Could a fast charger/OHLE combo work for remote lines?

[Meerkat]

I am thinking of lines that will always be uneconomic to wire properly and too long for BEMU - the sort that have been dumped in the 'maybe hydrogen' pile.
A Greenford type charger for mid-journey boosts probably isn't quick enough, and island OHLE is tricky due to weak local power supplies.
Could you have a Greenford type battery trickle-charging off the local power supply (give it its own hydro/solar/wind for extra greenpoints) to power up a length of OHLE either side of a station when the train turns up, giving the charging time needed?
Speeds will be low and most of it will be single track so the metalwork could be relatively simple.
Can anyone with a better brain for electrics and maths do a back of an envelope model for length of wiring v distance it would get you, and how frequent a service it could cope with?
A single line station would be best for simplicity (not so available on WHL), a passing place needs more wire, and more storage to handle two trains, but probably has more time stationary (so need less wire either end).
It means the train can be a standard 25kv BEMU and run normally under the wires when it gets toward the busier end, and you wouldn't need the Greenford style charging gubbins on the track and train (but would need some kind of trigger system to juice the wire when the train gets there).
I'm hoping remoteness would protect the wires from metal fairies during the overnight no trains times!

 

[snowball]

Before the Greenford trial was announced, Vivarail suggested that fast charging could work for the West Highland lines, with fast chargers at Crianlarich, Oban, Fort William and Mallaig.

A pantograph and transformer may also have been part of the plan, for recharging on the move while at or near Glasgow, but the brief report I saw didn't mention that.

 

[Meerkat]

Before the Greenford trial was announced, Vivarail suggested that fast charging could work for the West Highland lines, with fast chargers at Crianlarich, Oban, Fort William and Mallaig.

A pantograph and transformer may also have been part of the plan, for recharging on the move while at or near Glasgow, but the brief report I saw didn't mention that.

Interesting. From the stuff about Greenford I didn't get the impression that just Crianlarich would be enough en route, and do they stop there for long enough?

 

[Bald Rick]

It’s a straight trade off between size of battery and length of OLE charging section. With a big enough battery, you don’t need any OLE!

However the principle of ‘trickle’* charging a lineside battery to then charge a train has been doing the rounds for over a decade. It was looked at for Uckfield, but didn’t get traction (pun entirely intended).

*trickle charging will still be in the order of 100-200kw, such that you could charge a train at 1MW or more.

With, say, a 1MW charging rate, you would want 12 minutes on the wire to charge 200kWh. Assuming three station stops, and a linespeed of 60mph, that would be about 4-5 miles. Also assuming a 4 car BEMU, on a slow speed route with frequent stops, 200kWh will buy you about half an hour of off wire operation.

 

[Meerkat]

It’s a straight trade off between size of battery and length of OLE charging section. With a big enough battery, you don’t need any OLE!

However the principle of ‘trickle’* charging a lineside battery to then charge a train has been doing the rounds for over a decade. It was looked at for Uckfield, but didn’t get traction (pun entirely intended).

*trickle charging will still be in the order of 100-200kw, such that you could charge a train at 1MW or more.

With, say, a 1MW charging rate, you would want 12 minutes on the wire to charge 200kWh. Assuming three station stops, and a linespeed of 60mph, that would be about 4-5 miles. Also assuming a 4 car BEMU, on a slow speed route with frequent stops, 200kWh will buy you about half an hour of off wire operation.

Interesting thanks.
The use I was thinking of was WHL, Far North, Kyle
Any idea what the vague cost comparison (and maybe timescale might be relevant) for a trickle charged battery set up vs a grid connection - there are big power lines across the wilds of Scotland after all.
Is a 100-200kw connection too much for rural areas?

 

[Nottingham59]

I think the answer is dual-voltage BEMUs able to use both normal OHLE and 3000V DC overhead.

The thing about Battery traction is that you can in principle charge them up taking equal current from each phase of a three-phase supply. (The emerging MCAS standard does this at Megawatt levels of power for EV trucks. But that would involve plugging in units, which is deemed acceptable for buses, but not apparently for trains.)

Using traditional 25kV AC overhead uses just a single phase, which can cause severe phase imbalances in the grid supply. This is why most rail electrification feeder stations are fed by 400kV or 250kV circuits which are chunky enough to absorb the unbalanced loading.

Away from the big circuits, you can use static frequency converters which take a balanced 3-phase supply, convert it to DC and then convert that back to a single phase AC to feed the OHLE. But if the only electric trains on the line are battery powered, then that AC is converted back into DC a second time to recharge the batteries.

So it appears to me that the simplest way to recharge BEMUs at a remote location is to use DC overhead. And the highest standard DC voltage for that sort of thing is, I think, 3000V. I assume that this is why the Belgians are keeping their 3kV DC lines and the French their 1500V DC, rather than converting.

The use I was thinking of was WHL, Far North, Kyle

If you look at www.openinframap.org you can see that these lines actually tend to follow the same corridors as the main power lines to places like Cruachan pumped storage, Grudie bridge power station, and the Dounreay ex-nuclear power plant. Even Kyle has two 33kV circuits feeding the town; Oban has three. So electrical supply is probably not as big an issue as you might expect.

All it needs is a big enough battery to get you to the next site. 100 mile guaranteed range should do it easily. (Though if I were specifying the trains, I'd include a 1500cc diesel engine and tank as an emergency-only backup to be used if the trains ever got stranded in a snowdrift!)

 

[Bald Rick]

Interesting thanks.
The use I was thinking of was WHL, Far North, Kyle
Any idea what the vague cost comparison (and maybe timescale might be relevant) for a trickle charged battery set up vs a grid connection - there are big power lines across the wilds of Scotland after all.
Is a 100-200kw connection too much for rural areas?

200kw is fine.

No idea of the cost comparison. But I think on single lines of that nature the most a battery train would charge is 2MW, and that’s well without the capability of most connections to the local electricity network.

Phase imbalances off the grid only become an issue when you’re after >20MW etc. Not a problem on single line charging sections where there can only be one or at most two trains in any section.

 

[Trainbike46]

I think the answer is dual-voltage BEMUs able to use both normal OHLE and 3000V DC overhead.

The thing about Battery traction is that you can in principle charge them up taking equal current from each phase of a three-phase supply. (The emerging MCAS standard does this at Megawatt levels of power for EV trucks. But that would involve plugging in units, which is deemed acceptable for buses, but not apparently for trains.)

Using traditional 25kV AC overhead uses just a single phase, which can cause severe phase imbalances in the grid supply. This is why most rail electrification feeder stations are fed by 400kV or 250kV circuits which are chunky enough to absorb the unbalanced loading.

Away from the big circuits, you can use static frequency converters which take a balanced 3-phase supply, convert it to DC and then convert that back to a single phase AC to feed the OHLE. But if the only electric trains on the line are battery powered, then that AC is converted back into DC a second time to recharge the batteries.

So it appears to me that the simplest way to recharge BEMUs at a remote location is to use DC overhead. And the highest standard DC voltage for that sort of thing is, I think, 3000V. I assume that this is why the Belgians are keeping their 3kV DC lines and the French their 1500V DC, rather than converting.


If you look at www.openinframap.org you can see that these lines actually tend to follow the same corridors as the main power lines to places like Cruachan pumped storage, Grudie bridge power station, and the Dounreay ex-nuclear power plant. Even Kyle has two 33kV circuits feeding the town; Oban has three. So electrical supply is probably not as big an issue as you might expect.

All it needs is a big enough battery to get you to the next site. 100 mile guaranteed range should do it easily. (Though if I were specifying the trains, I'd include a 1500cc diesel engine and tank as an emergency-only backup to be used if the trains ever got stranded in a snowdrift!)

I thought there was a suggestion of 9kV DC as a theoretical upgrade in France.

Personally, I'd leave out the diesel engine, it just adds complexity you don't want/need

 

[zwk500]

So it appears to me that the simplest way to recharge BEMUs at a remote location is to use DC overhead. And the highest standard DC voltage for that sort of thing is, I think, 3000V. I assume that this is why the Belgians are keeping their 3kV DC lines and the French their 1500V DC, rather than converting.

The French are looking at options, IIRC. The Dutch are certainly planning for forward compatibility with a 3KV network.

I thought there was a suggestion of 9kV DC as a theoretical upgrade in France.

There were, although mainly for their long-distance lines as a compromise instead of leaping to 25KV. You can upgrade from 1.5KV to 9KV DC relatively easily, changing from DC to AC is much more complicated (although I think the Czechs are doing some of it).

 

[Nottingham59]

The other thing about using OHLE to recharge only battery trains is that low bridges etc. are no longer a problem. Just use an insulated contact rod to push the pantograph down to clear the bridge and start the contact conductor again on the other side. By definition, a battery train can handle dead sections.

And you can locate the recharging hardware at whatever locations on the track are easiest to access and cheapest to build. Signal sighting issues? Wire up a different bit of track!

 

[mike57]

I dont see why you would go to the trouble and cost for the really remote lines, take the Far North line, 170 miles and about 8 trains per day each way with less than that doing the whole route. I understand the need to drive down emissions, but to be honest on a line such as the Far North diesel powered internal combustion has to be the best and and most efficent option. Although BEMUs/OLE combos may be zero emmision at point of use they still contribute emissions due to the need for considerably more energy intensive infrastructure requirements, e.g. steel, copper, lithium batteries etc.

Hydrogen may be a way forward but as has been pointed out before power in v power out is very poor.

Maintenance of a diesel engine can take place in central depot, electrical infrastructure spread out along the route is going to need regular attention, so its going to need visits by people in vans.

Rural lines which are busier and or less remote than the real outliers would benefit from electrification, but you have to get the power from the grid into the train, and thats is the problem. 25kV AC OH requires a heavy duty grid connection due to the unbalanced load. You can use static frequency converters, but 25kV OH wiring requires a lot of infrastructure even if you miss out the tricky bits, bridges and tunnels.

Could you develop a side/bottom contact protected 3rd rail solution running at say 1500v DC. By going DC grid connections are easier as load is balanced, yes lower voltage results in higher losses, but I assume we are talking about 4/6 car units at maybe 1 tph each way, so current draw would not as high as on a busy main line. This sort of route would probably be 70mph max, maybe upto 90mph, well within third rail capability. An on board battery would mean that not all the route would need powering and would allow regen braking and boost power for acceleration. "Pre packaged" feed stations, containerised. If one fails you go out, load it up, and drop a new one in its place. Worst case load on a section would probably be 3MW, and by using the battery to handle peaks during acceleration could probably be driven down even lower if need be. Installation would be easier and quicker, with no issues with bridges or tunnels. Stretch the distance between feed points, and accept a higher voltage drop at the remotest points, efficency would still be higher that charge/discharge of a battery.

This solution would only be for lightly used lines, its not a replacement for 25kV OH its a lower cost lower spec alternative for lines which dont warrant full wiring. Dual voltage 1.5kV DC/25kV AC stock is already in regular use on the continent, so the only development is a protected 3rd rail contact system, but the design could be like a giant meccano kit, using a standard kit of bits.

 

[Meerkat]

Rural lines which are busier and or less remote than the real outliers would benefit from electrification, but you have to get the power from the grid into the train, and thats is the problem. 25kV AC OH requires a heavy duty grid connection due to the unbalanced load. You can use static frequency converters, but 25kV OH wiring requires a lot of infrastructure even if you miss out the tricky bits, bridges and tunnels.

The trickle charger is intended to reduce the problems of grid deficiency. Someone has suggested that the recharging lengths of OHLE use DC with a dual voltage BEMU.

 

[mike57]

The trickle charger is intended to reduce the problems of grid deficiency. Someone has suggested that the recharging lengths of OHLE use DC with a dual voltage BEMU.

From a grid connection point of view DC is easier than AC, but remember that every time you charge and then withdraw the charge from a battery there is a loss of input kWh v output kWh. I think with current lithium batteries the loss is of the order of 20%.

Given that the onboard battery is also DC doing away with the AC part makes sense away from main lines. converting from DC to AC and back to DC just introduces more conversion losses. What is probably needed is a new DC standard voltage, and 1500v DC seems to make sense, the mechanics of getting that to the train are probably less important and could vary depending on where. You can go to higher DC voltages but as you increase the voltage you need more clearance. Assuming we are talking rural routes with about 1tph 1500v DC will deliver more than enough power. Anything busier get 25kV AC.

How about DC EMUs with no battery beyond a very small one to assist with gapping, and go for a protected 3rd rail with batteries to boost supply between feed points instead of lugging the batteries around, on a 1 tph route batteries charging slowly from the DC to boost it back when the train passes would mean your grid connection points could be much more spaced out. Moving the bulk of the batteries to the fixed installation also means there is more room and no weight issue.

 

[Meerkat]

From a grid connection point of view DC is easier than AC, but remember that every time you charge and then withdraw the charge from a battery there is a loss of input kWh v output kWh. I think with current lithium batteries the loss is of the order of 20%.

Given that the onboard battery is also DC doing away with the AC part makes sense away from main lines. converting from DC to AC and back to DC just introduces more conversion losses. What is probably needed is a new DC standard voltage, and 1500v DC seems to make sense, the mechanics of getting that to the train are probably less important and could vary depending on where. You can go to higher DC voltages but as you increase the voltage you need more clearance. Assuming we are talking rural routes with about 1tph 1500v DC will deliver more than enough power. Anything busier get 25kV AC.

How about DC EMUs with no battery beyond a very small one to assist with gapping, and go for a protected 3rd rail with batteries to boost supply between feed points instead of lugging the batteries around, on a 1 tph route batteries charging slowly from the DC to boost it back when the train passes would mean your grid connection points could be much more spaced out. Moving the bulk of the batteries to the fixed installation also means there is more room and no weight issue.

Would 1.5kV DC deliver enough power to charge batteries quickly?
I don't think the 3rd rail idea will delight the safety people, and seems rather complicated.

 

[mike57]

Would 1.5kV DC deliver enough power to charge batteries quickly?
I don't think the 3rd rail idea will delight the safety people, and seems rather complicated.

I have seen fully protected 3rd rail systems abroad, I am not thinking an open steel rail. You might even have a combined DC system, 3rd rail in tunnels and OLE in open country, with automated switching.

Assuming we are talking a rural route with max 6 car EMUs at about 1tph with battery boosters between feed points then I think 1500v would be OK, its a balance, higher voltage = more power, but a cost increase. Its probably about finding the most economical combination for lightly used rural routes. And 1500v DC is used widely so plenty of equipment out there.

 

[Meerkat]

Mixing 3rd rail and OHLE sounds unnecessarily complicated. If the trains will have pantographs for use at the busy end of the route anyway then use them for DC on the booster sections. And protected 3rd rail out in the sticks sounds harder to get safety approved than OHLE.

 

[Bald Rick]

I dont see why you would go to the trouble and cost for the really remote lines, take the Far North line, 170 miles and about 8 trains per day each way with less than that doing the whole route.

Maintenance of a diesel engine can take place in central depot, electrical infrastructure spread out along the route is going to need regular attention, so its going to need visits by people in vans.

but then you have to get the diesel engines to a central point, and when there’s not many of them, it becomes quite inefficient. Maintaining OLE is, by comparison, a once very few months inspection job, much of which can now be done by suitably equipped trains or drones.

25kV AC OH requires a heavy duty grid connection due to the unbalanced load.

not for the sort of application talked about here, ie charging one battery train at say 1-2MW.

I think with current lithium batteries the loss is of the order of 20%.

it’s less than 2%.