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Topic Title: Third-and-fourth rail DC electrification?
Topic Summary: Another option for DC routes
Created On: 27 January 2014 03:58 PM
Status: Read Only
Related E&T article: Rail electrification: Engineers consider the overheads
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 27 January 2014 03:58 PM
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jkinghorn

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Joined: 29 July 2002

As I understand it, the electrification debate for DC third rail routes has considered two options: leave them alone, or convert to overhead AC. Perhaps there is another compromise alternative: upgrade to third-and-fourth rail?
This is not like London Underground's four rail system, but simply involves installing a second conductor rail on the opposite side of the track, and connecting it in parallel at the substations. This halves the electrical resistance between the substation and the train, and halves the losses in that part of the circuit.
Sure you need more conductor rail, insulators, cables etc., but you can avoid the disruption of installing masts and modifying bridges. No changes to trains or substations.
Any thoughts on the practicality and cost effectiveness of such an idea? Regards, John Kinghorn MIET
 27 January 2014 04:40 PM
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jarathoon

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Part of the argument for changing to overhead is that it would allow for faster trains and faster accelerating trains.

It may be worthwhile to consider adding battery/inertia energy storage system in new trains and/or at stations that allows them to operate outside the power constraints of the existing third rail system. Higher top speeds, faster acceleration from stop, faster regenerative braking etc.

Most of the power is required in accelerating trains from stop out of stations (or from intermediate signalling), or in powering the train up gradients. Why not map where the power is actually needed and develop a third or fourth rail investment strategy from this starting point?

For some reason civil engineers have got themselves trapped in a cul-de-sac. It is becoming too expensive to employ them and their existing methods. I think you are right to kickstart a debate on other more cost effective options.



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James Arathoon
 29 January 2014 05:03 PM
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jarathoon

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Summary Third Rail Report from 2011
http://www.rssb.co.uk/sitecoll...rch/T950_rb_final.pdf

Full Report from 2011
http://www.rssb.co.uk/sitecoll...ch/T950_rpt_final.pdf

No mention of energy storage techniques and technologies.

However they do consider it here in a 2010 document

http://www.rssb.co.uk/sitecoll...rch/T779_rb_final.pdf

Oher Energy Strategies are here including "T777 - Understanding the effects of 'gaps' in electrical continuity of the traction contact system" (2010) also not mentioned the the above third rail report.

http://www.rssb.co.uk/RESEARCH...s/EnergyStrategy.aspx

"RSSB underpinning knowledge based decision-making"

http://www.rssb.co.uk/AboutUs/Pages/a_guide.aspx

How is it possible to conduct research where even relevant reasearch published by the same organisation the year before doesn't warrant a mention?

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James Arathoon
 29 January 2014 07:58 PM
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jkinghorn

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Thanks for your comments James. I agree with you that energy storage on the train and at the substation has a major part to play in solving the third rail 'problem'. I haven't read the reports, but I shall.

Part of the argument for converting the Southampton to Basingstoke line to AC is how to deal with substantial and increasing volumes of freight. I assume, however, that a future electric freight locomotive will contain a substantial rechargeable battery anyway, to get it from the main line to unelectrified sidings, do a fair amount of shunting, and back to the electrified lines again. Since the traction package of such a locomotive has to be capable of working from DC from the battery, it does not seem a very big step from there to make it dual voltage AC/DC overhead/third rail capable as well. Out on the main line, the battery helps to boost acceleration or climb hills, and on a typical freight run much of its energy would come for 'free' from regenerative braking.

It seems likely that using the three ideas: storage at the substation, reducing the distribution impedance with a fourth rail, and storage on the locomotive might not be sufficient individually, but the combination might be good enough. Quite how the economics of such an approach compares with conversion to AC, I have no idea. It will be interesting to hear what the experts have to say about that.

Regards, John Kinghorn MIET
 30 January 2014 12:28 AM
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jarathoon

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The freight argument may well be a red herring. Every part of every route would have to be converted to avoid installing a diesel locomotive for freight, including sidings goods by-pass routes and segments etc.

I suspect the fuel costs are a small faction of the overall costs of getting a goods train from A to B across the railway network. The cost savings on fuel will be easily drowned by spending too much money on overly expensive rail infrastructure investment.

I am not necessarily saying that investment in AC overhead line infrastructure will never make sense. However we probably need to go through one more round of investment in DC to allow a future change over to AC to take place without it becoming a logistical nightmare.

Having some self power capability in new stock would dramatically ease the logistics of change close to Clapham Junction, Waterloo etc. and would help to improve overall system reliability.

Keeping the commuter throughput going reliably through any period of change is in my opinion the overriding constraint. Energy savings, electrifying freight etc are secondary to this constraint.

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James Arathoon
 03 February 2014 12:59 PM
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jkinghorn

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I have now read the reports, interesting; I was aware of the background but not some of the numbers. Good conclusions within the scope of the issues considered.

Assuming that the third-and-fourth rail idea doesn't get a mention because nobody thought of it rather than there being a fundamental snag with it, what effects might it have? For energy efficiency a rough estimate could be made from the relative impedances of the supply seen at the substation outputs, the resistance of the supply path through the conductor rail and collection shoes, and the resistance of the return path through the train wheels and running rails. I don't know those figures, but for the sake of argument let's assume they are in the ratios of 25%, 50% and 25% respectively. Adding a second conductor rail could reduce the 50% by half, cutting the supply chain resistance to 75% of its current value.

If that saving were applied generally (a big if) this could cut the Import Losses in fig.22 of the report from 27% to 20%. Regenerative braking energy recovery would improve a bit too, not by much. Perhaps overall losses might reduce from 21% to 17%, or 103MWh in for every 100 MWh out instead of 114 MWh in by the time you include the effects of regenerative braking. Sufficiently interesting to be worthy of further study by those who know the real numbers, I think.

The idea doesn't solve the weather resistance problem of top contact conductor rails, but it should help in marginal conductions as there are twice as many conductor shoes potentially operating. Also, when the sun eventually does come out to melt the frost, the chances are better that one of the two conductor rails might not be in shadow.

Perhaps the idea is worth looking at in more detail by the experts.
My book 'Beyond the HST' is mostly about future passenger rolling stock design, but it does have some suggestions for improving the network and its infrastructure, including the third-and-fourth rail idea.

http://www.melrosebooks.co.uk/buy-online/beyond-hst


Regards, John Kinghorn MIET
 03 February 2014 01:58 PM
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acsinuk

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My feeling is that diesel fuel is so reasonably priced that there is no financial case to electrify at present. There is an environment case however that applies in polluted cities.
But it may be possible to design a diesel electric that can be run from the DC rails, which would be a really neat solution.
CliveS
 03 February 2014 03:52 PM
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jarathoon

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Large catalytic converters to diesel electric locomotives perhaps?

Given that a single goods train can take ten's of lorries of the road, the fuel and manpower savings are considerable. The relative efficiency of moving from diesel to electric once on rail is small, and can be easily washed away with bad investment strategies (e.g the badly misguided HS2 proposals). Better to have a CMS1 design, "Cheap Medium Speed 1",

In terms of handling goods traffic from Southampton the best thing would be to reopen the Great Central Main Line from Banbury/Aylesbury to Rugby. Which would also form part of my "Cheap Medium Speed 1" rail design.

Government spending that is cost-effective and revenue raising seem to be actively discouraged by people like HS2 Chairman Sir David Higgins; despite the fact that this will give increased revenue and productivity benefits to the Tax payer sooner, which will in turn support further increases in investment in two or three decades time.



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James Arathoon
 05 February 2014 09:01 PM
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jkinghorn

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I am no expert on the details of diesel engines, so cannot comment about catalytic converters. I understand, however, that the hybrid drive concept is a very useful one for better fuel efficiency and making exhausts conform to the latest regulations. Also, it does not seem a good idea to start up (or leave running) a big diesel engine just to generate a couple of hundred horsepower for a minute or so to shunt a few wagons in a siding, the sort of task a general purpose freight locomotive will often have to perform.

So I think a future freight diesel loco needs a modestly sized energy storage system, e.g. a battery, just as much as an electric one does to cope with the odd unelectrified freight loop or shunting in sidings. Although the financial case for doing it might be a bit marginal at present, battery costs will go down and fuel costs are likely to increase in real terms, maybe a lot, which tips the balance. It is good to see the EIT supporting trials of new battery technology in the adapted EMU, and it will be interesting to see how they get on.

It seems very likely that moderate on-train energy storage, enough for discontinuous electrification, will become common for many 'heavy rail' applications in the medium term. Since there will probably be a significant amount of third rail DC route still in use then (or third-and-fourth rail if that turns out to be useful), it seems sensible to make the technology work from a DC supply too.

So Clive's neat future engine would be modular, with a standard bodyshell, three phase traction arrangement and battery, with the power electronics capable of working from a transformer, alternator or DC. You then add a diesel engine/alternator, transformer/pantograph or third rail shoes according to needs: all three in the same loco if you like. No doubt there are many details to solve, but the concept seems feasible to this non-expert.

Many nice technical challenges to think about, anyway!

Regards, John Kinghorn MIET

 12 February 2014 12:13 AM
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ToniSM

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The idea of a forth rail may seem a relatively easy solution. One thing is nagging in the back of my mind. The inherent impedance of the running rails, OK the forth rail boosts the supply, but the return lets the idea down.

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Could there be a better way?

In theory yes, but in practice?
 12 February 2014 01:03 AM
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jarathoon

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Originally posted by: ToniSM

The idea of a forth rail may seem a relatively easy solution. One thing is nagging in the back of my mind. The inherent impedance of the running rails, OK the forth rail boosts the supply, but the return lets the idea down.


One other option is to increase the voltage of the third rail (eg. from 750V to 1500V) for certain sections where the extra power is needed. (accelerating out of stations and driving up gradients). That would involve converting all the trains so that they could be powered from more than one DC voltage - or - sensing equipment at the substation level that varied the third rail voltage to meet the needs and capabilities of the train passing through the line segment it powered.



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James Arathoon
 14 February 2014 11:00 AM
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jkinghorn

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Yes you are quite right that the success of the fourth rail idea will depend on the return impedance of the running rails. I don't know how that compares with the supply impedance. So the idea might help a bit, but whether that is enough to be financially worth it is another question. The experts who know the numbers need to do the calculations to find out.

Having higher voltages on the third rail and automatic sensing of which voltage it is sounds like lots of complicated and expensive modifications to trains. It seems a better idea to leave the trains alone and have trackside energy storage units in strategic locations where trains accelerate or climb hills, keeping the supply at the nominal 750V.

Of course this may well be considered as a stop-gap expedient, as ideally we would want to convert all the DC routes to 25kV AC eventually. But it is an enormous task, and will take a long time, so such interim solutions might be worth considering to improve the situation on DC lines in the meantime and make the conversion task more manageable for those who have to undertake it.

Regards, John Kinghorn MIET
 14 February 2014 03:11 PM
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jarathoon

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Changing voltage on certain segments of certain routes may well add to the electrical supply infrastructure complexity slightly, but is likely to be much cheaper than completely re-engineering the railway to accept overhead 25 KV lines.

Let the government set up a competition to focus on cost and ease of logistical change over between:

1. civil engineering route revamp + 25 kv infrastructure + new trains / refurbished trains
2. smart electrical engineering route revamp for dual voltage 750V/1500V + new trains / refurbished trains with some energy storage.



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James Arathoon
 14 February 2014 03:29 PM
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jarathoon

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At the same time if we add train position and detection infrasturcture to the line in analogy to the Victoria Underground line say, the southwest trains out of waterloo can be converted to be driverless trains.



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James Arathoon
 26 March 2014 11:08 PM
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ToniSM

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Only one running rail is used for return as far as I know. The other rail being used for track circuiting.

Sorry the idea of a fourth rail seems fraught with problems.

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Could there be a better way?

In theory yes, but in practice?
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