[Electrification] Reference List of 2x25kV AT systems

[GraphitProjekt]

I thought it might be interesting to start a discussion to keep tab on all the stretches of AT fed railway for wider reference. I'll update this initial message as people inform and correct me. Pedantry and excessive detail (especially about substations) is welcomed and encouraged as I my knowledge will run out pretty easily. Substation info in [square brackets]
LAST UPDATE: 13/03/2025
GWML + branches

• In Service
  • GWML: Paddington [Kensal Rise ATFS] to (N of) Chippenham [Christian Malford ATS]
  • SWlsML: Wooten Basset Junction [Wooten Basset ATFS] to Cardiff Central [Canton ATFS]
• Passive Provision
  • Reading & Taunton Line: Reading [Reading ATFS] to Newbury [Newbury TSC(/SATS)]
• Under construction
  • n/a

 Anglia

• In Service
  • GEML: Bow Junction [Pudding Mill Lane ATFS] to Gidea Park [Gidea Park MPATS]
    • Romford to Upminster likely just feeds off a +25kV line
  • XR: Westbourne Park [Westbourne Park ATS] to Pudding Mill Lane [Pudding Mill Lane ATFS]/ Abbey Wood [Plumstead ATS]
• Passive Provision
  • GEML: Gidea Park [Gidea Park MPATS] to Shenfield [Shenfield SATS]
• Under Construction
  • Shenfield to Kelvedon ???? (Autotransformer work seems to be going on currently at Springfield FS)

ECML

• In Service
  • ??
• Passive Provision
  • ??
• Under Construction
  • Welwyn [Welwyn SATS] to Hitchin [Hitchin SATS] [route fed from new Corey's Mill ATFS]

HS1

• In service
  • Corsica Street OHNS [Stratford International SATS] to Channel Tunnel Portal (Cheriton OHNS) [last substation Sellinge ATFS ??]
    • St Pancras International platforms to Corsica Street is possible classically fed by a St Pancras FS (clarity needed on this)
• Passive Provision
  • n/a
• Under Construction
  • n/a

Trans-Pennine Route (only as far as Standedge Tunnel region boundary)

• In Service
  • ??
• Passive Provision
  • ??
• Under Construction
  • Church Fenton to Neville Hill TSC(/SATS)

MML

• In Service
  • St Pancras/Farringdon [Kentish Town SATS] to Borehamwood [Borehamwood ATFS] (installed as part of Thameslink work in 2010)
  • Kettering [Kettering North SATS] to South Wigston [South Wigston MPATS]
• Passive Provision
  • Borehamwood [Borehamwood ATFS] to Ketterinh [Kettering North TSC/SATS]
• Under Construction
  • n/a

WCML

• In Service
  • Main route:
    • Bourne End [Bourne End MPTSC/ATS] to Whitmore [Whitmore MPTSC]
      • Northampton Loop: Ashton [Ashton MPATS] to Hilmorton [Hilmorton MPATS]
    • Weaver Junction [Weaver Jnc ATFS] to Euxton Junction [Euxton Jnc MPTSC]
    • Hest Bank MPTSC [Carnforth ATS] to Great Strickland [Great Strickland MPTSC/ATS]
  • Stoke-on-Trent Line: Norton Bridge [??]/Colwich Jnc [??] to Stone [??]
• Passive Provision
  • Great Strickland [MPATS] to Glasgow C [??]
• Under Construction
  • ??

NW England

• In Service
  • "TPML": Stalybridge [Heyrod ATFS] to Baguley Fold [Baguley Fold MPATS]
  • "Chat Moss": Windsor Street [Ordsall Lane MPATS] to Wavertree OHNS [Edge Hill MPTSC]
    • (Liverpool Lime Street to Edge Hill MPTSC is classically fed by adjoining Runcorn Branch by Speke FS)
  • "Bolton Line": Windsor Bridge South Junction [Ordsall Lane MPATS] to Buckshaw OHNS [Euxton Jnc MPATS]
    • (Note that "Central Manchester" is all classically fed by Edgeley FS:
      • Cheadle Hulme [Cheadle Hulme MPTSC] to Levenshulme OHNS [Slade Lane MPTSC] (Edgeley FS has no OHNS)
      • Levenshulme OHNS [Slade Lane MPTSC] to Windsor Street OHNS/Windsor Bridge South Junction OHNS [both Ordsall Lane MPATS/ATFS]
      • and Levenshulme to Baguley Fold [Miles Platting MPATS])
• Passive Provision
  • ??
• Under Construction
  • n/a

Glossary if anyone wants it
FS = Feeder Station: Connection with electrical supply utility ("National Grid" or a distribution network)
MPTSC = Mid-Point Track Sectioning Cabin: Substation between two FSs that separates the incoming supplies
TSC = Track Sectioning Cabin: Substation (on one supply) fitted with circuit breakers to isolate tracks (typically fitted at junctions)
OHNS = Overhead Line Neutral Section: Short permanently earthed component of OLE that separates supplies at either side (fitted at MPTSCs and most FSs)

Autotransformer (AT) system - Type of AC electrification system where an extra auxiliary feeder runs at -25kV next to the +25kV catenary and regularly connects with the catenary in order to supply greater current and reduce voltage drop over distance.
AT systems have their own names for the same kinds of substations as above
ATFS = Autotransformer Feeder Station (like FS)
MPATS = Mid Point Autotransformer Transformer Station (like MPTSC)
SATS = Sectioning Autotransformer Station (like TSC)
And a new type, ATS = Autotransformer Site: similar to SATS but has no circuit breakers, mainly acts to just connect -25kV and +25kV lines together

 

[59CosG95]

I thought it might be interesting to start a discussion to keep tab on all the stretches of AT fed railway for wider reference. I'll update this initial message as people inform and correct me. Pedantry and excessive detail (especially about substations) is welcomed and encouraged as I my knowledge will run out pretty easily. Substation info in [square brackets]
GWML

• In Service
  • Paddington [Kensal Rise ATFS] to Cardiff Central [Cardiff ATFS]
    • Reading [???] to Newbury
• Passive Provision
  • ??
• Under construction
  • n/a

 Anglia

• In Service
  • GEML: Bow Junction [Pudding Mill Lane ATFS] to Shenfield [Shenfield SATS ?]
    • Romford to Upminster likely just feeds off a +25kV line
  • XR: Westbourne Park [Westbourne Park MPATS] to Pudding Mill Lane [Pudding Mill Lane ATFS]/ Abbey Wood [Plumstead ATS]
• Passive Provision
  • n/a
• Under Construction
  • Shenfield to Kelvedon ???? (Autotransformer work seems to be going on currently at Springfield FS)

ECML

• In Service
  • Welwyn [Welwyn SATS] to Hitchin [Hitchin SATS] [route fed from new Corey's Mill ATFS]
• Passive Provision
  • Hambleton Junction [(AT)FS] to ???
• Under Construction
  • ??

Trans-Pennine Route (only as far as Standedge Tunnel region boundary)

• In Service
  • ??
• Passive Provision
  • Colton Junction [Colton Junction TSC] to Church Fenton [end at the moment] [fed from Hambleton Junction (AT)FS on ECML]
• Under Construction
  • Church Fenton to [what substation?]

MML

• In Service
  • St Pancras/Farringdon [Kentish Town SATS] to Borehamwood [Borehamwood ATFS] (installed as part of Thameslink work in 2010)
• Passive Provision
  • Borehamwood [Borehamwood ATFS] to South Wigston [Wigston MPATS]
  • Kettering [Kettering North TSC/SATS] to Corby
• Under Construction
  • n/a

WCML

• In Service
  • Main route: North Wembley [North Wembley MPATS] to Great Strickland [Great Strickland MPATS]
    • Northampton Loop: Ashton [Ashton MPATS] to Hilmorton [Hilmorton MPATS]
  • Manchester Line: Crewe [??] to Levenshulme [Levenshulme MPATS]
  • Macclesfield Line: Norton Bridge [??]/Colwich Jnc [??] to Cheadle Hulme [??]
  • Liverpool Line: Weaver (Liverpool) OHNS [??] to Liverpool Lime Street [??]
• Passive Provision
  • Great Strickland [MPATS] to Glasgow C [??]
• Under Construction
  • ??

NW England

• In Service
  • "TPML": Stalybridge [Hayrod ATFS] to Baguley Fold [Baguley Fold MPATS]
  • "Central Manchester":
    • Levenshulme [Levenshulme MPATS] to Windsor Street OHNS/Windsor Bridge South Junction OHNS [both Ordsall Lane MPATS]
    • and Levenshulme to Baguley Fold [Baguley Fold MPATS]
  • "Chat Moss": Windsor Street [Ordsall Lane MPATS] to Liverpool Lime Street [Waverley MPATS??]
  • "Bolton Line": Windsor Bridge South Junction [Ordsall Lane MPATS] to Buckshaw OHNS [??]
• Passive Provision
  • ??
• Under Construction
  • n/a

Glossary if anyone wants it
FS = Feeder Station: Connection with electrical supply utility ("National Grid" or a distribution network)
MPTSC = Mid-Point Track Sectioning Cabin: Substation between two FSs that separates the incoming supplies
TSC = Track Sectioning Cabin: Substation (on one supply) fitted with circuit breakers to isolate tracks (typically fitted at junctions)
OHNS = Overhead Line Neutral Section: Short permanently earthed component of OLE that separates supplies at either side (fitted at MPTSCs and most FSs)

Autotransformer (AT) system - Type of AC electrification system where an extra auxiliary feeder runs at -25kV next to the +25kV catenary and regularly connects with the catenary in order to supply greater current and reduce voltage drop over distance
AT systems have their own names for the same kinds of substations as above
ATFS = Autotransformer Feeder Station (like FS)
MPATS = Mid Point Autotransformer Transformer Station (like MPTSC)
SATS = Sectioning Autotransformer Station (like TSC)
And a new type, ATS = Autotransformer Site: similar to SATS but has no circuit breakers, mainly acts to just connect -25kV and +25kV lines together

Well, here's your starter for ten!
GWML and tributaries:

GWML
Paddington [Kensal Green ATFS/Westbourne Park ATS] to Christian Malford ATS; ground-level connection from Christian Malford ATS to Thingley Junction ATFS. IN SERVICE.

SWML (South Wales)
Royal Wootton Bassett ATFS (where GWML & SWML diverge) to Canton ATFS (current limit of wiring). IN SERVICE.

Berks & Hants
Reading ATFS to Newbury SATS. PASSIVE PROVISION; while OLE structures were installed with provision for ATF, and the sites at Theale (ATS), Midgham (ATS) and Newbury (SATS) had space for the transformers, the electrical infrastructure was descoped.

ECML:
No passive provision at Hambleton Jn (regrettably!), at least as far as I'm aware. Hambleton is an SFC + FS (Static Frequence Converter + Feeder Station).

Trans-Pennine Route:
As above. Additionally, construction work is happening from Church Fenton to Neville Hill TSC.

MML and branches:
Unsure if Kettering North SATS has provision for Corby to be AT fed.
The extension north from Kettering North SATS to Wigston MPATS (fed from Braybrooke ATFS) has been commissioned and is now LIVE, but it has NOT yet been authorised for entry into service by the ORR.

 

[jfollows]

I didn’t think Crewe-Cheadle Hulme was AT from memory and looking, but perhaps I’ll go and look later on.

 

[LNW-GW Joint]

AT on the WCML is not in service all the way to Great Strickland.
Some sections north of Crewe are partially installed but not in service.
Great Strickland to Glasgow was descoped when coal traffic declined/finished.

 

[Edvid]

CTRL (HS1) is AT-fed throughout, save perhaps for the St Pancras station throat.*

Don't believe Welwyn Garden City** - Hitchin (ECML) or Gidea Park - Shenfield (GEML) are AT-fed yet. Both stretches currently lack the requisite ATF (Autotransformer Feeder) runs.

WCML is still classically-fed south of Bourne End; the project to provide an AT feed and install a neutral section at Bushey was deferred again not too long ago.

[* Bonus trivia - CTRL and MML traction supplies share headspans across platforms 1-5]
[** WGC (the big one) and Welwyn (the little, old one) are two different / adjacent places]

 

[GraphitProjekt]

CTRL (HS1) is AT-fed throughout, save perhaps for the St Pancras station throat.*

Silly me, i totally forgot hs1. Hs1 has some strange feeding arrangements going on with Barking (ctrl) atfs and Singlewell atfa not separated with a neutral section.

Don't believe Welwyn Garden City** - Hitchin (ECML) or Gidea Park - Shenfield (GEML) are AT-fed yet. Both stretches currently lack the requisite ATF (Autotransformer
Feeder)

So is Crowlands FS still in use or has it turned into an ATFS? I have seen evidence that Shenfield and Gidea Park are AT substations of some kind both are mentioned in planning/construction documents. But no mention of Crowlands, the neutral sections are all still there for it to be feeding.

If Gidea Park is the end of AT then Shenfield must still be operating as a classic FS (which would also give N2 capability on the victoria branch)

 

[Edvid]

I'm not particularly familiar with GEML feeding arrangements, but Crowlands might be like Grahame Park on the MML - originally built as a FS, then reclassified as a SATS or MPATS when AT feeding and a 400kV-supplied ATFS (like Pudding Mill Lane or Borehamwood) came along, but still has its 132kV connection as a backup.

OHNS on the Great Eastern (at the London end) are admittedly closer to each other than those on the Midland, though!

 

[Elecman]

AT on the WCML is not in service all the way to Great Strickland.
Some sections north of Crewe are partially installed but not in service.
Great Strickland to Glasgow was descoped when coal traffic declined/finished.

Section between Wigan and Carnforth the installation want even finished.

 

[GRALISTAIR]

AT on the WCML is not in service all the way to Great Strickland.
Some sections north of Crewe are partially installed but not in service.
Great Strickland to Glasgow was descoped when coal traffic declined/finished.

Euxton Jct to Catterall Grid Feeder has some Autotransformer kit in place (SPS and insulators) but no wires and definitely not installed.

Edited - sorry did not realise it was as far south as Wigan - thought it was Euxton Jct.

Section between Wigan and Carnforth the installation wasn't even finished.

 

[GraphitProjekt]

I'm not particularly familiar with GEML feeding arrangements, but Crowlands might be like Grahame Park on the MML - originally built as a FS, then reclassified as a SATS or MPATS when AT feeding and a 400kV-supplied ATFS (like Pudding Mill Lane or Borehamwood) came along, but still has its 132kV connection as a backup.

OHNS on the Great Eastern (at the London end) are admittedly closer to each other than those on the Midland, though!

Likewise bow junction FS (directly opposite to Pudding Mill Lane) surely still feeds Liverpool street to bow/hackney downs as well as north london line and temple mills lines probably via ducting to stratford

In classic days, i believe Crowlands (up) was Manor part mptsc to Crowlands and "down" was there to Gidea Park mptsc where Shenfield FS took over.

If AT ends at Gidea Park then it'd make more sense that Crowlands and Manor Park are both just now SATSs with a (semi-?)permanently bypassed neutral section. And maybe Shenfield FS remains unchanged (normally powering Gidea park to Shenfield, N1 capability to Springfield on the mainline and to Rayleigh on the Southend line).

The point of contention for me is not only that all the neutral sections are still there but also that these guys say they installed a SATS at Shenfield as part of crossrail work in 2018 https://vgcgroup.co.uk/case-studies/shenfield-sats-sub-stations/

Maybe it's there but not in use yet. There's certainly AT related work going on at Springfield (n of chelmsford) and Rayleigh is adjacent to a 400kV substation. This might suggest that the aspiration is Pudding Mill Lane ATFS - Gidea Park MPATS - Shenfield SATS (/MPATS for southend line) - Springfield ATFS and to Rayleigh ATFS.

My understanding is that an Autotransformer railway is not especially compatible with classic one for backup feeding. I could be wrong on that; is it possible to switch on a backup FS to the +25kV switch out all the Autotransformers and just live with EMI temporarily? If not the N2 situation for Pudding mill lane is something like Kensal Rise to Gidea Park via XR core, which sounds silly.

----------



Literally just passing through shenfield right now and i can see some bare ATF fittings. (25kV Insulator + bracket but no wire)

This isn't totally relevant but I've noticed a stretch of very old and rusty looking brackets just about ground level north of romford (and in other places) i believe these are remnants of the 33kV distribution lines that fed the 1.5kV dc system of the 1940s. Lots of very interesting electrification history all on top of each other on GEML

 

[GRALISTAIR]

Great thread btw. Thanks for posting.

I have linked it in the Pinned thread at the Top of the Infrastructure page.

 

[Nicholas Lewis]

Reading this through shines a spotlight on how much has been expended on installing ATF kit but not yet commissioned. Money that would have been better spent on extending electrification.

 

[GRALISTAIR]

Reading this through shines a spotlight on how much has been expended on installing ATF kit but not yet commissioned. Money that would have been better spent on extending electrification.

You know, thinking about it, you maybe right. I hadn’t thought about it that way before.

 

[GraphitProjekt]

Great thread btw. Thanks for posting.

I have linked it in the Pinned thread at the Top of the Infrastructure page.

Thank you for this! Hopefully it'll stay lively and I'll have lots to add - I'll do a proper review/update of everything on monday when I'm back home. Do keep talking about wcml, it sounds messy and confusing and I have a lot to learn about it.

Reading this through shines a spotlight on how much has been expended on installing ATF kit but not yet commissioned. Money that would have been better spent on extending electrification.

I suppose it's to do with the multi-decade lead times for transmission grid connections. If national grid have incorporated it into their plans it may actually be less disruptive to just go ahead with the grid connections even if the OLE work is blowing against the changing winds of politics. I don't know generally how competent/willing the government is at funding the electrical supply industry but i have a general sense that they get taken a lot more seriously than rail and are not allowed to fail. It's actually mentioned in garru Keenor's book that it's a good idea to let NG take the lead (hah) on substation work because they have some specific planning laws that can make buying land a bit easier.

‐‐---------
Also, if SFC prove viable then we might actually see a lot fewer Autotransformers in future as the grid connections can be cheaper/more plentiful. So the AT systems could become islands of historical oddity and operational complexity especially if they don't get fully rolled out.

 

[Sir Felix Pole]

A pedant writes - the Stalybridge feeder is at Heyrod (not Hayrod) - but pronounced as in King Herod!

 

[GraphitProjekt]

Good to know, I've been saying "hey rod" in my head the whole time

 

[Nicholas Lewis]

Also, if SFC prove viable then we might actually see a lot fewer Autotransformers in future as the grid connections can be cheaper/more plentiful. So the AT systems could become islands of historical oddity and operational complexity especially if they don't get fully rolled out.

Indeed thats a good point SFC's allow connection back down at 132kV if not 33kV for lines with sub 10MVA requirements.

 

[GraphitProjekt]

Indeed thats a good point SFC's allow connection back down at 132kV if not 33kV for lines with sub 10MVA requirements.

Just a thought but could a 132kV connection could support a 50kV Autotransformer with an SFC? This could make AT conversions potentially a lot easier.

 

[ABB125]

Just a thought but could a 132kV connection could support a 50kV Autotransformer with an SFC? This could make AT conversions potentially a lot easier.

I think I've asked this question (or something similar) before, and I think the answer was yes. All it needs is more (double the number of?) converter modules to produce the higher voltage. But I can't remember exactly

 

[GraphitProjekt]

Well, here's your starter for ten!
GWML and tributaries:

GWML
Paddington [Kensal Green ATFS/Westbourne Park ATS] to Christian Malford ATS; ground-level connection from Christian Malford ATS to Thingley Junction ATFS. IN SERVICE.

SWML (South Wales)
Royal Wootton Bassett ATFS (where GWML & SWML diverge) to Canton ATFS (current limit of wiring). IN SERVICE.

Berks & Hants
Reading ATFS to Newbury SATS. PASSIVE PROVISION; while OLE structures were installed with provision for ATF, and the sites at Theale (ATS), Midgham (ATS) and Newbury (SATS) had space for the transformers, the electrical infrastructure was descoped.

Thankyou, I've updated the GWML list with a bit more detail. I did some digging in the old thread and found this graphic from ABB (presumably a good chunk of this stiff didn't go ahead): https://resources.news.e.abb.com/attachments/published/13013/en-US/DB69E86CEEAE/ABB-GWEP-Map.pdf What is going on in Wales though? Why is there 3 ATFSs so close together, or are those prospective sites?

Euxton Jct to Catterall Grid Feeder has some Autotransformer kit in place (SPS and insulators) but no wires and definitely not installed.

Edited - sorry did not realise it was as far south as Wigan - thought it was Euxton Jct.

Trawling through the old WCML PSU thread I found some information. Especially this graphic (and commentary) from @thecrofter (this post)

From this picture (and other discussion) I have given the WCML AT areas as:
- Bourne End to Whitmore. Weaver Junction to Euxton Junction. Carnforth to Great Strickland
- and on the Stoke-on-Trent line: Colwich/Norton Bridge to Stone
Also it seems like the section I labelled as Central Manchester is all classic fed by one half of Edgeley 132kV FS. It must be seriously stretched having to cover the approach into Piccadilly, Longsite depot, all 3 Manchester stations, the Castleford Corridor, the odd set of class 90s and Trafford and the entire Hadfield/Glossop line.

CTRL (HS1) is AT-fed throughout, save perhaps for the St Pancras station throat.*

Don't believe Welwyn Garden City** - Hitchin (ECML) or Gidea Park - Shenfield (GEML) are AT-fed yet. Both stretches currently lack the requisite ATF (Autotransformer Feeder) runs.

I've changed GEML accordingly and moved the ECML limits to the "under construction" category.
Furthermore, I think St Pancras ATFS might not exist anymore. This bulletin from UKPN (working as an electrical construction contractor rather than a DNO here) says that they had 4 FSs and then reduced that to 3 by using some high tech power electronics stuff. This little document by ABB explains what those power electronics are (most of which went over my head) but mentioned that the equipment was setup at Barking, Singlewell and Sellindge. Confusingly, this asset management document by HS1 from last year (quite a big pdf but just ctrl+f for "feeder station") says there are 4 FSs but that two of them are normally on standby. It's a bit contradictory - potentially the HS1 doc is counting Singlewell twice since (referring to the ABB document) it's the only FS with an "Up" and "Down" supply (the others are Tee-feeders i guess). The only mention for St Pancras FS I've ever found is from this RAIB report in 2009. The HS1 sectional appendix from 2013 says there's a neutral section at Corsica Street right out of St Pancras - so St Pancras FS could have been removed anytime since 2013. But confusingly again, the 2026 network statement by HS1 mentions a 12kA fault current for the route with 6kA for "the St Pancras area" (page 28). It's all a bit mysterious - perhaps someone with a better understanding of things can interpret some more conclusions from these documents.

 

[stuving]

St Brides has a supply from NG Imperial Park. A 25-0-25kV independent feeder runs along the track to Canton, roughly half in conduit (see here for details from Enable), to provide its power supply. (Bramley and Thingley Junction ATFSs also take in power from NG and provide the supply to a remote ATFS via an independent feeder, but partly along a line with with no OLE.) The original design had a separate similar feeder from St Brides to Long Dyke, but I think that was never built. So both Canton and St Brides are ATFSs for the railway.

 

[GraphitProjekt]

St Brides has a supply from NG Imperial Park. A 25-0-25kV independent feeder runs along the track to Canton, roughly half in conduit (see here for details from Enable), to provide its power supply. (Bramley and Thingley Junction ATFSs also take in power from NG and provide the supply to a remote ATFS via an independent feeder, but partly along a line with with no OLE.) The original design had a separate similar feeder from St Brides to Long Dyke, but I think that was never built. So both Canton and St Brides are ATFSs for the railway.

Thankyou for this! Very Interesting. Looks like there is a neutral section at St Brides but not anywhere further in the Cardiff direction, so Canton is like an extension of St Brides "B" and are on the same grid supply. Similarly, Wootton Basset ATFS is an extension of Thingley ATFS via an independent feeder, although Thingley doesn't connect to any OLE itself. What's the situation with Bramley and its extension lead to Reading? Was Reading connected to the grid before Bramley (which seems to only have come online a couple of years ago)? Or was it at that point a SATS - there doesn't seem to be any neutral sections around Reading so is Reading feeding to Maidenhead and Didcot on the mainline, and towards Newbury?

 

[swt_passenger]

Thankyou for this! Very Interesting. Looks like there is a neutral section at St Brides but not anywhere further in the Cardiff direction, so Canton is like an extension of St Brides "B" and are on the same grid supply. Similarly, Wootton Basset ATFS is an extension of Thingley ATFS via an independent feeder, although Thingley doesn't connect to any OLE itself. What's the situation with Bramley and its extension lead to Reading? Was Reading connected to the grid before Bramley (which seems to only have come online a couple of years ago)? Or was it at that point a SATS - there doesn't seem to be any neutral sections around Reading so is Reading feeding to Maidenhead and Didcot on the mainline, and towards Newbury?

There’s no grid supply at Reading. IIRC Maidenhead is the mid point between Didcot and Kensal Green, ie Didcot feeds as far as Maidenhead, but I think although some early diagrams describe Reading as an ATFS, perhaps that was only to become true when the “Reading independent feeder” was eventually added. That turned out to be from the grid near Bramley, but as an alternative option it could have been an along track supply from Didcot. I’m sure there’s a diagram somewhere in the main GW wiring thread that shows the original details. Bramley was intended to provide an alternate resilience supply for the Reading depot and station area. But is Didcot still the normal grid supply for the Reading area and to Newbury?

 

[59CosG95]

There’s no grid supply at Reading. IIRC Maidenhead is the mid point between Didcot and Kensal Green, ie Didcot feeds as far as Maidenhead, but I think although some early diagrams describe Reading as an ATFS, perhaps that was only to become true when the “Reading independent feeder” was eventually added. That turned out to be from the grid near Bramley, but as an alternative option it could have been an along track supply from Didcot. I’m sure there’s a diagram somewhere in the main GW wiring thread that shows the original details. Bramley was intended to provide an alternate resilience supply for the Reading depot and station area. But is Didcot still the normal grid supply for the Reading area and to Newbury?

I think Didcot (Foxhall ATFS) was the main feeder down to Reading, Newbury & Maidenhead at the time, but with the commissioning of Hollycross ATFS (Bramley, or the Reading Independent Feeder) that might well have changed.

 

[GraphitProjekt]

I think Didcot (Foxhall ATFS) was the main feeder down to Reading, Newbury & Maidenhead at the time, but with the commissioning of Hollycross ATFS (Bramley, or the Reading Independent Feeder) that might well have changed.

Yeah, I mean Bramley and it's feeder are very recent additions so Didcot must have been doing it all beforehand. But I can't find any neutral sections in the Reading area so I don't quite understand what Reading ATFS could be feeding? Is it a hot standby option for the section Maidenhead-Didcot/Newbury?

I’m sure there’s a diagram somewhere in the main GW wiring thread that shows the original details.

I've seen this one which honestly raises more questions than it answers https://resources.news.e.abb.com/attachments/published/13013/en-US/DB69E86CEEAE/ABB-GWEP-Map.pdf. But if there's another map out there I'd be curious to see it.

 

[stuving]

Yeah, I mean Bramley and it's feeder are very recent additions so Didcot must have been doing it all beforehand. But I can't find any neutral sections in the Reading area so I don't quite understand what Reading ATFS could be feeding? Is it a hot standby option for the section Maidenhead-Didcot/Newbury?

I've seen this one which honestly raises more questions than it answers https://resources.news.e.abb.com/attachments/published/13013/en-US/DB69E86CEEAE/ABB-GWEP-Map.pdf. But if there's another map out there I'd be curious to see it.

The latest I have on the Bramley Independent feeder is this, from Enable in November, saying they'd just completed phase 2 testing, and "the site was de-energised in preparation for stage 3 entry into service". I've not seen EIS announced, but it must be due about now. While their terminology isn't consistent (nor the name, which has been Bramley/Holly Cross/Hollycross) they do describe what's installed as an NG substation at each end of the buried cables, and NR's ATFS with two ATs. (I see that Reading and Canton ATFSs both appear to have three ATS.)

When AT feeding was new here and being explained and justified, having fewer feed stations further apart was claimed as one of the big advantages. Of course now the NG supply circuits have to be bigger, and losing one has more impact as a result. Meeting the security of supply rules (N-2 or however it's defined in this case) becomes more challenging.

For Reading, it's a long way from Kensal Green to Didcot, plus there's the Newbury branch and the depot and station at Reading, very important during disruption. So when the Electric Spine was cancelled, and along with it Reading-Basingstoke's OLE, doing the obvious and dropping the supply feed at Bramley was judged to be too risky. AIUI Kensal Green can't supply the Crossrail core and GEML to Didcot off one 80MVA circuit, so some extra power, and independent supply to Reading itself, is needed.

To get full benefit from this independent feed to Reading, I presume you have to be able to disconnect it (i.e. the station and the triangle) from all three lines. So there should be three section breaks and feed connections beyond each break and in the triangle too. I can't see section breaks on Google Earth, but the across track span wires for the connection are usually visible.

Winding the zoom level up, I can see those to the east (300 m east of Horseshoe Bridge over the Kennet), to the south (between Tilehurst Road and Bath Road), and the the west (next to Scours Lane). The last of those was not visible from overhead, but was on Street View. I've not yet found a connection to the triangle itself, and I guess it might not be next to the ATFS site.

 

[GraphitProjekt]

So Bramley is there to take over from Foxhill ATFS "Up" supply, but if no neutral sections exist (or are planned) it can only be a hot standby feeder station and not supplying anything under normal scenarios. Is this why Reading ATFS has three transformers? Because normally it's a SATS with feeds in three directions. And so I gather Bramley has two transformers just so it can be sending extra power to Reading and for even more resilience?

AIUI Kensal Green can't supply the Crossrail core and GEML to Didcot off one 80MVA circuit,

Is this what the N-2 situation would be if both sides of Pudding Mill Lane went offline? Even having Maidenhead to Gidea Park/Abbey Wood sounds like a major strain. As I was discussing earlier, I don't think there is another ATFS on GEML, but there is autotransformer work going on at Springfield FS (north of Chelmsford) and I found this article today which is the only mention I've seen on the matter (also looks like the feeder station has been renamed to Beulieu) https://www.amey.co.uk/media/news/2...-upgrade-beaulieu-feeder-station-grip-2-to-8/

so this has been my best guess at visually representing the situation with Reading and Bramley/Holly Cross based on our collective speculation

So there was a power failure on GWML yesterday morning (on 28/01/25). Probably of Kensal Rise ATFS, but I'm not sure. Sounds like Reading Independent Feeder could have helped but it's just not quite in service yet!!