Great Western Electrification Progress

[jimm]

A maximum nominal voltage of 750V DC is the maximum allowed on conventional 3rd rail. 1500V DC is normally OLE.

Perhaps on the national network now, but side-contact 1200V DC third rail was used between Manchester and Bury before the conversion to Metrolink and 1200V DC is used on most of the Hamburg S-Bahn network in Germany. Not that it is a serious contender for use elsewhere and I think the chief benefit is supposed to be better acceleration than you get with 750V.

1200V seems to be a dividing line between third rail and overhead wires, with some Swiss light rail systems using 1200V overhead.

 

[route:oxford]

This has been dealt with several times before:
DC third rail is not cheaper on a 150+ mile long main line electrification because:
LV DC 3rd rail electrification is not viable for speeds above 100mph (forget one-off records)
LV DC 3rd rail costs much more on long routes where frequent feed points are required and need a lot more electric plant to convert the national grid supply to LV DC.
LV DC 3rd rail cannot provide enough current for heavy mixed freight and high speed passenger trains
LV DC 3rd rail does not cope well in frost, ice and snow conditions
LV DC 3rd rail is considered an unnecessary safety hazard for PW staff
LV DC 3rd rail on high speed long distance lines does not allow much power regenerated during braking to be used by other trains as there are often no trains in the same short sections.
HV AC OLE has none of the above disadvantages.
OK, so what are the disadvantages of OLE, well:
An additional clearance in the order of 250mm above the minimum for non-OLE powered vehicles, is required in tunnels, under bridges and other structures. This is often easier to acheive on main trunk routes where structures have been cleared to W10 standards for freight traffic. In the case of GWML, much of the route benefits from the original GWR's generous structure gauge, unlike those of the former Southern Railway lines.
So that leaves a part 3rd rail/part OLE line. There you would get the worst of both worlds, i.e. high power feed costs on the unreliable DC bits and the need for dual voltage trains throughout including freight locos.
The effect of OLE on the landscape view is a subjective opinion and not shared by everybody, and as has been said here before, Switzerland doesn't seem to have been ruined by it.

You forgot to mention the badgers...

 

[AM9]

Perhaps on the national network now, but side-contact 1200V DC third rail was used between Manchester and Bury before the conversion to Metrolink and 1200V DC is used on most of the Hamburg S-Bahn network in Germany. Not that it is a serious contender for use elsewhere and I think the chief benefit is supposed to be better acceleration than you get with 750V.

1200V seems to be a dividing line between third rail and overhead wires, with some Swiss light rail systems using 1200V overhead.

Until the advent of electronic inverters in trains (mainly for providing variable frequency for synchronous drive to ac motors) there were optimum DC voltage standards for standard DC traction motors. Practical motors would have insulation that could sustain up to about 1000 VDC, thus the nominal operating voltage would need to be not much more than 750V to allow for transients. So a 750 'ish supply would mean all motors in parallel when all the taps were switched out. With a 1500VDC supply, either from OLE or output from a transformer-rectifier set (as was the case with the GE converted class 306 & 307s) the motors were run in series pairs so the standard EE/GEC/BTH motors each ran from a 750VDC supply.

For lower power motors, as would be more common on tramways and light rail systems, 600VDC or less may be enough to drive the motors giving rise to 600V and 1200V contact wire voltages.

 

[PhilipF]

Excellent post by AM9 as to why OLE had to be used instead of third rail, really informative.
I'd be interested in the amount of extra electricity this will be drawing off the national grid. Massive amount of work being going on near the Bathampton junction for the past month to help feed in all this "juice".

 

[LNW-GW Joint]

Some numbers after a run today - Newport to Hayes and back.
There are 160 booms up between Moreton and Scours Lane (Reading).
About half of these have registration arms attached, which start just west of Pangbourne.
But going the other way (north side) I counted 86 missing masts (and 2 red kites!) over the same stretch, which I reckon should have about 360 structures over the 20km/13 miles.
Doing the sums that means the masts are 75% complete, the booms 45% and the registration gear 20%.
Piling has extended east almost to Reading station (including at least some of the new underpass lines), and west beyond Didcot up to about MP66.
Bases are more intermittent on the north side around Didcot, where the layout is more complicated.
The grid connection at Didcot looks well advanced.
Nothing much to speak of through Swindon (MP66-80), then a few more bases leading up to Wootton Bassett Jn.
Further west, just the short stretch at Pilning and a rather longer one at Llanwern have bases.

East of Reading, bases have increased around Twyford and Sonning (but still nothing in the deep section of the cutting).
There is still a gap of about 4 miles without bases from about Ruscombe to Maidenhead East.

The Crossrail work starts at Maidenhead East Jn and there are 43 booms up towards Stockley, of which 27 have registration arms.
Balfour Beatty have made significant progress on this stretch, and have piled most of the gap from Slough West to West Drayton on the south side.
The north side is less advanced, but there still plenty of booms up. BB seem to be getting the registration gear up more quickly than Amey.
The stretch near West Drayton is very confusing: you can see some booms up but often with piling still needed either side.
All this progress contrasts strangely with BB's work in the NW, where they have left the project blaming Network Rail as a "difficult customer".
Maybe the Crossrail contract is more lucrative for them...

Anyway, some decent progress to report overall in the last 8 weeks.
The sections not yet piled must be giving cause for concern.

 

[AM9]

Excellent post by AM9 as to why OLE had to be used instead of third rail, really informative.
I'd be interested in the amount of extra electricity this will be drawing off the national grid. Massive amount of work being going on near the Bathampton junction for the past month to help feed in all this "juice".

If you mean the total draw of the services on the new electrified route then somebody here may have an idea of that. The power 'wasted' by 3rd rail is about 15% over the same traction requirements on an ac line.
The practical maximum current that can be drawn from the 3rd rail in a section is somewhere in the region of 8000A, which would power about 8000 hp of traction. I don't know the traction power of a 9-car class 801 but a nine-car Pendolino has over 5MW maximum draw which would equate to over 6500A from a 750V 3rd rail system. Thus it would be very restrictive on train operation, which is why the Basingstoke to Southampton route is slated for conversion asap..
These limits aren't there with 25kV where the current for a given power is about 1/33rd of that on a 750V system. So a composite copper/steel OLE conductor of 10-20mm cross section can carry much more than a much larger steel conductor rail.

 

[Philip Phlopp]

If you mean the total draw of the services on the new electrified route then somebody here may have an idea of that. The power 'wasted' by 3rd rail is about 15% over the same traction requirements on an ac line.
The practical maximum current that can be drawn from the 3rd rail in a section is somewhere in the region of 8000A, which would power about 8000 hp of traction. I don't know the traction power of a 9-car class 801 but a nine-car Pendolino has over 5MW maximum draw which would equate to over 6500A from a 750V 3rd rail system. Thus it would be very restrictive on train operation, which is why the Basingstoke to Southampton route is slated for conversion asap..
These limits aren't there with 25kV where the current for a given power is about 1/33rd of that on a 750V system. So a composite copper/steel OLE conductor of 10-20mm cross section can carry much more than a much larger steel conductor rail.

18% in South England, 11% on MiseryRail, is the losses experienced by 750V DC. That indicates rather well how losses increase as you have a larger DC network with wider spacing of transformers, more transformers, more wiring and more third rail itself.

 

[SpacePhoenix]

"Dual voltage capable" units like 444s and 450s are limited (in software iirc) as to how much power they can draw. If they were running on AC (and therefore not needing to be limited), what sort of increase would be possible in how quickly they could accelerate to and decelerate? from a given speed?

If the AC was extended to Poole (probably going a certain number of meters past the western end of the carriage sidings and including the carriage sidings, would they better acceleration and deceleration make the extending XC to Poole viable?

 

[swt_passenger]

"Dual voltage capable" units like 444s and 450s are limited (in software iirc) as to how much power they can draw. If they were running on AC (and therefore not needing to be limited), what sort of increase would be possible in how quickly they could accelerate to and decelerate? from a given speed?

If the AC was extended to Poole (probably going a certain number of meters past the western end of the carriage sidings and including the carriage sidings, would they better acceleration and deceleration make the extending XC to Poole viable?

Unlikely without further changes to the overall timetable, I'd have thought. XC spend about 30 mins at Bournemouth, but Poole and back takes about 24 minutes. SWT take about 12 mins each way with a couple of stops.

Line speed is surprisingly low along there as well, only short sections of 75 with many significantly lower sections of PSR, so I think that would be the the main deciding factor.

Last but not least, there is no mention of wires west of Southampton Docks yet.

 

[SpacePhoenix]

Unlikely without further changes to the overall timetable, I'd have thought. XC spend about 30 mins at Bournemouth, but Poole and back is about 24 miles. SWT take about 12 mins each way with a couple of stops.

Line speed is surprisingly low along there as well, only short sections of 75 with many significantly lower sections of PSR, so I think that would be the the main deciding factor.

Last but not least, there is no mention of wires west of Southampton Docks yet.

Poole-Bournemouth in a straight line is about 5.5 miles, i'd be surprised in by the route the line follows that it would be 24 miles, probably half that.

What's the reason(s) for the PSRs? Would the low overall linespeed be down to the relative distances between Poole, Parkstone, Branksome and Bournemouth once semis and slows are thrown into the mix?

 

[swt_passenger]

Poole-Bournemouth in a straight line is about 5.5 miles, i'd be surprised in by the route the line follows that it would be 24 miles, probably half that.

Yeah, I mixed up time and miles. (My post now amended.) Running time is about 12 mins each way is what I should have said, presumably because of all the PSRs. The online sectional appendix shows it is a really slow section of track.

 

[edwin_m]

"Dual voltage capable" units like 444s and 450s are limited (in software iirc) as to how much power they can draw. If they were running on AC (and therefore not needing to be limited), what sort of increase would be possible in how quickly they could accelerate to and decelerate? from a given speed?

To get the answer to that, ride on a 350. This is effectively a 450 that was delivered as an AC version and I don't believe it has any current limitation.

I would expect the braking rates to be the same though, as this is specified by standards. If too much current is regenerated during braking to be fed back into the network then it is dissipated as heat in resistors on the train.

 

[HSTEd]

Of course estimates that have 25kV cheaper than renewing third rail on Southern Region were based on estimates for OLE installations that have been shown to be absolute junk.

 

[Philip Phlopp]

Of course estimates that have 25kV cheaper than renewing third rail on Southern Region were based on estimates for OLE installations that have been shown to be absolute junk.

Which estimates in particular are you wanting to discuss in detail ?

 

[GRALISTAIR]

If you mean the total draw of the services on the new electrified route then somebody here may have an idea of that. The power 'wasted' by 3rd rail is about 15% over the same traction requirements on an ac line.
The practical maximum current that can be drawn from the 3rd rail in a section is somewhere in the region of 8000A, which would power about 8000 hp of traction. I don't know the traction power of a 9-car class 801 but a nine-car Pendolino has over 5MW maximum draw which would equate to over 6500A from a 750V 3rd rail system. Thus it would be very restrictive on train operation, which is why the Basingstoke to Southampton route is slated for conversion asap..
These limits aren't there with 25kV where the current for a given power is about 1/33rd of that on a 750V system. So a composite copper/steel OLE conductor of 10-20mm cross section can carry much more than a much larger steel conductor rail.

Power (Watts) = Voltage x current (amps)
So power stations produce and sell power not voltage or current.
Power loss = I^2 x R (current squared x resistance)
So for a given power, the higher the voltage the lower the current. Since power loss is directly proportional to the current squared, transmitting at higher voltage as per 25kV AC OHL is more beneficial than at 750 V DC 3rd rail in terms of power loss/wasted.
So I f we wanted to deliver 5 MW (a nine-car Pendolino has over 5MW draw = 5000000 Watts)
So for 25kV AC OHL equates to 5000000/25000 = 200 amps
750 DC = equates to 5000000/750 = 6667 amps = 1/33rd approximately

 

[Philip Phlopp]

Power (Watts) = Voltage x current (amps)
So power stations produce and sell power not voltage or current.
Power loss = I^2 x R (current squared x resistance)
So for a given power, the higher the voltage the lower the current. Since power loss is directly proportional to the current squared, transmitting at higher voltage as per 25kV AC OHL is more beneficial than at 750 V DC 3rd rail in terms of power loss/wasted.
So I f we wanted to deliver 5 MW (a nine-car Pendolino has over 5MW draw = 5000000 Watts)
So for 25kV AC OHL equates to 5000000/25000 = 200 amps
750 DC = equates to 5000000/750 = 6667 amps = 1/33rd approximately

That's before we take into account the 1.5 tonnes of EM filters Bombardier fit to the DC Electrostars to deal with the poor quality, noisy electric supply 750V DC (nominal) actually is.

That's a lot of weight shuffling around just to deal with an obsolete electrical supply system that's barely fit for model trains and toy racing cars.

 

[AM9]

Power (Watts) = Voltage x current (amps)
So power stations produce and sell power not voltage or current.
Power loss = I^2 x R (current squared x resistance)
So for a given power, the higher the voltage the lower the current. Since power loss is directly proportional to the current squared, transmitting at higher voltage as per 25kV AC OHL is more beneficial than at 750 V DC 3rd rail in terms of power loss/wasted.
So I f we wanted to deliver 5 MW (a nine-car Pendolino has over 5MW draw = 5000000 Watts)
So for 25kV AC OHL equates to 5000000/25000 = 200 amps
750 DC = equates to 5000000/750 = 6667 amps = 1/33rd approximately

I did those sums before posting but decided not to include the calculations. They are also simple figures that ignore the effect of supply conductor resistances. The (nominal) 750V DC supply at the collector shoes is probably much less stable than the 25kV at the pantograph head owing to a number of factors e.g.:
Shoe bounce giving variable contact resistance has a greater impact on traction bus voltage than catenary/pantograph performance, particularly at speed. Ice, water leaf mulch etc., can only make that variability worse.
Steel rail resistance per track metre gives a greater percentage voltage drop than contact wire (both at their respective currents).
Both of the above mean that for the same power to be there for traction, the current drawn is higher (for trains with inverter supplies) or the available tractive power at the axle is lower for simple DC resistance tap controls.

Another weakness of low voltage supplies on main lines is the reduced likelyhood of using regen power during braking. That's because with higher power trains, the sections can still only be quite short because of the maximum current limits. This lack of other trains means that the power must be wasted in resistor banks either on the train or at the substations.

All this without the problems of keeping return currents out of the ground, but still having to bond station earths to the running rails.

In essence, DC was the better proposition when electrification was being rolled out in the suburbs and trains were simple and relatively low power. With safety, signal immunity, EMC and electricity costs being major issues, 750V DC 3rd rail is well past its time on fast mainlines.
--- old post above --- --- new post below ---

Of course estimates that have 25kV cheaper than renewing third rail on Southern Region were based on estimates for OLE installations that have been shown to be absolute junk.

Who is to say that NR would keep within estimates is it was decided to electrify Paddington to Cardiff with 3rd rail?

 

[HSTEd]

Which estimates in particular are you wanting to discuss in detail ?

The ones for just about any of the 25kV schemes since privatisation.

NR have shown that they are unable to deliver electrification for the costs they claimed and their overreach has done serious damage to the electrification programme.
--- old post above --- --- new post below ---

Who is to say that NR would keep within estimates is it was decided to electrify Paddington to Cardiff with 3rd rail?

I'm not - just pointing out that the arguments that 3rd rail is more expensive in all circumstances are based on faulty data.

 

[Philip Phlopp]

The ones for just about any of the 25kV schemes since privatisation.

Which ones ?

What projects are over budget, behind schedule and what is the reason(s) for projects being over budget or behind schedule ? Who is at fault for projects suffering cost increases and timescales slipping ?

Network Rail has put together costings for lots of work, the bulk of it is accurate and robust, some of it relates to electrification which is on or ahead of time and under budget, some of it is for other engineering works which is over budget and behind time.

It's not just Network Rail which agrees with the electrification costings - ORR signed off on the CP5 work programme, and dozens of contractors have all tendered for and won contracts, with no massive differences between Network Rail's estimates and actual tendered prices.

 

[HSTEd]

Network Rail has put together costings for lots of work, the bulk of it is accurate and robust, some of it relates to electrification which is on or ahead of time and under budget, some of it is for other engineering works which is over budget and behind time.

EGIP - Over budget, late and half of it got cancelled.
Lancashire Triangle - late
Great Western - late and enormously over budget
Midland Main Line - so late that it is now effectively cancelled

That is the bulk of the electrification work committed since privatisation with the exception of about seven miles as part of the WCRM. Any project before that was committed to construction by BR.

It's not just Network Rail which agrees with the electrification costings - ORR signed off on the CP5 work programme, and dozens of contractors have all tendered for and won contracts, with no massive differences between Network Rail's estimates and actual tendered prices.

And yet the projects are miles behind schedule and running enormously over budget. Of course the contractors tendered for the prices Network Rail projected - if they hadn't they would not have won the contract.

I can only think of one contract that was completed on time and on budget off the top of my head - and that was Paisley Canal.
If the bulk of their costings were accurate and robust why have they managed to screw up CP5 so badly that the electrification programme is just waiting for news to bury the cancellation under?

EDIT:

If you want a reason - for a start look at the HOOP train debacle.
Network Rail has become so obsessed with obliterating any trace of BR that they decided to use a brand new, essentially untested in an operational setting, overhead wiring scheme with their brand new high output plant train. Which had not been designed to be used with this all singing all dancing new equipment scheme.

 

[AM9]

I'm not - just pointing out that the arguments that 3rd rail is more expensive in all circumstances are based on faulty data.

And where has anybody here argued that 3rd rail is more expensive "in all circumstances"?

 

[67018]

And where has anybody here argued that 3rd rail is more expensive "in all circumstances"?

Aren't we losing the very interesting point previously made? - that the proposed 'trial' conversion from third rail was based on the fact that substantial renewals were needed anyway to the existing infrastructure, and the conversion was not much more expensive than the renewal work - and would pay back over time. The well-publicised cost overruns suggest that the 'not much more expensive' comparison may not be valid and the payback not as good.

Not to mention the fact that, if other schemes are being deferred due to delays and resource limitations, it seems less sensible to give priority to converting a line that's already electrified.

 

[AM9]

Aren't we losing the very interesting point previously made? - that the proposed 'trial' conversion from third rail was based on the fact that substantial renewals were needed anyway to the existing infrastructure, and the conversion was not much more expensive than the renewal work - and would pay back over time. The well-publicised cost overruns suggest that the 'not much more expensive' comparison may not be valid and the payback not as good.

Not to mention the fact that, if other schemes are being deferred due to delays and resource limitations, it seems less sensible to give priority to converting a line that's already electrified.

Except that the railway is run as a network, and a relatively small scheme of conversion releases benefits for heavy freight along trunk routes that are several times the distance in question. This thread is however about electrifcation of a long main line, and reference to the portion of the SWML was just an example of reasons why OLE was considered better for fast and heavy trains than a low voltage system designed 90 years ago for metro and suburban traffic. My statement didn't mention relative cost, I said "it would be very restrictive on train operation", although a through-life cost comparison of the two options would make an interesting separate topic for discussion, especially in the light of the current programme and budget issues with OLE schemes.
Back to the GWML; there is no sensible argument for the current scheme to have 3rd rail in preference to 25kV OLE for all the reasons I gave in post #1386, unless the policy was to save money at all costs!

 

[po8crg]

It's also worth asking whether the 3rd rail renewal estimates are accurate.

It might well be that the renewal would also have cost overruns.

 

[Philip Phlopp]

Aren't we losing the very interesting point previously made? - that the proposed 'trial' conversion from third rail was based on the fact that substantial renewals were needed anyway to the existing infrastructure, and the conversion was not much more expensive than the renewal work - and would pay back over time. The well-publicised cost overruns suggest that the 'not much more expensive' comparison may not be valid and the payback not as good.

Not to mention the fact that, if other schemes are being deferred due to delays and resource limitations, it seems less sensible to give priority to converting a line that's already electrified.

25kV conversion in the southeast and indeed of Merseyrail will be a significantly easier project than electrification of non electrified routes, though there will be some big engineering projects in the fullness of time

The big cost will generally be bridge replacement and track lowering works, but that's running really rather beautifully at the moment across all the various electrification projects. There will also be tunnel reboring needed, but many of those structures are getting towards the end of their lives in any case and rebuilding for 25kV clearance won't cost any extra, indeed, with equipment like Fillie available, 25kV clearance will be the cheaper option.

Network Rail have a pretty damn good contractor in Murphy and their sub-contractors, like Shay Murtaugh and Buckingham. These guys have really improved in the last few years and they're quick, safe, reliable and get things done on time and on budget, with minimum fuss. The utilities like BT, United Utilities, National Grid, Scottish and Southern and so on, they're now more aware of what needs to be done when a bridge is removed and replaced, and they now have the skills and understanding to get all their wires and pipes off the old bridge, out of the way, first time.

The S&T people in third rail land know electrification and things like EM interference inside out and back to front, 750V DC is noisy, dirty electricity and isn't kind to S&T kit and it isn't kind to traction kit, as a result, everything that needs to be in third rail land is screened cable and EM hardened, yes, some immunisation works will be needed but it'll be done by teams that have worked on an electrified railway previously and just have that extra little bit of hard won experience, keeping their signalling running in places like Clapham Jn.

The southern S&T people tend to be a damn site more disciplined with their signalling cabling runs too - none of this silly buried and forgotten about cabling that Western managed round Reading, which did so much to put the GWML electrification behind schedule.

The good thing about converting the Southern is it's electrified already, dual voltage stock is in common use - so conversion can be a relatively slow process dictated by the replacement of the life expired 750V DC equipment - you can install the actual overhead catenary at a fairly constant pace to keep the engineering teams fully utilised, but choose to energise and make the switch when it suits the TOCs. You could be installing 150 track miles a year but choosing only to use 100 miles one year and 200 miles the next year.

 

[Cletus]

Link to some pictures of work in Bath:

http://www.bathchronicle.co.uk/pict.../pictures-27680528-detail/pictures.html?765#1

Pictures: Network Rail starts electrification preparatory work at Sydney Gardens...

 

[67018]

It's also worth asking whether the 3rd rail renewal estimates are accurate.

It might well be that the renewal would also have cost overruns.

I had thought of that, and assumed that regular maintenance would be less likely to go horribly pear shaped since it's presumably a fairly constant and routine activity anyway. Assuming, also, that the present difficulties are due to the complexity of the work, skills shortages and use of new designs and equipment, rather than generalised incompetence. (People are always keen to assume it's the latter when I believe it usually isn't).

25kV conversion in the southeast and indeed of Merseyrail will be a significantly easier project than electrification of non electrified routes, though there will be some big engineering projects in the fullness of time

The big cost will generally be bridge replacement and track lowering works, but that's running really rather beautifully at the moment across all the various electrification projects. There will also be tunnel reboring needed, but many of those structures are getting towards the end of their lives in any case and rebuilding for 25kV clearance won't cost any extra, indeed, with equipment like Fillie available, 25kV clearance will be the cheaper option.

Network Rail have a pretty damn good contractor in Murphy and their sub-contractors, like Shay Murtaugh and Buckingham. These guys have really improved in the last few years and they're quick, safe, reliable and get things done on time and on budget, with minimum fuss. The utilities like BT, United Utilities, National Grid, Scottish and Southern and so on, they're now more aware of what needs to be done when a bridge is removed and replaced, and they now have the skills and understanding to get all their wires and pipes off the old bridge, out of the way, first time.

The S&T people in third rail land know electrification and things like EM interference inside out and back to front, 750V DC is noisy, dirty electricity and isn't kind to S&T kit and it isn't kind to traction kit, as a result, everything that needs to be in third rail land is screened cable and EM hardened, yes, some immunisation works will be needed but it'll be done by teams that have worked on an electrified railway previously and just have that extra little bit of hard won experience, keeping their signalling running in places like Clapham Jn.

The southern S&T people tend to be a damn site more disciplined with their signalling cabling runs too - none of this silly buried and forgotten about cabling that Western managed round Reading, which did so much to put the GWML electrification behind schedule.

The good thing about converting the Southern is it's electrified already, dual voltage stock is in common use - so conversion can be a relatively slow process dictated by the replacement of the life expired 750V DC equipment - you can install the actual overhead catenary at a fairly constant pace to keep the engineering teams fully utilised, but choose to energise and make the switch when it suits the TOCs. You could be installing 150 track miles a year but choosing only to use 100 miles one year and 200 miles the next year.

Many thanks for such an illuminating explanation. Which, if I read it right, argues that the conversion from third rail is less risky than the GWML and so unlikely to suffer from the same overruns. Suggesting that the main constraints might be resources (are skilled staff and equipment going to be used that are then not available for other schemes like the MML) and, more importantly, political - how do you explain all that you have said to the politicians and general public?

Is there a risk that lessons will have been learnt and skills built up just in time for the people with the money to lose faith in NR's ability to deliver?

 

[LNW-GW Joint]

In Sept Modern Railways, Roger Ford compares the GWML electrification with the ECML project c1990, and concludes GW costs are 4 times higher (£1.73m per stkm as opposed to £0.45k).
He examines costs of piling foundations versus concreting, which is one of the major factors.
The ECML tried piling but went back to concrete for 90% of the route. The GWML is the other way round (90% piles, 10% concrete).
The foundation piling rate for HOPS was 5.0/4.6/6.8 average piles per shift over the last 3 quarters, against a target of 18. The ECML kit did 4-5 bases per hour.
Another factor is the high spec of the Series 1 OHLE design, for 140mph running.
There is comment elsewhere that this is not necessary west of Bristol (or the Cotswold tunnels really), and that the business case into South Wales is very weak for only 2tph electric working.

 

[Tw99]

I'm a recent member of this forum, but have been interested in railways since I was a kid, and was interested to read a lot of the detail in this thread.

I thought I'd chip in since we live 400m away from the GWML between Purley and Pangbourne, and have a good view of it from the front of the house. We actually moved here last year, just before the electrification work started in earnest.

We had quite a few nights of piling earlier in the year, and as many others have observed, the masts and portals have been slowly going up ever since, in a somewhat piecemeal fashion.

The bit we look out over has a long stretch of full portals (including a couple of the A-braced ones), and only a couple of cantilevers. I guess there's a good technical reason for this, but from a selfish point of view it's a bit of a shame as I think the cantilevers are slightly less obtrusive.

In the last few weeks, some of the "wire hangers" (sorry, don't know the correct term!) have been installed, but not in any consistent pattern that I can make out. It's been faintly interesting to see if you can spot what's changed overnight when opening the curtains in the morning, anyway.

As a local resident, I'll enjoy benefiting from the improved train service. On the plus side in terms of impact on where I live, I imagine the new trains will be somewhat quieter. On the other hand, I suppose there may be some visible arcing at night, and I'm not sure how obtrusive that might be.

 

[po8crg]

There is comment elsewhere that this is not necessary west of Bristol (or the Cotswold tunnels really), and that the business case into South Wales is very weak for only 2tph electric working.

Surely the Valley Lines electrification is the core business case for electrification west of the Severn Tunnel.

It would be ridiculous to electrify everything bar Newport to Bristol Parkway.