What’s more efficient: overhead or 3rd rail electrification?

[plugwash]

network rail regions don't necessarily line up exactly with train operating companies.

In terms of TOCs it seems castle cary to yeoville has both SWR and GWR services while yeoville to waymouth has only gwr.

 

[Rush Matafu]

Good morning British Rail enthusiasts. I am new here, just joined.
Thank you you all for your lovely comments and chats. You can't read them all but for those which I was able to read, they were very helpful.
I was wandering whether the Diesel Shunting locomotives are still in use and how many of them are out there doing this fantastic job.
Is there any information on their environmental impact?
Thank you all for your comments! Enjoy your day.

 

[AlastairFraser]

Good morning British Rail enthusiasts. I am new here, just joined.
Thank you you all for your lovely comments and chats. You can't read them all but for those which I was able to read, they were very helpful.
I was wandering whether the Diesel Shunting locomotives are still in use and how many of them are out there doing this fantastic job.
Is there any information on their environmental impact?
Thank you all for your comments! Enjoy your day.

Welcome to the forum!
Diesel Shunters?
Have a look at the "large shunters" section of this article - should be able to tell you more about the classes of shunters which are still in operation!

List of British Rail modern traction locomotive classes - Wikipedia

en.wikipedia.org

 

[plugwash]

There are also road-rail shunters. A recent example is

Zephir rail-road depot shunters launched in UK | ROLLINGSTOCK

UK: Three LOK 16.300 vehicles have replaced 60-year-old Class 08 shunting locomotives on the tracks of Celsa Steel in Cardiff.

rollingstockworld.com

But i'm sure I've seen an older example round one of the depots near manchester for years.

 

[Alfonso]

Re having standardised, large fleets...perhaps just one suburban design and a high speed design, there are pros and cons: Costs can be lower with long production runs, and lots of people will know how they work, how to fix them, drive them etc. On the downside it slows adoption of improved technology, differing requirements etc, and if something goes wrong with one of them, such as a design fault, poor reliability etc , then your whole fleet is stuffed. When something new and therefore risky comes along there is a tendency to want to try a small order to get real world knowledge before ordering lots of them.

 

[Silent]

You’re right, 25kV AC is far more efficient. But back when the original electrification south of London took place DC was the normal solution. High voltage AC and the ability to convert it onboard to safely drive motors came much later on. So the issue now is that we’ve got a choice of priorities, and most people would agree that whatever funds are available should be used to electrify routes for the first time, eg Chiltern and XC NE<>SW, rather than change routes that are already DC powered.

Chiltetn was useful recently when there was a power cut that disrupted London rail services recently.

Overhead lines are more efficient than third rail. They are safer for lineside workers and animals, less susceptible to weather effects (ice in particular), more energy efficient and able to deliver both AC and DC currents, allow faster trains when necessary, and in time will pay for themselves despite having a higher up-front cost. If costs and disruption wasn't a factor I've no doubt third rail would be ripped up from the ground it sits on. The only time it may be better than overhead is for high-capacity underground metro systems in order to reduce the width and height of the tunnels.

As for all types of services using the exact same type of train, it seems like we are leaning towards streamlining our fleets as much as possible. CAF Civity units are prevelent at Northern, Transport for Wales and West Midlands Trains, and practically every new flagship InterCity train in the country is a Class 80x train. The only reason it's not the flagship at Avanti West Coast is because the Pendolino fills that role and is simply being complimented by the 807s on the Birmingham and Liverpool routes. Different regions also have different needs, so you'll never get an entirely uniform fleet, but operators do seem to be wanting to get as close as possible.

I think the only issue with overhead cables is maybe that they break. For example, I haven’t heard of a train disrupted because of broken third/fourth rails however I’ve heard and experienced disrupted services because of damaged overhead wires.

 

[The exile]

It’s been touched on elsewhere, but 3rd rail (or similar) is widespread on metro systems or extensive suburban systems already built for steam as it requires less space vertically (important if you’re trying to electrify under a bridge that has had property built on it but there’s a sewer and a gas main immediately under the railway.) Systems like the Berlin and Hamburg S-Bahn (as well as our own DLR) use side- or bottom-contact collection - which is a bit more complicated to install and operate than our top/contact, but several degrees safer (it’s more difficult to touch the liberal accidentally) - but conversion would be a nightmare.

 

[Dstock7080]

For example, I haven’t heard of a train disrupted because of broken third/fourth rails however I’ve heard and experienced disrupted services because of damaged overhead wires.

On the Underground displaced current rail is a rare but possible occurrence. The new aluminium rail is lighter and is therefore held down in place, the heavier steel rail just sits on top of the pots under gravity.
Ice is certainly a significant problem, new trains require a cleaner source and the disruption of supply due to ice is fundamental.

 

[DelW]

exeter <-> basingstoke (via yeovil and salisbury).
castle cary <-> dorchester (via yeovil)
Warminster <-> eastleigh/southampton (via salisbury)
shalford <-> reigate (via dorking)
oxted <-> ukfield
ore <-> ashford

Also on the North Downs line, Wokingham <-> Aldershot.

 

[Bald Rick]

I think the only issue with overhead cables is maybe that they break. For example, I haven’t heard of a train disrupted because of broken third/fourth rails however I’ve heard and experienced disrupted services because of damaged overhead wires.

Disruption due to broken / faulty conductor rail happens all the time. As do issues with the very heavy duty power cabling to supply the third rail. Also frequent issues with signalling systems in third rail areas which only happen because of the way they have to be configured in third rail areas.

 

[norbitonflyer]

Yes you're right. I didn't think of the SW direction.

Although isn't Castle Cary to Dorchester via Yeovil a GWR route?

Operated by GWR, but maintained by Network Rail's Southern Region.

I think given the narrow nature of the Merseyrail tunnels having a third rail system was the only option.

The Mersey Tunnel Railway was electrified in 1903, initially on the 4-rail system. The rest of the Wirral system was not electrified until 1936.

However, the Liverpool Exchange to Southport route was part of the Lancashire & Yorkshire Railway, a comletely separate concern, with no physical connection with the Mersey Railway. Had the LYR adopted the overhead system in 1904 when it electrified the Southport line, the 1977 extension to Moorfields and Liverpool Central would have been built to use OLE, with the new tunnels built large to accommodate it.

 

[Trainman40083]

I have to say I have found this thread utterly fascinating. I was involved with material supply of both third rail and OHLE for many years..We had copper and aluminium track feeder cables. OHLE wires with cadmium etc. The rising price of copper that saw aluminium being used. We saw OHLE sagging , tensioned with weights now being replaced by Auto tensioners. The real goal is a totally reliable railway, where there are no unexpected failures.

 

[DJ_K666]

I have to say I have found this thread utterly fascinating. I was involved with material supply of both third rail and OHLE for many years..We had copper and aluminium track feeder cables. OHLE wires with cadmium etc. The rising price of copper that saw aluminium being used. We saw OHLE sagging , tensioned with weights now being replaced by Auto tensioners. The real goal is a totally reliable railway, where there are no unexpected failures.

That's interesting. I've seen aluminium conductor rails on the London Underground before.

I also still see a lot of the weight tensioners on OHLE.

 

[Trainman40083]

That's interesting. I've seen aluminium conductor rails on the London Underground before.

I also still see a lot of the weight tensioners on OHLE.

Probably Pfisterer ones. When the wire says, they tension up.

 

[Sorcerer]

I think the only issue with overhead cables is maybe that they break. For example, I haven’t heard of a train disrupted because of broken third/fourth rails however I’ve heard and experienced disrupted services because of damaged overhead wires.

Like I said, in regular circumstances the overhead lines shouldn't be breaking, and the vast majority of the time there is no risk of them going out of action, contrasted to third rail which has a risk of cold weather forming an insulating layer of ice. Of course that is just one of several reasons why overhead is better, so even if we accept their susceptibility to damage and subsequent disruption they are still more efficient than third rail in the vast majority of cases.

The Mersey Tunnel Railway was electrified in 1903, initially on the 4-rail system. The rest of the Wirral system was not electrified until 1936.

However, the Liverpool Exchange to Southport route was part of the Lancashire & Yorkshire Railway, a comletely separate concern, with no physical connection with the Mersey Railway. Had the LYR adopted the overhead system in 1904 when it electrified the Southport line, the 1977 extension to Moorfields and Liverpool Central would have been built to use OLE, with the new tunnels built large to accommodate it.

Interesting. Thank you for that history lesson. It seems that despite being from that part of the country my knowledge is lacking, because I didn't quite realise (or had possibly forgotten) that the loop tunnels were so recent.

 

[507 001]

Composite conductor rail, mostly aluminium for lower resistance with a steel layer on top to reduce wear from the shoes. This presumably allowed fewer substations while keeping voltage drop within limits. I don't think it was used anywhere else so I assume there were problems with it.

Off topic, but there’s a fair bit of it on the Merseyrail network, not least on the Chester line.

As it is becoming life expired, it seems to be being replaced with conventional steel con rail.

 

[edwin_m]

Not sure why you think wires provide less resitance than rails. The resitance depends on the thickness of the conductor - double the cross-sectional area and twice the current will pass for the same voltage.

However, wires are some sort of copper alloy and third rails are usually steel. The conductivity of the copper is around four times better, so a steel conductor needs four times the cross-section to be as good as a copper one. The third rail is obviously thicker than that, but the benefit isn't as significant as it might first appear.

But the real killer is the power loss being inversely proportional to the square of the voltage, so a 750V conductor would have about 1000 times the loss of a 25kV one of the same length, material and cross-section. Even if the steel rail at 750V was 40 times the cross-section of the 25kV copper wire, it would still waste 100 times more power over the same length.

This also makes circuit protection more challenging, as the resistance may limit the current drawn by a short a long way from a substation to something similar to what is seen normally if a few trains happen to be accelerating at once. The fault current in a 25kV system will be much more than the normal current.

 

[Minstral25]

Disruption due to broken / faulty conductor rail happens all the time. As do issues with the very heavy duty power cabling to supply the third rail. Also frequent issues with signalling systems in third rail areas which only happen because of the way they have to be configured in third rail areas.

Issues happen with all conductors or wiring systems. As someone who regularly uses Third rail services from London to Redhill, I find it significantly more likely to have services cancelled due to a fault North of London as the wires have come down than to have it attributed to a conductor issue south of the river.

In fact, less scientifically on the latter conductor issues I can only remember one journey disrupted in memory (Clapham Junct train taking out conductor pots early one morning), whereas so many disrupted due to the wires being down that I couldn't list here.

 

[Trainman40083]

Issues happen with all conductors or wiring systems. As someone who regularly uses Third rail services from London to Redhill, I find it significantly more likely to have services cancelled due to a fault North of London as the wires have come down than to have it attributed to a conductor issue south of the river.

In fact, less scientifically on the latter conductor issues I can only remember one journey disrupted in memory (Clapham Junct train taking out conductor pots early one morning), whereas so many disrupted due to the wires being down that I couldn't list here.

And now conductor pots are polymeric rather than porcelain

 

[Zomboid]

The 3rd rail contact system is less vulnerable in itself than overhead lines, but it does create other issues.

Efficiency depends what you're measuring, but one of the big expenditures of overhead line is sorting out clearances, which is a job that is usually only needed once, whereas 3rd rail systems need lots of distribution equipment installed along the route, which are then an ongoing maintenance and renewals liability. And if you want to deal with both go for DC overhead...

There are also greater transmission losses in DC and less power available because of the low voltage.

In general, there's no way that a major electrification project would use DC if starting from scratch now, but it's not beyond the realms of possibility that an existing system would be extended.

 

[renegademaster]

Still some overhead and third rail DC being built in completely new metro systems. Wuhan metro started 2004 entirely DC

 

[Zomboid]

Metros are different to the main line. DC allows the tunnels to be built smaller, and more frequent distribution sites can be advantageous in highly intensive service areas.

 

[GRALISTAIR]

We are interested in power. Power in watts is given by current in amps multiplied by voltage. So as 3rd rail DC is only 750 volts, to deliver the same power as 25kV AC requires a huge amount of current. Power loss is given by current squared multiplied by resistance. So resistive losses from 3rd rail are much higher and hence efficiency is lower too.

 

[4COR]

Which is what was said in post 20, but without the I^2R explanation.

 

[norbitonflyer]

Which is what was said in post 20, but without the I^2R explanation.

and post #47 (power is proportional to both current and voltage, so for a given power, current and voltage are in inverse relation)

 

[brad465]

I think the only issue with overhead cables is maybe that they break. For example, I haven’t heard of a train disrupted because of broken third/fourth rails however I’ve heard and experienced disrupted services because of damaged overhead wires.

Another issue (though one personally I'm not bothered by), is NIMBYs hate them because they are far more of an eyesore than third rail, especially in designated areas. There are also places where, to make them suitable, some very hefty remediation works and bespoke designs are required, such as the Severn tunnel.

 

[norbitonflyer]

Another issue (though one personally I'm not bothered by), is NIMBYs hate them because they are far more of an eyesore than third rail, especially in designated areas. There are also places where, to make them suitable, some very hefty remediation works and bespoke designs are required, such as the Severn tunnel.

I would imagine the Severn Tunnel would have needed a bespoke solution for 3rd rail as well, given its propensity for flooding

 

[edwin_m]

In general, there's no way that a major electrification project would use DC if starting from scratch now, but it's not beyond the realms of possibility that an existing system would be extended.

Main line railways are extending DC systems all the time, because the disadvantages of bringing and different and incompatible system in often outweigh the benefits of using something that's intrinsically more efficient.

However, I can't think of any totally new main line electrification scheme (ie not connecting to existing electrification) using DC or any AC voltage below 25kV, since that system became established in the 1960s. A few heavy haul railways have actually gone to 50kV, but they tend to be in unpopulated areas where transmitting large amounts of power over distance is more difficult, but there are fewer worries about larger clearances. By contrast some countries with well-established DC networks have adopted 25kV AC despite the downsides of having two systems - France and Russia for example.

No doubt somebody can find an exception but I don't believe there are any major ones.

 

[Class 170101]

Another issue (though one personally I'm not bothered by), is NIMBYs hate them because they are far more of an eyesore than third rail, especially in designated areas. There are also places where, to make them suitable, some very hefty remediation works and bespoke designs are required, such as the Severn tunnel.

Didn't a NIMBY suggest 3rd Rail for Sydney Gardens and around Bath Spa?

 

[Bald Rick]

Issues happen with all conductors or wiring systems. As someone who regularly uses Third rail services from London to Redhill, I find it significantly more likely to have services cancelled due to a fault North of London as the wires have come down than to have it attributed to a conductor issue south of the river.

In fact, less scientifically on the latter conductor issues I can only remember one journey disrupted in memory (Clapham Junct train taking out conductor pots early one morning), whereas so many disrupted due to the wires being down that I couldn't list here.

Well, the thing is that for whatever reason, displaced conductor rails, or major faults with the conductor rail distribution equipment are rarely described as such.

There have been several major issues with the conductor rail system in Southern Region in the last week or so. Two of them were displaced conductor rails, one of which completely ruined the Southeastern Kent Coast peak. Another incident closed the West Coastway for several hours. and so on.

And the last week or so was not untypical.

Didn't a NIMBY suggest 3rd Rail for Sydney Gardens and around Bath Spa?

It was suggested for the Royal Border bridge in 1985!