would 9Kv DC OHLE make sence for the southen region?

[popeter45]

so with france looking into higher voltage DC OHLE to replace its 1.5Kv system wonder if it would make sence for converting parts of the southen region to OHLE?

being DC would make it less complex to dual electrify existing 750v third rail systems so rollout could cheaper and let existing stock still be used while introduing newer stock over time

even while DC, 9Kv would be safer as overhead and lower current, would also reduce running cost with less sub-stations needed and the potental higher power limit would allow electric locos for freight without needed to plan special paths and rules like 92's need if running on third rail

also would be a useful stepping stone to 25Kv AC over time once third rails are removed

 

[Trainbike46]

Why do you want to replace the third rail at all?

 

[Energy]

Still need to install OHLE. What's the advantage over 25kv?

 

[popeter45]

Still need to install OHLE. What's the advantage over 25kv?

no need to redo all the earthing compared to third rail

Why do you want to replace the third rail at all?

as stated, safer, higher power, cheaper to maintain etc

 

[ac6000cw]

also would be a useful stepping stone to 25Kv AC over time once third rails are removed

If you've gone to all the expense of installing new 9kV DC OHLE and feeder station equipment plus new/converted rolling stock to use it, you're not going to replace it with 25kV AC equipment later...

 

[Railcar]

OHLE makes a fearful clutter in the landscape. Third rail leaves the view looking clear

 

[randyrippley]

OHLE makes a fearful clutter in the landscape. Third rail leaves the view looking clear

But third rail kills foxes and badgers

 

[DerekC]

But third rail kills foxes and badgers

And people, sometimes. I must say that if you are going to convert to OLE I can't see why 9kV DC would save much money compared with 25KV AC. You would need more substations, for a start.

 

[Snow1964]

France might be considering it, but as any new scheme there tends to be 25kv, and they have lots of dual voltage locos and EMUs.
But nothing is equipped for 9kv

As for changing the Southern Region, can't put high voltage on third rail, so basically it would be a new system to convert. But if going to install overhead, why not just do 25kv ac

 

[75A]

Never going to happen, it would cost far, far too much to sort out the loading gauges alone.

 

[zwk500]

And people, sometimes. I must say that if you are going to convert to OLE I can't see why 9kV DC would save much money compared with 25KV AC. You would need more substations, for a start.

The advantage would be that the railway is already suitably equipped for DC currents so it'd be a matter of upping the ratings rather than the much more costly conversion from DC to AC.

Having said that, it would still be one hell of an upgrade and leave you with an incompatible system so the benefits of avoiding the DC to AC transition are lost. Notably Belgium has recently transitioned some of it's OLE DC lines to 25kv AC, so the advantages of building such a system from new appear to be pretty marginal. The French are looking at 9kv because it means they can reduce the number of substations in their 1.5kv DC system by potentially up to a factor of 6. It also allows for a step up to 3kv as a mid-point which allows slightly easier interworking with neighbouring countries.

For the third rail area it really makes very limited sense to make such a substantial change to another compromise system.

 

[Nym]

Then the small matter of the TSIs and NTSNs requiring all new OLE to be 25kV AC…?

 

[zwk500]

Then the small matter of the TSIs and NTSNs requiring all new OLE to be 25kV AC…?

Tbf the NTSN would be relatively simple to amend or derogate if there was a compelling technical case for 9kv dc. Would.hardly be the first time the TSIs had been pointless.

 

[Bald Rick]

You’d still need to change all the bonding to deal with a voltage 12 x larger, and presumably with higher power flows too.

I reckon the cost saving would be in low single digit %, and that‘s before the costs of gaining type approval for a whole new power system, and then going to market for a while new family of dual voltage trains.

 

[Grecian 1998]

As has been said above, the loading gauge might cause a few issues. There are plenty of long tunnels S and SE of London e.g. the Brighton Main Line has 6 tunnels, 3 of them over a mile long (Clayton, Quarry and Merstham). Most of those tunnels aren't far off 200 years old, and have historically had drainage issues. Whilst the line did originally have overhead electrification, I suspect clearance specifications a century later might have changed. Plenty of long tunnels through the North Downs as well.

There's also the political angle. Spending a fortune converting the SE's network might be a tad controversial when numerous urban areas still have nothing.

Barring any plans for the SWML due to its significance as a freight route north of Southampton, I can't see anything ever changing for as long as the railways have a part to play in transport in the SE. Whilst no-one would choose 3rd rail now, changing the system seems far too complicated and expensive to justify the benefits.

 

[zwk500]

As has been said above, the loading gauge might cause a few issues. There are plenty of long tunnels S and SE of London e.g. the Brighton Main Line has 6 tunnels, 3 of them over a mile long (Clayton, Quarry and Merstham). Most of those tunnels aren't far off 200 years old, and have historically had drainage issues. Whilst the line did originally have overhead electrification, I suspect clearance specifications a century later might have changed. Plenty of long tunnels through the North Downs as well.

I'm fairly sure the tunnels on the Brighton Line never saw the original Overhead electrification, the LBSCR system was not very extensive (part of the reason third rail won is that it had more track by the time the decision was made). Some of the shorter tunnels in South London may have had it, would have to double check. As you say, it was of a different spec and standards have changed now.

 

[RobShipway]

Would the pantograph's of the class 387/700 units be able top operate on 9KV DC OHLE? I point is that any existing rolling stock is setup to work with 3rd rail and AC Overhead, so with the class 700 units you would need to be building an extra pantograph on them to work with 9KV DC OHLE?

 

[WAO]

I would have thought that a 25kV ac conversion would now be the simplest for the SR, if OLE has to be erected. (As there's no rush, the third rail can't be that unsafe).

The SR dc system is actually a 33kV system, with a heavy duty track-side feeder cable to the transformer/rectifier substations dotted alongside the route. These have to be quite frequent for 750V dc. The 33kV could be dropped somewhat via the Grid transformer tappings and then fed at normal intervals into the new contact wire, eliminating the substations.

The fact that this is not a live issue for investment is to me proof that third rail safety is adequate and that the ban on its modest expansion is nonsense.

WAO

 

[renegademaster]

25kv ac third rail would stop the graffiti problem that seems to plague Southernland at the moment

 

[edwin_m]

I would have thought that a 25kV ac conversion would now be the simplest for the SR, if OLE has to be erected. (As there's no rush, the third rail can't be that unsafe).

The SR dc system is actually a 33kV system, with a heavy duty track-side feeder cable to the transformer/rectifier substations dotted alongside the route. These have to be quite frequent for 750V dc. The 33kV could be dropped somewhat via the Grid transformer tappings and then fed at normal intervals into the new contact wire, eliminating the substations.

Could probably get rid of most or all of the 33kV network, and just feed into a 25kV system wherever the 33kV gets its Grid feeds. That would be similar to how a 25kV network operates elsewhere. Static frequency converters could be used if there were phase imbalance issues.

Would the pantograph's of the class 387/700 units be able top operate on 9KV DC OHLE? I point is that any existing rolling stock is setup to work with 3rd rail and AC Overhead, so with the class 700 units you would need to be building an extra pantograph on them to work with 9KV DC OHLE?

The pantograph would probably be OK, but it would need replacement of much or all of the traction electronics to be able to work on 9kV dc. I assume the French proposal makes the locomotives fully solid state with no transformer (as that would need an AC supply), essentially a giant laptop power supply.

But I agree it's all theoretical - replacement of third rail might save 20% on energy costs but unlikely to happen when there are many other areas still running on diesel and not enough money to do either.

 

[SeanG]

As well as the cost of putting up the wires, one needs to factor in installing pantographs to all of the 3rd rail units. Of course the modern stuff has space for pantographs but what about the older stock such as 465s which don't...

 

[N1]

The 33kV could be dropped somewhat via the Grid transformer tappings and then fed at normal intervals into the new contact wire, eliminating the substations.

33kV is the line to line voltage. Line to Earth at this voltage is 33k / √3 = 19.05kV. So the voltage would have to be increased at Grid supply point. As the 25kV is single phase different cables have to be used anyway, and new supply points are almost certainly going to need to be SFC to prevent phase imbalances

 

[DanNCL]

I think if this were to happen anywhere in the British Isles it would be in Ireland, as a conversion and possibly extension of the 1.5kV DC wires used for DART.

 

[N1]

You’d still need to change all the bonding to deal with a voltage 12 x larger, and presumably with higher power flows too

Bonding would have to be completely redone. Voltage is 12 x larger, and although power might increase, current is going to decrease significantly. However, the rail potential rise will be significantly higher at 9kV DC, and probably pose a risk to life without change to the bonding and earthing of rails. More bonding of rails to earth increase stray current corrosion. Lots of trade-offs

 

[ac6000cw]

I assume the French proposal makes the locomotives fully solid state with no transformer (as that would need an AC supply), essentially a giant laptop power supply.

...except that those have (high-frequency) transformers inside to provide mains isolation in that application. The usual topology is to rectify and smooth the mains input to DC, then chop it at high frequency into a (small & light) double-wound ferrite-cored transformer, and rectify the low-voltage transformer output to DC for the output. (There is also a feedback control path to regulate the output voltage).

I don't know how practical/cost-effective a high-power 9kV to 1.5kV (or possibly lower inside a loco) transformer-less DC-DC converter is i.e. efficiency/noise/cost versus using an intermediate high-frequency transformer in the DC-DC to step-down the voltage.

This is from a presentation in 2018, which shows both techniques:

 

[edwin_m]

I think if this were to happen anywhere in the British Isles it would be in Ireland, as a conversion and possibly extension of the 1.5kV DC wires used for DART.

The DART+ programme extends the 1.5kV to pretty much the entire Dublin suburban network (battery operation on a few routes) and they have a large fleet of 1.5kV units on order, so that's unlikely for the foreseeable future. I believer the intention is to electrify other routes at 25kV with dual-voltage units.

 

[AlastairFraser]

so with france looking into higher voltage DC OHLE to replace its 1.5Kv system wonder if it would make sence for converting parts of the southen region to OHLE?

being DC would make it less complex to dual electrify existing 750v third rail systems so rollout could cheaper and let existing stock still be used while introduing newer stock over time

even while DC, 9Kv would be safer as overhead and lower current, would also reduce running cost with less sub-stations needed and the potental higher power limit would allow electric locos for freight without needed to plan special paths and rules like 92's need if running on third rail

also would be a useful stepping stone to 25Kv AC over time once third rails are removed

A good chunk of the network has no room for the wires, mostly due to bridges and tunnels.
In addition, the 9kv voltage has never been used before and the UK railway seems to be frequently hopeless at implementing projects of this scale without any support from overseas operators using this system.

I believe the long term plan for third rail replacement is battery on most lines, a technology which is rapidly maturing, but 3rd rail will do for the minute.

 

[Bald Rick]

I believe the long term plan for third rail replacement is battery on most lines

I can confirm there is no long term plan for replacing third rail.

 

[edwin_m]

I believe the long term plan for third rail replacement is battery on most lines, a technology which is rapidly maturing, but 3rd rail will do for the minute.

Battery is an option for services that run a shortish distance beyond the end of electrification, but I've not heard of any intention to remove third rail and run battery instead. Do you have a source for this?

There might be a few lightly-used routes where batteries would make more sense, and they get round the safety concerns for short extensions of electric services beyond the existing third rail. But on most of the network it would add extra cost and weight and need more trains and charging infrastructure if the journey no longer includes any electrified routes to charge on.