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

[Gooner18]

Living in North London I’ve always been puzzled why north of the river uses OHL and the south using 3rd rail which got my thinking:
Out of the two which is more efficient to use , in my heard surely it’s got to be OHL as the wires should provide less resistance, thus consuming less energy and surely it costs less to install OHL compared to the 3rd rail set up ?
On top of this surely it cost would be better for the whole country to use either OHL or 3rd rail again driving down cost.

The other thing that has always confused me is why are there so many classes of trains in use ?
Again surely the logical thing to do is for everyone to use the same train for the same job, I.e suburban can all use the same train with all OHL using the same train and all 3rd rail suborbital using the same train , all HST operators using the same HST. This would drive down cost in both maintenance and the need to learn types etc

 

[swt_passenger]

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.

 

[Sorcerer]

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.

 

[AlastairFraser]

Living in North London I’ve always been puzzled why north of the river uses OHL and the south using 3rd rail which got my thinking:
Out of the two which is more efficient to use , in my heard surely it’s got to be OHL as the wires should provide less resistance, thus consuming less energy and surely it costs less to install OHL compared to the 3rd rail set up ?
On top of this surely it cost would be better for the whole country to use either OHL or 3rd rail again driving down cost.

The other thing that has always confused me is why are there so many classes of trains in use ?
Again surely the logical thing to do is for everyone to use the same train for the same job, I.e suburban can all use the same train with all OHL using the same train and all 3rd rail suborbital using the same train , all HST operators using the same HST. This would drive down cost in both maintenance and the need to learn types etc

3rd rail in South London is a side effect of the Southern Railway's decisions to electrify quite early on in the 1930s.

There are lots of line with limited clearance (especially with bridges and tunnels), so, in addition to the technology factors other forum members mentioned, there's the factor of cost-effectiveness - there are areas where lots of rebuilding would have had to take place to accommodate OHLE.

One of the Southern predecessors (the London, Brighton and South Coast railway or LBSCR) did experiment with overhead line, but when the LBSCR and other railways (the London and South Western Railway or LSWR, the South Eastern Railway or SER, and finally the London, Chatham and Dover Railway or LCDR) were merged to form the Southern Railway in the Grouping, the LSWR's third rail system won as it was better established than the LBSCR's overhead line system.

 

[Western Gaffer]

The Southern did also deliver DC via overhead catenary in some yards where it was considered unsafe to have third rail everywhere, hence the pantographs on the class 71s.

 

[fandroid]

HA Walker was the General Manager of the LSWR who instigated the 3rd rail system on that company's lines. He then became General Manager of the Southern Railway, so 3rd rail became the system for all electrification of the new company's lines.

 

[Grecian 1998]

I don't think there have been any significant third rail electrifications since around 1990 when Southampton - Portsmouth and Eastleigh - Fareham were electrified. The Office of Rail Regulation is not a fan and it would seem any new projects need to show rather stringent safety measures which the existing network doesn't have.

There is a proposal to use discontinuous third rail electrification between Basingstoke and Exeter on the West of England line using battery fitted 450s. Whilst it's questionable whether this will happen, if it does then the electrified sections are likely to be in countryside areas where the risk of contact is lower.

There are fairly regular threads in the Speculative Discussion section of this forum about whether 'diesel islands' south of London such as Oxted - Uckfield and Hastings - Ashford should be electrified with third rail.

 

[NSEWonderer]

Exeter line is better off going OHLE till Basingstoke then run third rail down. Still shocked that there isn't an incline of a bi mode replacement

 

[AlastairFraser]

Exeter line is better of going OHLE till Basingstoke then run third rail down. Still shocked that there isn't an incline of a bi mode replacement

Sadly OHLE as far as Exeter couldn't really be justified at the moment, hence the discontinuous electrification plan.

 

[NSEWonderer]

Sadly OHLE as far as Exeter couldn't really be justified at the moment, hence the discontinuous electrification plan.

Yeah that plan won't work efficiently. Desiros are notoriously heavy already and the underside is packed already as is. How'd they find enough space to fit the extra batteries I'd not know.

Better off with the 701/5s

 

[AlastairFraser]

Yeah that plan won't work efficiently. Desiros are notoriously heavy already and the underside is packed already as is. How'd they find enough space to fit the extra batteries I'd not know.

Better off with the 701/5s

Perhaps removing some of the existing traction equipment and fitting batteries there?
The batteries won't have to be massive for a first phase as far as Salisbury - you'd only really need 50 mile of off-3rd rail capability to operate the service.

 

[Deepgreen]

I don't think there have been any significant third rail electrifications since around 1990 when Southampton - Portsmouth and Eastleigh - Fareham were electrified. The Office of Rail Regulation is not a fan and it would seem any new projects need to show rather stringent safety measures which the existing network doesn't have.

There is a proposal to use discontinuous third rail electrification between Basingstoke and Exeter on the West of England line using battery fitted 450s. Whilst it's questionable whether this will happen, if it does then the electrified sections are likely to be in countryside areas where the risk of contact is lower.

There are fairly regular threads in the Speculative Discussion section of this forum about whether 'diesel islands' south of London such as Uckfield - Lewes and Hastings - Ashford should be electrified with third rail.

Yes, and Reigate to Guildford, plus bits towards Reading!

 

[hwl]

3rd rail in South London is a side effect of the Southern Railway's decisions to electrify quite early on in the 1930s.

There are lots of line with limited clearance (especially with bridges and tunnels), so, in addition to the technology factors other forum members mentioned, there's the factor of cost-effectiveness - there are areas where lots of rebuilding would have had to take place to accommodate OHLE.

One of the Southern predecessors (the London, Brighton and South Coast railway or LBSCR) did experiment with overhead line, but when the LBSCR and other railways (the London and South Western Railway or LSWR, the South Eastern Railway or SER, and finally the London, Chatham and Dover Railway or LCDR) were merged to form the Southern Railway in the Grouping, the LSWR's third rail system won as it was better established than the LBSCR's overhead line system.

The main cause for the lack of progress in LBSCR's 6.6kV 25Hz electrification was the problem sourcing traction equipment parts from AEG in Berlin after the 28th July 1914.

 

[NSEWonderer]

Perhaps removing some of the existing traction equipment and fitting batteries there?
The batteries won't have to be massive for a first phase as far as Salisbury - you'd only really need 50 mile of off-3rd rail capability to operate the service.

Desiros are pretty compact as is. You won't be able to remove any existing traction equipment without tanking the performance which is already limited as is due to the software imitations imposed on the trains during their introduction. 701/5s would be more of a better candidate and also quite a way lighter but the idea of this proposal just wouldn't work well. Better of spending the money on two tracking the line and getting rid of the notorious bottleneck.

 

[AlastairFraser]

The main cause for the lack of progress in LBSCR's 6.6kV 25Hz electrification was the problem sourcing traction equipment parts from AEG in Berlin after the 28th July 1914.

Makes sense.

Desiros are pretty compact as is. You won't be able to remove any existing traction equipment without tanking the performance which is already limited as is due to the software imitations imposed on the trains during their introduction. 701/5s would be more of a better candidate and also quite a way lighter but the idea of this proposal just wouldn't work well. Better of spending the money on two tracking the line and getting rid of the notorious bottleneck.

We will wait and see, but I don't see the point of getting rid of the single track sections just yet - there's not likely to be justification for a frequency upgrade west of Salisbury for a while yet, unless you want to spend more subsidy on this route (which could be better spent reopening and reconnecting towns to the network elsewhere in the South West IMHO).

 

[Trainman40083]

I don't think there have been any significant third rail electrifications since around 1990 when Southampton - Portsmouth and Eastleigh - Fareham were electrified. The Office of Rail Regulation is not a fan and it would seem any new projects need to show rather stringent safety measures which the existing network doesn't have.

There is a proposal to use discontinuous third rail electrification between Basingstoke and Exeter on the West of England line using battery fitted 450s. Whilst it's questionable whether this will happen, if it does then the electrified sections are likely to be in countryside areas where the risk of contact is lower.

There are fairly regular threads in the Speculative Discussion section of this forum about whether 'diesel islands' south of London such as Uckfield - Lewes and Hastings - Ashford should be electrified with third rail.

I seem to recall from my time at British Rail HQ, that Eastleigh to Fareham area was done on the cheap. Was it aluminium conductor rail or cable? A long time ago. Of course with OHLE we had lines like the Bedpan (Bedford to St Pancras) electrified for suburban trains say 100/110mph.. Those lines are now seeing modification to the OHLE to allow for the EMR Class 810s.

 

[61653 HTAFC]

Isn't AC also preferable to DC due to lower transmission losses (and fewer substations required) regardless of which method the train uses to pick up the power?

 

[3141]

he 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 this misinterprets the situation. The successful bidders for Northern, Wales and Borders, and West Midlands were all different and are unlikely to have proposed ordering CAF Civity units on the grounds of "streamlining our fleets as much as possible". It's more likely that no-one else offered DMUs. I remember it being claimed on these forums that it would be impossible to build a DMU within the British loading gauge that could meet the latest emissions requirements.

As for class 80x, operators who want an inter-city 125 mph train are aware that Hitachi produce such a thing, and if they want one (relatively) quickly that's what they need to order. But there is an exception: LNER have ordered some new inter-city trains from CAF. It seems that in their view the advantages of streamlining are outweighed by not acquiring any more Hitachi products.

 

[edwin_m]

I seem to recall from my time at British Rail HQ, that Eastleigh to Fareham area was done on the cheap. Was it aluminium conductor rail or cable?

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.

Isn't AC also preferable to DC due to lower transmission losses (and fewer substations required) regardless of which method the train uses to pick up the power?

This isn't an intrinsic feature of AC systems, more that AC allows a much higher line voltage to be stepped down by a transformer on the train to a voltage that can be fed into the motors. The higher voltage on AC systems means less current to transmit the same amount of power, which in turn reduces the transmission losses.

With modern traction electronics a higher voltage DC system would be possible, but unlikely to happen as the world has pretty much standardised on 25kV AC for new main line electrification so train and infrastructure equipment is widely available.

Also worth noting that a third rail AC system would be less efficient than a DC one, because something called the skin effect means that only the outermost few millimetres of a conductor carries any current at 50Hz.

 

[4COR]

Isn't AC also preferable to DC due to lower transmission losses (and fewer substations required) regardless of which method the train uses to pick up the power?

Higher Voltage certainly leads to lower transmission losses than lower voltage, but (generally) DC actually has lower transmission losses than AC (for equivalent voltages).

Also worth noting that a third rail AC system would be less efficient than a DC one, because something called the skin effect means that only the outermost few millimetres of a conductor carries any current at 50Hz.

The skin effect at 50Hz is about 9mm (where the current carried drops to 1/e of that at the surface). Not quite as bad as a few mm, but still significant for HVAC power distribution. As you say HVDC doesn't suffer this problem either (nor losses due to line capacitance)..

 

[Sorcerer]

I think this misinterprets the situation. The successful bidders for Northern, Wales and Borders, and West Midlands were all different and are unlikely to have proposed ordering CAF Civity units on the grounds of "streamlining our fleets as much as possible". It's more likely that no-one else offered DMUs. I remember it being claimed on these forums that it would be impossible to build a DMU within the British loading gauge that could meet the latest emissions requirements.

As for class 80x, operators who want an inter-city 125 mph train are aware that Hitachi produce such a thing, and if they want one (relatively) quickly that's what they need to order. But there is an exception: LNER have ordered some new inter-city trains from CAF. It seems that in their view the advantages of streamlining are outweighed by not acquiring any more Hitachi products.

You're right actually, the British loading gauge doesn't exactly leave much room for off-the-shelf requirements. However I do still think it very likely that the railway, especially under GBR in the near future, will probably like the idea of less fleet diversity for purposes such as maintenance and transferability. Airlines tend to prefer a streamlined fleet for much of the same reasons. I think the reason LNER went for a CAF fleet rather than Hitachi is due to cost factors, but on the other hand the railways are lacking in a second tier InterCity train. The 397s and 897s can easily fill this role for TPE and LNER while the 800s serve as the flagship fleet.

 

[61653 HTAFC]

Thanks both for the technical stuff. Weren't the contact wires used on the Woodhead DC Overheads considerably thicker and heavier than what we use on the 25kv 50hz, too?

 

[edwin_m]

Thanks both for the technical stuff. Weren't the contact wires used on the Woodhead DC Overheads considerably thicker and heavier than what we use on the 25kv 50hz, too?

Yes, DC has a higher current so a larger cross-section reduces losses and heating. The Woodhead locos also ran with both pantographs raised, or four pans on a double header, to reduce the current between the wire and the pan which might otherwise start melting them. That wouldn't be possible at higher speeds on lighter AC overhead line because the vibrations from the first pantograph affect contact for the later ones, then again it isn't necessary for the lower current.

I believe some heavily-used DC routes in the Netherlands actually have twin contact wires for similar reasons.

 

[norbitonflyer]

I don't think there have been any significant third rail electrifications since around 1990 when Southampton - Portsmouth and Eastleigh - Fareham were electrified.

There were the extensions to the Jubilee and Northern lines (the former not all in tunnel either!)

Living in North London I’ve always been puzzled why north of the river uses OHL and the south using 3rd rail which got my thinking:
Out of the two which is more efficient to use , in my heard surely it’s got to be OHL as the wires should provide less resistance, thus consuming less energy and surely it costs less to install OHL compared to the 3rd rail set up ?
On top of this surely it cost would be better for the whole country to use either OHL or 3rd rail again driving down cost.

DC has some advantages - all electric trains require DC supply (even with modern AC motors, you need to remove the (fixed) supply frequency before you can apply the (variable) control frequency). But electricity is usually generated and carried overb the National Grid using AC

There is a trade-off between carrying the transformers and rectifiers needed to convert high voltage AC to low voltage DC on board, or having them "shore-based". This depends partly on the distance electricity has to be transmitted (AC can be transmitted at high voltages (low current) which involves less power loss over distance - I^2 x R, where I is current and R is the resistance of the conductor, which is proportional to its length) but also on the number of such equipments required. For an intensive suburban service with many closely spaced substations and a large number of trains, it is more economical to put the transfomers and rectifiers on shore rather than on board.

And until solid state electronics came in in the 1970s, rectifiers required thermionic valves (big vacuum tubes, similar to cathode ray tubes) or mercury arcs (requiring metallic, i.e liquid, mercury). For neither of these was a moving train an ideal environment.

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. That is why low voltage DC overheads have to use thicker gauge wire than high voltage AC. A rail is of course much thicker than a wire.

One reason the LSWR (and the LNWR) went for live rail systems for their suburban systems was for compatiblity with the Underground, with which they shared (and still share) tracks between Gunnersbury and Richmond, East Putney and Wimbledon, Earls Court and Olympia (or the LNWR route to Willesden Junction closed in 1940), and Queens Park and Watford Junction

 

[DJ_K666]

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.

The Third Rail south of the river was basically the LSWR system, the LBSCR used a DC Overhead which went as far south as Coulsdon North, as well as a good number of other routes, but IIRC after Grouping the Southern Railway board was dominated by ex LSWR men and so their system won out.
There are only a tiny number of non-electrified passenger lines left on the Southern Region now. 3, I think.
I still remember Southampton to Portsmouth before electrification in 1990 and Tonbridge to Redhill in the early 90s, which I first travelled on in a class 101!

I can't speak for the Merseyside third rail system though.

 

[norbitonflyer]

The other thing that has always confused me is why are there so many classes of trains in use ?
Again surely the logical thing to do is for everyone to use the same train for the same job, I.e suburban can all use the same train with all OHL using the same train and all 3rd rail suborbital using the same train , all HST operators using the same HST. This would drive down cost in both maintenance and the need to learn types etc

Of late it has been partly due to different private operating companies (TOCs) having different preferences, just as there is now a wide variety of London buses when in the late 1950s, when Londonn Transport reigned supreme, nearly every double decker was an RT. Similarly, you will note that most rolling stock of the 1980s and 1990s were based on a standard bodyshell (Mark 3 carriages, classes 150, 210, 317-322, 455, 456), albeit even then there was some evolution, notably in cab design,

But there has always been some variety, simply because of the longevity of rolling stock. Trains typically last for about 40 years, and technology evolves over such a long period - what was state of the art in 1985 is very outdated now. The only way you could have a standardised fleet would be to renew the entire fleet at once, which would present several challenges for the builders - the biggest being staying in business for 35+ years between orders. Or continue to build trains tom the same basic design over and over again (which is why the Southern Region was building trains to essentially the same design in 1960 that it was doing in 1915, preventing the introduction of such innovations as sliding doors, which had been a feature of trains on other networks since the 1920s)

Note that for a small network, like an individual Tube line or the Tyne & Wear Metro, there is usually just one type of rolling stock, as the entire fleet can be changed over one short period. But even then, over The Underground as a whole, each line has its own stock, from the Bakerloo's 1972 stock, to the "2024" stock currently being built for the Piccadilly Line

I can't speak for the Merseyside third rail system though.

The Lancashire & Yorkshire Railway and the Wirral Railway were both early adopters of electrification, when DC was the most practical option, for which overhead wiring has little advantage over 3rd rail (and would have been difficult to install in the Mersey Tunnel without major strucural alteration)

 

[plugwash]

There are only a tiny number of non-electrified passenger lines left on the Southern Region now. 3, I think.

Comparing https://railmap.azurewebsites.net/Public/ElectrificationMap and https://www.projectmapping.co.uk/Reviews/Resources/NR Regions & Routes map v11.pdf I count siz

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

 

[norbitonflyer]

Overhead lines are more efficient than third rail. They are ...........less susceptible to weather effects (ice in particular),

However, I've never seen a live rail blow away in a gale. Nor is it likely to be dislodged by faulty current-collection gear (a damaged pantograph can bring down the catenary, a 3rd rail train is more likely to just lose a shoe - although that's not why the Southern Region was considered the Cinderella of British Rail!

 

[Sorcerer]

I can't speak for the Merseyside third rail system though.

I think given the narrow nature of the Merseyrail tunnels having a third rail system was the only option. Indeed that usually is the only case where third rail is the better choice against overhead line systems. It helps keeps tunnel sizes down which in turn keeps down the construction costs, historically an ideal for when you were building a railway with significant portions deep underground in tunnels (albeit more so with metros than suburban commuter rail).

Even then the Elizabeth Line was still built with wider tunnels and overhead lines simply because it was better than having a switchover to third rail through the core, and today it's probably not considerably more costly to just build to that size and standard anyway, especially since it's more compatible with existing railways and allows for futureproofing.

However, I've never seen a live rail blow away in a gale. Nor is it likely to be dislodged by faulty current-collection gear (a damaged pantograph can bring down the catenary, a 3rd rail train is more likely to just lose a shoe - although that's not why the Southern Region was considered the Cinderella of British Rail!

Third rail can have issues with layers of ice forming an insulation though, and in the UK this is not something particularly unusual during the winter months. In any case of the pantograph damaging the overhead lines there is something clearly going wrong, be it poor maintenance of the rolling stock and infrastructure or because of an object that shouldn't be there. In any normal situation though the pantograph should not be damaging the wires.

 

[DJ_K666]

Comparing https://railmap.azurewebsites.net/Public/ElectrificationMap and https://www.projectmapping.co.uk/Reviews/Resources/NR Regions & Routes map v11.pdf I count siz

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

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

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