Pros and cons of different electrification schemes (e.g. 3rd rail / OHLE / battery power)

[Roast Veg]

Moderator note: Split from https://www.railforums.co.uk/thread...extension-of-3rd-rail-electrification.205175/

A really good way of making [3rd rail] lot safer would be to convert it to OHLE...

 

[edwin_m]

Where to transition to 25kV would be a key part of any strategy. I agree it makes little sense to consider 25kV islands in the likes of Uckfield which would be worked as part of the general Southern fleet so a microfleet of 25kV-fitted units would be difficult to manage. Also a 25kV feeder is a major item, normally feeding several tens of kilometres and needing a high voltage Grid supply. This might be a bit easier with the solid-state inverter feeder stations now being pioneered.

Salisbury might be a different matter. It's a much larger extension, probably big enough to warrant duplicated 25kV feeders, and would need a new fleet for which dual voltage is the obvious choice. And adding the line to Southampton and Reading-Basingstoke provides a route for electric freight that would avoid the busy route via Winchester.

 

[Bletchleyite]

It would strike me that surrounding the third rail with fibreglass shielding leaving only a gap wide enough for the shoegear would considerably reduce the risk it poses, as someone stepping over it would have to deliberately make contact with it rather than being able to accidentally catch it. Indeed, isn't this done in some depot areas already?

A good amount of the risk from third rail is to staff in depots - and I believe that's the reason why all the 777s are fitted with shunting batteries, so the depot need not have third rail in areas where it would pose risk.

Another thing you can do is to add fibreglass or plastic shrouding to top-contact third rail, leaving a gap big enough for the shoegear, making accidental contact a lot less likely, for example:

Third rail with plastic shielding boards

 

[mmh]

A good amount of the risk from third rail is to staff in depots - and I believe that's the reason why all the 777s are fitted with shunting batteries, so the depot need not have third rail in areas where it would pose risk.

As I think I mentioned above, another thing you can do is to add fibreglass or plastic shrouding to top-contact third rail, leaving a gap big enough for the shoegear, making accidental contact a lot less likely, for example:

Third rail with plastic shielding boards

Those (I believe they're called guard boards) are generally used to protect track circuits and signalling and prevent short circuit bars from being used, not to shield the rail from humans, which is why outside depots and sidings their locations appear "random."

 

[HSTEd]

Does not make you wonder whether they could make rails that have an insulating coating directly pultruded onto the sides of the rail, with only short exposed sections to enable cables to be attached.

 

[Dr Hoo]

Something that seems to be largely missing in this discussion is that any mitigation of the current ten-fold greater risk of electrocution is likely to cost more. So, for example, there might be continuous 'kick boarding', palisade fencing, bridges to replace some level crossings, revised maintenance regimes (to effectively remove the need for people to be routinely 'working' in energised areas) or much more sophisticated control and switching arrangements (perhaps with the conductor rail only energised when a train is actually passing).

These additional costs would be added to the inherent relatively inefficient electrical aspects of transmission loss at low voltage. This would be at the same time as alternative solutions such as batteries to cover short hops may be becoming cheaper as well as offering other advantages.

With regard to the selection of 'suitable' routes I would have thought that any line carrying a significant amount of freight really ought to be 25kV, especially given the weight and power requirements of future 775m formations at 75mph. This includes Redbridge/Eastleigh and Basingstoke to Salisbury. Third rail will always struggle to meet this sort of duty cycle.

 

[HSTEd]

These additional costs would be added to the inherent relatively inefficient electrical aspects of transmission loss at low voltage. This would be at the same time as alternative solutions such as batteries to cover short hops may be becoming cheaper as well as offering other advantages.

The costs of 25kV installations are now so enormous that you could buy an awful lot of mitigation before it matters.

With regard to the selection of 'suitable' routes I would have thought that any line carrying a significant amount of freight really ought to be 25kV, especially given the weight and power requirements of future 775m formations at 75mph. This includes Redbridge/Eastleigh and Basingstoke to Salisbury. Third rail will always struggle to meet this sort of duty cycle.

Given that freight manages perfectly fine with very low performance diesels, the power demand of freight trains on third rail will be near negligible.

A Class 66 has only ~2MW at rail.
Which makes it roughly equivalent to a Class 444.

 

[philthetube]

Does not make you wonder whether they could make rails that have an insulating coating directly pultruded onto the sides of the rail, with only short exposed sections to enable cables to be attached.

The danger here is that it would not be fail safe, and you can imagine someone going, "it's of this rail is insula.......................

 

[Bletchleyite]

Those (I believe they're called guard boards) are generally used to protect track circuits and signalling and prevent short circuit bars from being used, not to shield the rail from humans, which is why outside depots and sidings their locations appear "random."

Interesting, though they also would as a side-effect protect against accidental contact with the side of the rail while working (which is much more likely than accidental contact with the top of it), or evacuating a train, on the line.

 

[HSTEd]

The danger here is that it would not be fail safe, and you can imagine someone going, "it's of this rail is insula.......................

This argument could be used against any non safety-grade risk mitigation procedure though........
And there would still be an obviously shiny conductive part on top where shoe goes.

 

[Dr Hoo]

Given that freight manages perfectly fine with very low performance diesels, the power demand of freight trains on third rail will be near negligible.

A Class 66 has only ~2MW at rail.
Which makes it roughly equivalent to a Class 444.

Given your regular comments about the supposed inefficiency of rail freight in GB (and also criticism of the allegedly 'obsolescent' air brake system) I am surprised that you are so attached to "low performance" and, for that matter, a most definitely obsolescent method of electric traction supply that would have been made illegal over 30 years ago if it hadn't been for a 'grandfather rights' fudge!

 

[HSTEd]

Given your regular comments about the supposed inefficiency of rail freight in GB (and also criticism of the allegedly 'obsolescent' air brake system) I am surprised that you are so attached to "low performance"

I'm not attached to low performance.
I'd love a fleet of high power electric freight Co-Cos with ECP brakes.

But since the freight industry has no interest in that, I see no reason to squander money trying to allow them to do something they have little interest in.

And even the limited power output of third rail will enable performance drastically better than diesel can manage. A Class 92 on third rail manages four traction megawatts, meaning it has double the power of a Class 66!

and, for that matter, a most definitely obsolescent method of electric traction supply that would have been made illegal over 30 years ago if it hadn't been for a 'grandfather rights' fudge!

Most obsolescent except for the fact it costs far less than the "modern" 25kV system.
And given that almost all the very high intensity railways are already electrified - what matters is reducing the capital cost of the installation.

 

[HSTEd]

The ORR document claimed the risk level was significantly higher but there seems to be no evidence in the public domain to substantiate this. Something the RSSB report ought to try to get to the bottom of.

I have stuff that I obtained using an FOI study.

I've attached it, the risk is clearly much greater. Note that this is Fatality Weighted Injuries nationally, and there is much less third rail track than 25kV track, but don't know how much there is on a route basis.

Two things that are noticeable - huge risk from tresspassers, and significant risk of station injuries, which is why I have often suggested gapping the conductor rail at the centre portion of station platforms (providing conductor rail on both sides at the end of the platform to mitigate against a shoe loss).

EDIT:

It seems any efforts should focuso n reducing risk to tresspassers, hence why I thought about trying to have an integral insulation on the sides and bottom of the third rail to reduce the risk of people coming into contact with it by accident.

 

[mmh]

Interesting, though they also would as a side-effect protect against accidental contact with the side of the rail while working (which is much more likely than accidental contact with the top of it), or evacuating a train, on the line.

If you shielded all of the third rail there would be nowhere to short circuit it, though. You'd only ever want to do it in emergency, in a normal evacuation you'd get the power turned off, it's a pretty extreme way of blowing the power. You basically short from the third rail to the running rail, but not where the running rail is the track circuit as it'll just likely blow up the signalling.

The approaches to London Bridge, since the Thameslink rebuild, as well as boards have sections of yellow painted rail to show where not to short circuit, I don't know if that's common anywhere else.

Perhaps a compromise for 3rd rail extensions could be a ban on working in energised sections. Coupled with the highest protection of track from the public possible (HS1 style?) that leaves the platforms as the high risk area. You could fence between the tracks to reduce the attraction of deliberately crossing.

 

[Dr Hoo]

Why is so much effort needed to mitigate risks with 3rd rail,it's not like it's been around for 5 mins. It's benefits and risks are well known . As I asked earlier,would a new installation need to be installed to new or existing standards?
What benefits would putting OHLE between Basing and Salisbury bring,surely that would create an isolated pocket in an otherwise 3rd rail area. Shoes and Pans up at Basingstoke?

 

[O L Leigh]

Most obsolescent except for the fact it costs far less than the "modern" 25kV system.
And given that almost all the very high intensity railways are already electrified - what matters is reducing the capital cost of the installation.

I'd like to raise the question as to whether or not the cost of 25kV AC electrification has been over-inflated due to the clusterf**k that was the GWML electrification scheme. Would the cost of future schemes really be so high if the industry went away and learnt the planning, operational and engineering lessons of the GWML scheme? Also, how much of the additional cost of uncompleted sections where preparatory works had been carried out (e.g. Didcot-Oxford) was added on to the "cost per mile" of the completed scheme?

I'm aware from reading the industry press that a very high proportion of the supposedly standard installations had to be individually redesigned and that a large amount of unused structures were to be sold for scrap. Both of these factors alone would have had significant cost implications.

 

[HSTEd]

I'd like to raise the question as to whether or not the cost of 25kV AC electrification has been over-inflated due to the clusterf**k that was the GWML electrification scheme.

Even the schemes that have run comparatively well have cost enormous sums though.

Even Network Rail concedes third rail is cheaper at this point (see the options for Ashfield-Ore in the Kent Route study)

 

[Dr Hoo]

Why is so much effort needed to mitigate risks with 3rd rail,it's not like it's been around for 5 mins. It's benefits and risks are well known . As I asked earlier,would a new installation need to be installed to new or existing standards?

What benefits would putting OHLE between Basing and Salisbury bring, surely that would create an isolated pocket in an otherwise 3rd rail area. Shoes and Pans up at Basingstoke?

Firstly, it is necessary to mitigate the risks of third rail because it is around ten times more dangerous than overhead according to the RSSB's own consultancy proposal (quoted previously). 'Current' standards have not fundamentally reduced the risks from the system that has been around largely unchanged for over 100 years (apart from having been made even more dangerous by raising the voltage from 600 to 750 in many areas).

Secondly, against a background where most of the network is electrified in future the Reading-Basingstoke line will be equipped at 25kV as will Newbury-Exeter-Cornwall. So Basingstoke-Salisbury will be part of a route with 25kV at both ends. Although it may not be immediately obvious the route via Andover and the Laverstock Curve to Romsey and Redbridge is often used by intermodal trains to/from Southampton. Even the Bristol-Bath-Westbury-Salisbury-Southampton axis is likely to be electrified in future. This would also sensibly be at 25kV.

Even a mid-range modern freight locomotive, such as a Bo-Bo Vectron, can use over 6MW and I can remember times in Eastleigh signalbox with four stone trains running on the block between Salisbury and Romsey. There is no way that third rail can sensibly feed that sort of operation.

A voltage/system change for modern EMUs at Basingstoke and other locations would not be a big deal.

 

[HSTEd]

Even a mid-range modern freight locomotive, such as a Bo-Bo Vectron, can use over 6MW and I can remember times in Eastleigh signalbox with four stone trains running on the block between Salisbury and Romsey. There is no way that third rail can sensibly feed that sort of operation.

Good luck sensibly using 6 traction megawatts on a stone train using a weedy Bo-Bo locomotive.
It won't be able to generate enough tractive effort to make use of it.

It would have to be going ~70km/h before it could even make use of all its horsepower.

Even a Class 92 will do far better on a stone train, even with only 4MW of traction power.

And the third rail standard requires trains to reduce power demand dynamically if the voltage on the rail falls too low.

A modern Co-Co with ~4MW of traction power on third rail, and as many megawatts as possible on 25kV, with something like ~530kN of tractive effort is what we really need for freight operations

 

[AM9]

The enthusiasm for 3rd rail extensions being bolstered here by various mitigation of the considerable health and safety issues seems to befogetting one major cost driver: that of inspection and maintenance. Areas that spring to mind include:

The additional cost of debris, leaves and occasionally snow and ice on any live 3rd rail shielding hardware​

The requirement to ensure the integrity of fences and barriers designed to prevent trespasser access to the live track, - note that the railway has been severely punished for failing to secure damaged fencing around sidings when a child trespassing received life-changing injuries following an electric shock.​

The maintenance of ever more complex signalling and power supply integration through EMC issues​

So labour and material costs associated with those are added to the perennial big number extra costs, e.g. higher power distribution costs, greater power losses, reduced performance of traction and the ever present climatic interruptions of snow and ice.
The other consideration is that those costs are perennial so for an expected life of 50 years, the 3rd rail solution has all of those addirtional running costs. The higher costs that might occur when 25kV schemes are implemented is a once-off cost, so the balance might be considerably different if all of the true costs are included, rather than just thinking about the high cost of replacing a few low bridges a bit earlier than might have been necessary otherwise.

 

[A0]

Even Network Rail concedes third rail is cheaper at this point (see the options for Ashfield-Ore in the Kent Route study)

But in the case of Ashford to Ore how much of this is because the power can be fed from existing installations at each end of the line? Which I guess wouldn't be possible with 25kv - on the basis HS1 through Ashford is segregated?

 

[A0]

The requirement to ensure the integrity of fences and barriers designed to prevent trespasser access to the live track, - note that the railway has been severely punished for failing to secure damaged fencing around sidings when a child trespassing received life-changing injuries following an electric shock.​

​

Of course in both those cases it was one company and the electrocutions occurred from OHLE not 3rd rail.

There remains a problem in that the 3rd rail doesn't just electrocute humans, it does a fair bit to wildlife which doesn't tend to respect trespass laws. Yes, I know OHLE can take out birds - I've seen a pigeon lose a fight with the OHLE, but that's much less common than foxes etc on 3rd rail - and part of the risk there is when the power gets knocked out when Foxy Woxy wanders over the lines, bringing all trains to a halt.

 

[HSTEd]

But in the case of Ashford to Ore how much of this is because the power can be fed from existing installations at each end of the line? Which I guess wouldn't be possible with 25kv - on the basis HS1 through Ashford is segregated?

Isn't Ore essentially fed from Hastings as an afterthought because it used to have a bunch of carriage sidings there?
Its doubtful they could arrange for entirely end feeding the third rail system.

Just have to remember that you need more feeder points for a third rail system, but they cost nothing like what a feeder station for 25kV costs.

 

[O L Leigh]

But in the case of Ashford to Ore how much of this is because the power can be fed from existing installations at each end of the line? Which I guess wouldn't be possible with 25kv - on the basis HS1 through Ashford is segregated?

Isn't Ore essentially fed from Hastings as an afterthought because it used to have a bunch of carriage sidings there?
Its doubtful they could arrange for entirely end feeding the third rail system.

Just have to remember that you need more feeder points for a third rail system, but they cost nothing like what a feeder station for 25kV costs.

This is kind of my point. It's hard to be definitive about the relative costs when by reference to specific schemes which may end up costing more or less than equivalent schemes due to factors not necessarily replicated between individual schemes.

Even the schemes that have run comparatively well have cost enormous sums though.

I don't disagree. There is no escaping that electrification of the existing network is an expensive old business. But should that be putting us off? My own belief is that a proper rolling programme of electrification would result in a reduction of the per mile cost over the long term. No loss of expertise, full utilisation of the plant and other equipment, economies of scale by having ongoing contracts to procure equipment and so on. Do we always want to be doing things "on the cheap"?

 

[AM9]

Of course in both those cases it was one company and the electrocutions occurred from OHLE not 3rd rail. ...

What's that got to do with it? It was a fence - it wasn't a 750V DC or a 25kV ac fence and had it been a diesel depot and the child fallen from the roof of a train, the prosecution would have gone the same way.

 

[hwl]

Good luck sensibly using 6 traction megawatts on a stone train using a weedy Bo-Bo locomotive.
It won't be able to generate enough tractive effort to make use of it.

It would have to be going ~70km/h before it could even make use of all its horsepower.

Even a Class 92 will do far better on a stone train, even with only 4MW of traction power.

And the third rail standard requires trains to reduce power demand dynamically if the voltage on the rail falls too low.

A modern Co-Co with ~4MW of traction power on third rail, and as many megawatts as possible on 25kV, with something like ~530kN of tractive effort is what we really need for freight operations

3MW is easily do able on 3rd rail in decent supply areas, about 1.6MW in poor supply areas without causing problems. 7.8MW is a sensible go anywhere AC limit (worst supply areas)

Most diesel locos can't get down a useful amount power below 19-24mph with various control mechanisms limiting power to traction motors below that so even a bad DC supply would be surprisingly good. The main issue with a Co-Co is adding enough weight in the UK to help with tractive effort hence 530 might be a bit high for the UK...

 

[hwl]

The requirement to ensure the integrity of fences and barriers designed to prevent trespasser access to the live track, - note that the railway has been severely punished for failing to secure damaged fencing around sidings when a child trespassing received life-changing injuries following an electric shock.

​

​

​

You still need the fences in very good condition for OHLE now...​

e.g. no difference what thyep of electrification you go for.​

 

[A0]

What's that got to do with it? It was a fence - it wasn't a 750V DC or a 25kV ac fence and had it been a diesel depot and the child fallen from the roof of a train, the prosecution would have gone the same way.

Because it was cited in this thread which was about extension of 3rd rail. Yet the injuries sustained weren't a consequence of the 3rd rail on these occasions.

 

[hwl]

Two things that are noticeable - huge risk from trespassers, and significant risk of station injuries, which is why I have often suggested gaping the conductor rail at the centre portion of station platforms (providing conductor rail on both sides at the end of the platform to mitigate against a shoe loss).
EDIT:
It seems any efforts should focus on reducing risk to trespassers, hence why I thought about trying to have an integral insulation on the sides and bottom of the third rail to reduce the risk of people coming into contact with it by accident.

In terms of lower risk:
Quieter rural route helps.
No additional depot space helps.
Reducing crossing especially foot crossings helps
High well maintained fencing helps.
The yellow fibreglass boards should help in stations.
Better station access so there is less temptation to cross the tracks helps.

Hence North Downs, Marshlink and Uckfield are ideal lower risk candidates to further de-risk.

 

[hwl]

Because it was cited in this thread which was about extension of 3rd rail. Yet the injuries sustained weren't a consequence of the 3rd rail on these occasions.

Poor fencing is one of the main trespass risk drivers for 3rd rail risk