Possible electrification schemes in the pipeline?

[BerkshireRails]

So it's essentially a 25Kv (only) system, with a fairly long battery extension? (i.e. no DC) That should improve the case, for putting wires all the way between Brent Cross and Acton Wells.

I suspect a static battery fast charging solution (like GWR's 230) would be pushing it, on a higher frequency LO service.

And a DC upgrade (while perhaps desirable for other services) doesn't solve the third rail gap.

If DC Upgrade takes place they will install third rail between Kew Bridge and South Acton. Personally I think they should wire to Brentford if the DC Upgrade takes place so that then there is no need to install third rail in the Kew Bridge area and it would be an extension of the AC & DC system already in use at Acton Central. North London Line services in the Down Direction would pan Down at Acton Central and if they fail to switch they can run on the wires to South Acton and be turned there and Up North London Line services would pan up at South Acton and if they fail to switch they would reverse at Acton Central and stored in a platform at Richmond.

Map from Network Rail which publicly accessible.

== Doublepost prevention - post automatically merged: 8 Jul 2025 ==

There was a brief mention in that PWI video about how SWR wish to run more Hounslow Loop services but power supply is the most limiting factor. Wimbledon Grid is quite stretched powering everything from Clapham Jnc to Surbiton, Virginia Water and Windsor (and a few other bits) - maybe a new Grid supply in Twickenham (where there is a 132kV substation) would help? Well out of the scope of the LO project though it may have to happen eventually.

They mentioned if they went for Third rail they would have to pay a lot of money to upgrade the third rail.

 

[Bald Rick]

And the power supply issues on the Hounslow Loop as well as rest of Windsor Lines due to Wimbledon grid being at capacity. This means no more electric services than are currently being operated can be operated.

It doesn’t mean that.

 

[GraphitProjekt]

So it's essentially a 25Kv (only) system, with a fairly long battery extension? (i.e. no DC)

That then surely improves the case, for putting wires all the way between Brent Cross and Acton Wells?

I suspect a static battery fast charging solution (like GWR's 230) would be pushing it, on a higher frequency LO service.

I'd honestly suspect that dual electrifying half the of the Hounslow loop is a lot more disruptive and expensive compared to reinforcing the 33kV AC feeder network in the area and running straight dual-voltage EMUs. That latter option also adds resilience and flexibility to part of the Wessex Suburban lines in general

 

[Sonik]

I'd honestly suspect that dual electrifying half the of the Hounslow loop is a lot more disruptive and expensive compared to reinforcing the 33kV AC feeder network in the area and running straight dual-voltage EMUs. That latter option also adds resilience and flexibility to part of the Wessex Suburban lines in general

As I understood it, the AC would end at Acton as it does now, and the WLL trains would use battery from there to Hounslow

Besides lack of DC capacity, the main impediment to a simple dual voltage solution is the gap at Kew and ORR policy against new third rail. So a DC supply upgrade has other benefits, but it's not much help for WLL.

 

[BerkshireRails]

As I understood it, the AC would still end at Acton, and the new trains would use battery from there to Hounslow

Besides lack of DC capacity, the main impediment to a simple dual voltage solution is the gap at Kew and ORR policy against new third rail. So a DC supply upgrade has other benefits, but it's not much help for WLL.

The plan is if they do the DC Upgrade is to do a bit of infill third rail in the Kew area.

 

[MarkyT]

As I understood it, the AC would end at Acton as it does now, and the WLL trains would use battery from there to Hounslow

Besides lack of DC capacity, the main impediment to a simple dual voltage solution is the gap at Kew and ORR policy against new third rail. So a DC supply upgrade has other benefits, but it's not much help for WLL.

I suspect they could make a good case for 3rd rail to the ORR as a short connecting link, if they really wanted to. There's the level crossing risk, but there's already another one electrified 70 metres away along Bollo Lane and battery trains could potentially bridge longer gaps provided for safety. Alternatively, perhaps move the OHLE/3rd rail boundary to South Acton, then continue wires along the connecting line. where the WLO trains could switch over on the move. That could have wider signalling implications however, extending AC closer to more DC railway which uses AC track circuits and point detection widely. Using battery for the DC section and unequipped connection is a sensible compromise. While not used routinely, it might be sensible for the trains to have DC pick up capability, so they could draw DC in an emergency out on the Hounslow line. It should be noted that direct 3rd rail supply can be less efficient overall than the same electricity stored and delivered by a battery because of resistive losses from high current in the supply and return conductors. high voltage AC OHLE is much better in this regard.

 

[BerkshireRails]

I suspect they could make a good case for 3rd rail to the ORR as a short connecting link, if they really wanted to. There's the level crossing risk, but there's already another one electrified 70 metres away along Bollo Lane and battery trains could potentially bridge longer gaps provided for safety. Alternatively, perhaps move the OHLE/3rd rail boundary to South Acton, then continue wires along the connecting line. where the WLO trains could switch over on the move. That could have wider signalling implications however, extending AC closer to more DC railway which uses AC track circuits and point detection widely. Using battery for the DC section and unequipped connection is a sensible compromise. While not used routinely, it might be sensible for the trains to have DC pick up capability, so they could draw DC in an emergency out on the Hounslow line. It should be noted that direct 3rd rail supply can be less efficient overall than the same electricity stored and delivered by a battery because of resistive losses from high current in the supply and return conductors. high voltage AC OHLE is much better in this regard.

TfL would like to close one of the crossings on Bollo Lane. Hounslow Loop should be all Axle Counters as it was resignalled a few years ago to Basingstoke from Feltham. In emergencies the units will be allowed to escape via Whitton and Clapham Junction to reach the OLE at Shepherd's Bush.

 

[Sonik]

I suspect they could make a good case for 3rd rail to the ORR as a short connecting link, if they really wanted to.

I think this possibility was mentioned, but there are the external issues you mention (DC supply capacity, immunisation) to resolve. With a following wind and some luck all that could get done, making a standard AC/DC solution viable.

Personally I think that would be better, because using bespoke battery trains on a high frequency urban metro is very limiting operationally for LO in terms of units, training etc.

But as ever it will likely come down to costs and funding.

 

[AndrewE]

I think this possibility was mentioned, but there are the external issues you mention (DC supply capacity, immunisation) to resolve. With a following wind and some luck all that could get done, making a standard AC/DC solution viable.

Personally I think that would be better, because using bespoke battery trains on a high frequency urban metro is very limiting operationally for LO in terms of units, training etc.

But as ever it will likely come down to costs and funding.

Agreed. What a shame we can't do "vision" or strategic thinking and investment. What particularly angers me is that while politicians seem to be able to ignore the effects of climate change (presumably because the worst effects are being felt in places like Pacific islands or Texas) the health effects of not electrifying and reducing traffic in our cities are certainly causing problems and costs here and now.

 

[GraphitProjekt]

reinforcing the supply on the hounslow loop would surely have wider benefits for SWR as well.

 

[Bald Rick]

Personally I think that would be better, because using bespoke battery trains on a high frequency urban metro is very limiting operationally for LO in terms of units, training etc.

Like, say, having a fleet of bespoke DC only trains that can’t be used elsewhere on the LO network?

 

[BerkshireRails]

Like, say, having a fleet of bespoke DC only trains that can’t be used elsewhere on the LO network?

It would be a fleet of 11 units for West London Orbital which will be stabled in new sidings at Willesden South Western Sidings.

 

[GraphitProjekt]

Like, say, having a fleet of bespoke DC only trains that can’t be used elsewhere on the LO network?

why would they be DC only? They still have to go up from Acton Central to Cricklewood on AC? They would be dual voltage like all LO trains currently are.

 

[BerkshireRails]

why would they be DC only? They still have to go up from Acton Central to Cricklewood on AC? They would be dual voltage like all LO trains currently are.

Currently there is two options which are Dual voltage or bi-mode in the form of AC + Batteries. TfL seems to be leaning towards Batteries due to the Wimbledon supply and the cost of fixing it. With both dual voltage and bi-mode they would use the wires between Acton Central and Brent Cross West, for the dual voltage unit the would make use the juice rail between Hounslow and Acton Central and for the bi-mode units they would use battery power with enough range to get back to the wires via Whitton and Clapham Junction and on to Shepherds Bush.

 

[Bald Rick]

why would they be DC only? They still have to go up from Acton Central to Cricklewood on AC? They would be dual voltage like all LO trains currently are.

My point is that LO already have a fleet of DC only trains whcih (technically) is ’limiting operationally’, and it doesn’t bother them one bit.

There will be no issues with a smallish fleet of BEMUs.

 

[GraphitProjekt]

Currently there is two options which are Dual voltage or bi-mode in the form of AC + Batteries. TfL seems to be leaning towards Batteries due to the Wimbledon supply and the cost of fixing it. With both dual voltage and bi-mode they would use the wires between Acton Central and Brent Cross West, for the dual voltage unit the would make use the juice rail between Hounslow and Acton Central and for the bi-mode units they would use battery power with enough range to get back to the wires via Whitton and Clapham Junction and on to Shepherds Bush.

well yeah, it's seems pretty obvious they're going to go with a battery option because it costs less in infrastructure investment while new trains were always going to be needed and also expensive.

== Doublepost prevention - post automatically merged: 10 Jul 2025 ==

And who wants to fight the regulator for a few hundred metres of new conductor rail

 

[MarkyT]

well yeah, it's seems pretty obvious they're going to go with a battery option because it costs less in infrastructure investment while new trains were always going to be needed and also expensive.

== Doublepost prevention - post automatically merged: 10 Jul 2025 ==

There's likely little or no change to track and signalling required in the Acton-Kew area under the battery option. Quicker, cheaper, less programme risk.
Edit: Perhaps an additional crossover at Lionel Road to allow short turn backs to Acton in event of Hounslow Loop problems.

And who wants to fight the regulator for a few hundred metres of new conductor rail

It wouldn't be much of a fight, I suspect, as a short connecting line.

 

[BerkshireRails]

There's likely little or no change to track and signalling required in the Acton-Kew area under the battery option. Quicker, cheaper, less programme risk.
Edit: Perhaps an additional crossover at Lionel Road to allow short turn backs to Acton in event of Hounslow Loop problems.

The plan was always with dual voltage or bi-mode to be able to turn back at Lionel road.

 

[Harlequinuk]

A question.

What's the powerdraw difference (if any) between a 92 and a 700 on third rail?

 

[BerkshireRails]

A question.

What's the powerdraw difference (if any) between a 92 and a 700 on third rail?

It isn't just about the power draw but also the Third Rail index which allows an index of up to 16 to be operated depending on the line. A class 700 Reduce Length Unit draws 4,400hp of traction power, a class 92 on third rail draws 5,360hp on third rail and a class 700 full length unit draws 6,700hp on third rail. The third rail index is based on an English Electric 507 traction motor.

 

[Harlequinuk]

So in thats the case, why cant 92`s be used on BML third rail?

 

[Nicholas Lewis]

It isn't just about the power draw but also the Third Rail index which allows an index of up to 16 to be operated depending on the line. A class 700 Reduce Length Unit draws 4,400hp of traction power, a class 92 on third rail draws 5,360hp on third rail and a class 700 full length unit draws 6,700hp on third rail. The third rail index is based on an English Electric 507 traction motor.

Your quoting the installed power of the 700's. They are limited to 6kA whether its an 8 or 12 on high current rated lines otherwise its 4.5kA . A class 92 can draw 6.8kA but was only cleared for this on the West London line to Dollands Moor via Sevenoaks or Maidstone East. The route via Redhill across to Tonbridge had the power upgrades completed for the class 92's but the signalling immunisation for 3 phase drives was never completed in 1994 (it was subsequently undertaken) as it was evident by then that freight traffic was going to be much slower to materialise.

 

[BerkshireRails]

Your quoting the installed power of the 700's. They are limited to 6kA whether its an 8 or 12 on high current rated lines otherwise its 4.5kA . A class 92 can draw 6.8kA but was only cleared for this on the West London line to Dollands Moor via Sevenoaks or Maidstone East. The route via Redhill across to Tonbridge had the power upgrades completed for the class 92's but the signalling immunisation for 3 phase drives was never completed in 1994 (it was subsequently undertaken) as it was evident by then that freight traffic was going to be much slower to materialise.

6.8KA = 6934hp
6KA = 6118hp
4.5KA = 4588hp
Only Full length units get limited on the third rail, reduced length units can draw full power.

 

[ac6000cw]

Only Full length units get limited on the third rail, reduced length units can draw full power.

That's what Nicholas Lewis said previously, in a different way ("They are limited to 6kA whether its an 8 or 12 on high current rated lines otherwise its 4.5kA")

6.8KA = 6934hp
6KA = 6118hp
4.5KA = 4588hp

Current and power are different units so fundamentally they can't be 'equal' (=) to each other.

It would probably be better to say one 'implies' the other e.g.

6.8KA => 6934hp
6KA => 6118hp
4.5KA => 4588hp

 

[BerkshireRails]

Current and power are different units so fundamentally they can't be 'equal' (=) to each other.

Third rail is set a nominal voltage of 750v and you can do P=VI (Power = Volts x Amps). The Substation supply 6.8KA at 750v so it is possible for the Amps to equal a certain hp.

That's what Nicholas Lewis said previously, in a different way ("They are limited to 6kA whether its an 8 or 12 on high current rated lines otherwise its 4.5kA")

A 8 car will never go above 4.5kA so only the 12 car will be limited by the third rail. 8 car 4400hp≤4.5kA 4588hp.

 

[Snow1964]

So in thats the case, why cant 92`s be used on BML third rail?

When they were being planned, in early 1990s weren't expected to use the line south of Redhill, just via Tonbridge on one of Channel Tunnel routes.

There is also history, the Purley-Brighton line was electrified in 1932, and was the first to have unmanned substations. By the time the substations were upgraded and voltage increased to 750v in 1980s and 1990s the line was served by much lower power trains (think CIGs and VEPs and class 73 + motor van on Gatwick services).

At the time no one envisaged regular trains of 6000-7000HP. And the substations are not yet due for next upgrade.

 

[Harlequinuk]

So if the max amps (as above) is 6000 on third rail and of course its 750v DC, therefore the max wattage is 4.5 MW , or 6034 horsepower. (Please correct my ancient maths if im wrong!)

Therefore, according to British Rail Main Line Electric Locomotives (2nd ed.) p133 the 92 draws 4MW or 5360 horsepower on third rail (and of course more under the wires). Or am i missing something?

 

[HSTEd]

So if the max amps (as above) is 6000 on third rail and of course its 750v DC, therefore the max wattage is 4.5 MW , or 6034 horsepower. (Please correct my ancient maths if im wrong!)

Therefore, according to British Rail Main Line Electric Locomotives (2nd ed.) p133 the 92 draws 4MW or 5360 horsepower on third rail (and of course more under the wires). Or am i missing something?

Whilst the nominal voltage is 750Vdc, a fully compliant supply can have a permanent voltage of up to 900V.

 

[Nicholas Lewis]

When they were being planned, in early 1990s weren't expected to use the line south of Redhill, just via Tonbridge on one of Channel Tunnel routes.

There is also history, the Purley-Brighton line was electrified in 1932, and was the first to have unmanned substations. By the time the substations were upgraded and voltage increased to 750v in 1980s and 1990s the line was served by much lower power trains (think CIGs and VEPs and class 73 + motor van on Gatwick services).

At the time no one envisaged regular trains of 6000-7000HP. And the substations are not yet due for next upgrade.

The 92's were planned to go via Redhill that was the justification for electrifying Redhill to Tonbridge. As i said above it was immunisation of the signalling that prevented that happening initially but BR was then entering the privatisation era an railtrack wouldn't spend money on anything without a return and there was insufficient demand.

 

[ac6000cw]

Third rail is set a nominal voltage of 750v and you can do P=VI (Power = Volts x Amps). The Substation supply 6.8KA at 750v so it is possible for the Amps to equal a certain hp.

The equation 'P=VI (Power = Volts x Amps)' explains exactly why electrical current does not equal power... (in any scientific/engineering sense).