Which is better and why - over head or third rail electrification?

[Mikey C]

5 years ago (or whatever) there seemed to be a genuine possibility that the 3rd rail network would be converted to OHLE.

That possibility seems really unlikely now, thus surely if longer infill happens (Uckfield, Marshlink) it should be done with 3rd rail? It makes no sense to say that it's dangerous, when the rest of Kent and Sussex are already covered in 3rd rails with no realistic plan for converting these lines.

 

[geoffk]

5 years ago (or whatever) there seemed to be a genuine possibility that the 3rd rail network would be converted to OHLE.

That possibility seems really unlikely now, thus surely if longer infill happens (Uckfield, Marshlink) it should be done with 3rd rail? It makes no sense to say that it's dangerous, when the rest of Kent and Sussex are already covered in 3rd rails with no realistic plan for converting these lines.

While I agree with others that OHLE is the way to go, it seems to make little sense not to use 3rd rail for small infill schemes. Are the arguments against related mainly to safety or higher operating costs? As well as Uckfield and Marshlink, there's the remainder of Reading - Reigate and several possible Merseyside extensions (Kirkby to Skelmersdale/Wigan, Ormskirk to Burscough Bridge and even Bidston - Wrexham.)

 

[Camden]

As a staff member, I’d also much rather third rail.

Reports like the below explain why: when 25kV OHLE comes down (and it does) it’s far more dangerous than the third rail you already know is there, and can switch off yourself with a short circuit bar, if necessary.

(“Serious injuries” presumably means wheelchair/vegetable status for the rest of his life. I’m not aware of any such incidents from
Third rail equipment other than for trespassers or people “falling out” of trains in depots (people who shouldn’t have been there in the first place)).

https://www.gov.uk/government/news/report-072015-accident-involving-a-train-driver-at-sutton-weaver

Yes, its very clear that the third rail "danger" argument is nonsense. City third rail networks operate perfectly safety, including with foot crossings, while regularly stories appear in the press about people being electrocuted by overhead. If you want a railway which is electrocution risk free, then the answer is diesel!!

Hopefully now that overhead costs have gone through the roof we will start to see a more sensible approach to allowing more third rail where necessary, efficient and appropriate.

 

[NSEFAN]

While I agree with others that OHLE is the way to go, it seems to make little sense not to use 3rd rail for small infill schemes. Are the arguments against related mainly to safety or higher operating costs? As well as Uckfield and Marshlink, there's the remainder of Reading - Reigate and several possible Merseyside extensions (Kirkby to Skelmersdale/Wigan, Ormskirk to Burscough Bridge and even Bidston - Wrexham.)

Safety is only one aspect. Given the higher currents, third rail systems need more substations than 25kV overhead. Getting enough feeder points along more rural routes like the North Downs, Hurst Green-Uckfield and Hastings-Ashford may be tricky, such that it might be easier to instead install overhead 25kV on these sections and use dual-voltage stock instead.

 

[JamesT]

ORR claims third rail is more dangerous when "normalised" to take account of the different amounts of the two types of electrification, but when we last discussed this a few months ago nobody could point to any actual statistics to justify this. However the overhead line is probably less dangerous than it looks - although "safe distance" for working near live line is several metres, the actual distance the voltage will jump is much less - as shown by how close the wires can be underneath a bridge. Again there are no statistics but I believe nobody has ever been electrocuted by overhead line by using a platform in the normal way - it is usually kids who climb up on a train.

http://orr.gov.uk/__data/assets/pdf_file/0017/17621/dc-electrification-policy-statement.pdf has the line:

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

Unfortunately my google-fu is failing me in locating the referenced document.

 

[JamesT]

Yes, its very clear that the third rail "danger" argument is nonsense. City third rail networks operate perfectly safety, including with foot crossings, while regularly stories appear in the press about people being electrocuted by overhead. If you want a railway which is electrocution risk free, then the answer is diesel!!

Hopefully now that overhead costs have gone through the roof we will start to see a more sensible approach to allowing more third rail where necessary, efficient and appropriate.

https://www.bbc.co.uk/news/uk-england-kent-41722254 - Teenager electrocuted on third rail last year.
https://www.bbc.co.uk/news/uk-england-sussex-42031519 - Cleaner electrocuted on third rail at depot last year.
That's from about 30 seconds of searching. Third rail danger is nonsense?

 

[Esker-pades]

https://www.bbc.co.uk/news/uk-england-kent-41722254 - Teenager electrocuted on third rail last year.
https://www.bbc.co.uk/news/uk-england-sussex-42031519 - Cleaner electrocuted on third rail at depot last year.
That's from about 30 seconds of searching. Third rail danger is nonsense?

Reading the articles, the electrocutions were caused by tresspass and employers cutting corners by ignoring the safety systems.

The way I read the comments I think you're referring to, it was a debate between whether or not 3rd rail was safer than OHLE.

 

[edwin_m]

http://orr.gov.uk/__data/assets/pdf_file/0017/17621/dc-electrification-policy-statement.pdf has the line:
Unfortunately my google-fu is failing me in locating the referenced document.

The safety risk model isn't a specific document. The levels of risk for particular events (ie what is quoted by HSE) are somewhere on the RSSB website - I accessed some a few years back but I think I had to get a login by quoting an industry email address. However the underlying analysis and evidence isn't publically accessible even with a login as far as I'm aware. Hence it's not possible for anyone without special access to independently verify or challenge the HSE policy.

 

[JamesT]

Reading the articles, the electrocutions were caused by tresspass and employers cutting corners by ignoring the safety systems.

The way I read the comments I think you're referring to, it was a debate between whether or not 3rd rail was safer than OHLE.

No, the electrocutions were caused by coming into contact with the third rail.
A large part of the debate as to the safety of third rail versus OHLE is the ease of someone getting into a situation where they can come into contact with live rail/cable.

 

[GB]

As a staff member, I’d also much rather third rail.

Reports like the below explain why: when 25kV OHLE comes down (and it does) it’s far more dangerous than the third rail you already know is there, and can switch off yourself with a short circuit bar, if necessary.

(“Serious injuries” presumably means wheelchair/vegetable status for the rest of his life. I’m not aware of any such incidents from
Third rail equipment other than for trespassers or people “falling out” of trains in depots (people who shouldn’t have been there in the first place)).

I can't find any reference to it online so not sure if I am misremembering or the story I was told was bull, but a fair few years ago a Freightliner driver was killed by 3rd rail when he went in between to uncouple his loco.

 

[Mikey C]

Safety is only one aspect. Given the higher currents, third rail systems need more substations than 25kV overhead. Getting enough feeder points along more rural routes like the North Downs, Hurst Green-Uckfield and Hastings-Ashford may be tricky, such that it might be easier to instead install overhead 25kV on these sections and use dual-voltage stock instead.

On the other hand maybe the new substations would also be of benefit to the existing 3rd rail network, much of which needs more juice?

 

[Jimini]

I can't find any reference to it online so not sure if I am misremembering or the story I was told was bull, but a fair few years ago a Freightliner driver was killed by 3rd rail when he went in between to uncouple his loco.

This one?

https://www.gov.uk/raib-reports/fatal-accident-involving-a-train-driver-deal

"On Saturday 29 July 2006 a freight train stopped at a signal near Deal station in Kent. Whilst checking the brakes of one of the wagons, the driver elected to cross between that wagon and the wagon behind to reach the other side of the train. In doing so, he came into simultaneous contact with the live conductor rail and the buffer of the wagon, and was fatally injured.

The immediate cause of the accident was the driver’s leg coming into contact with a live conductor rail at the same time as his arm was in contact with the buffer, thus causing an electric shock. Causal factors were the driver’s decision to pass between two wagons and a subsequent misjudgement, loss of balance or slip by the driver. There were two further possible causal factors, one contributory factor and four factors that may have influenced the behaviour of the driver."

 

[Bikeman78]

Having had to deal with a couple of electrocutions on third rail equipped lines there is only one answer.

Live conductors at a lethal voltage close to where staff regularly have to walk and work, let alone trespassers, passengers falling from platforms, evacuating from trains, etc., have no place on 'the safest railway in Europe'. (Certainly not an expanded future role.)
Words

I don't think the existing third rail is going anywhere for decades. There was talk, maybe 10 years ago, of wholesale conversion to OHL, but the late and over budget projects have killed that idea. Even Basingstoke to Southampton seems to have been forgotten unless I'm mistaken?

 

[Bikeman78]

Trains running on 3rd rail electrification are capable of operating in floodwater. Modern Nanny State rules prevent it now.

https://upload.wikimedia.org/wikipedia/commons/a/ac/Flooding_on_the_Southern_Railway_(CJ_Allen,_Steel_Highway,_1928).jpg[/QUO

I wouldn't want any train to go over track where the driver would expect to see, umm, the rails, no matter how it's powered.

Nothing to do with caring whether the train could or couldn't do it, or elfin safety gone mad.

I can't find it, but I'm sure I read something about this a few years ago which claimed going through water above a certain level (the under of the railhead, maybe?) was a no-no. Sounds sensible to me.

I'd have thought that running at reduced speed would be a reasonable compromise. After all, you can't see very far ahead at night time.

A few months ago the railway was closed at Gillingham (in Kent) because water off the road had flooded the level crossing. No doubt road traffic was still plodding across quite happily.

 

[Bikeman78]

thats a wooden bodied vehicle so much safer for the occupants in a flood than a conductive metal body would be

That doesn't make sense. Even if the bodywork became live, people inside would be fine.

 

[NSEFAN]

On the other hand maybe the new substations would also be of benefit to the existing 3rd rail network, much of which needs more juice?

Do you mean using the electrification as a chance to upgrade the existing substations further along the line, or putting them in parallel? I'm not fully aware of how adjacent sub-stations can be re-configured, but I can't imagine that there would be that much extra benefit to the existing areas of 3rd rail nearby. If available connections to the national grid is already the limiting factor in power delivery then you'll still have localised bottlenecks if you're using the new substations to help prop up the power levels in adjacent areas.

Speaking of limited power, I understand that this was one of the factors preventing more trains running on the SWML. I'm not sure if this is a case of simply uprating the existing sub-stations, or having to deploy additonal ones.

 

[GB]

This one?

https://www.gov.uk/raib-reports/fatal-accident-involving-a-train-driver-deal

"On Saturday 29 July 2006 a freight train stopped at a signal near Deal station in Kent. Whilst checking the brakes of one of the wagons, the driver elected to cross between that wagon and the wagon behind to reach the other side of the train. In doing so, he came into simultaneous contact with the live conductor rail and the buffer of the wagon, and was fatally injured.

The immediate cause of the accident was the driver’s leg coming into contact with a live conductor rail at the same time as his arm was in contact with the buffer, thus causing an electric shock. Causal factors were the driver’s decision to pass between two wagons and a subsequent misjudgement, loss of balance or slip by the driver. There were two further possible causal factors, one contributory factor and four factors that may have influenced the behaviour of the driver."

Yes think that must be the one...thanks

 

[Camden]

High speed, longer distance trains are disadvantaged by third rail. The system is more efficient though for frequent stop metros.

 

[randyrippley]

That doesn't make sense. Even if the bodywork became live, people inside would be fine.

Not when they try to leave

 

[Lucan]

I find that being on a station platform where there is overhead electrification feels much less dangerous than walking alongside the road into town with tons of metal hurtling past at 30mph.

I even find that walking along the 4 foot with 3rd and 4th electrified rails and service trains running (not in the tunnel!) feels much less dangerous than walking alongside the road. In fact I'm pretty sure that statistics will show that it is less dangerous (for a worker, not for a trespasser).

 

[Carlisle]

Safety is only one aspect. Given the higher currents, third rail systems need more substations than 25kV overhead. .

Didn’t some of the last 3rd rail schemes use rail mostly composed of aluminium so that less substations would be needed?

 

[Tio Terry]

While I agree with others that OHLE is the way to go, it seems to make little sense not to use 3rd rail for small infill schemes. Are the arguments against related mainly to safety or higher operating costs? As well as Uckfield and Marshlink, there's the remainder of Reading - Reigate and several possible Merseyside extensions (Kirkby to Skelmersdale/Wigan, Ormskirk to Burscough Bridge and even Bidston - Wrexham.)

There's no chance of any further 3rd rail railway of any note. The same people who wrote the addendum to the Energy Technical Standard for Interoperability that covers the UK 3rd rail network are still with the DfT. Any further requirements for "infill" are likely to be met with either dual or multi fuel/energy traction units. Much cheaper than all that 3rd rail, power supplies and the like - and a lot safer too!

 

[DenmarkRail]

When you say that third rail is unsafe, I think the general opinion is wrong... Third rail isn't safe, the people who are cutting corners are being plain silly when they are operating near the electricity...

Will future tube lines have 4th rail, because its unsafe? Probably not... And... Elizabeth Line isn't a tube line.

 

[cjmillsnun]

Presmably back in the 1920s, the cost of an EMU was proportionally similar to what it is today? As has been shown, it is perfectly feasible to run 3rd rail EMUs in floodwater. Why is it that the Southern Railway was willing to run the risk, yet todays TOCs aren't?

A very simple DC unit with camshaft control compared to complex units today. I somehow doubt that modern units would go so well in floodwater.

 

[Re 4/4]

The high voltage in overhead lines can "jump" a significant distance so even being within a few metres of the live parts is dangerous.

I don't disagree that coming into contact with 25KV is dangerous, and that may well be the safety distance for working with metal tools/ladders, but if the current really could jump several metres then surely running a diesel-operated metal-bodied train on a line with overhead wires on a wet day wouldn't be a safe thing to do?

 

[AM9]

When you say that third rail is unsafe, I think the general opinion is wrong... Third rail isn't safe, the people who are cutting corners are being plain silly when they are operating near the electricity...

Will future tube lines have 4th rail, because its unsafe? Probably not... And... Elizabeth Line isn't a tube line.

It is unlikely that a future tube line (as in a 12ft diameter tunnel type) again anyway. Metro lines under cities are normally built like Crossrail, i.e. mainline structure gauge, (6.2m internal finished diameter) because:

to accommodate larger trains with greater capacity and/or increased passenger comfort
to reduce ventilation and cooling problems
to reduce pressure wave issues
to allow emegency access/escape
to give adequate clearance for the OLE​

The modern method of constructing high capacity subterranean stations usually involves a large excavation to create a 'station box'. There is little difference in the size of box required for tube-sized trains compared with mainline sized vehicles and modern tunneling methods as used in clay/sandy substrates are less sensitive to the removed volume of overburden than in the '60s when the Victoria Line was built. Thus lines built with full-sized tunnels are more cost effective in terms of capacity and some running costs.
Third rail is unlikely to be the choice of new underground railways in the UK even if safety disadvantages are completely ignored.

 

[Busaholic]

A very simple DC unit with camshaft control compared to complex units today. I somehow doubt that modern units would go so well in floodwater.

Cross Country's Voyagers routinely get cut back from Dawlish when a Spring Tide occurs, let alone weather events, because they can't cope with a bit of water underneath them, so it's not just electrics!

 

[AM9]

I don't disagree that coming into contact with 25KV is dangerous, and that may well be the safety distance for working with metal tools/ladders, but if the current really could jump several metres then surely running a diesel-operated metal-bodied train on a line with overhead wires on a wet day wouldn't be a safe thing to do?

You are confusing the maximum length of an arc with the safe clearance for working. In air, electricity will flashover about 1mm per thousand volts. This equates to about 40mm for 25kV OLE because:
highest voltage that the OLE can encounter under exceptional conditions is 29kV
and the peak voltage of an ac voltage (assuming a sinewave waveform) is about 1.4 times the rms value (29kV)
thus the maximum distance is in the order of 40mm. However, the cable is suspended allowing for movement in winds and oscillations induced by the moving contact of an upward pressing pantograph. I believe the current standard is for the risk assessed absolute minmum clearance to be 200mm, the lowest nominal to be 270mm and the recommended minimum to be 370mm. The minimum clearance to an exposed live part for humans whether rail workers or the public is I believe 3.75 metres which allows for the tallest person on a platform to the OLE even with an umbrella on a wet day. Staff working near live lines are trained on the use of tools under such circumstances.
Note: some of the dimensions given as regulations may not be the latest figures but are indicative of the difference between likely arcing distances and working clearance.

 

[cjmillsnun]

Cross Country's Voyagers routinely get cut back from Dawlish when a Spring Tide occurs, let alone weather events, because they can't cope with a bit of water underneath them, so it's not just electrics!

I thought that was because of salt on the resistor panels on the roof causing the engine to cut out.

 

[Robsignals]

Do you mean using the electrification as a chance to upgrade the existing substations further along the line, or putting them in parallel? I'm not fully aware of how adjacent sub-stations can be re-configured, but I can't imagine that there would be that much extra benefit to the existing areas of 3rd rail nearby. If available connections to the national grid is already the limiting factor in power delivery then you'll still have localised bottlenecks if you're using the new substations to help prop up the power levels in adjacent areas.

Speaking of limited power, I understand that this was one of the factors preventing more trains running on the SWML. I'm not sure if this is a case of simply uprating the existing sub-stations, or having to deploy additonal ones.

My understanding is that substations are supplied by lineside HV cables (33kV?) in separate troughing fed from a limited number of grid stations so no local issues and additional ones can go anywhere, halfway between is best for lower losses. There are/were restrictions on some lines due to heating of the rectifiers, more/longer peak trains and a basic off-peak service.

My impression is there's much more disruption reported due to OHL problems than conductor rail, unless they're only given as 'track defect', but not much can go wrong and few problems would require trains being stopped.