Third rail - becoming a better option for electrification?

[Lurcheroo]

Another draw back that no one seems to have mentioned is the risk that 3rd rail poses to anyone who shouldn’t be on the line. Wether that be trespassers or passengers having to evacuate off a train in an emergency.
I suspect this is a fair consideration for the ORR.

 

[The Snap]

A key disadvantage of third rail is the effect on overnight possessions, work cannot start on the running rails until the juice rail is both switched off and made safe by earthing straps, around a third of the overnight possession period is lost to strapping at the start and end of theline occupation.
Work on the running rails does not require the 25kV OHL to be isolated. The costs of lost of production time mounts over many years, third rail is not a cheap solution in the long-term

Your point about OLE is not quite right. The majority of work on lines with OLE require the OLE to be isolated, unless the work can remain 2.75m/9ft away from the OLE. Other than surveining and work done using hand tools at track level, most other work will come within that limit. Remember, on track plant and machines are all within than limit as soon as they go onto the track, and only a few specific Network Rail MDU's have authrority to operate OTP/OTM under live OLE. Contractors cannot work under live OLE, and it's contractors who do most of the work. Even a simple signal head inspection using hand tools could easily be within 2.75m of the OLE, never mind anything more complex.

These days, whether its OLE or third rail, time lost in possessions whilst isolation and test-before-touch procedures are carried out is the norm.

From a railway staff perspective, I much prefer working under OLE than third rail. Lets say I was working lineside whilst trains are running - I'd much rather be under the OLE which I can't reach and is well above my head, than walk next to DC rail where one wrong step could see me fried!

How much does fixing up downed over head lines cost?

The cost of fixing the OLE itself is relatviely small. Its the delay minutes that cost the money.

 

[swt_passenger]

Another draw back that no one seems to have mentioned is the risk that 3rd rail poses to anyone who shouldn’t be on the line. Wether that be trespassers or passengers having to evacuate off a train in an emergency.
I suspect this is a fair consideration for the ORR.

Those risks are surely already implied every time the so called ‘ORR ban’ is mentioned, eg in post #3. There’s not really a need to keep repeating that electric shock to staff, passenger or trespasser is the main reason, it’s been discussed in these forums so many times now…

 

[Jozhua]

Pretty sure ORR doesn't ban things like short extensions of 3rd rail, rather you wouldn't electrify something like the Chiltern mainline with it. Something like Guildford - Redhill would probably make a lot of sense tho.

A lot of wire down incidents are due to legacy designs, such as those often seen on ECML and WCML. Head spans across four tracks using wires to hold up wires are the biggest culprit typically:
https://www.railengineer.co.uk/back-to-portals/

A lot of that kit needs renewing now with newer, more resilient designs. Pretty sure head spans are a big problem on MML south of Bedford, which is why OLE speeds are restricted to 110mph.

 

[Diedinium]

We just need to get on with electrifying via OLE - if we had a rolling programme aiming to do 200-400 miles a year you'd eventually get to the point where it would make sense to start doing OLE for 3rd rail areas, probably as a "alongside" operation to start with where 3rd rail is left in place until rolling stock that depends on it is replaced.

Obviously though, we are just politically incapable in the UK of doing anything apart from building roads apparently, so I doubt this will ever happen.

 

[Pigeon]

But the existing DC distribution system design assumes that it is all connected in parallel, and DC regeneration also requires the system to be connected in parallel to improve receptivity. If the third rail itself wasn't to be live, you'd need a separate high current path running alongside it to provide the same traction current if it couldn't be passed along the third rail...

I'd assumed that to be part of the idea anyway. Third rails at present are laid in relatively short stretches, with a gap of a few metres to the next stretch spanned by a pair of heavy jumper cables. So to my mind the immediately obvious way to do it is (1) instead of chaining those short sections to each other, supply them from a heavy bus bar alongside the track; and (2) run each set of cables from a rail section to a bus bar through a switch. So everything still looks the same in terms of the "all in parallel" assumptions,

Since the bus bar does not have the dimensional and mechanical constraints of a third rail, it can be eg. a big chunky bar of aluminium to improve conductivity, which would make the system less lossy. Also since no more than a couple of hundred metres at a time of the third rail itself would be contributing to losses, it might be possible to use a smaller section that would be cheaper than the present standard.

This has been proposed several times before on other threads and the answer is that the switchgear would get hammered switching on and off so frequently, as well as the further potential for delay if a fault develops. Many parts of the southern region have trains 2 or 3 minutes apart for substantial portions of each hour. Trains are up to 240m long with very close signal spacing, the length of sections and continuous switching in and out would hammer the system.

Not if you use solid state switchgear, and these days I'd not imagine using anything else. Reliability is now pretty much bomb-proof. The control system need be no more than a unit associated with each switch that detects if the load side is connected to a train, which is not difficult. As an emergency fault bodge until someone can come and plug a new switch module in, you could simply make a temporary bridge to the adjacent section of third rail with jump leads.

AC conductors primarily conduct along the edges so no need for the mass of 3rd rail.

Actually that is a nuisance, not an advantage. To handle the same current you still need the same effective cross sectional area of conductor. But when skin effect is significant, the central part of the cross sectional area is no longer "effective", so it's wasted mass. So to get an efficient conductor you have to make it in the form of a hollow tube, which is more awkward than a solid bar.

The size of conductor wire used for overhead AC electrification is roughly one "skin depth" in radius, so it's not yet fat enough to have to worrry about that.

 

[NSEWonderer]

DC requires much more substations per 2 to 3 miles than OHLE which is costly. Our national grid uses overhead wires because power delivery needs to happen over a very long distance and with wires sending current at a very high voltage you increase the efficiency of that energy transfer as the current is pushed to where it needs to be faster.

Third rail is just inefficient when it comes to power delivery over a distance. You always want more Volts pushing current than more current as you don't lose as much energy wasted in heat etc.

 

[yorksrob]

Pretty sure ORR doesn't ban things like short extensions of 3rd rail, rather you wouldn't electrify something like the Chiltern mainline with it. Something like Guildford - Redhill would probably make a lot of sense tho.

That was always the traditional pragmatic approach, which was why extensions and infill to the third rail network took place until the 1990's.

However, this is clearly no longer the case, hence why Merseyrail had to waste money on a battery microfleet to extend its electric service by one station.

 

[HSTEd]

DC requires much more substations per 2 to 3 miles than OHLE which is costly. Our national grid uses overhead wires because power delivery needs to happen over a very long distance and with wires sending current at a very high voltage you increase the efficiency of that energy transfer as the current is pushed to where it needs to be faster.

Third rail is just inefficient when it comes to power delivery over a distance. You always want more Volts pushing current than more current as you don't lose as much energy wasted in heat etc.

The substations cost a small fraction of the cost of 25kV capable substations though. At the traffic levels prevailing on the remaining non-electrified portion of the railway network, it is unlikely that substation costs for DC would be significantly greater than they would be for AC.

As for efficiency, this is currently true, yes, but electricity costs are only a small portion of total costs, and likely technological improvements abroad will seriously reduce losses. See the ongoing superconducting installation at Paris Gare Montparnasse.

The reality is, given how badly the 25kV programme has failed, the choice is between third rail electrification or no electrification.

If adopting London Underground operational practice is what it takes to get third rail installations past the ORR (who's de-facto prohibition excludes London Underground), then it needs to happen sooner rather than later.

 

[NSEWonderer]

Improving how OHLE is maintained and installed would be much better than third rail modernisation. Other countries make it work, Japan has several earthquakes and yet in many cases their OHLE is still standing.

Installing new 3rd rail also requires track rework to be done in areas to make enough spacing. It also increases the number of contact points between the train and power source compared to OHLE where it may be at any time 4 Pans on the wire you could have 8 shoes in the case of an 8 car Class 465. More if the train has powered bogies on other cars like the Class 701s.

A Class 345 at max draw requires something like 4.4 Megawatts

Current is what you want to keep down the most in any electrical transfer as it reduces efficency the higher it goes.We know that the higher the voltage the less the current and also the lower technically the cost for the same amount of work done(P) The equation below will be used to help illustrate what system provides a more realistic output for a Class 345.

I = P/E

I = Current(A)
E = Voltage
To simplfy.

OHLE
4400000W / 25000V = 176A

DC 3rd Rail
4400000W / 750V = 5867A

The amount of current needed by the DC system to supply the same amount of power / work as the OHLE is nearly 34x more and such current would run much hotter and thus inefficiently than the OHLE aswell as cost more. Realistically isn't any DC rail systems I believe that would be delivering anywhere near 5867A where as there would be some delivering 176A like the OHLE but without the higher voltage to maintain the same Power / Work requirement.

Below is a freedom of information source used for the 345 max power equation value above.
FOI Request

 

[trebor79]

ORR won't even allow that, which is why the electrification programme has collapsed.

There will be no more third rail electrification in the UK, but there will be precious little new electrification full stop.

Not without reform of ORR at any rate.

OR a technical solution such as the rail only being energised when the train is actually there, as is used in some street pick-up systems abroad I believe. This would effectively remove the electrocution risk.

 

[Deepgreen]

Modern?

Stud contact electrification was in use on a few tramway systems over a century ago. Magnet plus gravity was all it needed. More recently, Alstom's APS is fashionable in France and there are other intermittent supply systems.

In the end, losses favour AC at higer voltages over DC for anything beyond light rail or metro. AC conductors primarily conduct along the edges so no need for the mass of 3rd rail. Put it overhead and most of your insulation gap problems go away.

Yes, but it's the 'overhead' bit which seems to put it at such high risk of failure, and which puts its installation costs so high.

 

[Flange Squeal]

ORR won't even allow that, which is why the electrification programme has collapsed.

There will be no more third rail electrification in the UK, but there will be precious little new electrification full stop.

This thread has got me wondering what the most recent/last third rail electrification scheme was (excluding small scale projects like the new Feltham depot, sidings or Brading loop etc). Would it be the Redhill to Tonbridge electrification of the ‘90s?

 

[HSTEd]

This thread has got me wondering what the most recent/last third rail electrification scheme was (excluding small scale projects like the new Feltham depot, sidings or Brading loop etc). Would it be the Redhill to Tonbridge electrification of the ‘90s?

It will either be that or the last of the Merseyrail projects of the 1990s, Chester was 1993 and Ellesmere Port was 1994.

This is if you assume the ~mile of new rail installed as part of the East London Line project is not significant.

 

[Trainbike46]

With the increases effeciency of electric motors, their lighter weight, increased power to weight ratio, potentially backed up by batteries, is third rail becoming a better option for electrifcation than overhead line electrification (OLE) installation. Able to be installed at a lower cost,easier to maintain, less vulnerable to wind related damage, providing both a core supply and a battery charge option, could a third rail be a better, easier, more reslient alternative to OLE. Maybe not for high speed, but for the other parts of the network?

One of the ways in which third rail (and lower voltage systems in general) can be more costly is that it needs a lot more feeder stations; This is not much of a problem in relatively densely populated areas where there will be an electricity supply nearby, such as the southern region. For areas where the tracks run through areas where regular electricity supply isn't available it would raise costs.

It's also important to note speed limitations on 3rd rail, which make it unsuitable for higher speed lines (anything over 100 mph).

Regarding reliability, two relevant things:
- For OHLE the reliability varies significantly between installations due to differences and potentially differences in maintenance
- I vaguely recall reading somewhere that overall OHLE was more reliable than 3rd rail (could be wrong though!)

Overall I think it's pretty obvious that OHLE is superior to 3rd rail (safer, faster accelleration, higher max speed possible, etc.)

The substations cost a small fraction of the cost of 25kV capable substations though. At the traffic levels prevailing on the remaining non-electrified portion of the railway network, it is unlikely that substation costs for DC would be significantly greater than they would be for AC.

That depends on electricity grid connections availability. Every extra connection adds costs in even the best situation, but where grid availability is limited that is a particular issue (that raises costs)

As for efficiency, this is currently true, yes, but electricity costs are only a small portion of total costs, and likely technological improvements abroad will seriously reduce losses. See the ongoing superconducting installation at Paris Gare Montparnasse.

The reality is, given how badly the 25kV programme has failed, the choice is between third rail electrification or no electrification.

If adopting London Underground operational practice is what it takes to get third rail installations past the ORR (who's de-facto prohibition excludes London Underground), then it needs to happen sooner rather than later.

I don't understand why you have faith in better third rail being possible but not in better OHLE being possible?

 

[urbophile]

ORR won't even allow that [third rail infill], which is why the electrification programme has collapsed.

There will be no more third rail electrification in the UK, but there will be precious little new electrification full stop.

Hence chaos and seemingly regular delays on the battery-operated Kirkby to Headbolt Lane section of Merseyrail.

Your second sentence is both pessimistic and unrealistic. No-one expects anything now from this failing government, but the fight against climate change goes on and we can't carry on indefinitely with main lines (even between major cities – Sheffield, Hull eg) served by polluting diesel trains. Starmer and his gang are far from being knights in shining armour, but they at least appear to have some awareness of the real world.

 

[12LDA28C]

OR a technical solution such as the rail only being energised when the train is actually there, as is used in some street pick-up systems abroad I believe. This would effectively remove the electrocution risk.

It's already been mentioned how this would not be suitable for a high speed main line railway.

 

[Trainbike46]

Your second sentence is both pessimistic and unrealistic. No-one expects anything now from this failing government, but the fight against climate change goes on and we can't carry on indefinitely with main lines (even between major cities – Sheffield, Hull eg) served by polluting diesel trains. Starmer and his gang are far from being knights in shining armour, but they at least appear to have some awareness of the real world.

I agree; especially given that there are OHLE electrification projects currently under construction (e.g. East Kilbride, MML, some northern lines), some more at various stages semi-committed (e.g. Fife, Aberdeen), and under discussion (e.g. Oxford, Bristol both ways, some more northern lines)

 

[HSTEd]

I don't understand why you have faith in better third rail being possible but not in better OHLE being possible?

Because we don't have evidence of many years of total failure to deliver third rail electrification despite promises to the contrary.

The 25kV programme has failed catastrophically, the third rail programme has not yet done so (as it does not yet exist), so it has a greater chance of not failing.
By about 2018 (Kent RUS from before coronavirus), even Network Rail admitted that third rail was cheaper than 25kV, and 25kV has kept climbing in price since then.

Hence chaos and seemingly regular delays on the battery-operated Kirkby to Headbolt Lane section of Merseyrail.

Your second sentence is both pessimistic and unrealistic. No-one expects anything now from this failing government, but the fight against climate change goes on and we can't carry on indefinitely with main lines (even between major cities – Sheffield, Hull eg) served by polluting diesel trains. Starmer and his gang are far from being knights in shining armour, but they at least appear to have some awareness of the real world.

Given current capabilities and budgets, it will be impossible for any government to deliver sufficient 25kV electrification to matter before road transport decarbonisation renders the diesel railway an irrelevance.

Starmer isn't going to pay £4m/stkm+ to electrify to Hull or wherever when he wants that money for the triple lock or Nurse pay rises. Meanwhile, the window of opportunity for the railway to stake its claim to a major role in the post carbon world slips away with every electric car to drive out of a dealership

 

[Trainbike46]

Because we don't have evidence of many years of total failure to deliver third rail electrification despite promises to the contrary.

The 25kV programme has failed catastrophically, the third rail programme has not yet done so (as it does not yet exist), so it has a greater chance of not failing.
By about 2018, even Network Rail admitted that third rail was cheaper than 25kV, and 25kV has kept climbing in price since then.

I suspect the current industry structure is at least partly to blame for high costs, and those issues will exist for 3rd rail as well as OHLE.

The safety and performance (top speed and accelleration) disadvantages of 3rd rail to me at least would make it an unacceptable solution for most lines.

That said, I would be in favour of infill 3rd rail electrification, which could then also be a ground for proving these 3rd rail claims in the real world. I am not personally convinced they will succeed, but am always up for being surprised.

Given current capabilities and budgets, it will be impossible for any government to deliver sufficient 25kV electrification to matter before road transport decarbonisation renders the diesel railway an irrelevance.

Starmer isn't going to pay £4m/stkm+ to electrify to Hull or wherever when he wants that money for the triple lock or Nurse pay rises. Meanwhile, the window of opportunity for the railway to stake its claim to a major role in the post carbon world slips away with every electric car to drive out of a dealership

The main way in which the railway can (and should) contribute is by taking a larger passenger share, primarily from the airlines and cars, as well as large, long-distance freight flows.

More electrification is also essential, but mostly because it delivers a better, more reliable railway. Reduced emissions are a bonus.

Absolutely agree that the government and the industry need to get their **** together on project costs, including electrification.

 

[Geogregor]

3rd rail electrification won't happen. It really is that simple.

 

[Deepgreen]

3rd rail electrification won't happen. It really is that simple.

It is, and I do wonder what the solution is - OHLE is far too expensive and fragile (even the over-engineered stuff, it seems) to be a viable and reliable transmission system.

 

[Trainbike46]

It is, and I do wonder what the solution is - OHLE is far too expensive and fragile (even the over-engineered stuff, it seems) to be a viable and reliable transmission system.

The recent GWR/EL failures weren't on the "over-engineered" section

 

[Deepgreen]

I suspect the current industry structure is at least partly to blame for high costs, and those issues will exist for 3rd rail as well as OHLE.

The safety and performance (top speed and accelleration) disadvantages of 3rd rail to me at least would make it an unacceptable solution for most lines.

That said, I would be in favour of infill 3rd rail electrification, which could then also be a ground for proving these 3rd rail claims in the real world. I am not personally convinced they will succeed, but am always up for being surprised.

The main way in which the railway can (and should) contribute is by taking a larger passenger share, primarily from the airlines and cars, as well as large, long-distance freight flows.

More electrification is also essential, but mostly because it delivers a better, more reliable railway. Reduced emissions are a bonus.

Absolutely agree that the government and the industry need to get their **** together on project costs, including electrification.

In theory - but recently it has seemingly delivered a far less reliable railway!

 

[Trainbike46]

In theory - but recently it has seemingly delivered a far less reliable railway!

Overall, electric railways are more reliable. Network rail reported that for long-distance services electric trains are 40% more reliable than diesel. Suburban electric services were reported as 300% more reliable. (source: https://www.whatdotheyknow.com/requ... Route Modernisation.pdf?cookie_passthrough=1 )

Mostly because electric trains have way fewer faults than diesel trains (apparently EMUs have an average MTIN of 36,805 vs 15,971 for diesel. Source: https://www.railengineer.co.uk/why-electrify/ )

So, while wires down and 3rd rail issue incidents are frustrating, the data shows that electric railways are more reliable.

 

[NSEWonderer]

In theory - but recently it has seemingly delivered a far less reliable railway!

The GEML barely has any issues for example and thats nonsurprised due to it being well maintained and not long ago recebtly upgrades. The GWML is plagued with issues on the less maintained and older sections of the line. The recently upgraded areas of Reading barely have any issues or play in the recent GWML plague. The ECML again that's with the older headspans.

As said other countries with OHLE clearly can't have missed something especially those like Japan and France who replacing the wires with 3rd rail would increase journeys by tenfolds let alone the sheer cost accumulated due to maintaining 3rd rail current on the many long stretches would destroy any viability of those railways.

3rd rail just isn't efficient in the types of projects these days.

 

[nwales58]

In theory - but recently it has seemingly delivered a far less reliable railway!

Is DfT orthodoxy. Mr Baker re-incarnated?

Dearer infrastructure, cheaper trains. More effort keeping the knitting reliable. Less effort to make the trains likewise.

Engineering is about making things work.

Oxford-educated minds in DfT and HMT only see costs and paper benefits, uncertainty and reliability are a bit alien to their thinking.

 

[Bikeman78]

Another draw back that no one seems to have mentioned is the risk that 3rd rail poses to anyone who shouldn’t be on the line. Wether that be trespassers or passengers having to evacuate off a train in an emergency.
I suspect this is a fair consideration for the ORR.

A crash or derailment will almost certainly trip out the power supply anyway. How many trespassers get electrocuted each year? Can't be many or the media would be jumping up and down about it. My son is seven. He understands that messing about on the track is a bad idea. And he's someone that absolutely loves to push boundaries.

 

[Nicholas Lewis]

This thread has got me wondering what the most recent/last third rail electrification scheme was (excluding small scale projects like the new Feltham depot, sidings or Brading loop etc). Would it be the Redhill to Tonbridge electrification of the ‘90s?

In terms of line of route it was Tonbridge to Redhill

 

[urbophile]

Meanwhile, the window of opportunity for the railway to stake its claim to a major role in the post carbon world slips away with every electric car to drive out of a dealership

Well no, because the problem of mass car use is not only about pollution and the carbon footprint, but congestion. Quite simply, our roads, particularly in cities, were not designed for the volume of traffic we have, let alone any increase.