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Given the cancellation of various electrification schemes, what future is there for the Valleys electrification, which the Welsh Government is currently saying will still go ahead.  Is it time to be truly innovative to try and keep the costs down?

One of the biggest costs is bridge raising, even more so since the goalposts in terms of clearance have changed recently.  Could a new emu fleet avoid this by facilitating neutral sections under each bridge.  A small battery in each emu could normally be used to produce a kick start on acceleration (thus providing a day to day benefit), but a small amount of charge would always be retained as insurance in the event that a unit got stuck in a neutral section.  Come to think of it, with all the IEP fleet having diesel engines, why wouldn't the SW main line be similarly engineered?

Has NR missed a trick here, or am I missing something?

 

The idea of having sections of electrification out in the boondocks, where line speeds are fast and bridges are few, has been floated; not sure how far it got, or if it's still live.

What flavour electricity do tram systems use? Isn't generally 750v DC? And what flavour electricity do the third rail networks in Mersyside and the Network South East (NSE) area use? Isn't that also 750v DC?

All the new stock built for the NSE 3rd rail area since privatisation has been dual-voltage capable, so rather than neutral sections could you just drop the voltage to 750v for the low bridges? I guess there would be issues trying to isolate the different voltages from each other, and possibly with both power sources from the same pantograph rather than the 750v supply coming from a third rail shoe but you did say "truly innovative". Alternatively, do for bridges what the 3rd rail network does with level crossings and have gaps (neutral sections) in the electrification system but multiple pickup points on the train (two shoes for 3rd rail, two pantographs in the case of OHLE) to avoid the need for batteries.

I suspect dropping to 750v for the couple of seconds taken to pass the bridge and back again wouldn't be worth it.  Under normal circumstances the train could coast pass, and it's only in the very rare situation whereby a train comes to a halt at precisely that point that there would be an issue.

In the early days of 25kv electrification there were a number of reduced voltage sections and lines where clearances were reduced to the absolute minimum.  The voltage used was 6.25kv and switching between the two voltages was carried out automatically onboard the trains/locomotives.

Personally, for areas such as the Welsh Valleys, I believe that reducing the cost should be considered by using the lower 6.25kv arrangement and using BR MK3 OLE.

Why were those sections taken out and changed to 25kV?

Reducing the voltage means the current goes up therefore the OLE conductor size is larger and hence the weight of the OLE increases ............ heavy OLE larger structure to support it also in the case of the 6.25kV reduced speed.

The 6.25kV schemes allowed BR to retain the old 1500 V dc OLE clearances under bridges, it did mean extra wayside equipment transformers, circuit breakers and cables; as insulator technology improved and BR's engineers understanding of dynamic clearances allow the removal of the 6.26kV.

The designs of 25kV OLE are not suitable for 750V dc the current is too high and the volt drop too great, the other issue with 750V dc is the number of sub stations compared to higher voltages.  A better option would be 1500V dc the same as the Tyne & Wear metro, also I believe some tram systems use 1500V dc when they are non street running like the Manchester tram.

There is another method used by NR in Scotland to run 25kV OLE through low over bridges and that is to use an earthed section of contact wire; the train VCB is tripped and reset by an APC the same way as a neutral section, the train just coasts through the earthed section.

If for some reason a train was gapped in such a section - after, say, emergency braking, etc. - is there a way to move it under power using shed leads for instance, or must it wait for a shove from behind?

First the sections are short 20 or 30 meters so the likelihood of being stranded in a dead spot is very small, these earthed sections are only used for bridges and not tunnels, the signalling would also need to be assessed to ensure the earthed sections are not located where a signal my require a train to slow down or in its acceleration point past a signal.   

Shed leads are now fixed trolley systems so loose leads are not used, Electricity at Work Regs etc.

The use of earthed sections would based on a Designers Risk Assessment something like a Drivers emergency braking and train being stranded in the earthed section would likely to come out as Improbable ie a once in 50 to 100 year occurrence and the consequence to safety ie the risk of injury or death very low.   Inconvenient if it should happen but not a danger   

The standard way of changing over between overhead voltages is to coast across an insulated (and perhaps earthed) section. This may seem surprising, and of course it's rare here, but pretty common elsewhere - e.g. France with 25kV/1500VDC and Germany or France with tram-trains.

While (as usual) almost every way of doing this has been tried somewhere sometime, the consensus now is that you provide one pantograph per unit, tell it what to expect and switch it over, but provide fast-acting switchgear so it will change automatically and not be destroyed by the wrong voltage (which could be more difficult than snow!).

EMUs up to four cars usually have 1 pan (e.g. 387s), and tram-trains do too - they are even shorter. Five-cars seem to be 1-pan too if suburban (e.g. 707s - yes they are DC, but they have a bit of flat roof for a pan), but IEPs have two. Above eight cars two is usual, and sixes and sevens are too rare to really say.

While designs vary, a lot now put the electronics and motors on one self-contained vehicle, and about half of a train made up of those motor cars. The pantograph goes on a trailer of its own, due to the weight of the transformer (mainly) and switchgear. Power is then fed to the motor cars at some suitable "low" voltage, such as 750V up to 3kV - most likely as DC.

So longer trains, or multiple units, can rescue themselves from stranding with another pantograph. Short ones can't, and have to wait for the next train to come along, and do whatever the rules demand about giving another train a shove. OK for trams, otherwise I suspect it's going to be a slow procedure. Obviously the trick is to make sure it's very rare.

It does occur to me that one of the few things that's likely to strand a train is stopping to push another one at just that point ... so I guess you'd be best to couple them first.

I read somewhere that for 25kV OLE it is usual to put manual isolating switches between the tracks of a line, so each track can be disconnected individually, and that means there is an isolating gap there too. While you'd never intend to stop part-way across such a crossover, you could well be going very slowly - so is that a potential issue?

One possible problem I can see with dead sections in the ValleyLines OHLE is that those lines have many stations, meaning bridges could be very near stations (so trains will be going slowly and not have much momentum for coasting).

One big worry is Cathays (not somewhere I've seen for myself), where there is not only a low footbridge at the station but also a building built above the track (https://commons.wikimedia.org/wiki/File:Cathays_(15641367118).jpg). I've only been on a ValleyLines service north of Queen Street once (I spotted Cathays with Google Earth) so there could be more difficult spots like that.

If there's serious concern about trains getting occasionally stranded in dead sections, there's an old article in the Daily Mail (http://www.dailymail.co.uk/sciencetech/article-3462885/The-electricity-generator-pedal-Free-Electric-bike-create-24-hours-electricity-just-hour-exercise.html) about an onboard generator. With one of these tucked under the driving console, could the train be peddled out of trouble?

I have used Cathays many times.  Yes there is a footbridge, but so have many stations. The Cardiff University buildings built over the line are relatively modern and I would be surprised if BR had not required sufficient clearance for electrification. They usually did.

Are you thinking of selling the stranded train, perhaps on Ebay, or of pedalling it along the track? If the latter, you might want to get Cardiff boy Geraint Thomas (https://en.wikipedia.org/wiki/Geraint_Thomas) to help!  :D

And there's his team-mate Luke Rowe (https://en.wikipedia.org/wiki/Luke_Rowe), also a Cardiff lad, for a tandem effort!

The concern is over exaggerated, in the dim distant past of 25kV the neutral sections used on the GE & LTS were 1/4 mile long of dead section of wire although they had bypass switches they were seldom if ever used to rescue a stranded train.  The high speed beaded neutral sections uses on the ECML, WCML ect are over 4 meters long and to the nest of my knowledge a train has never got stranded.   GWML and HS1 use an contact wire overlap system (similar in principle to the original 25kV GE / LTS) except the GW and HS1 neutral sections are only a couple of wire spans there is still a dead section it is not envisaged that even a single pan train will get stranded

BR electrification clearances or 2017 Network Rail / EU clearances?

An interesting discussion, and thanks to all who have contributed. I'll come back to the original question, is there any reason why equipping emus with a small battery pack which provides resilience in the event of a stop on a neutral section and which also enables zippier acceleration (which would be useful given the number of stops on valley services) wouldn't work or be cost effective when compared with the alternative of rebuilding numerous bridges?

There are two parts to your question.

1) Could you give an EMU a battery pack and/or diesel generator to allow it to work when the wires are off? Absolutely. The battery pack concept is newer on heavy rail, but there are a number of tramway systems that use it, Birmingham's have passive-provision and will be retro-fitted for when the next extension is complete. The all-electric version of the Hitachi IET has a small diesel engine for if the wires go down, though it's really just enough to keep the lights and A/C on whilst it limps to the next station. The new conversion of the 319's has a diesel engine that effectively pretends to be a 750v input from a third-rail, so if the pan is down, the engine feeds the 750v bus. If you've got a 25kV supply you'll have all the zip you need, but batteries could be helpful to improve the acceleration of a DEMU.

2) Can you get away without rebuilding structures? Yes and no. Generally the pantograph has to stay up (albeit that it can be pretty low), so you have to have a mechanical clearance for that. It's generally not the height of a structure that is a problem but the 'shoulder' so you don't foul the horns of the pantograph. You then have the electrical clearance between the pantograph, OLE and structures, which can be surprisingly small, particularly if insulated sections or rigid catenery is used. In certain circumstances the wires can be really low, for example on the Paisley Canal branch where low-roof rolling stock is used, but this means that stock like 66's can only be used with the OLE isolated. The clearances between humans and OLE have to be pretty large under the new rules however, hence all the wall raising and footbridge replacements, though there is scope for derogation with the right paperwork, for instance on some of the newly electrified platforms in Paddington.

As for new third rail, forget it. The only time that will ever be allowed is in locations where access is highly restricted e.g. tunnels, depots etc. 

From what I can remember, there should be plenty of space under the Students Union in Cathays, though I suspect the footbridge needs to go, but to be honest, a DDA compliant footbridge with lifts would probably be a pretty good idea anyway. And therein lies an interesting point. Much of the upgrades that accompany electrification are stuff that really ought to be done anyway - like re-signalling