Modern BR Overhead Equpiment

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Buntobox

Buntobox

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Can anybody tell me why it is that the overhead line equipment used in the UK these days is so bulky and apparently over-engineered? Look at this single line cantilever at Didcot...
30-01-2023 08-33-19.jpg
It's only holding up two 12mm wires and yet it looks as if it was designed to support the weight of a five ton truck! It's grotesquely ugly too as is all the GW main line kit, purely because of this ludicrous bulk. The stuff they put up on the Edinburgh & Glasgow is similarly heavy. Double track portals made with twin H beams across the track when previous installations only used one. Earlier electrification schemes were just not this substantial. Is it another health and safety overreaction? Looking at the enormously heavy steelwork, heavier even than they used for the Woodhead DC scheme, it's no wonder the GW electrification cost so much and had so many complaints about the visual intrusion from those living along the line.
I'm a fan of electrification but this stuff is grim.
 
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Renovater

Renovater

Western Thunderer
Buntobox said:
Can anybody tell me why it is that the overhead line equipment used in the UK these days is so bulky and apparently over-engineered? Look at this single line cantilever at Didcot...
View attachment 179222
It's only holding up two 10mm wires and yet it looks as if it was designed to support the weight of a five ton truck! It's grotesquely ugly too as is all the GW main line kit, purely because of this ludicrous bulk. The stuff they put upon the Edinburgh Glasgow is similarly heavy. Double track portals made with twin H beams across the track when previous installations only used one. Earlier electrification schemes just were not this substantial. Is it another health and safety overreaction? Looking at the enormously heavy steelwork, heavier even than they used for the Woodhead DC scheme, it's no wonder the GW electrification cost so much and had so many complaints about the visual intrusion from those living along the line.
I'm a fan of electrification but this stuff is grim.
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Have to agree with you there, it is rather surprising compared to other systems, a sensation of overkill. I've watched the cab video's on youtube of the GW main line as it is now, i don't know how drivers can handle it and that's coming from an ex-BR driver. If i'm correct the Swiss did the catenary, but i can't remember seeing it that bad in Switzerland !
 
Buntobox

Buntobox

Active Member
Renovater said:
Have to agree with you there, it is rather surprising compared to other systems, a sensation of overkill. I've watched the cab video's on youtube of the GW main line as it is now, i don't know how drivers can handle it and that's coming from an ex-BR driver. If i'm correct the Swiss did the catenary, but i can't remember seeing it that bad in Switzerland !
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Modern Swiss overhead is heavier than it used to be but it's nothing like this. From what I can gather the GW main line equipment was built by Furrey & Frey of Bern but there's nothing like it on the SBB or anywhere else so I can only assume it was built by them to a Network Rail specification. How they came up with such a specification is a mystery.
 
mickoo

mickoo

Western Thunderer
There was a spate of instances a few years back where high winds moved the OHLE clear of the pantograph which cost a fortune to repair and lost revenue due to closures. I believe part of the problem was found to be earlier lightweight portals and structure designs and partly due to wire tension, which in part cannot be increased because it'll pull the portals out of line.

The increase in tension to mitigate movement in the wind requires a stronger portal, you could of course place them closer together but that'd increase costs as well. You also need higher tension for higher speeds, maybe GWML will be higher than 125 in the future? Mind TGV gets away with lighter structures at 180 mph but then their posts are closer together I think.

I have to confess that even if the previous portals were 100% at fault, the current solution has not been engineered with grace.

Much of the GWR main line is relatively flat and prone to high winds, as would be Scotland and the WCML in the fells and Northamptonshire. The vast majority of high winds stem from the South west, in fact 90% of high winds come from the SW. We had a wind chart at work on the port detailing all the stoppages and duration nearly all stoppages for high wind were from the SW.

Switzerland on the other hand I suspect does not suffer from high winds (50mph+) very much at all.
 
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Yorkshire Dave

Yorkshire Dave

Western Thunderer
Mickoo has hit the nail on the the head.

The ECML and MML OHLE were built on the cheap and being lightweight they suffer badly in high winds causing speed reductions to ensure the pantograph head remains in contact with the catenary contact wire.

The Woodhead route was built to the known 1500v DC technology at the time and the line speeds were also much lower.

The trend today here and in Europe is to use single masts rather than cross spans or gantries where they can as they are easier, cheaper and quicker to replace in the event of being brought down.

From the photo of Didcot it appears the main arm is also spanning a non electrified track hence the solid construction. And as Mickoo alluded to the contact and catenary wires are under tension.

The heavier construction also allows higher line speeds which in turn requires a higher tension to minimise catenary wire oscillation and pantograph bounce.
 
G

Genghis

Western Thunderer
The designers of the GWML electrification clearly got it wrong: the piles are too deep and the support structures over-engineered. I think Network Rail has learned the lesson for more recent projects. It is useful to compare the GW design with this:

thsrc.jpg

Taiwan High Speed Rail. Electrification system designed for:

  • Frequent earthquakes
  • Frequent typhoons
  • 300km/h operation with heavy compound catenary.
 
76043

76043

Western Thunderer
I too read this on the GERS forum as much of the GEML is now of this type.

I suspect for over-engineered, read, less compensation claims from all and sundry?

Tony
 
Renovater

Renovater

Western Thunderer
Apart from severe high winds the GWML also suffers a lot from atmospheric ice more than other areas of Europe !;)
 
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michael080

michael080

Western Thunderer
The wire has a pretty high mechanical tension to remain on the same level without sagging. If the picture above has been taken in a curve, there would be a substantial force perpendicular to the wire requiring a massive post.
Nevertheless, I have to agree, this looks overengineered.
 
Buntobox

Buntobox

Active Member
mickoo said:
There was a spate of instances a few years back where high winds moved the OHLE clear of the pantograph which cost a fortune to repair and lost revenue due to closures. I believe part of the problem was found to be earlier lightweight portals and structure designs and partly due to wire tension, which in part cannot be increased because it'll pull the portals out of line.
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In the 70s BR found this to be a problem on the then new Weaver Junction to Glasgow electrification. As originally installed I do remember the contact wire noticeably sagged between the droppers in each span and it was down to fairly low tension and the fact that the wiring was a cost-saving simple design as opposed to the compound arrangement BR had previously used for lines in use at up to 100mph. The problem they had was the bearings in the three pulleys at each tensioning mast weren't good enough to allow extra tension because the friction involved prevented the contact wire from moving very much. They solved the problem by retrofitting the pulleys with roller bearings, installing intermediate masts to steady the catenary wire in mid-span and adding extra weight to the tensioning stacks at each end of wiring runs. These masts are still there to this day on the southern leg of the Beattock bank and possibly in other places too. They called this arrangement 'supertensioning' and I remember it was discussed in the Railway Magazine around 1977.
 
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Buntobox

Buntobox

Active Member
I understand that heavier portals might be needed to overcome winds and the stresses of trains passing at high speed, but look at this one spanning two tracks in sidings, again at Didcot. A touch over the top wouldn't you say? Did the people designing these things just forget everything that was learned in the previous sixty years?

31-01-2023 07-45-28.jpg
 
Osgood

Osgood

Western Thunderer
On the West Coast main line they tried additional intermediate wire support using helium balloons:
Helium Balloon trial.jpeg
www.networkrailmediacentre.co.uk

Helium balloon halts trains on West Coast main line in Tamworth

A helium balloon has caused delays to rail passengers after it got tangled in 25,000-volt overhead electric cables which power trains on the West Coast Mainline near Tamworth.
www.networkrailmediacentre.co.uk www.networkrailmediacentre.co.uk

Oh sorry, it reads halts, not trials.....:oops:
 
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