Overhead Line Power Capacity

[Dr Hoo]

Attaching and detaching bankers will cost more time than is saved by running faster up the incline.

It is pointless to think of that time in isolation. What about the 30 minutes saved waiting for a longer gap and/or having to get looped again further on because of the train’s speed differential?

We really ought to think about automatic coupling and uncoupling. Imagine the intermodal triumphantly cresting the bank at 90mph and the banker(s) dropping into a centre holding track as at Blackwell on the Lickey.

It’s amazing to think that over 100 years ago even passenger trains could be banked up the Lickey wholly ‘on the fly’ with no coupling or brake connection involved.

 

[edwin_m]

It is pointless to think of that time in isolation. What about the 30 minutes saved waiting for a longer gap and/or having to get looped again further on because of the train’s speed differential?

We really ought to think about automatic coupling and uncoupling. Imagine the intermodal triumphantly cresting the bank at 90mph and the banker(s) dropping into a centre holding track as at Blackwell on the Lickey.

It’s amazing to think that over 100 years ago even passenger trains could be banked up the Lickey wholly ‘on the fly’ with no coupling or brake connection involved.

You've suggested the extra locomotives would just be bankers, so any time saved anywhere else on the journey isn't relevant to your point.

The banker can only safely drop off or uncouple on the move only works if it does so at braking distance (from whatever speed it is doing) before the signal controlling the divergency onto the centre track. Otherwise if the points don't fully change it's heading into a serious derailment. Coupling on the move raises even more safety concerns, probably requiring real-time feedback between the train and the banker so the latter can hit the brakes if the main train slows down for any reason.

The banking of the Lickey without coupling is only possible because it's a continuous ascent. Any variation in gradient creates a risk of the banker falling back then re-colliding with the train, which has caused serious accidents in the past even when the separation has been small.

I just think there's little point considering such ambitious things if we can't even do the basic thing of getting one electric locomotive on each train over Shap!

 

[Bald Rick]

Given that a Class 99 has power on tap equivalent to the continuous rating of 6 x Class 76s, I don’t think there is anything to worry about that suggests their trains will need banking to deliver sensational performance comoared to what we are used to.

Someone with more recent (ie better) applied maths than me can do the sums, but I imagine that a 99 with an averagely loaded intermodal will have no issues up Shap or Beattock given a clear run.

As for looping - well they simply won’t need looping anywhere near as much as they are today. Preston - Carlisle won’t be that much slower than TPE, for example.

 

[noddingdonkey]

Wasn't it said that the first time they tried to send a 91 to Skipton the "on the cheap" nature of how the Airedale/Wharfedale triangle had been electrified became clear, every 308 on the line failed

 

[Class 170101]

Well it will be interesting to see if the Class 99s will be power limited. Class 90s are when running in pairs.

 

[edwin_m]

A lot of this is about tractive effort and adhesion rather than raw power. Like diesel locomotives from the 59 onwards, the 99 will be fitted with systems to maximise the coefficient of friction, thus getting more traction from the same weight on wheels. A 90 is significantly lighter than a 99 and is older technology, so its tractive effort is lower. Even with maximum power limited, a pair of 90s can be worthwhile to improve tractive effort and therefore performance at lower speeds.

At lower speeds no train can employ full power because of adhesion limitations. Power equals tractive effort multiplied by speed - so once the locomotive is supplying full power the tractive effort drops off with increasing speed. Hence more power counts at higher speeds, particularly when accelerating or climbing hills. Electric power is constrained by current limitation but a diesel is much more so based on the rating of the engine. I'd guess the reasons to run a pair of 99s would be largely about power in diesel mode, on routes where performance away from the wires is important.

 

[Paul AC]

Well it will be interesting to see if the Class 99s will be power limited. Class 90s are when running in pairs.

99s will be limited in AC mode to the 300 Amps OLE draw per train that is permitted by UK regulations (that's a very low figure compared to most European countries, but that's a separate matter). 90s were designed when there was no requirement to have a current limit so will draw what they like - and this can be up to 500 Amps when running as a pair. Not ideal on most of the better-rated WCML but well in excess of the acceptable level on the GEML for example. Hence a limiter circuit was fairly recently added to allow them to run in pairs on the GEML. It's not perfect but it's better than the previous workaround, which was to cut out a motor in each loco of the pair.

90s (and 91s) draw more supply current for their overall power rating due to the power conversion technique they employ. Technically speaking they use phase controlled rectifier technology - pretty much all that was available in the 1980s - so draw current from the OLE at a poor power factor; this means that a proportion of the supply current can't be converted into useful power at the rail. 99s (and 92/88/93) use a front end power convertor that runs at unity power factor so all the available OLE current gets converted into useful power at the rail (neglecting auxiliary circuit losses).

 

[Dr Hoo]

As for looping - well they simply won’t need looping anywhere near as much as they are today. Preston - Carlisle won’t be that much slower than TPE, for example.

I’m pleased to hear it, Rick.

99s will be limited in AC mode to the 300 Amps OLE draw per train that is permitted by UK regulations (that's a very low figure compared to most European countries, but that's a separate matter).

Who is it who set the UK regulations? Is it a piece of BR legacy when everything was done on the cheap?

I still find it bizarre that private British freight operators are investing £££ tens of millions in state of the art European electric locomotives that can put down a step change in grunt but everyone else here seems to be wringing their hands because it might exceed something that was set in the 1980s.

 

[Richard123]

I’m pleased to hear it, Rick.


Who is it who set the UK regulations? Is it a piece of BR legacy when everything was done on the cheap?

I still find it bizarre that private British freight operators are investing £££ tens of millions in state of the art European electric locomotives that can put down a step change in grunt but everyone else here seems to be wringing their hands because it might exceed something that was set in the 1980s.

7.5MW at 25kV is a huge amount of power; more significant for performance than the current limit difference is NR's attempts to reduce OLE voltage.

Since TSIs, NR were compelled to align with Europe and design for a minimum of 19kV, but accepted lower in practice due to the long distances between available 400kV supplies, which were preferred. Since Brexit, they have been pushing to remove the TSI limit and accept down to 12.5kV, at which the available locomotive power limit is down to 3.75MW.

It's still in dispute at RSSB with NR claiming infrastructure cost savings from "burning EU red tape" and train operators more cautious.

 

[Dr Hoo]

It's still in dispute at RSSB with NR claiming infrastructure cost savings from "burning EU red tape" and train operators more cautious.

Ah, we have someone to blame - Network Rail and some people in Government still trying to ‘extract some benefits from Brexit’ (plus usual suspects at the Treasury and DfT).

Situation normal.

 

[Paul AC]

7.5MW at 25kV is a huge amount of power; more significant for performance than the current limit difference is NR's attempts to reduce OLE voltage.

Since TSIs, NR were compelled to align with Europe and design for a minimum of 19kV, but accepted lower in practice due to the long distances between available 400kV supplies, which were preferred. Since Brexit, they have been pushing to remove the TSI limit and accept down to 12.5kV, at which the available locomotive power limit is down to 3.75MW.

It's still in dispute at RSSB with NR claiming infrastructure cost savings from "burning EU red tape" and train operators more cautious.

At 12.5 kV many existing loco and unit types will object to running at all. The operators need to be more forceful than just "cautious" in rejecting this idea.

I seem to recall that NR tried (or at least considered) increasing the voltage towards 29 kV in some areas on the basis that more voltage meant less current, which up to a point it does. However this failed to take into account that a train that regenerates power back into the OLE during braking will push up the local supply voltage and then disable regen brake to prevent the volts going dangerously high - reverting to friction braking instead.

 

[Richard123]

At 12.5 kV many existing loco and unit types will object to running at all. The operators need to be more forceful than just "cautious" in rejecting this idea.

I seem to recall that NR tried (or at least considered) increasing the voltage towards 29 kV in some areas on the basis that more voltage meant less current, which up to a point it does. However this failed to take into account that a train that regenerates power back into the OLE during braking will push up the local supply voltage and then disable regen brake to prevent the volts going dangerously high - reverting to friction braking instead.

Indeed. Receptivity depends mainly on other trains taking load (very little actually goes back into the supply as regen also lifts the supply voltage due to its transformer impedance, and there is normally load anyway, but where multiple trains brake at once voltage rises and rheostatic or friction braking blends in).

Overnight however, grid voltages drift upwards and so OLE voltages rise even without regen. Areas with long distances between supplies were often tapped higher by BR to maintain acceptable performance under load, and in some cases the interaction of new train harmonics with the supply grid and transformer characteristics has pushed up voltages further. (Most railway transformers have five tap settings available to allow the OLE voltage to be adjusted according to the local grid voltage, which are generally set at commissioning and not touched again)...

Some classes of train are particularly fussy; class 92s used to shut down well below 29kV, and 319s also didn't like high voltages.

There have been operational workarounds over the years, like entering n-2 overnight if class 92s were passing areas with higher voltages, although I think some of the 92s may have been modified since to bring them into compliance.

ENA P24 is a useful document for general background on railway traction power supplies...

 

[HSTEd]

I think we would be better off building six or eight axle (Bo-Bo+Bo-Bo is popular in Japan) battery hybrid locomotives with piles of installed power than trying to reinforce the overhead wiring for huge loads for accelerating freights up inclines.

 

[zwk500]

Attaching and detaching bankers will cost more time than is saved by running faster up the incline.

Which could be mitigated by planning for attachments and detachments to be done at suitable points, not just at the foot and crest at the bank. Lickey is difficult because of the limits of OLE, but for Shap you could just do an electric loco swap at Crewe and run under OLE all the way to Coatbridge, Mossend, or Grangemouth

We really ought to think about automatic coupling and uncoupling. Imagine the intermodal triumphantly cresting the bank at 90mph and the banker(s) dropping into a centre holding track as at Blackwell on the Lickey.

Automatic uncoupling is practiced today. Automatic coupling on the fly is considered a 'crash', however controlled. Don't the 93s have cameras to enable coupling at a stand to be a 1-man job?

It’s amazing to think that over 100 years ago even passenger trains could be banked up the Lickey wholly ‘on the fly’ with no coupling or brake connection involved.

over 100 years ago we also had the Quintinshill disaster. The safety culture has changed much in the meantime, and for the better. On some banks unattached assistance is still practiced - tours out of Victoria are sometimes banked out unattached.

 

[edwin_m]

Which could be mitigated by planning for attachments and detachments to be done at suitable points, not just at the foot and crest at the bank. Lickey is difficult because of the limits of OLE, but for Shap you could just do an electric loco swap at Crewe and run under OLE all the way to Coatbridge, Mossend, or Grangemouth

If you attach and detach at places the train would stop anyway, the extra locos would run a long distance without doing anything useful. Or you attach and detach close to the areas they would make a difference, in which case you add the time for the extra stops (which would probably involve looping and being overtaken too). Considering how much a single electric gains over a diesel, I really think adding multiple electrics is overkill in nearly all cases.

 

[zwk500]

If you attach and detach at places the train would stop anyway, the extra locos would run a long distance without doing anything useful. Or you attach and detach close to the areas they would make a difference, in which case you add the time for the extra stops (which would probably involve looping and being overtaken too). Considering how much a single electric gains over a diesel, I really think adding multiple electrics is overkill in nearly all cases.

The whole point of my suggestion was that instead of attaching extra locos, you're swapping the diesel out for an electric as a straight swap. On the Lickey it's difficult to make it work because of the lack of electrification on the Camp Hill, Barnt Green Fasts, and south of Bromsgrove. But on the WCML you've got wired access to multiple nodal yards where trains often have to wait anyway, such as at Crewe or Wembley, where a simple swap of 66 for 90 would be perfectly viable.

 

[edwin_m]

The whole point of my suggestion was that instead of attaching extra locos, you're swapping the diesel out for an electric as a straight swap. On the Lickey it's difficult to make it work because of the lack of electrification on the Camp Hill, Barnt Green Fasts, and south of Bromsgrove. But on the WCML you've got wired access to multiple nodal yards where trains often have to wait anyway, such as at Crewe or Wembley, where a simple swap of 66 for 90 would be perfectly viable.

I think we're at cross purposes - I was responding to @Dr Hoo on the suggestion of adding multiple locos to speed things up even more.

On the suggestion above, yes we try to do that. I've even suggested in official circles that the government should buy electric locomotives for freight operators as a cheaper solution than increasing capacity over Shap and Beattock (obviously subject to condition that they use them on those routes, and suggested when such enhancements were seriously being talked about). The challenges are how many freights actually do make an intermediate stop, and how it can be managed in a multi-operator environment where a loco could be sitting around for some time waiting for its operator's next train to haul - plus the risk of the loco's previous working being delayed and holding up its next one. That's probably why GBRf has gone for bi-modes rather than straight electrics.

 

[Nottingham59]

A 6MW Class 99 can raise a 2000 tonne train at 0.3m/s vertically. On a 1 in 85 gradient, that's 25 m/s (57mph). They really won't need banking over Shap or Beattock.

 

[Dazza12]

Hi,

You've suggested the extra locomotives would just be bankers, so any time saved anywhere else on the journey isn't relevant to your point.

The banker can only safely drop off or uncouple on the move only works if it does so at braking distance (from whatever speed it is doing) before the signal controlling the divergency onto the centre track. Otherwise if the points don't fully change it's heading into a serious derailment. Coupling on the move raises even more safety concerns, probably requiring real-time feedback between the train and the banker so the latter can hit the brakes if the main train slows down for any reason.

Whilst I support the statement about coupling on the move, the comments about separating are incorrect. The signalling system always has to be able to cope with a train splitting, whether that is as a result of a banker falling back or as a result of a coupler failure. The worst that would happen in the case described is a "technical" SPAD. The only risk of collision that arises is if the banker's brake rate is somehow lower than that of the main train.

The banking of the Lickey without coupling is only possible because it's a continuous ascent. Any variation in gradient creates a risk of the banker falling back then re-colliding with the train, which has caused serious accidents in the past even when the separation has been small.

I just think there's little point considering such ambitious things if we can't even do the basic thing of getting one electric locomotive on each train over Shap!

Yes, banking on non-continuous ascents would require coupling to the train. Of course, automatic uncoupling is possible with the right couplers.

In reality, banking is largely pointless on the modern railway. If a train needs more power to then it is usually more efficient overall for the additional locomotive to stay coupled throughout the journey.

 

[edwin_m]

Whilst I support the statement about coupling on the move, the comments about separating are incorrect. The signalling system always has to be able to cope with a train splitting, whether that is as a result of a banker falling back or as a result of a coupler failure. The worst that would happen in the case described is a "technical" SPAD. The only risk of collision that arises is if the banker's brake rate is somehow lower than that of the main train.

The problem arises if a point needs to change so the main train goes one way and the banker goes the other. If that point doesn't get detection then the banker needs to be far enough away and slow enough to stop at the signal protecting the divergence.

This can actually be avoided by having the banker stop and then reverse onto a trailing connection, as at Blackwell, but this increases the occupation of the main line by the time it takes for the driver to change ends and the loco to move back to the points.

 

[Dr Hoo]

A 6MW Class 99 can raise a 2000 tonne train at 0.3m/s vertically. On a 1 in 85 gradient, that's 25 m/s (57mph). They really won't need banking over Shap or Beattock.

That’s only mildly reassuring as it stands. Are you saying that if a full-length intermodal starts the climb at 75mph it will only drop back to (and sustain) 57mph? How well would it do from a standing start out of (say) Tebay?

My purpose in asking hard questions and proposing some possibly whacky ideas on this thread is to try and get a conversation going. Throughout my railway career from the early 1970s limited power supplies and locomotive capability have been seen as problems and constraints. It isn’t clear to me that we are yet leaving that era behind and moving to a world of solutions and enablers.

Thanks.

 

[Nottingham59]

That’s only mildly reassuring as it stands. Are you saying that if a full-length intermodal starts the climb at 75mph it will only drop back to (and sustain) 57mph?

Exactly. I've not included wind resistance, at that speed it's unlikely to be more than 0.1MW.

How well would it do from a standing start out of (say) Tebay?

Well the 4MW class 93 hauling 1800t achieved 39mph, so I'd expect a 6MW 99 to get close to the 57mph balancing speed.

See:

Class 93 Tri-mode Loco

93009 is now in the Uk. So expect it at Worksop this week.

www.railforums.co.uk

"Load Trial Update: A single Class 93 successfully hauled 1,800 tonnes from a standing start at Tebay and over the Shap summit in AC mode. This was a tougher test starting at the bottom of Shap but the locomotive still achieved an impressive speed of 39 mph. We also witnessed the state-of-the-art traction control system in action, working independently across all four axles to ensure we maintained maximum traction throughout the climb."

 

[Dr Hoo]

Thanks @Nottingham59 . Some good stuff there that non-specialists can appreciate.

 

[Bald Rick]

A 6MW Class 99 can raise a 2000 tonne train at 0.3m/s vertically. On a 1 in 85 gradient, that's 25 m/s (57mph). They really won't need banking over Shap or Beattock.

How about a more likely 1400t or 1600t?

How well would it do from a standing start out of (say) Tebay?

There’s very few trains planned to be looped at Tebay, and anything being hauled by a 99 is even less likely to be looped there, not least because its more than halfway up already, be well in front of anything calling at Oxenholme, and likely to be doing in the region of 60-70mph anyway.

 

[Dr Hoo]

There’s very few trains planned to be looped at Tebay, and anything being hauled by a 99 is even less likely to be looped there, not least because its more than halfway up already, be well in front of anything calling at Oxenholme, and likely to be doing in the region of 60-70mph anyway.

I dare say, for now. I just hope it all works as well with 75% freight growth, sharing with (part) HS2 trains after a major WCML timetable re-write, and during disruption.

 

[Nottingham59]

How about a more likely 1400t or 1600t?

6MW can raise 1500t vertically at 6/1.5g = 0.4 m/s. On a gradient of 1 in 85, that rate of climb is 0.4x85 = 34m/s (76 mph), ignoring wind resistance.

I would guess that GBRf specified 6.2 MW for its Class 99 for just that reason.

== ==
EDIT:
Oops. I just realised Shap is 1:76 from Tebay to the summit (not sure where the 1:85 came from. Apologies)

On a 1:76 gradient, that's 0.4x76 = 30.4 m/s (68 mph).

 

[Bald Rick]

I dare say, for now. I just hope it all works as well with 75% freight growth, sharing with (part) HS2 trains after a major WCML timetable re-write, and during disruption.

I think it is fair to say that the 75% is an ambition. When Drax closes (next decade, most likely) and HS2 is done, there will be a lot of catching up to do, not all of which will be backfiled by scrap to Port Talbot. The top end of the WCML has plenty of other constraints before we get to the need to be banking intermodals.

== Doublepost prevention - post automatically merged: 19 Aug 2025 ==

6MW can raise 1500t vertically at 6/1.5g = 0.4 m/s. On a gradient of 1 in 85, that rate of climb is 0.4x85 = 34m/s (76 mph), ignoring wind resistance.

I would guess that GBRf specified 6.2 MW for its Class 99 for just that reason.

== ==
EDIT:
Oops. I just realised Shap is 1:76 from Tebay to the summit (not sure where the 1:85 came from. Apologies)

On a 1:76 gradient, that's 0.4x76 = 30.4 m/s (68 mph).

Thank you. Close enough for the gradient to be irrelevant

 

[Dr Hoo]

I think it is fair to say that the 75% is an ambition. When Drax closes (next decade, most likely) and HS2 is done, there will be a lot of catching up to do, not all of which will be backfiled by scrap to Port Talbot. The top end of the WCML has plenty of other constraints before we get to the need to be banking intermodals.

Thank you for the view. I won’t deflect this thread any further with more comments about freight growth. I’m sure there will be other opportunities.

 

[ryan125hst]

This explains things. The London end of ECML and Hertford Loop are basically in their N-1 situation day-in day-out.

That isn't good, especially given it's on the busiest part of the ECML.

Since you said you actually are an electrical engineer this will make more sense to you than it does to me to be honest. This description is from Garry Keenor's book on OLE which freely available and a really good detailed overview of the whole situation.

Thank you, I'll have to do some more reading on this when I get a minute.

I'm pretty sure Retford FS is getting or has been upgraded to have a more powerful connection, I'm not sure what it is however. A higher power connection at Retford was agreed with the DNO many years ago but then retrospectively rejected by DNO some time later. This was enough of a big deal to make the press. (https://www.modernrailways.com/article/hardware-hamstrings-ecml-2022-timetable-plans)

"As part of this project, Network Rail had applied for a firm service capacity uplift from WPD at its existing feeder station at Retford. According to NR, this would ‘essentially’ increase the power draw to the rated capacity of the feeder station equipment. However, WPD [now NGED] highlighted existing voltage imbalance issues, known as negative phase sequence non compliances, both at Retford and Grantham feeder stations. These would have to be resolved before any increase would be granted. This imbalance results from electric traction power supplies drawing a single phase from the three-phase grid...According to Network Rail, a technical solution will take ‘two to four years’ to deliver. This is likely to be the installation of a Static Frequency Converter (SFC)."

It seems that the 25kV supply is derived from a single phase which causes phase imbalances as the load is on one phase so the other two phases are at a significantly lower load. Power is always generated in three phases as it is the most efficient way to generate and transmit power, and large motors run better on three phase too. I presume traditionally they had a 132kV/25kV transformer on one phase which they could get away with up to a certain power level, but increasing the power will take it beyond acceptable limits. From Rail Engineer: "SFCs work by taking a three-phase balanced load from a high-voltage transmission line, converting it to DC and then to a single phase 25kV OLE supply. As a result, their use does not affect the balance between the transmission line’s three phases. Hence, they can be fed from a local distribution network’s 33kV supply." https://www.railengineer.co.uk/static-frequency-converters-improving-the-25kv/

My vision is that the freight loops, wherever provided, should be reconfigured with greater length and much higher speed paintwork. So, if a 125mph Pendolino passes (say) Grayrigg the points can switch the moment that it passes, movement authority issued to a looped freight with 2 x Class 99 train locomotives and 2 x Class 99 bankers so that it can make a 'dragster start' with all eight pantographs raised. Six miles further on, at Tebay, a similar consist is let out behind the Pendolino around three minutes later, also with a dragster start. The two freights can continue at full thrash until they have achieved 90mph (subject, obviously, to any local PSRs).

Clearly such methods of operation would require a new approach to power feeding. However, the 15Es in South Africa haul trains over 40,000 tonnes uphill with 5 x 4,500kW locomotives in radio distributed power 'multiple' operation and have done for 15 years. (Yes, I know that it's 50kV, not 25kV, and narrow gauge but fundamentally I don't see that I'm expecting anything really novel.)

Four Class 99's will require up to 24,680 kW (24.68 MW) which is a huge amount of power. As can be seen from the calculations above, it isn't needed.

NoL sets found work on the continent after they were surplus to requirements here. The tranche of Three Capitals sets released when the Velaros arrived seemed to raise no interest from second operators on withdrawal and have been largely scrapped, or have become spares christmas trees at depots. Perhaps they were unattractive to operators due to their huge inflexible length and more sluggish acceleration? I think the NoL sets are a near equivalent in power/weight to the first-gen LGV Sud-Est sets, so they could probably keep up on that busy, steeply graded route to Lyon, while the 3Cs likely could not.

I think the majority of the Three Capitals sets were withdrawn as they were worn out from running at 186mph across the channel day in and day out. The NoL sets spent more time parked up so I guess have a bit more life in them. I don't think the full length sets have sluggish acceleration as they have a large amount of power available. Inflexible in length may be true as they are long train.

7.5MW at 25kV is a huge amount of power; more significant for performance than the current limit difference is NR's attempts to reduce OLE voltage.

Since TSIs, NR were compelled to align with Europe and design for a minimum of 19kV, but accepted lower in practice due to the long distances between available 400kV supplies, which were preferred. Since Brexit, they have been pushing to remove the TSI limit and accept down to 12.5kV, at which the available locomotive power limit is down to 3.75MW.

It's still in dispute at RSSB with NR claiming infrastructure cost savings from "burning EU red tape" and train operators more cautious.

That's madness if they want to lower the voltage and therefore reduce the power available. This is the opposite of what we need for net zero and removing diesel trains from the network, which is what the government want.

 

[MarkyT]

I think the majority of the Three Capitals sets were withdrawn as they were worn out from running at 186mph across the channel day in and day out. The NoL sets spent more time parked up so I guess have a bit more life in them. I don't think the full length sets have sluggish acceleration as they have a large amount of power available. Inflexible in length may be true as they are long train.

I expect they were clapped out by the end. When the NoLs first became available, they were significantly younger as well as very low mileage. Obsolescence and complexity also no doubt helped tipped the balance against any further use of the TCs.