38WN0?t=127

 

Not sure when the first was - but Flying Scotsman in the 1960's is a possibility if it ever ventured south of Crewe on the WCML.

 

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I have done hundreds of OLE surveys all over the country in all weathers, using a variety of gauges (All based around a Hilti Laser gauge mind) and never had these problems. The only time the equipment struggled was in torrential rain, when the random distances it was measuring appeared to be the height of the raindrop above it when you pressed the button! Had to wait until the rain eased off and then all was well.

 

Worst cases in twenty years of surveying, keep going and something interesting is bound to happen eventually.

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.....Unless the water stream is continuous, the electricity is no better able to travel through it than through air. It's the same principle that if you were to urinate on a live third rail, you would not get  electrocuted up the pee stream because the stream is not a solid arc of pee.

 

 

 

 

 

It has been tested!

https://m.youtube.com/watch?v=pDY-0ijiOEQ

 

Though as Phil advises don't try this at home.

 

 

 

But lets not try that! Hee hee

 

Phil

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Similar question to the OP, how does it work when an EMU or electric locomotive goes through the train wash?

Contact wires are usually set to their maximum height through washplants (they were at the two depots I worked at that had them)

 

Re insulators, this from GO/RT3440:

 

2.2.2 Operation under overhead line equipment

2.2.2.1 The infrastructure manager shall make available to railway undertakings information regarding the location of overhead line equipment that could be affected by emissions from the chimney or safety valve.

 

and

 

2.3.3 Operation under overhead line equipment

2.3.3.1 Railway undertakings shall, whenever possible (considering the possibility of unplanned events), prevent steam locomotives being brought to a stand at locations where emissions from the chimney or safety valve could affect overhead line equipment (as identified with reference to 2.2.2.1).

 

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Since the 68 finale.

 

That video of Mallard was in the 1980's, well before the 1994 you quoted. I particularly chose that clip as Mallard's last run was considerably before 1994, so that there could be no doubt about the proof.

 

Edit: More proof, Lion running under the wires in 1980!

 

https://youtu.be/oH7OTYgM3WU?t=119

 

Must be the oldest loco to run mainline under OLE!

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