Cost of electrification OHLE vs 3rd rail

Jozhua · 14 Sep 2019

There's a lot of comparisons made around UK electrification to other countries rolling projects, but I can't help feeling that difficulties faced with OHLE installation is to do with loading guages. Not only do you need space for cables and masts but also clearences under bridges, etc.

This generally means UK rail electrification projects get lumped in with station redesigns, new tunnels, track layouts, signalling and obviously this increases costs significantly. Sometimes ground conditions that can safely support trains can't support OHLE masts well due to the different loads.

Obviously under EU rules, new 3rd rail installations are not allowed, but in theory if/when this isn't a thing

it could open up opportunities for it!

There are other limitations such as speed, max power delivery and the like but I can think of so many routes where this wouldn't really be an issue. Bi-mode electric trains are very common in the UK and Northern already has 319's!

In regards to needing a lot of power feeding points, a thin, high voltage cable could be run at the side of the track with occasional points with rectifiers and transformers back to 750v DC.

I shall put forward Manchester - Leeds as an example:
-OHLE until Victoria in Manchester and from the outskirts of Leeds till the centre.
-Lots of tight tunnels and bridges limiting the guage.
-45 miles or so, so probably not an enormous amount of transformer stations needed.

Would I be right in thinking that this could be a reasonable amount cheaper than OHLE on many routes or am I missing some important points?

Open to discussion!

RailUK Forums

HSTEd · 14 Sep 2019

Jozhua said:
Obviously under EU rules, new 3rd rail installations are not allowed, but in theory if/when this isn't a thing it could open up opportunities for it!

It's not under EU rules.
The ORR has decided that new installations will not be approved, citing Electrical Health and Safety at work regulations - which happen to declare traction railway installations out of scope!

This is the same ORR that gave up the 25kV clearance exemptions - which just shows how engaged they are with the technical realities of the British railway system.

Because they are the ORR the railway must obey, and because Network Rail had hilariously optimistic 25kV cost estimates noone has decided to fight them on it.

Frankly even Network Rail is changing position on this as their Kent route study recently admitted that third rail systems are much cheaper to install than 25kV ones.

Jozhua said:
There are other limitations such as speed, max power delivery and the like but I can think of so many routes where this wouldn't really be an issue. Bi-mode electric trains are very common in the UK and Northern already has 319's!

There are very few currently unelectrified railways where substantial running will occur above 100mph, and where traffic densities are likely to be high enough to cause power delivery to become an issue.
The railway will not be running Class 700s everywhere any time soon!

Elecman · 14 Sep 2019

Jozhua said:
Obviously under EU rules, new 3rd rail installations are not allowed, but in theory if/when this isn't a thing it could open up opportunities for it!

In regards to needing a lot of power feeding points, a thin, high voltage cable could be run at the side of the track with occasional points with rectifiers and transformers back to 750v DC.

Firstly It’s not an EU law it’s the ORRs erroneous interpretation of the Electricity at Work Regulations that are to blame.

Secondly that is exactly how DC substations are fed within the Network Rail distribution system from a feeder stations to DC substation, it is however these substations that ar3 required quit3 frequ3ntly due to volt drop considerations etc

Jozhua · 14 Sep 2019

HSTEd said:
It's not under EU rules.
The ORR has decided that new installations will not be approved, citing Electrical Health and Safety at work regulations - which happen to declare traction railway installations out of scope!

This is the same ORR that gave up the 25kV clearance exemptions - which just shows how engaged they are with the technical realities of the British railway system.

Because they are the ORR the railway must obey, and because Network Rail had hilariously optimistic 25kV cost estimates noone has decided to fight them on it.

Frankly even Network Rail is changing position on this as their Kent route study recently admitted that third rail systems are much cheaper to install than 25kV ones.

There are very few currently unelectrified railways where substantial running will occur above 100mph, and where traffic densities are likely to be high enough to cause power delivery to become an issue.
The railway will not be running Class 700s everywhere any time soon!

I stand corrected! I didn't realise it was the ORR. How much more unsafe is 3rd rail than say OHLE or over just normal risks on the railway?

You see I've argued for a rolling OHLE electrification, but considering all of the major work that needs to be done to bring tunnels, bridges, etc to gauge the task is going to be much more sizable than say the rolling programmes in Germany.

Surely in 2019 ways to make 3rd rail electrically safer could be found. Although the high currents involved would probably make it quite difficult...

Yes 100mph is more than suitable for a lot of suburban routes and even perticularly curvy intercity ones.

Elecman said:
Firstly It’s not an EU law it’s the ORRs erroneous interpretation of the Electricity at Work Regulations that are to blame.

Secondly that is exactly how DC substations are fed within the Network Rail distribution system from a feeder stations to DC substation, it is however these substations that ar3 required quit3 frequ3ntly due to volt drop considerations etc

Yes, I guess my thoughts were as to wether the frequent substations would contribute to increased costs much but the electrical equipment seems simple enough, probably a lot more simple than just a hundred meters of OHLE :lol:

yorksrob · 14 Sep 2019

Well, the ORR have stated no new further third rail electrification.

They've also let the sensible pre-existing derogations on overhead electrification lapse.

Perhaps the ORR is the problem and its regulatory position needs to be reconsidered.

Nym · 14 Sep 2019

Perhaps, but a move back to self regulation is a recipe for disaster.

What one requires is a degree of pragmatism at the ORR, but when you employ people without any nerve or resolve to do anything that isn't in the TSI or handed down from above, none of them will take the risk and accept what was previously very sensible derrogations.

The story is unfortunately now the same in TfL (although it may have been for longer).

hwl · 14 Sep 2019

Jozhua said:
There's a lot of comparisons made around UK electrification to other countries rolling projects, but I can't help feeling that difficulties faced with OHLE installation is to do with loading guages. Not only do you need space for cables and masts but also clearences under bridges, etc.

This generally means UK rail electrification projects get lumped in with station redesigns, new tunnels, track layouts, signalling and obviously this increases costs significantly. Sometimes ground conditions that can safely support trains can't support OHLE masts well due to the different loads.

Obviously under EU rules, new 3rd rail installations are not allowed, but in theory if/when this isn't a thing it could open up opportunities for it!

There are other limitations such as speed, max power delivery and the like but I can think of so many routes where this wouldn't really be an issue. Bi-mode electric trains are very common in the UK and Northern already has 319's!

In regards to needing a lot of power feeding points, a thin, high voltage cable could be run at the side of the track with occasional points with rectifiers and transformers back to 750v DC.

I shall put forward Manchester - Leeds as an example:
-OHLE until Victoria in Manchester and from the outskirts of Leeds till the centre.
-Lots of tight tunnels and bridges limiting the guage.
-45 miles or so, so probably not an enormous amount of transformer stations needed.

Would I be right in thinking that this could be a reasonable amount cheaper than OHLE on many routes or am I missing some important points?

Open to discussion!

Most 3rd rail substations are fed from NR's 33kV 3phase traction supply network which in London and a few other places is directly tapped off NatGrids 400/275kV and in others off DNO supplies with exclusive circuit and in some more remote places DNO 11kV supplies.

33kV represents a sweet spot in terms of maximizing voltage and minimising cable cost and cable maintenance (hence the decommissioning of the remaining original 66kV pressurised oil fill insulation cable network 3-4 years ago.)

The 3rd rail currents are over 30x higher than OHLE, hence fault current and protection quickly become limiting factors with most substations being no larger than 4kA (including metro systems globally), the maximum allowed current per circuit is 12kA. (Also a conveniently transportable size and weight e.g container sized).
The monster Ludgate Cellars substation is infact 8x 3.3kA with lots of clever switch gear.

A full lenght 12 car train will easily take all the juice from a single substation.

Jozhua · 14 Sep 2019

hwl said:
Most 3rd rail substations are fed from NR's 33kV 3phase traction supply network which in London and a few other places is directly tapped off NatGrids 400/275kV and in others off DNO supplies with exclusive circuit and in some more remote places DNO 11kV supplies.

33kV represents a sweet spot in terms of maximizing voltage and minimising cable cost and cable maintenance (hence the decommissioning of the remaining original 66kV pressurised oil fill insulation cable network 3-4 years ago.)

The 3rd rail currents are over 30x higher than OHLE, hence fault current and protection quickly become limiting factors with most substations being no larger than 4kA (including metro systems globally), the maximum allowed current per circuit is 12kA. (Also a conveniently transportable size and weight e.g container sized).
The monster Ludgate Cellars substation is infact 8x 3.3kA with lots of clever switch gear.

A full lenght 12 car train will easily take all the juice from a single substation.

But, a lot of routes in the South West/Mids/North have a fraction of the traffic of the 3rd rail network, 12 car trains are somewhat of a rarity!

I don't doubt it's not as great as OHLE, but realistically the UK railways are too old for it to be within the current budget constraints.

It's just looking at the OHLE installation issues faced on the Manchester-Blackpool route via Bolton, it's unbelievable. Floods, poor ground conditions, new tunnels, lifting historical archways to fit the lines in and it was all delivered years of disruption behind schedule. All to run trains that for the most part can use 3rd rail anyway (319's)...

AM9 · 14 Sep 2019

hwl said:
... The monster Ludgate Cellars substation is infact 8x 3.3kA with lots of clever switch gear. ...

Slightly OT, but maybe very much an issue with a bearing on the environmental case for LVDC, does such complex switching, (and much of the switching required for 3rd rail installations) use SF6 as an arc suppressant?

hwl · 14 Sep 2019

Jozhua said:
But, a lot of routes in the South West/Mids/North have a fraction of the traffic of the 3rd rail network, 12 car trains are somewhat of a rarity!

I don't doubt it's not as great as OHLE, but realistically the UK railways are too old for it to be within the current budget constraints.

It's just looking at the OHLE installation issues faced on the Manchester-Blackpool route via Bolton, it's unbelievable. Floods, poor ground conditions, new tunnels, lifting historical archways to fit the lines in and it was all delivered years of disruption behind schedule. All to run trains that for the most part can use 3rd rail anyway (319's)...

Bolton etc. You forgot the old mines issues.

3rd rail - the losses are horrific (lower voltage higher current and losses proportional to IR^2) so a substation every 3 to 4 miles is the minimum on a quiet route even with shorter trains and 1mile spacing is fairly typical.

Train performance is also far worse on DC for example a 12car 700 can take 5.1MW but in a high available power area 3.3MW or even less in normal (2.8MW) or poor DC supply area (GPS controlled regimes)

All Desiros and Electrostars have software controlled DC current limits that limit the available power to 50-70% of AC level.

hwl · 14 Sep 2019

AM9 said:
Slightly OT, but maybe very much an issue with a bearing on the environmental case for LVDC, does such complex switching, (and much of the switching required for 3rd rail installations) use SF6 as an arc suppressant?

No as low enough voltage not to need SF6 to be contemplated locally but more HV switch gear overall. Worth pointing out the GWML electrification is free from SF6 in switch gear.

hwl · 14 Sep 2019

hwl said:
Bolton etc. You forgot the old mines issues.

3rd rail - the losses are horrific (lower voltage higher current and losses proportional to IR^2) so a substation every 3 to 4 miles is the minimum on a quiet route even with shorter trains and 1mile spacing is fairly typical.

Train performance is also far worse on DC for example a 12car 700 can take 5.1MW but in a high available power area 3.3MW or even less in normal (2.8MW) or poor DC supply area (GPS controlled regimes)

All Desiros and Electrostars have software controlled DC current limits that limit the available power to 50-70% of AC level.

Even the Isle of Wight with 8.25miles of route and 2 very short trains has 3 substations..

Bald Rick · 15 Sep 2019

Perhaps the main key point is that as a system, third rail is less reliable and has a higher whole life cost than third rail.

Jozhua · 15 Sep 2019

Surely 750v DC isn't completely hopeless though? Pretty sure Metrolink and the Supertram manage to use it on thin overhead catenary.

Yes, 3rd rail it isn't as ideal as OHLE, I don't think anyone would claim that, but it could be significantly cheaper and more acessable. If running costs are still lower than diesel, then perhaps it is worth looking into?

I was also considering wether it could be hotswapped within a route, using 3rd rail where OHLE could prove very impractical/costly. Perhaps for a perticularly long tunnel with low clearances.

hwl · 15 Sep 2019

Jozhua said:
Surely 750v DC isn't completely hopeless though? Pretty sure Metrolink and the Supertram manage to use it on thin overhead catenary.

Yes, 3rd rail it isn't as ideal as OHLE, I don't think anyone would claim that, but it could be significantly cheaper and more acessable. If running costs are still lower than diesel, then perhaps it is worth looking into?

I was also considering wether it could be hotswapped within a route, using 3rd rail where OHLE could prove very impractical/costly. Perhaps for a perticularly long tunnel with low clearances.

The earthing arrangements are completely different for AC OHLE and DC 3rd rail so change over areas are very expensive and metal structures in the change over areas are very prone to corrosion issues.

mike57 · 15 Sep 2019

Could a higher voltage side or bottom contact 3rd rail be used for areas where where OHLE is going to be expensive and/or difficult to install. Manchester - Bury used 1200v DC, and side or bottom contact can be made safer. Increasing the voltage from 750v to 1200v would reduce losses for a given power by about 2.5x. Taking the example of Leeds Manchester speeds on the current alignments are never going to challenge 3rd rail, and a quick fix even if not perfect would probably be better than bi-mode or diesel only operation for the foreseeable future. I am also assuming that installing a 3rd rail installation of some sort would be less intrusive into day to day operation of the existing railway than OLHE.

Jozhua · 15 Sep 2019

mike57 said:
Could a higher voltage side or bottom contact 3rd rail be used for areas where where OHLE is going to be expensive and/or difficult to install. Manchester - Bury used 1200v DC, and side or bottom contact can be made safer. Increasing the voltage from 750v to 1200v would reduce losses for a given power by about 2.5x. Taking the example of Leeds Manchester speeds on the current alignments are never going to challenge 3rd rail, and a quick fix even if not perfect would probably be better than bi-mode or diesel only operation for the foreseeable future. I am also assuming that installing a 3rd rail installation of some sort would be less intrusive into day to day operation of the existing railway than OLHE.

San Francisco's BART uses 1000v DC third rail and is relatively new. (Built in 1972)

Bottom contact is in use on the MTA Metro North Railroad, but it's only 750v...

If 3rd rail is that terrible though, we wouldn't still be using it, clearly it's better than running diesel trains and safe enough for the existing installations to still operate...

Bessie · 15 Sep 2019

What was the last 3rd rail project in the UK? I’m thinking Hastings or East Grinstead electrification. It seems very short sighted that no others will be done. Uckfield and North Downs line are obvious candidates

AM9 · 15 Sep 2019

Jozhua said:
... If 3rd rail is that terrible though, we wouldn't still be using it, clearly it's better than running diesel trains and safe enough for the existing installations to still operate...

Not necessarily. If somebody tried introducing from sctrach, gas as a form of domestic heating and cooking or petrol to be carried around for internal combustion engines they wouldn't get very far with a safety case, let alone the environmental issues. Grandfather rights (and sheer inertia) allows existing 3rd rail installations to be operated despite their relatively poor safety case. The ORR has decided that extending the risk with new exposed medium voltage conductors when there are safer alternatives, will not be tolerated. OLE only requires the civils to be able to accommodate it once as a capital cost, the continuing cost is then much lower than for 3rd rail, thus the longer life the infrastructure has, the lower overall cost of ownership.

DarloRich · 16 Sep 2019

Jozhua said:
Obviously under EU rules, new 3rd rail installations are not allowed, but in theory if/when this isn't a thing it could open up opportunities for it!

Could you provide me a link to the relevant EU rules please?

Jozhua said:
Would I be right in thinking that this could be a reasonable amount cheaper than OHLE on many routes or am I missing some important points

just a couple of missing points but one will do: The ORR they say NO!

Jozhua said:
If 3rd rail is that terrible though, we wouldn't still be using it, clearly it's better than running diesel trains and safe enough for the existing installations to still operate

sigh.

Bald Rick said:
Perhaps the main key point is that as a system, third rail is less reliable and has a higher whole life cost than third rail.

to technical!

Camden · 16 Sep 2019

AM9 said:
despite their relatively poor safety case.

Unsubstantiated, especially "relative".

AM9 said:
the continuing cost is then much lower than for 3rd rail, thus the longer life the infrastructure has, the lower overall cost of ownership.

Again, unsubstantiated. And takes no account of local circumstance. For example, maintaining 3rd rail for the use of high speed trains will be much higher than for low speed metro trains. Additionally, the power cost of 25kV OHLE may be lower for high speed trains, but will be higher for metro.

Third rail DC is trusted around the globe for what it does well, and where other countries get on and let their cities do what they need to, our country is paralysed by oddball nonsense that makes a meal out of a few miles of railway line.

Jozhua · 16 Sep 2019

DarloRich said:
Could you provide me a link to the relevant EU rules please?

just a couple of missing points but one will do: The ORR they say NO!

sigh.

to technical!

Thanks for taking some points out of context, some of which have already been more politely corrected by other users on the forum and posting sarcastic replies

Only trying to pose the case for 3rd rail, doesn't seem to make much sense as to why it is in such wide use if it is completely unsuitable. Perhaps you can link some data on running costs for 3rd rail vs diesel traction before you sigh?

AM9 · 16 Sep 2019

Camden said:
Unsubstantiated, especially "relative".

Again, unsubstantiated. And takes no account of local circumstance. For example, maintaining 3rd rail for the use of high speed trains will be much higher than for low speed metro trains. Additionally, the power cost of 25kV OHLE may be lower for high speed trains, but will be higher for metro.

Third rail DC is trusted around the globe for what it does well, and where other countries get on and let their cities do what they need to, our country is paralysed by oddball nonsense that makes a meal out of a few miles of railway line.

Where in the UK (or elsewhere) does the power draw of an HV ac OLE fed metro railway in the UK exceed that of an equivalent performing DC metro railway?

hwl · 16 Sep 2019

AM9 said:
Where in the UK (or elsewhere) does the power draw of an HV ac OLE fed metro railway in the UK exceed that of an equivalent performing DC metro railway?

How do you define performance - tph?

If so Crossrail, Thameslink, RER etc...

hwl · 16 Sep 2019

Camden said:
Unsubstantiated, especially "relative".

Again, unsubstantiated. And takes no account of local circumstance. For example, maintaining 3rd rail for the use of high speed trains will be much higher than for low speed metro trains. Additionally, the power cost of 25kV OHLE may be lower for high speed trains, but will be higher for metro.

Third rail DC is trusted around the globe for what it does well, and where other countries get on and let their cities do what they need to, our country is paralysed by oddball nonsense that makes a meal out of a few miles of railway line.

The ORR has actually substantiated the safety point in detail, the "relative" answer which you won't like is 7-8 fold on a risk weighted basis.

Typical DC losses are 20% of total energy used use higher than AC including the metro case and regenerative braking makes this difference bigger.

I'll dig the reports out later.

AM9 · 16 Sep 2019

hwl said:
How do you define performance - tph?

If so Crossrail, Thameslink, RER etc...

Acceleration for a given weight of train, number of trains possible in feed section*, temperature rise, performance in icy conditions, and the effect of these issues on ultimate TPH.

* acknowledging that LVDC feeds are much more numerous not only because the current draw on DC is 33 times that on ac for a similar power at the wheels, but also because the maximum practical current through steel rails is not much higher than what is regularly drawn by a high density train service, - hence the need to cripple the performance of trains to prevent power disconnection occurring.

mmh · 16 Sep 2019

Bessie said:
What was the last 3rd rail project in the UK? I’m thinking Hastings or East Grinstead electrification. It seems very short sighted that no others will be done. Uckfield and North Downs line are obvious candidates

I'd guess the London Overground's East London line. Conversion of New Cross Gate and New Cross to (north of) Whitechapel from London Underground 4 rail to 3rd rail, new 3rd rail line from Whitechapel North, and from south of Surrey Quays to the junction with the South London Line between South Bermondsey and Peckham.

Railwaysceptic · 16 Sep 2019

Camden said:
Third rail DC is trusted around the globe for what it does well, and where other countries get on and let their cities do what they need to, our country is paralysed by oddball nonsense that makes a meal out of a few miles of railway line.

It's also trusted in Kent, Sussex, Surrey, Hampshire and Dorset by a very large number of people who use it every day without qualms on some of the busiest railway lines in this country.

HSTEd · 16 Sep 2019

hwl said:
The ORR has actually substantiated the safety point in detail, the "relative" answer which you won't like is 7-8 fold on a risk weighted basis.

This is however not including any of the possible mitigation measures that can be implemented.
A substantial fraction of these are things like electric shock from people falling off station platforms - which can be mitigated producing pseudo-gaps in station platforms where the centre portion of the platform rail is only livened if necessary because a train can't get a shoe on the live component.

Also improved signage could be argued to reduce the tresspasser fatalities which are a major portion of the risk generated by third rail instalaltions. As could providing insulation on the sides of the conductor rail so only the top surface is actually a contact hazard.

hwl said:
Typical DC losses are 20% of total energy used use higher than AC including the metro case and regenerative braking makes this difference bigger.

Typical DC losses including very high density areas where volt drop in the rails will be huge and contribute to losses.
These are not regions typical of projected expansions to the electrification system.

Also why are AC systems allowed to return power to the grid from regeneration but DC systems are not?
Modern AC-DC converter stations are easily capable of this.
Have to compare apples toa pples.

hwl · 16 Sep 2019

HSTEd said:
This is however not including any of the possible mitigation measures that can be implemented.
A substantial fraction of these are things like electric shock from people falling off station platforms - which can be mitigated producing pseudo-gaps in station platforms where the centre portion of the platform rail is only livened if necessary because a train can't get a shoe on the live component.

Also improved signage could be argued to reduce the tresspasser fatalities which are a major portion of the risk generated by third rail installations. As could providing insulation on the sides of the conductor rail so only the top surface is actually a contact hazard.

Typical DC losses including very high density areas where volt drop in the rails will be huge and contribute to losses.
These are not regions typical of projected expansions to the electrification system.

Also why are AC systems allowed to return power to the grid from regeneration but DC systems are not?
Modern AC-DC converter stations are easily capable of this.
Have to compare apples to apples.

The losses in 3rd rail DC generally mean that most regenerated energy ends up being used by other trains, as restive losses or reducing voltage drop (and hence losses) in general meaning there is very little could go back to the typicality 33kV supply, hence a very low return on investment as a stand alone upgrade.

Cost of electrification OHLE vs 3rd rail

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