OHLE on GWR

[MotCO]

I've recently watched this in-cab view of the last day of HSTs on GWR.

One thing which I was surprised about was the way the OHLE, particularly between Reading and Paddington (at around 3:00:00) appeared to move from the left hand side of the track to the right hand side and back again, instead of staying dead centre.

Firstly, I found it difficult to concentrate whilst the line was swaying from side to side - do drivers find this off-putting?

Secondly, why does the OHLE move around? Is it to help with the tensioning on the wire; is it to even out wear on the pantographs, or is it for another reason?

 

[HSTEd]

Secondly, why does the OHLE move around? Is it to help with the tensioning on the wire; is it to even out wear on the pantographs, or is it for another reason?

If it stays dead centre it will wear a notch in the carbon contact strip on the pantograph, which has to be replaced whilst most of the material is still on the strip.

If it goes back and forth it wears the strip evenly.

 

[hexagon789]

I've recently watched this in-cab view of the last day of HSTs on GWR.

One thing which I was surprised about was the way the OHLE, particularly between Reading and Paddington, appeared to move from the left hand side of the track to the right hand side and back again, instead of staying dead centre.

Firstly, I found it difficult to concentrate whilst the line was swaying from side to side - do drivers find this off-putting?

Secondly, why does the OHLE move around? Is it to help with the tensioning on the wire; is it to even out wear on the pantographs, or is it for another reason?

If the OLE wires were not strung from side-to-side as it were a deep groove would be worn in the centre of the pantograph carbon strips particularly with trains running at higher speeds; by using a "sway" pattern it evens out wear and gives much longer life on the carbon strips. It's standard practice with OLE installations and not unique to the GWML.

 

[Pete_uk]

I do wonder if the supports ever give drivers a hypnotic effect!

 

[hexagon789]

I do wonder if the supports ever give drivers a hypnotic effect!

Not OLE supports, but the original Eurostars had smaller than normal windscreens to reduce the supposedly hypnotic effect of traversing the Channel Tunnel, presumably because it's done at speed (160km/h) and because it's so long, about 20 mins of continous tunnel running.

 

[themiller]

Not OLE supports, but the original Eurostars had smaller than normal windscreens to reduce the supposedly hypnotic effect of traversing the Channel Tunnel, presumably because it's done at speed (160km/h) and because it's so long, about 20 mins of continous tunnel running.

That was due to the joints between concrete tunnel segments causing a rapid flicker effect rather than overhead line supports which are spaced much further apart.

 

[MotCO]

That was due to the joints between concrete tunnel segments causing a rapid flicker effect rather than overhead line supports which are spaced much further apart.

But you don't get affected if driving the new Eurostars?

 

[popeter45]

But you don't get affected if driving the new Eurostars?

would not be surprised if 373's where designed not knowing if it would affect drivers so aired on side of caution but later found to not be an issue so 374 where allowed bigger front windows

 

[themiller]

It was a suspected problem which (I expect) turned out not to be a problem at all.

 

[hexagon789]

That was due to the joints between concrete tunnel segments causing a rapid flicker effect rather than overhead line supports which are spaced much further apart.

Indeed, but it was the only approximate example that came to mind

 

[edwin_m]

If the OLE wires were not strung from side-to-side as it were a deep groove would be worn in the centre of the pantograph carbon strips particularly with trains running at higher speeds; by using a "sway" pattern it evens out wear and gives much longer life on the carbon strips. It's standard practice with OLE installations and not unique to the GWML.

The notch could even contribute to dewirement in areas where the wire did move off to one side. There are various reasons apart from evening out pantograph wear why it has to do that, not least that the overhead has to be a straight line between supports but the track has curves.

 

[hexagon789]

The notch could even contribute to dewirement in areas where the wire did move off to one side. There are various reasons apart from evening out pantograph wear why it has to do that, not least that the overhead has to be a straight line between supports but the track has curves.

It's always amazed me how close pantographs seem to come to desiring on curves without actually doing so. The tolerance seems quite small but it could just be the way it appears

 

[hwl]

appeared to move from the left hand side of the track to the right hand side and back again, instead of staying dead centre.
Is it to help with the tensioning on the wire; is it to even out wear on the pantographs, or is it for another reason?

The technical word for it is "stagger" as other have said it is there to even out strip wear including the risks with notch formation, it actually makes tensioning etc. more difficult!

 

[Dr Hoo]

Original low-speed tramways often had trolley poles with grooved trolley 'wheels' for current collection, so stagger wasn't necessary (albeit still with the 'chord'/polygonal geometry over curved track) but obviously not suitable for higher speed applications.

 

[edwin_m]

It's always amazed me how close pantographs seem to come to desiring on curves without actually doing so. The tolerance seems quite small but it could just be the way it appears

Original low-speed tramways often had trolley poles with grooved trolley 'wheels' for current collection, so stagger wasn't necessary (albeit still with the 'chord'/polygonal geometry over curved track) but obviously not suitable for higher speed applications.

Trolley wheels (including those used by the original streetcar named desire in New Orleans - sorry I assume autocorrect strikes again but couldn't resist that one) had other advantages, particularly that they could stagger well off to one side of the whole vehicle let alone how far a pantograph could reach. So tight curves needed fewer supports or pull-wires to keep the stagger within limits, and it was even possible to do things like put the wires near the kerb instead of the middle of the road. But they were prone to dewirement and each support needed to be a bit more complicated to ensure it didn't foul the passing wheel.

 

[McRhu]

Never mind getting hypnotised by passing OLE, they should make the windscreens on GWML stock as tiny as possible to prevent the drivers getting depressed by the Series 1.

 

[Bald Rick]

I do wonder if the supports ever give drivers a hypnotic effect!

From my experience up front, you’re not looking at the wires, but the track and signals.

 

[pdeaves]

From my experience up front, you’re not looking at the wires, but the track and signals.

True, but what you are concentrating on and what the eyes/brain detect are not necessarily a 1:1 relationship.

 

[hexagon789]

Trolley wheels (including those used by the original streetcar named desire in New Orleans - sorry I assume autocorrect strikes again but couldn't resist that one) had other advantages, particularly that they could stagger well off to one side of the whole vehicle let alone how far a pantograph could reach. So tight curves needed fewer supports or pull-wires to keep the stagger within limits, and it was even possible to do things like put the wires near the kerb instead of the middle of the road. But they were prone to dewirement and each support needed to be a bit more complicated to ensure it didn't foul the passing wheel.

Blasted thing, twice I corrected that to de-wire and still it gets the better of me! I believe the Milwaukee Road used a trolley pole system on one of its more rural mainlines and at speeds up to ~70mph. One of the 'other' Hiawathas took this route for part of its journey. Not sure how they set up the stagger on that, I'd assume the higher speeds and nature of the operations would've made it higher spec than a trolleycar line

 

[popeter45]

whenever ive seen fixed feeder rails at St Pancreas Low Level or pictures of the Seven Tunnel i've never seen that set up to move from side to side
am i mistaken or does that not need to spread across the pantograph?

 

[hexagon789]

whenever ive seen fixed feeder rails at St Pancreas Low Level or pictures of the Seven Tunnel i've never seen that set up to move from side to side
am i mistaken or does that not need to spread across the pantograph?

Isn't the track fairly straight? And given the low speeds there, presumably it's not a issue for a brief period of use.

 

[Domh245]

There is still 'stagger' on rigid overhead conductors - with wires it's 'point-to-point' in straight lines, but with ROCS these take on a more curvy effect. It's talked about a bit in this article

 

[Taunton]

Blasted thing, twice I corrected that to de-wire and still it gets the better of me! I believe the Milwaukee Road used a trolley pole system on one of its more rural mainlines and at speeds up to ~70mph. One of the 'other' Hiawathas took this route for part of its journey. Not sure how they set up the stagger on that, I'd assume the higher speeds and nature of the operations would've made it higher spec than a trolleycar line

You are pretty much there, it wasn't the main line Milwaukee Road (CMStP&P) with the Hiawatha (conventional main line steam, then diesel, trains) but their competitor between Chicago and Milwaukee, the North Shore Line (CNS&M), who ran traditional USA Interurban trolleys, lashed up into trains of five or more, all with trolley poles up, at speeds up to 90mph. Double track, signalled, innumerable level crossings, wooden-bodied cars.

No, I don't quite know how they did it without dewiring either. But it lasted for 60 years. I understand the Pacific Electric around Los Angeles was similar.

 

[hexagon789]

You are pretty much there, it wasn't the main line Milwaukee Road (CMStP&P) with the Hiawatha (conventional main line steam, then diesel, trains) but their competitor between Chicago and Milwaukee, the North Shore Line (CNS&M), who ran traditional USA Interurban trolleys, lashed up into trains of five or more, all with trolley poles up, at speeds up to 90mph. Double track, signalled, innumerable level crossings, wooden-bodied cars.

No, I don't quite know how they did it without dewiring either. But it lasted for 60 years. I understand the Pacific Electric around Los Angeles was similar.

I'm aware of that line but it's not the one I mentioned. There was a Milwaukee Road route which used boxy electrics on trolley wires on a mountainous route and which had a secondary "Hiawatha" service over the route. The line was de-wired in the 1960s or 1970sas I recall.

 

[Western Lord]

You are pretty much there, it wasn't the main line Milwaukee Road (CMStP&P) with the Hiawatha (conventional main line steam, then diesel, trains) but their competitor between Chicago and Milwaukee, the North Shore Line (CNS&M), who ran traditional USA Interurban trolleys, lashed up into trains of five or more, all with trolley poles up, at speeds up to 90mph. Double track, signalled, innumerable level crossings, wooden-bodied cars.

No, I don't quite know how they did it without dewiring either. But it lasted for 60 years. I understand the Pacific Electric around Los Angeles was similar.

The Milwaukee Road's Pacific extension, of course, did have two sections of conventional overhead electrification.

 

[hexagon789]

I think the train service was the Olympian Hiawatha, electrically hauled for part of its journey on the Mountain division of the CMStP&P

 

[Taunton]

I'm aware of that line but it's not the one I mentioned. There was a Milwaukee Road route which used boxy electrics on trolley wires on a mountainous route and which had a secondary "Hiawatha" service over the route. The line was de-wired in the 1960s or 1970sas I recall.

Yes, though the locomotives of various types, many multi-part articulated, had substantial diamond pantographs, along with decidedly Heath Robinson-looking overhead held up with wooden poles, possibly no two adjacent ones ever the same height. https://donsdepot.donrossgroup.net/dr0600/klm018.jpg It can be a bit confusing that the USA calls the overhead, as here, "trolley wire". The two separate electric sections on the route, though each a division long in themselves and covering the worst gradients through Montana and Idaho, meant that through trains from Minneapolis to Seattle had to change traction four times along the way.

 

[edwin_m]

I don't think an overhead designed for trolley poles would have stagger, especially for high speeds, as the pole would be thrown from side to side with the risk of it dewiring as its lateral travel is reversed on passing a support.

Many mountainous sections in the States were electrified in the early 20th century, partly for hill-climbing but also because multiple steam locos working hard through a tunnel presented a very real risk of asphyxiation. Once diesels came along that problem largely went away - but not totally, as I recall being brought to a screeching halt on Amtrak in the Moffatt Tunnel on emergency lighting. The conductor came on the PA to announce that the driver had been instructed to stop and shut down until the fume levels went down a bit.

 

[hexagon789]

Yes, though the locomotives of various types, many multi-part articulated, had substantial diamond pantographs, along with decidedly Heath Robinson-looking overhead held up with wooden poles, possibly no two adjacent ones ever the same height. https://donsdepot.donrossgroup.net/dr0600/klm018.jpg It can be a bit confusing that the USA calls the overhead, as here, "trolley wire". The two separate electric sections on the route, though each a division long in themselves and covering the worst gradients through Montana and Idaho, meant that through trains from Minneapolis to Seattle had to change traction four times along the way.

I think it was references to "trolley wires" that made me assume it was such; it actually was a bit more substantial but still not as heavily engineered as we might make it.

 

[Taunton]

Although US catenary may not look as substantial as European, it also generally looks far more messy, with all sorts of sundry wires and cables all over the place, mirroring to quite an extent what you find on the streets of many American cities. There also seems a policy that no two masts look the same ... it is also common US practice for the high voltage feed from the power station to the various substations to be carried on either the same or adjacent masts at considerable height - at road overbridges, which the catenary passes beneath, these high voltage lines being carried way up high over everything.