North Downs line electrification

[Deepgreen]

And fizzy drinks cans.

The reality is delays caused by DC buggering up the signalling system will routinely exceed occasional but more severe delays from a de-wirement.

Is it only fizzy drinks that cause the problem?

 

[tsr]

Is it only fizzy drinks that cause the problem?

They're always fizzy when they touch the third rail...

 

[miami]

Why can't 3rd rail be run at 25kv? Arcing with the rails/ground?

 

[NSEFAN]

Why can't 3rd rail be run at 25kv? Arcing with the rails/ground?

Yes, and also arcing to nearby objects/people. I think it's been discussed on here before, and you wouldn't want to raise the 3rd rail much above its existing potential for safety reasons.

 

[edwin_m]

The issue of DC versus AC can be simply tested. The minutes lost per AC wire failure are enormously greater than the minutes lost per DC conductor rail failure. It should make the DC armchair converters hang their heads in shame. If there was a proper maintenance regime for the third rail,with ballast & footballs cleared from providing a current flow in wet weather, the power consumption comparisons would be favourable to third rail,specially as every DC 12 car train does not have to drag 10 tons of track bashing transformer up hill & downdale.

10 tonnes is only about 2% of the weight of a 12-car unit so not very significant. And if you're concerned about track bashing, pickup shoes are unsprung mass and transformers aren't.

 

[Philip Phlopp]

The issue of DC versus AC can be simply tested. The minutes lost per AC wire failure are enormously greater than the minutes lost per DC conductor rail failure. It should make the DC armchair converters hang their heads in shame. If there was a proper maintenance regime for the third rail,with ballast & footballs cleared from providing a current flow in wet weather, the power consumption comparisons would be favourable to third rail,specially as every DC 12 car train does not have to drag 10 tons of track bashing transformer up hill & downdale.

Will you please download and read through the DC losses report.

https://www.networkrail.co.uk/WorkArea/DownloadAsset.aspx?id=30064784498

It might finally help you stop perpetuating the myth that all of the losses on the third rail network are down to a lack of what you call 'proper maintenance'.

I'll certainly agree with the report, and with you about losses due to maintenance, but they're only ever a small percentage of the losses, and I'd also argue that's largely a result of using an outdated system which ties the traction current collection system to sleepers, any maintenance to rail, sleeper or ballast has implications for the third rail - both damage and losses - in a way which OLE of any type eliminates.

That all makes high output track maintenance difficult and as a result makes track maintenance significantly more expensive. In the interests of fairness, I will add that Network Rail has recently invested in a new design of HOBC which has third rail support, that should hopefully help reduce costs over the longer term.

What I would add to the report and your comments about the lack of 'proper maintenance' is that dealing with all the instances of ballast shoulders contacting third rail, removing debris etc, would need more boots on track and more/longer possessions. The very small electrical losses you would prevent by enhanced maintenance would recoup only a tiny fraction of the total losses - in both electrical and financial terms - and would be completely overshadowed by the disruption and service reductions caused by longer possessions.

The biggest loss, and the problem you can't escape, and which can't be blamed on Network Rail's good, bad or ugly maintenance is the behaviour of electrons in a lump of pig iron. Basic physics is involved when it comes to variable losses (the P=I^2R losses) and that gets worse as stock length (and ultimately energy requirement) increases.

There's also the quite convoluted 400kV/275kV to 33kV AC to 750V DC transformer regime to feed DC, all those additional transformers - 33kV and 750V DC buzzing away, they're all causing losses too.

 

[Deepgreen]

10 tonnes is only about 2% of the weight of a 12-car unit so not very significant. And if you're concerned about track bashing, pickup shoes are unsprung mass and transformers aren't.

How so? They have to be sprung almost by definition (and weigh virtually nothing, and don't affect the running rails).

 

[Philip Phlopp]

How so? They have to be sprung almost by definition (and weigh virtually nothing, and don't affect the running rails).

They're not unsprung in any case - they sit between the primary suspension (that between axle and bogie) and the secondary suspension (that between the bogie and vehicle body).

 

[reddragon]

Will you please download and read through the DC losses report.

https://www.networkrail.co.uk/WorkArea/DownloadAsset.aspx?id=30064784498

It might finally help you stop perpetuating the myth that all of the losses on the third rail network are down to a lack of what you call 'proper maintenance'.

I'll certainly agree with the report, and with you about losses due to maintenance, but they're only ever a small percentage of the losses, and I'd also argue that's largely a result of using an outdated system which ties the traction current collection system to sleepers, any maintenance to rail, sleeper or ballast has implications for the third rail - both damage and losses - in a way which OLE of any type eliminates.

That all makes high output track maintenance difficult and as a result makes track maintenance significantly more expensive. In the interests of fairness, I will add that Network Rail has recently invested in a new design of HOBC which has third rail support, that should hopefully help reduce costs over the longer term.

What I would add to the report and your comments about the lack of 'proper maintenance' is that dealing with all the instances of ballast shoulders contacting third rail, removing debris etc, would need more boots on track and more/longer possessions. The very small electrical losses you would prevent by enhanced maintenance would recoup only a tiny fraction of the total losses - in both electrical and financial terms - and would be completely overshadowed by the disruption and service reductions caused by longer possessions.

The biggest loss, and the problem you can't escape, and which can't be blamed on Network Rail's good, bad or ugly maintenance is the behaviour of electrons in a lump of pig iron. Basic physics is involved when it comes to variable losses (the P=I^2R losses) and that gets worse as stock length (and ultimately energy requirement) increases.

There's also the quite convoluted 400kV/275kV to 33kV AC to 750V DC transformer regime to feed DC, all those additional transformers - 33kV and 750V DC buzzing away, they're all causing losses too.

I lot of those stray currents, in particular as a train passes, ends up in the ground earthing to metal pipes. I do not think that the NR report fully covers losses properly and in my dealings with them, NR do have their heads in the sand a bit maintenance wise. That is much wider than just ballast shoulders and rubber pads, it's the inadequate nature of earth return cables that shows up as trains draw current and earths to ground rather than back to the sub station.

This issue is so severe, the East London Line 3rd rail electrification had to be block isolated from the SR DC electric by a whole train length. The ELL 3rd rail has minimal losses, because it is in a tunnel with metal objects and it required the degree of stray & return current isolation offered by the LULs 4 rail system.

So in answer, it is possible to install a 3rd rail DC system without these substantial losses, but not ideal.

I would install a 3rd rail system between Wokingham & Ash to tie in with what is there, but Guildford to Reigate would probably better end up as 25kV OH as the Brighton Line will inevitably have to switch to 25kV at some point due to power supply issues / age of equipment and the availability of dual voltage stock.

Thrilling subject!

 

[AM9]

... So in answer, it is possible to install a 3rd rail DC system without these substantial losses, but not ideal. ...

Even if a perfect installation reduced all of those losses to zero, there would still be the series resistance power loss which is orders of magnitude greater than the total leakage and galvanic losses.

 

[edwin_m]

They're not unsprung in any case - they sit between the primary suspension (that between axle and bogie) and the secondary suspension (that between the bogie and vehicle body).

Surely they are on a beam linking the axleboxes?

https://upload.wikimedia.org/wikipedia/commons/8/88/Top_contact_pickup_shoe.jpg

 

[Philip Phlopp]

Surely they are on a beam linking the axleboxes?

https://upload.wikimedia.org/wikipedia/commons/8/88/Top_contact_pickup_shoe.jpg

You're right. I was thinking of the new Bombardier and Siemens bogies, which have the shoe gear on the bogie frame.
--- old post above --- --- new post below ---

Even if a perfect installation reduced all of those losses to zero, there would still be the series resistance power loss which is orders of magnitude greater than the total leakage and galvanic losses.

That's drifting towards a partial re-design of the system - if DC to AC conversion isn't progressed further during the replacement life cycle of the DC feeders, then reducing losses and improving efficiency will have to be undertaken. The downside is it risks further cost which might not be recouped by reduced losses, and there's the possibility more return wiring and heavier wiring will make maintenance that tiny little bit more difficult.

 

[AM9]

That's drifting towards a partial re-design of the system - if DC to AC conversion isn't progressed further during the replacement life cycle of the DC feeders, then reducing losses and improving efficiency will have to be undertaken. The downside is it risks further cost which might not be recouped by reduced losses, and there's the possibility more return wiring and heavier wiring will make maintenance that tiny little bit more difficult.

Actually I wasn't advocating investment to reduce the parallel leakage which reddragon asserted would be possible. I was indicating the the I2R loss is far greater than the leakage, (accepted that it is proportional to the total amount of train power demand).
3rd rail DC must be at its practical limit of current per circuit (c.8000A) from a circuit protection standpoint anyway. Upgrading the cabling to reduce stray earth current might give a martginal increase in prospective short circuit current, but the big problem is the up to 6000A maximum draw of modern 12-car EMUs being so close to the maximum practical current that even the highest 3rd rail can sustain. Practical section lengths vs a sensible amount of traction, - it's a the law of diminishing returns.

 

[JohnElliott]

I thought that was due to direction from the top bosses at the newly formed Southern Railway who had come from the LSWR who had been using the third rail system. IIRC they either wanted to save face and use their system as the superior system, or that the third rail was simply cheaper than the OHLE.

I've taken a quick look at what David Brown's "Southern Electric: A New History" says. During the Grouping there were various attempts to come up with a standard system, with different recommendations each time. The LSWR were using third-rail DC, the LBSCR were using overhead AC, and the SECR were planning to use four-rail DC at 3000v (one conductor rail at +1500v, the other at -1500v).

Come the grouping, the new SR Board wanted to press ahead with electrification as quickly as possible, so they decided to go ahead with the SECR's proposed conductor-rail electrifications, but using the LSWR 3-rail system (the most recent independent report had recommended that conductor rail voltage should not exceed 750v). In the interests of standardisation (and because maintenance costs on the LBSCR's overhead AC units were considerably higher than on the LSWR's DC ones) they decided in 1926 to replace the LBSCR system with third-rail DC.

 

[GRALISTAIR]

3rd rail DC must be at its practical limit of current per circuit (c.8000A) from a circuit protection standpoint anyway. Upgrading the cabling to reduce stray earth current might give a martginal increase in prospective short circuit current, but the big problem is the up to 6000A maximum draw of modern 12-car EMUs being so close to the maximum practical current that even the highest 3rd rail can sustain.

That is a horrendous I squared R .

 

[NSEFAN]

That is a horrendous I squared R .

Having thousands of amps of load current also presents a safety problem: it's much harder to tell the difference between a train and a short circuit! A failure on the Tyne & Wear Metro (overhead DC system) showed how this could easily occur.

 

[AM9]

That is a horrendous I squared R .

That is the maximum demand that a section might satisfy. But of course, trains not only accelerate, they also spend a lot of time coasting or, these days, even return power to the network when braking, so the losses are proportional to the power actually used.
Now protecting this high current souce is not easy. The sensors and circuit breakers need to discriminate between a simultaneous heavy demand from multiple trains, and a short circuit, e.g. the infamous fizzy drinks can. If the short circuit physically occurs near the feed point, it will cause a very high current that the system will easily recognise as a fault. Power will then be removed quickly to protect the infrastructure. On the other hand, if the short circuit is 1km away from the feed point, the reasistance of the 1km of conductor and running rails/return conductor could mean that the current falls within the range of normal (albeit peak) loads. Because of that, the supply will be maintained, and the short circuit could result in a track fire or worse. I believe that was the situation near Gatwick a few weeks ago.
Also, trains in that section would find that their supply voltage was dependent on how far they were from the fault.

 

[snowball]

What's the rating of a Tango can functioning as a fuse?

No doubt an Irn Bru can would be stronger.

 

[HSTEd]

If you were designing a conductor rail standard entirely from scratch you might want to actually go with very low frequency AC - like down to 10Hz or similar.
THat would give you conductor rails without suffering from skin effect and you could deploy auto transformers every few hundred meters.

At the very least you would make it polarity agnostic so that you could have a two track main line with one line at + and another at -

 

[AM9]

If you were designing a conductor rail standard entirely from scratch you might want to actually go with very low frequency AC - like down to 10Hz or similar.
THat would give you conductor rails without suffering from skin effect and you could deploy auto transformers every few hundred meters.

At the very least you would make it polarity agnostic so that you could have a two track main line with one line at + and another at -

That would give rise to transformers with very large inductances which in turn would be very difficult to screen. There would be difficulty providing a smooth continuous supply for motors without considerable energy storage on board, (think capacitance or even batteries), and there would be problems in ground coupling to anything ferrous. Of course, all the safety issues inherent with 3rd rail power still exist.
Why not use a very effective proven system where the inadvertent risk is far lower, performance is consistently better and safe maintenance of infrastructure can usually be executed without power shutdown. Yes, that's right, HV ac OLE. All the technology is understood, available and for mainline use, has a lower through-life cost than any other rail electric power delivery.

 

[edwin_m]

That is the maximum demand that a section might satisfy. But of course, trains not only accelerate, they also spend a lot of time coasting or, these days, even return power to the network when braking, so the losses are proportional to the power actually used.

However when the power is regenerated into the third rail you get another set of I2R losses. Also, for regeneration to work at all, there has to be another train motoring at the same time*. Because of voltage drop issues the braking and motoring trains must be much closer together on the 750V system than they would have to be on 25kV. Therefore, for a similar density of network, regeneration will be possible less often at a lower supply voltage.

*Or return regenerated power to the grid, but as far as I know substations on Network Rail aren't capable of doing this.

 

[XDM]

An unshielded 800v conductor inches from the ground seems a dangerous insanity to laymen. Hence the embarrassment for any railway professional advocating more of it,even if just short fill in. Yet our third rail DC is less dangerous than AC. The most fervent AC advocate on this thread promised to come back with the stats proving DC killed more than AC,adjusted for pop density etc. He never came back. He couldn't as there is no evidence,just hearsay.. So it is no more dangerous. True, DC faces the inevitable heat losses due to ohm's law. But these are reduced through the lower weight of DC trains,& a better aerodynamic profile,both of which reduce the demand for IxV. Three rail born AC transformers per AC train designed to withstand the shock of rail bounce are ten times more expensive per kW than static transformers that sit on a level concrete floor in a DC substation. A failed organisation like Network Rail( despite some great people who work for it) can barely run the railway structure let alone supervise within time & budget a massive AC wiring programme. The facts prove it. True, DC can't do 125mph & heavy freight up long inclines,but otherwise its failings are far less disruptive than the regular dewirings across the AC network. With limited cash DC infill is a no brainer. And it is not true there is an absolute ban on it. The rules say a case has to be made. See above.

 

[NSEFAN]

An unshielded 800v conductor inches from the ground seems a dangerous insanity to laymen.

It is insanely dangerous, and only allowed because of grandfather rights. You would never get approval these days for a self-contained and similarly widescale new system which worked like that. If you had to have rail-level electrification it would be a DLR-style bottom contact system.

Yet our third rail DC is less dangerous than AC. The most fervent AC advocate on this thread promised to come back with the stats proving DC killed more than AC,adjusted for pop density etc. He never came back. He couldn't as there is no evidence,just hearsay.. So it is no more dangerous

Overhead electrification must be safer for staff to work with and for passengers to be around, as it's much harder to accidentally come into contact with it. Should you choose to, you could walk off the platform at Gatwick and form a nice path to earth from the 3rd rail. To do the same for OLE you'd need to either climb the masts or a train, which is much harder to do accidentally!

True, DC faces the inevitable heat losses due to ohm's law. But these are reduced through the lower weight of DC trains,& a better aerodynamic profile,both of which reduce the demand for IxV. Three rail born AC transformers per AC train designed to withstand the shock of rail bounce are ten times more expensive per kW than static transformers that sit on a level concrete floor in a DC substation.

AC or DC, you're still pushing a brick on rails at reasonably high speed. The added drag of a pantograph and weight of transformers (10 tons on top of 100s of tons) will be quite small by comparison.

With limited cash DC infill is a no brainer.

Quite possibly, but only because surrounding networks are also DC. Given how easy it is to make a dual voltage EMU however, it may not be a problem these days to infill with AC. There are other considerations too, such as the location of substations and availability of power from the grid. Perhaps the NDL has few locations for such substations, which combined with a historic lack of dual voltage EMUs in a largely DC-only region is why it has never been electrified?

 

[XDM]

It is insanely dangerous, and only allowed because of grandfather rights.

It is not. Third rail DC appears to be,but going through recent yearly safety reports demonstrate it safer than AC. A poster who claimed he could show DC killed more than ac(Adjusted for pop density & mileage) never came back with the evidence,although he continued his stream of postings. The evidence does not exist.
Remember NR is spending unbelievable amounts of our,& our childrens',money. We have a right to know it is being spent wisely. If the AC advocates win the day the north downs line will be permanently a diesel bye way because of NR's incredible AC ole costs. DC could be laid down cheaply,& power lines intersect the north downs tracks. DC,if properly maintained,has lower total cost than AC.
If AC is so safe why are all new AC territory bridges having the parapets expensively raised by a foot; for fun? DC for DC infilling is a no brainer.

 

[NSEFAN]

It is not. Third rail DC appears to be,but going through recent yearly safety reports demonstrate it safer than AC. ... If AC is so safe why are all new AC territory bridges having the parapets expensively raised by a foot; for fun?

Please share this information if you have it. Given the Edison Vs Tesla mindset you seem to have over DC vs AC, I wouldn't be surprised if you next start electrocuting peoples' dogs to demonstrate your point about how dangerous AC is.

The public are most likely to come into contact with the railway at stations and on level crossings, both will usually see them at ground level. Staff may also need to work on the live railway. Why put the HV conductor in easy reach of any of them when you can keep it well out of the way by putting it above the train? Bridge parapets should consequently be raised to prevent people from doing themselves harm, whereas you can't realistically fit platform-edge doors at most mainline stations to protect pax from the electrified rails.

Remember NR is spending unbelievable amounts of our,& our childrens',money. We have a right to know it is being spent wisely. If the AC advocates win the day the north downs line will be permanently a diesel bye way because of NR's incredible AC ole costs.

You're right, we should be spending money wisely. That's why we should be using the most efficient mode of power delivery to trains as possible. Given I^2 R, dropping from 25kV to 750V cranks up the current by over 30 times, meaning over 1000 times greater dissipated power for a given transmission resistance. Are you really suggesting that this, as well as the added cost of more substations, is better than the extra 10 or so tons on top of a couple of hundred for a 4 car EMU?

Doing anything on NR is expensive, OLE or 3rd rail, and that's down to the way it is structured. Privatisation smashed any form of organisation to bits, and we're only starting to get back to normal now. We now have a programme of electrification going on the GWML, so it should be possible to redeploy experienced teams and equipment to other parts of the network once this is complete. Meanwhile, where are the teams of trained people itching to lay new 3rd rail?

If the AC advocates win the day the north downs line will be permanently a diesel bye way because of NR's incredible AC ole costs. DC could be laid down cheaply,& power lines intersect the north downs tracks. DC,if properly maintained,has lower total cost than AC. ... DC for DC infilling is a no brainer.

Again, 3rd rail will only be viable if you can actually deliver the power at the correct feeder points. The lower efficiency of our 3rd rail systems means we need more substations. If it was so easy, why has it not been done already? Consider the power restrictions in place for the Weymouth electrification in the 1980s, caused by a lack of suitable feeder points, which still pose problems even to this day.

Why constrain ourselves to working with 1930s technology when we could explore modern alternatives that actually solve the problem of electrification? Dual-voltage stock is easy nowadays: I'm sure Bombardier would be happy to sell you trains which do just this. Changeover between OLE and 3rd rail on the move shouldn't be seen as witchcraft. Heck even battery EMUs may be a good option, that way NR wouldn't have to do a thing!

 

[QueensCurve]

For a train heading onto the North Downs Line at the Reading end from Basingstoke, would it need to reverse at Reading?

In the case of passenger trains, Reading would probably be a major marked to serve.
--- old post above --- --- new post below ---

Had the Southern gone for the 6.25kV system we might have ended up standardising on German-style 16Hz electrification across the network...

German electrification is 16 2/3 Hz at 15kV.

That system originated in Switzerland having bin pioneered by the Bern Lötschberg Simplon railway and adopted as standard by the Swiss Federal Gov't in 1913.

I understand the frequency on some routes has since been converted to 17Hz but I don't know the extent to which this is now standard.

I would assume that modern power electronics on trains don't care what the supply frequency is?

 

[Philip Phlopp]

It is not. Third rail DC appears to be,but going through recent yearly safety reports demonstrate it safer than AC. A poster who claimed he could show DC killed more than ac(Adjusted for pop density & mileage) never came back with the evidence,although he continued his stream of postings. The evidence does not exist.
Remember NR is spending unbelievable amounts of our,& our childrens',money. We have a right to know it is being spent wisely. If the AC advocates win the day the north downs line will be permanently a diesel bye way because of NR's incredible AC ole costs. DC could be laid down cheaply,& power lines intersect the north downs tracks. DC,if properly maintained,has lower total cost than AC.
If AC is so safe why are all new AC territory bridges having the parapets expensively raised by a foot; for fun? DC for DC infilling is a no brainer.

You keep repeating these myths.

I and several other posters have provided copies of every publicly available report, we can't force you to read them, but it's somewhat disingenuous to claim you've never been provided with the data you asked for.

The document you need (and which has been posted previously) is an ORR document http://orr.gov.uk/__data/assets/pdf_file/0017/17621/dc-electrification-policy-statement.pdf

I'll quote the relevant parts, because I don't think you know how to open the reports you keep being linked to.

ORR’s most significant concern in regard to legacy third rail systems (the “legacy network”) is the running of bare, live conductors through publicly accessible areas. These conductors are not insulated or shrouded. The legacy network does not allow quick, secure isolations, and exposes individuals to a range of risks whilst carrying out isolations (1). Due to the difficulty in obtaining isolations on the legacy network, a lot
of work tends to be carried out on or near the live conductor, further undermining safety and weakening compliance with the applicable legislation. This is not an abstract or theoretical risk: the harm done to both workers and members of the public by the legacy network occurs significantly more frequently than on the overhead AC network (2). A duty holder proposing the laying of new bare third rail (as used across the legacy network) would therefore have to make a compelling case that it had
considered all other possibilities and could satisfactorily demonstrate that all such possibilities would be grossly disproportionate in comparison to using third rail.

The references for this (and I include both to be fair to DC).

(1) This weakness has been recognised by Network Rail in its acknowledgment of the safety benefits of DC – Electrical
Power Asset Policy December 2012 (page 284) and is why ORR has agreed to a ring fenced fund for ‘safer, faster isolations’ in CP5.

(2) This is borne out by data from RSSB’s safety risk model – despite the legacy network being only half the size of the AC network (4400km compared to 8200km), it contributes almost eight times more (in terms of fatalities and weighted injuries per year) to overall risks on the railway. See FWI comparative data for OLE / conductor rail / non-electrified: Network Rail Electrical Power Asset Policy December 2012 (Table 2.1, page 52).

You're stuck perpetuating the same sorry, tired myths, and woe-betide anybody who disagrees with you. I expect I'll be attacked for daring to post in response to you, or for daring to suggest some of your criticism of Network Rail is wrong, but I've seen the risk calculated and it's fair and reasonable, and it calculates OLE and third rail risk on the same basis.

The North Downs Line won't permanently be a diesel bye-way, GWR and SWT both have dual voltage stock, there's absolutely nothing wrong with on the fly voltage changes if that's how best to do it.

The suggestion DC could be laid down cheaply is laughable - there's HV grid connectors, quite correct, but there's no 33kV AC network to feed the chain of a dozen 750V DC feeder stations the route will need, it'll also need some limited resleepering to provide the necessary insulator pot mounts, and the same signalling immunisation work needed for AC. 25kV AC would need one feeder at Farnborough, no resleepering and pretty much the same signalling immunisation.

It also then adds to the maintenance costs for the route.

AC is more expensive than DC to maintain - £1000 per single track kilometre (stk) per year, not disputing that (though will add people like Furrer+Frey are researching ways to reduce cost and increase reliability, so they've a good chance of keeping those costs fairly static over the next couple of Control Periods).

DC third rail costs about £400 per stk to maintain, maybe could go up to £500 per stk to deal with your noted ballast concerns.

Track maintenance cost per single track kilometre works out around 50% higher for DC track, that can be over £2,000 of difference, even after taking the £500 saving for having DC and not AC, you're still significantly more expensive maintaining - just maintaining - a DC route than you are maintaining an AC route.

So you have a DC railway that's 35% more costly to maintain, is eight times more dangerous when you switch the electric on, starts losing more kW to earth the moment you switch it on, even in as ideal a world as you can get, and when you start running trains over it, it uses something in the region of 25% more energy to make the same train with the same mass move the same distance at the same speed with the same acceleration.

Even your rant about parapets is simplified and pretty wrong. It's obviously good practice to keep OLE further away from the public, and general modifications are of course an additional cost one wouldn't face with DC, but some of the route clearance work kills more than two birds with one stone.

Do you remember Oxshott - cement mixer on top of a Class 455 unit - rebuilding parapets to meet the new DfT restraint requirements protects not just the public from 25kV wires, but also the railway from car and lorry incursions, rebuilding bridges and parapets clears routes for W10 and W12 boxes at the same time, and it removes life expired bridges which may be ready to collapse (maybe like Barrow on Soar - report pending, of course).

Bridge rebuilding can also be done with help and funding from councils, where NR and the LA have eliminated bridges with weight limits (Orlando, Bolton) or have allowed narrow one way bridges to be replaced with two way bridges (Benhar, Shotts).

Finally - no power system for the railway is perfect. Steam has issues. Diesel has issues. DC electric has issues. AC electric has issues. Electric of either type provides the highest levels of reliability, and AC edges DC for a number of reasons, plenty of evidence for you to choose and acknowledge or ignore, but if I could ask a favour, I've been pleasant, helpful and cheerful with you, could you please stop being unpleasant towards me. Thanks.

 

[QueensCurve]

every DC 12 car train does not have to drag 10 tons of track bashing transformer up hill & downdale.

We seem to have a bad case of transformer inflation. They have gone from 2t to 10t.

 

[Domh245]

specially as every DC 12 car train does not have to drag 10 tons of track bashing transformer up hill & downdale.

Correct me if I'm wrong, but don't Southern's fleet of 377s carry a lump of concrete in lieu of a transformer, so there is actually no mass saving. Does this also apply to other modern 3rd rail EMUs?

 

[Philip Phlopp]

Correct me if I'm wrong, but don't Southern's fleet of 377s carry a lump of concrete in lieu of a transformer, so there is actually no mass saving. Does this also apply to other modern 3rd rail EMUs?

Bombardier stock does, Siemens doesn't (I think).

It's not a massive issue in terms of track wear, because it's fully sprung mass, but it's a waste of energy accelerating it up hill and down dale.

Siemens AC Desiro stock is lighter than their DC stock (the dual voltage stock is heavier though) so presumably different approach taken for suspension settings etc and concrete block not needed.