Wires down - how does it happen?

[southernyoshi]

Hello, the event at York today has reminded me to ask a question I’ve wanted to ask for ages. I’m not involved in the railway, just an ordinary norm passenger but I’ve always been intrigued by the idea of trains pulling wires down from below.

Can anyone explain in non-technical (norm) language how wire-pulls happen? How can a wire - which should be securely attached to its supports & thus the ground - be pulled down by a train - which should in theory always be under the wire? Always wanted to know but too afraid to ask

 

[swt_passenger]

Hello, the event at York today has reminded me to ask a question I’ve wanted to ask for ages. I’m not involved in the railway, just an ordinary norm passenger but I’ve always been intrigued by the idea of trains pulling wires down from below.

Can anyone explain in non-technical (norm) language how wire-pulls happen? How can a wire - which should be securely attached to its supports & thus the ground - be pulled down by a train - which should in theory always be under the wire? Always wanted to know but too afraid to ask

One possibility is that a dropper fails, that’s the vertical wire between contact and catenary, so the pantograph catches it.

With an extreme wind a wire might be moved such as the pantograph might come off the wire and rise. When it comes down it’ll bring everything down with it. Not sure how often that can happen in reality.

On the ECML four track sections the overall assembly of wires and insulators supporting the contact and catenary wires is known as a head span, and is under tension, if anything within the head span fails it can all go out of alignment with respect to all four of the tracks. So one failure can close four tracks.

 

[mwmbwls]

https://www.railengineer.co.uk/2019/09/27/back-to-portals/
As SWT reports head span is less operationally robust - Rail Engineer reports on how this situation can be retrieved by converting head spams to portal structures.

 

[swt_passenger]

If you check out the Twitter pics in post #30 of today’s ECML dewirement thread here:
https://www.railforums.co.uk/thread...e-damage-near-york-02-12.196059/#post-4314850
...then it looks as if the bottom wire of the head span has failed at the insulator where it connects to the stanchion. My understanding is that all four contact wires would then be able to move sideways across the track ie away from the stanchion.

 

[pdeaves]

In super, super simple terms, if the pantograph head ends up above the wire for any reason, it acts like a knife and slices through all the supporting bits.

 

[southernyoshi]

So a train can’t be an initial cause (as I say, it should always be below), but if something else causes any bit of the wire to fall below where it should be (without any technical knowledge, I guess it getting too hot/cold can do that?) then when a train gets there...it’s oops time.

Thank you, I think it’s the way it’s described as the train pulling down the wires that confused me as it implies the train was the initial cause.

 

[Bald Rick]

Put simply, OLE is a combination of various bits of metal tube and wire bolted together, with some insulators in the mix as well.

It only takes one component to fail - through corrosion, wear, or poor manufacture, and that can (at best) create a weakness that over time will lead to a failure and (at worst) cause an immediate failure.

I remember a case on the GEML where it all came down because one small hook bolt about 150mm long had not been welded properly in the factory, and missed by 4 separate quality checks (2 in the Swiss factory, one before installation, one after). After a particularly cold frost the weld failed, which caused the registration of the contact wire to drop by about 200mm, and that was that. (Every other component the same was checked, and it was the only one with the defect.)

Typical failures are bolts breaking through corrosion, insulators shattering through freeze-thaw, or droppers snapping. The latter is most common, but is less likely to cause a major issue.

 

[eman_resu]

Examples from Youtube;

 

[GRALISTAIR]

Typical failures are —-insulators shattering through freeze-thaw—.

I assume the move to polymeric insulators rather than ceramic might alleviate this going forward ( Glass Transition Temperatures Tg ( T sub gee) will I assume have been taken into account in the design and material choice?

 

[deltic08]

No wind here today so cannot be movement in contact or headspan wires. Coldest night of the Winter so far, down as low as -9 degrees C in the Vale of York with a rapid thaw by dawn.
Most likely lack of maintenance. I have never seen a wiring maintenance train on sight in 30 years.
Am booked on the Azuma press launch from Harrohate tomorrow so may know more then.
One very good reason for reinstating Harrogate-Ripon-Northallerton for diversions at a time like this. Completely closed for many hours while the wiring is cleared and how many hours to put back up. Bustitution still at 22:30 tonight. Absolute chaos at York and Newcastle for 2 hours 30 minutes before buses were found.

 

[ComUtoR]

So a train can’t be an initial cause (as I say, it should always be below),

The recent event at City Thameslink would be a result of the train pulling down the wires. As the Driver left the pan up :/

but if something else causes any bit of the wire to fall below where it should be (without any technical knowledge,

Helium balloons tend to get caught on the wires and the occasional plastic carrier bag also gets caught. Item + Pantograph = Wires down.

IIRC heat also causes he wires to droop and that has been caught in a pantograph before ?

 

[GB]

So a train can’t be an initial cause (as I say, it should always be below), but if something else causes any bit of the wire to fall below where it should be (without any technical knowledge, I guess it getting too hot/cold can do that?) then when a train gets there...it’s oops time.

Thank you, I think it’s the way it’s described as the train pulling down the wires that confused me as it implies the train was the initial cause.

A train could be the cause if the pantograph is already damaged in someway or has some debris already wrapped around it. Freight trains could damage the wires if the load has not been loaded correctly. Raising a pantograph at an improper location or speed or having too many pantographs up close together could cause issues. This is the problem when there are issues with the wires...most people (not saying you) are quick to blame Network Rail and their infrastructure without realising there could be other factors at play.

 

[DarloRich]

Hello, the event at York today has reminded me to ask a question I’ve wanted to ask for ages. I’m not involved in the railway, just an ordinary norm passenger but I’ve always been intrigued by the idea of trains pulling wires down from below.

Can anyone explain in non-technical (norm) language how wire-pulls happen? How can a wire - which should be securely attached to its supports & thus the ground - be pulled down by a train - which should in theory always be under the wire? Always wanted to know but too afraid to ask

Bluntly: usually one component ( often very small) fails causing the system to break. It may not happen instantly but will fail at some point usually by the pantograph being moved out of alignment by the fault. At, say, 125 mph a lot of wire will be ripped down very very quickly!

 

[AM9]

... Typical failures are bolts breaking through corrosion, insulators shattering through freeze-thaw, or droppers snapping. The latter is most common, but is less likely to cause a major issue.

The old pocelain/ceramic insulators were both heavy and when they did break, could be a danger to passengers if they failed near station platforms. I remember in the early '70s an incoming up 309 pulled the wiring down spectacularly despite only moving at about 40mph. Passengers were moved onto the down island platform but there was a nearly whole insulator (about 10 inclhes long and 6 inches diameter) laying on the platform. It could have caused serious injury or worse had it been a non-stopping up train in the evening when the down platforms might have been crowded.

 

[Pakenhamtrain]

You can also have a fault with the train that can cause massive current draw. Eventually the wire will just melt.

Even a train sitting in the wrong bit of an airgap can cause the overhead to melt:
The Oaks day chaos from 2008 is a nice example of that:

https://www.google.com/url?sa=t&rct...C977DC75DAE2&usg=AOvVaw1NpzqrtSuU8HF0torVDNZc

Recently we had incorrectly tensioned overhead cause a couple of damaged pantographs because it was a hot day.

 

[gordonthemoron]

AFAIR the OHLE came down at Stevenage in the early 90s because a Swan landed on it

 

[nlogax]

AFAIR the OHLE came down at Stevenage in the early 90s because a Swan landed on it

..and maybe this is how the idea of roast swan was resurrected.

 

[Bald Rick]

I assume the move to polymeric insulators rather than ceramic might alleviate this going forward ( Glass Transition Temperatures Tg ( T sub gee) will I assume have been taken into account in the design and material choice?

One would hope so.

 

[Bald Rick]

No wind here today so cannot be movement in contact or headspan wires. Coldest night of the Winter so far, down as low as -9 degrees C in the Vale of York with a rapid thaw by dawn.
Most likely lack of maintenance. I have never seen a wiring maintenance train on sight in 30 years.
Am booked on the Azuma press launch from Harrohate tomorrow so may know more then.
One very good reason for reinstating Harrogate-Ripon-Northallerton for diversions at a time like this. Completely closed for many hours while the wiring is cleared and how many hours to put back up. Bustitution still at 22:30 tonight. Absolute chaos at York and Newcastle for 2 hours 30 minutes before buses were found.

You won’t have seen a wiring maintenance train as no such thing exists on Network Rail. Most OLE maintenance is inspection, which can be done from ground level. When they need to get up to the wires themselves, they use elevated platforms off road railers. Or even ladders.

 

[southernyoshi]

I don’t really blame NR or anyone, I just wanted to know why these things happen - I especially never realised that the pantograph would act as a knife if the wire came low, I thought it’d be like running your finger along the bottom of a curtain - the curtain rising to match your height along the way lol . Also loving the stories of the strangest things to bring a wire down...

 

[swt_passenger]

I don’t really blame NR or anyone, I just wanted to know why these things happen - I especially never realised that the pantograph would act as a knife if the wire came low, I thought it’d be like running your finger along the bottom of a curtain - the curtain rising to match your height along the way lol . Also loving the stories of the strangest things to bring a wire down...

Somewhere in the Cambridge area (from memory) an OHLE stanchion very gradually fell over due to some sort of embankment failure, and eventually the wind took the wire completely out of alignment with the track and therefore trains. I think there’s a RAIB accident report about it:
https://assets.publishing.service.g...b60244000165/R062013_130520_Littleport_V2.pdf

bit of a slog but it also explains how the monitoring train can record the position of the contact wire.

 

[tsr]

The recent event at City Thameslink would be a result of the train pulling down the wires. As the Driver left the pan up :/

I don't believe that was the exact cause of the recent dewirement. Pantographs left raised after departing City Thameslink don't generally cause any damage until they hit the roof of Blackfriars Station...

Somewhere in the Cambridge area (from memory) an OHLE stanchion very gradually fell over due to some sort of embankment failure, and eventually the wind took the wire completely out of alignment with the track and therefore trains. I think there’s a RAIB accident report about it:
https://assets.publishing.service.g...b60244000165/R062013_130520_Littleport_V2.pdf

bit of a slog but it also explains how the monitoring train can record the position of the contact wire.

That is possibly similar to what happened on the West Coast Mainline last week near Bay Horse.

 

[Bald Rick]

Somewhere in the Cambridge area (from memory) an OHLE stanchion very gradually fell over due to some sort of embankment failure, and eventually the wind took the wire completely out of alignment with the track and therefore trains. I think there’s a RAIB accident report about it:
https://assets.publishing.service.g...b60244000165/R062013_130520_Littleport_V2.pdf

bit of a slog but it also explains how the monitoring train can record the position of the contact wire.

Yes that was a nasty one.

Other weather causes - blocked drains on Brick Lane (cause by unscrupulous restauranteurs throwing stuff in the gutter that should go in the bin), water backed up onto the bridge (OB18) over the GEML, this seeped through the brickwork, icicles, pan damage, wires down. That had Liverpool St shut for the best part of a day.

 

[swt_passenger]

Yes that was a nasty one...

Would RAIB only report if there was a risk to passengers, like in that case?
I’m assuming they don’t attend every ‘routine’ dewirement?

 

[ChiefPlanner]

Lost carbons on pantograph heads , or very badly chipped ones are another cause of dewirements , - along with a particularly bad incident I recall at Wembley Central many years ago - when a ground warming plastic sheet off a nearby allotment , blew onto the OLE , flashed over and as hit by a passing 87 , damaged the pan badly - then the flaming mass of plastic then landed on the (open) signalling troughing which were then burnt through. That was a terrible evening peak for all , with only 2 lines open and significant asset recovery needed overnight.

 

[Bald Rick]

Would RAIB only report if there was a risk to passengers, like in that case?
I’m assuming they don’t attend every ‘routine’ dewirement?

Yes, RAIB were only interested in Littleport as the pantograph came into the train, with the clear risk of passenger injury or worse. This is not the case for dewirements as a rule.

 

[deltic08]

You won’t have seen a wiring maintenance train as no such thing exists on Network Rail. Most OLE maintenance is inspection, which can be done from ground level. When they need to get up to the wires themselves, they use elevated platforms off road railers. Or even ladders.

That is what I meant. Not even one of those.

 

[Bald Rick]

That is what I meant. Not even one of those.

Well in that part of the world it would only ever be in the early hours of Sunday or Monday mornings, and each particularly stretch will have been visited by an elevated platform perhaps half a dozen times since it was put up. So you’d be lucky to see one even if you lived right next to it and stayed up all night every night.

 

[HOOVER29]

What we all want to know is was the electrification on the ECML don’t on the cheap?
Is it me or is there a massive amount of overhead failures on the ECML compared to the WCML?
Is it the way they are constructed?
There are many overhead supports on the WCML yet on the ECML there isn’t yet the former doesn’t seem to suffer anywhere near the amount of failures that the latter does.

 

[GRALISTAIR]

What we all want to know is was the electrification on the ECML don’t on the cheap?
Is it me or is there a massive amount of overhead failures on the ECML compared to the WCML?
Is it the way they are constructed?
There are many overhead supports on the WCML yet on the ECML there isn’t yet the former doesn’t seem to suffer anywhere near the amount of failures that the latter does.

North of Warrington there are many headspans of 1973isg vintage. South it is more robust being done in the 50s and 60s. The ECML was done in the 1980s and used different kit. I do think it is perception to a degree as we have had a few failures recently.