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Discussion in 'Infrastructure & Stations' started by Altnabreac, 27 Sep 2013.
That was my interpretation too.
Technically electrification from Central Belt to Aberdeen and Inverness is already Scottish Government policy as they were identified as schemes in STPR1.
So all we're really talking about is firming up the timetable for that.
Aberdeen - Inverness would be a new commitment but you'd imagine it would be bottom of the priority list of any Seven Cities rolling electrification scheme.
There's also a PS at Loch Luichart, but nothing after that to Kyle. The supply to Skye crosses just North of Glenelg.
Would they ever allow masts over Glenfinnan viaduct and in other scenic bits?
Agreed, but once you have got both ends done the business case or whatever stacks up much better I would think.
It basically, at that point, becomes an "infill", albeit a rather large one. Any major physical obstacles other than the Aberdeen tunnels?
Probably not, but if you're relying on batteries you can avoid most of those complications.
A technological aspect that might need to be worked out soon is the way that trains would charge up rapidly. Where 25kV AC is available, it's the natural choice as we know it can handle the highest possible power loads without needing a fundamental re-think. However, on isolated sections of OHLE only usable for recharging rather than running, it's unclear if it's still the best option. Fast charging of cars depends on high-voltage DC going straight into the batteries rather than AC converted to DC in the onboard power electronics. Should we create a standard for high voltage DC overhead power for charging? Using 25kV AC might allow you to get the power transmission you want but then you might an issue when a charging station is powered by trickle grid or renewables into a static battery. In that case it has to convert the static battery DC to 25kV AC for the few metres of conductor, down the pantograph and into the train's electronics, where it's then turned back into DC to charge the batteries. If you're going to use a static battery you don't want to do unnecessary conversions - extra power waste and extra electronics needed at the lineside. Since this would only be for isolated sections requiring battery technology the incompatibility with existing 25kV AC or 750V DC electric stock would be irrelevant.
I think you'd still have to step up the voltage to far more than any battery could supply directly, otherwise the current needed for fast charge of a train would be enough to weld the train to the charging equipment. So you'd need a solid state DC-DC converter at the charging station and another one on the train to step it down. If you're doing that then I think it would be much easier to step up and invert the battery voltage to 25kV AC at the trackside, so the train could just use the equipment it needs anyway to charge on standard 25kV sections.
If they are serious about electric cars etc, then there will need to be improved grid supply to remote locations too. Now I am not suggesting OHLE on the WHL or Kyle - but at least there maybe grid connections to help with the charging etc logistics.
Not necessarily, as the power is already there. It might need beef in up a little in places perhaps. It’s a different order of magnitude to To sufficient power to parts of the far north line, where there is currently little or none, and particularly to cover voltage drop over 30-50 miles.
It does seem there will be plenty of work for the electrical engineers! 25kV AC can support 7MW through a single pantograph (on the Eurotunnel Class 9) which works out as 280A. That amperage is on the same order of magnitude as the cutting-edge DC fast car chargers can manage. On a train we could expect there to be many more battery packs than on cars so it could presumably take more than the 800V the Porsche Taycan can manage. Trains wouldn't be able to use multiple lower-voltage connections in parallel (as is planned for megawatt-level chargers for trucks - e.g. the Tesla Semi megacharger is effectively just four supercharger connections combined) if they're going to use a simple pantograph arrangement. 3kV DC is already a well-known quantity on world rail networks but I don't know what limits exist going beyond that point. If it's just for charging, then performance over long distances of conductor doesn't matter much.
The 2043 Route Study has 1tph to Crianlarich so we could expect there to be plenty of places to charge up to that point. A not-unreasonable amount of the total distance to Crianlarich would be under the 25kV North Clyde electrification, and all of the line is adjacent to 'major' populations and the A82 trunk road. It seems semi-plausible that the electrification on this section could be more complete so that batteries were only really needed for the lower-frequency sections north of Crianlarich. Any electric trains would have batteries, so all difficult parts to wire could be avoided with long neutral sections.
Not forgetting the Battery DMU used on the Deeside railway, which came from a proposal from the Hydro.
OHLE to Crianlarich seems feasible (very few bridges north of Garelochhead) and would allow pure electric trains for a Faslane commuter service, Glen Douglas freight, and maybe a tourist service to the top end of Loch Lomond to offer boat/train loops out of Glasgow.
It’s still a long way from there to Oban/Fort William, with gradients and station restarts though....
Doesn't necessarily require fast charging. Cars do it because they don't/can't charge whilst moving.
The extra expense of more complex equipment would cover some length of standard OHLE, & you could always charge whilst on the move. There's also regen braking.
eg. electrify the 58miles of Montrose-Inverurie*, & that covers the power need for accelerating out of Aberdeen & the stations at each end, & about an hours running under OHLE. That gives a long time for charging. (* currently the section with more intensive use)
It's then 30miles to Dundee, which may well be doable on battery.
Even hydrogen trains are electric, so could use OHLE to save on fuel.
The line speed on the rural lines will always remain low, so I assume that simpler OHLE structures will suffice. I can see a problem crossing the Rannoch Moor bogs, though.
Yes more of a challenge than Chat Moss I would have thought.
There's two levels of using batteries to run electric train services.
The first level is what I expect the rest of the mainline electrification programme to rely on. In this, you have standard 25kV AC OHLE along 90-99% of the route and you rely on battery power only for specific obstacles like the Forth Bridge or a tunnel. This doesn't really require special power handling as the total battery capacity would be fairly small and could be charged up over the long stretches of running where overhead power is available. For instance, an electric Edinburgh to Aberdeen train would be fully charged leaving Waverley. It'd use the battery to get over the Forth Bridge, then have power again up to Kinghorn tunnel, and back onto OHLE up to Wormit and the Tay Bridge. Dock Street tunnel and Montrose bridge might require the battery again but you'd have half an hour to an hour of charging time available for every 5 minutes of battery necessity.
The second level is probably how you'd handle the low frequency (<1tph) stretches of the WHL, Far North and Stranraer lines. Here you'd have to make the decision about how much overhead line to provide versus the amount of battery storage required and the rate of charge. If you just put up charging points at stations, you'd need to be able to refill enough power to get to the next charger without requiring a longer stop. When the most difficult/sensitive sections can now be handled by battery power alone, your cost of electrification would be much more linearly proportional to the length of track you want to cover. Time under electrical power is more important than the distance. You'd need to build many kilometres of OHLE to provide the same amount of charging time as a few hundred metres around the station could. Shorter charging sections would indeed necessitate more expensive lineside equipment and power supplies, but you'd save on the cost of installing the OHLE.
N.B. in the same 2043 Route Study document suggesting 1tph to Crianlarich it also has 2tph from Inverness to Dingwall. I think that'd be high enough to justify first-level battery electrification.
I wonder how feasible a half way system would be, where a station, and say the first mile of track either side of the station has OHLE. That would allow charging to occur during station dwell time, and also provide power for the initial acceleration out of a station to get up to line speed, which takes a lot of energy. Obviously steep gradients and increases in line speed would drain batteries just as significantly, but it would provide both increases time charging while (somewhat) reducing the energy required from the battery
Another issue with short sections of OLE around stations (or elsewhere) is supply redundancy. Linking the sections together would need a high voltage cable along the entire route, which is unlikely. So either each electrified section needs dual supplies (which could at a stretch be mains or battery) or the trains need to have the battery capacity to cover two dead sections. With continuous electrification this isn't really a problem because they are designed so if one feeder goes offline the sections can be switched to be supplied from other feeders.
25kV feeders are expensive items, although the current ones are designed to feed a large number of trains. One to feed just one or two trains ought to be cheaper and possibly need a lower voltage supply (for example with rectifiers, DC link and inverters so the load is balanced across the supply phases).
The challenges involved in battery operation on the WHL are probably best thought of as orders-of-magnitude. It's quite easy for something to be twice or half, but somewhat harder for something to be 10x more or 1/10th. The relatively small amount of time to charge you'd gain by adding OHLE either side of a station wouldn't make that much of a dent in the size of the battery capacity and charging problem, but you'd then have much more OHLE to install.
I think each section would be independent and equipped with a local static battery. The likelihood of supply failure will be a very different calculation compared to now. While you'd lose the ability to cross-feed power, you'd also have a much more local supply of power in the first place. You'd have lots of independent batteries rather than one single grid supply, so you could still provide a charge even with individual failures of batteries.
There'd have to be a safety case for running battery power over long rural stretches. It's easy to propose that buses recharge at urban bus stops, since it's not the end of the world if it were to run out of charge between stops. Out on Rannoch Moor it'd be quite a big problem. Again, the likelihood of total failure will be a different calculation - batteries and electric motors are far more reliable than diesel engines and gearboxes - but a real risk of running out of energy wouldn't be acceptable.
In terms of visual impact I am not sure it would be too great unless they were to opt for a GW-type overkill. There is plenty of OHLE in mountainous areas of Europe such as the Alps and Pyrenees, and it is not generally obtrusive.
But you might need GW type masts to ensure the OLE stays up rather than it fall doen in a Scottish Gale. It would be quite exposed there as well and difficult to maintain / repair in case of failure.
It would be almost entirely single track, so the heaviest types of OHLE (multi-track spans) would have no reason to be there. The speed of the trains using the wire would also be pretty low compared to the GWML project.
Agreed. Don't think we need GWML style because of this. I suppose Rannoch Moor would need something akin to Chat Moss style- but I suppose will not fully be know until/if/when a geological survey is done. Anyway 7 cities will be first so point is moot.
Are there any plans ever to use Series 1 again anywhere? Are we not due to switch to the Master Series which combines Series 1 and 2?
The mast types used are academic if the foundations are the problem. One shudders to imagine how much concrete would need to be used to get masts up on Rannoch Moor...
Driving piles would be a complete non-starter too as the equipment (usually a Movax) would need sufficiently strong ground beneath the rails to drive them, I would've thought.
The ground conditions on Rannoch Moor aren’t that different to the Fens.
Easy enough to sink piles in those conditions they just have to be long / deep larger diameter so a larger vibrating piling head which then needs a bigger excavator (RRV or not) to mount it on
Triang had the solution years ago - click fit to the track
Another common way is to drive 3 mini piles at angles (rather than exactly vertical) with their tops in virtually same place, then join them together with a reinforced concrete cap, effectively get a tripod in the ground which is much less likely to move in very soft ground. The disadvantage is much slower as need to do 3 piles and a separate capping, the advantage is a small crawler machine can usually work trackside to insert the piles without disrupting the running line. A concreting train can then follow to do the pile heads.
On a single line it is usually single poles, rather than gantry type, which simplifies the mast design. Presumably on exposed sections would use closer mast spacing to avoid high wind problems.