Great Western Main Line electrification - ongoing discussion

[whole diary]

[onthecushions]

With this in mind, would it not be more beneficial to prioritise electrification of stopping services? Every stop is followed by acceleration, so the more stops, the more time is gained by higher acceleration.

To be fair this is generally what has happened in the past, when the railway had overall control of its projects. Electrification would start from the terminal spreading out to include the stopping services initially. These were the ones most in need of greater capacity and the hardest to work with steam. Some enormous tank locos were devised for these purposes. The lower marginal costs then allowed outer suburban services to be electrified progressively, until, on the Southern, they reached the beach!

The first WC^▸ (Wiltshire Council (Unitary Authority)) electrification was criticised for starting at the wrong (Manchester) end but 25kV was very experimental and needed proving outside of a London main line. In any case the Watfords were already dc.

What has complicated the GWEP^▸ (Great Western Electrification Program) is Crossrail being quite separate and the need for proving the new (and on-time!) bought out Hitachis. Otherwise the sensible and cost effective approach would have been to convert the Oxfords as soon as possible, much earlier than 2017/8. The scheme would have begun to pay for itself sooner and avoided the excessive apparent first cost. I'm sure GWR^▸ (Great Western Railway) would have preferred to compete with Chiltern using 319's rather than turbos.

Roll out the wires,

OTC

[ellendune]

Are the GEWP structures ugly yep and so are the WCML^▸ (West Coast Main Line), ECML^▸ (East Coast Main Line)

While all three may be considered ugly by some, I'm sure they aren't considered equally ugly. The East Coast OHLE in this pic (not one of mine) is a little unsightly, but far less obtrusive than most of the new stuff Network Rail is installing. One way this ECML OHLE could be further improved aestheticly I think would be making the main vertical posts cylindrical (like lamposts) (I've probably already posted this earlier in the topic, but I can't remember for sure).

The price paid for the very slender design of the ECML OHLE is its poor reliability. The very poor reliability of the ECML equipment was one reason electrification was opposed by many - indeed you can read some on this community making that point when there was an OHLE failure outside Paddington recently.  But that is old style OHLE.

[broadgage]

The price paid for the very slender design of the ECML^▸ (East Coast Main Line) OHLE is its poor reliability. The very poor reliability of the ECML equipment was one reason electrification was opposed by many - indeed you can read some on this community making that point when there was an OHLE failure outside Paddington recently.  But that is old style OHLE.

Indeed, I have previously expressed doubts about the potential unreliability of the GW^▸ (Great Western) electrification, having previously suffered from the failed East Coast scheme.
I find the very substantial structures being erected at present on the GWR^▸ (Great Western Railway) route to be at least somewhat re-assuring.

I remain a little doubtful, but less so than in the past.

[John R]

And to clarify, headspan suffers from a) being easier to bring down b) when it comes down, all four lines are taken out and c) it takes much longer to put back together again.  So both the frequency and severity of disruptions are magnified several-fold.

If money were no object then the overlap between the introduction of IEP^▸ (Intercity Express Program / Project.) and the withdrawal of the HSTs^▸ (High Speed Train) would be used to run the east coast on diesel for a few months whilst they replaced the east coast headspan (at least north of Hitchin). It's a once in a generation opportunity to do it at a lower cost and less disruption.

[stuving]

Moving away from the pretty><ugly, to the wider scope of electrification, beyond what is currently being done on the GWML^▸ (Great Western Main Line): it's my understanding ^ which could well be incorrect, I'm not an engineer ^ that the main benefits of electric traction over diesel are efficiency and cost of energy, reduced pollution (air and noise pollution). In performance terms, the first would seem to be much improved acceleration, with higher top speeds being more dependent on track and signalling as well as arguably benefiting fewer services. With this in mind, would it not be more beneficial to prioritise electrification of stopping services? Every stop is followed by acceleration, so the more stops, the more time is gained by higher acceleration.

In practice, acceleration from a stop may not be that much better than with diesel power - in part because it's limited by adhesion, and by "weight over the wheels". In addition, electric motors (especially with a modern variable-frequency drive) give pretty much a constant torque (and traction force) at low speed, with power slowly rising with speed. When the power reaches the maximum for the motor (or the source) then at higher speeds it's the power that is constant, with torque falling off with speed.

So the real advantage of electrics is better acceleration at high speed. How high is "higher"? For IEP^▸ (Intercity Express Program / Project.) it was expected the power limit threshold would be at about 55 km/hr, or only 35 mi/hr. So electrics do still have a big advantage, not just at stops but when speeding up after every speed check.

[onthecushions]

The price paid for the very slender design of the ECML^▸ (East Coast Main Line) OHLE is its poor reliability. The very poor reliability of the ECML equipment was one reason electrification was opposed by many - indeed you can read some on this community making that point when there was an OHLE failure outside Paddington recently.  But that is old style OHLE.

Let's not be too hard on the Mark 3 OLE^▸ (Overhead Line Equipment, more often "OHLE"). The system was supplied to the KCR (Kowloon Canton Railway) in 1982 in Typhoon proof mode!

It was half the price of the previous Mark 1 but required more and cleverer maintenance, such as an  O level or two in geometry. At the low point in RT/NR^» (Network Rail - home page)'s privatised maintenance history, this wasn't around. Today's powers and speeds need roundly double the tension in the contact wire and catenary, so a bit more than washing line needs to be strung between the masts, if enhanced use is to be made of the system.

Time marches on,

OTC 

[Chris from Nailsea]

It was half the price of the previous Mark 1 but required more and cleverer maintenance, such as an O level or two in geometry. At the low point in RT/NR^» (Network Rail - home page)'s privatised maintenance history, this wasn't around. Today's powers and speeds need roundly double the tension in the contact wire and catenary, so a bit more than washing line needs to be strung between the masts, if enhanced use is to be made of the system. 

Priceless! 

[paul7575]

If money were no object then the overlap between the introduction of IEP^▸ (Intercity Express Program / Project.) and the withdrawal of the HSTs^▸ (High Speed Train) would be used to run the east coast on diesel for a few months whilst they replaced the east coast headspan (at least north of Hitchin). It's a once in a generation opportunity to do it at a lower cost and less disruption.

They have already done a trial fit to replace headspan with portal on the ECML^▸ (East Coast Main Line) near Potters Bar, it would probably be done overnight and/or during normal weekend possessions in the same way as it is being done between Paddington and Airport Junction at the moment.   There'd be no real need for running on diesel for a few months,  as it could only be done when trains were not running anyway.

There's a contractor's video/photos of the procedure as used in the Paddington approaches here:   https://vimeo.com/150907486

Shame about the music, but it does show how the new registration arms etc are fitted around the existing catenary and contact wires, which remain in use.

Paul   

[IndustryInsider]

Thanks for linking the video, Paul.  Hopefully the strong winds today aren't affecting such planned work too much!

[John R]

That's interesting, so thanks Paul. I'm not convinced it could be done in an overnight possession, so wonder how long it would take to do a meaningful amount of the ECML^▸ (East Coast Main Line).  That's why I thought a period where the power were switched off, the headspan removed and portal built could be a much more cost effective approach. Yes, the work would still be done overnight, but as we've seen on the GWML^▸ (Great Western Main Line), that's perfectly feasible. 

[John R]

And guess what - long delays on the ECML^▸ (East Coast Main Line) tonight because of overhead line problems at Sandy. Delays showing of up to 3 1/2hrs, although things starting to move again.   

[Electric train]

That's interesting, so thanks Paul. I'm not convinced it could be done in an overnight possession, so wonder how long it would take to do a meaningful amount of the ECML^▸ (East Coast Main Line).  That's why I thought a period where the power were switched off, the headspan removed and portal built could be a much more cost effective approach. Yes, the work would still be done overnight, but as we've seen on the GWML^▸ (Great Western Main Line), that's perfectly feasible. 

The vid does say all done in 20 hours, and that will be an all lines block.

The ECML have been concentrating their headspan to portal conversations at the Neutral Section locations and a few key junctions / locactions

[Bmblbzzz]

With this in mind, would it not be more beneficial to prioritise electrification of stopping services? Every stop is followed by acceleration, so the more stops, the more time is gained by higher acceleration.

To be fair this is generally what has happened in the past, when the railway had overall control of its projects. Electrification would start from the terminal spreading out to include the stopping services initially. These were the ones most in need of greater capacity and the hardest to work with steam. Some enormous tank locos were devised for these purposes. The lower marginal costs then allowed outer suburban services to be electrified progressively, until, on the Southern, they reached the beach!

The first WC^▸ (Wiltshire Council (Unitary Authority)) electrification was criticised for starting at the wrong (Manchester) end but 25kV was very experimental and needed proving outside of a London main line. In any case the Watfords were already dc.

What has complicated the GWEP^▸ (Great Western Electrification Program) is Crossrail being quite separate and the need for proving the new (and on-time!) bought out Hitachis. Otherwise the sensible and cost effective approach would have been to convert the Oxfords as soon as possible, much earlier than 2017/8. The scheme would have begun to pay for itself sooner and avoided the excessive apparent first cost. I'm sure GWR^▸ (Great Western Railway) would have preferred to compete with Chiltern using 319's rather than turbos.

Roll out the wires,

OTC

Moving away from the pretty><ugly, to the wider scope of electrification, beyond what is currently being done on the GWML^▸ (Great Western Main Line): it's my understanding ^ which could well be incorrect, I'm not an engineer ^ that the main benefits of electric traction over diesel are efficiency and cost of energy, reduced pollution (air and noise pollution). In performance terms, the first would seem to be much improved acceleration, with higher top speeds being more dependent on track and signalling as well as arguably benefiting fewer services. With this in mind, would it not be more beneficial to prioritise electrification of stopping services? Every stop is followed by acceleration, so the more stops, the more time is gained by higher acceleration.

In practice, acceleration from a stop may not be that much better than with diesel power - in part because it's limited by adhesion, and by "weight over the wheels". In addition, electric motors (especially with a modern variable-frequency drive) give pretty much a constant torque (and traction force) at low speed, with power slowly rising with speed. When the power reaches the maximum for the motor (or the source) then at higher speeds it's the power that is constant, with torque falling off with speed.

So the real advantage of electrics is better acceleration at high speed. How high is "higher"? For IEP^▸ (Intercity Express Program / Project.) it was expected the power limit threshold would be at about 55 km/hr, or only 35 mi/hr. So electrics do still have a big advantage, not just at stops but when speeding up after every speed check.

Thanks.

To be clear, I wasn't meaning GWML electrification should have been done differently, it was a general question. Partly from my observation off the electrified suburban tracks around eg Birmingham and that in some countries "electric train" and "local train" are equivalent. (And I'm also not saying they've done it right and we've done it wrong; different places have different needs and possibilities, obviously.)

[Rhydgaled]

And to clarify, headspan suffers from a) being easier to bring down b) when it comes down, all four lines are taken out and c) it takes much longer to put back together again.  So both the frequency and severity of disruptions are magnified several-fold.

I don't think all ECML^▸ (East Coast Main Line) OHLE is the same. I'm 99% sure that the picture I posted does NOT show the type you are talking about, I think the OHLE which comes down on all tracks has a horrizonal wire going across all the tracks, from which the contact wires are hung, apparently. The picture I showed does not have this horrizontal contact wire, the tracks have their own independent supports.

As well as being poor operationally (because of the tendancy to de-wire all tracks), I think the horrizonal wire version looks more cluttered than the OHLE in the link I posted. The 'portals' in the 'headspan conversions' video somebody posted are also messy; basically I think any form of OHLE I have seen that has a horrizontal element spanning more than a single line looks very ugly. Are there loading guage constraints that prevent the installation of independent structures for the middle tracks of a 4-track railway?

[paul7575]

I don't think all ECML^▸ (East Coast Main Line) OHLE is the same. I'm 99% sure that the picture I posted does NOT show the type you are talking about, I think the OHLE which comes down on all tracks has a horrizonal wire going across all the tracks, from which the contact wires are hung, apparently. The picture I showed does not have this horrizontal contact wire, the tracks have their own independent supports.

You're right that the whole ECML is not done in the same way, some sections do have completely independent single track cantilevers as in your linked picture.

Elsewhere there are either four track or two track headspans, which have a collection of various span wires, insulators and registration arms, forming a support 'mesh' but the contact wire is still supported in the same way as any other, with a catenary running along the length of the track with droppers every few yards to hold the contact wire.

This earlier thread was about the MML^» (Midland Main Line. - about), but it's basically the same stuff as much of the ECML:
http://www.firstgreatwestern.info/coffeeshop/index.php?topic=13665.0
includes this pic:
https://upload.wikimedia.org/wikipedia/commons/0/05/Otterington_railway_station_MMB_01.jpg

Even if the other wires don't fall down, they'll go out of normal alignment and a pantograph will go off the wire, rise too high, then be automatically dropped...

Paul