GraphitProjekt
Member
I've always been interested in the 6.25kV era of the Anglia region and how it was built out of the earlier 1.5kV DC scheme and also slowly became 25kV, many of the details of the latter conversion are still obscure to me. In this thread I want to get into the traction power arrangements and how they changed over time because they are quite unique for an AC railway in Britain. A lot of this information came from the recollections of @PeteK, this is basically a summary of everything we've talked about so far and pretty much everything I know about the topic.
(If anyone wants close ups or pdfs, can easily be arranged)
1.5kV DC
Starting out with the 1.5kV DC system. It can summarised thus:
There's pretty good information about the the Liverpool Street/Fenchurch Street to Shenfield section from this article in The Engineer (7th Oct 1949, page 391). The most intriguing feature is the integration of the 33kV feeders with the local area board infrastructure. A substation in Brentwood is mentioned (indeed there is a 33/11 primary there still) as well as circuits from Gidea Park that go to just "EEB Network". It's hard to know exactly where but I've guessed that this would have been Romford Primary Substation. This is because it's right next to the railway, the buildings sort of look a bit 1930s-ish, and Romford would have definitely been a fairly built-up area at the time. The practice of mixing local power infrastructure with railway controlled (or even owned) lines is a bit unusual but maybe it's something that happened in the 1930s sometimes. There are UKPN documents (see here page 8-9) that mention 'finally' getting rid of 33kV powerlines that are carried along the GEML alignment as late as the 2010s. Around the time of Crossrail I think they were finally decommissioned and you can see the replacement routes in the area on openinframap. It's clear that the main grid connection at Chadwell Heath came from Barking power station, but what the 22kV source at Crosswall was I'm not sure, I don't believe there's any 22kV in that part of London these days. There is a very brief mention of 6.3kV distribution lines used for general heating and lighting at railway properties. Very intriguing but not elaborated on at all.
Information on the Chelmsford and Southend extensions is less detailed. There are a few articles however (Chelmsford: The Engineer, vol 201, issue 5238, 15th June 1956, page 684) (Southend: The Engineer, vol 203, issue 5268, 11th Jan 1957, page 68).
Unlike the earlier article, the number of transformers at each substation isn't mentioned and so I've purely guessed. I'm not entirely sure about the EEB connections either but they represent fairly educated guesses.
AC Conversion
The move to 50hz AC in 1960 is where it gets interesting. The map represents ~1962 when the Chenford, LT&S and Colchester schemes had also come about.
Firstly, it is mentioned in several sources that the original 33kV distribution feeders were kept and used to feed the AC lines. The most important source being the papers of the BR Electrification Conference of 1960 (see them here) specifically paper 05 where it mentions that where BR operates 33kV circuits on the GEML, the phase connections were arranged so that sections could be double end fed between adjacent FSs - something never seen again on AC lines here. It then says (and specifically in paper 28) that Scott connected transformers were to be used on the Southend Vic line which I presume allowed Ramsden and Rayleigh to operate as a double end fed section. A Scott transformer can generate evenly balanced 2 phase AC out of a 3 phase input.
Briefly I'll mention that Alrewas TSC on the Clacton Test Line briefly had a neutral sections and a 6.25kV transformer to test voltage changeover for the trains. Substations that step down the OLE voltage from 25kV to 6.25kV were sometimes called "sub-feeder stations" on these mixed voltage systems (see Leigh and Cheshunt). But that name was used in Scotland also to refer to substations that received a 25kV feeder cable from another FS.
33kV
The actual number of single phase 6.25kV transformers and their capacities at each FS on the GE, Victoria branch and LT&S is not known (except for Bethnal Green) so I just guessed 2 each.
The matter of the 33kV infrastructure is also quite interesting. It's well attested that the 22kV sourced Crosswall supply was removed at this point and there's good information on the 66/33kV supply point put in at Bethnal Green at this point, although I still haven't found where Stepney substation is (or was). But since the cables already went in the Fenchurch Street direction, they decided to run the LT&S's 6.25kV FS at Gas Factory Jnc off the Bethnal Green supply.
At the Chadwell Heath end, I have a number of speculations to make. I propose that the 4x 33kV feeds from Barking were diverted to a new CEGB/EEB substation at Crowlands which additionally had (or was to soon have) a 132kV presence. Crowlands grid is still there today and later became a 25kV supply point. I say this because there are still some UKPN 33kV lines broadly connecting Crowlands to Barking to this day. This then means that Chadwell Heath would have had some empty bays as the connections to Gidea Park also go to Crowlands (as is known today). UKPN documents also say they operate a large 33kV switching station at Gidea Park with no other voltages present, therefore it seems to me that this was former BR infrastructure that was handed over at this point along with the lineside cables. We also know that the original Shenfield DC substation was not re-used as a new 25kV supply point was put in that also distributed at 6.25kV. Another point of contention is whether or not a link between Chadwell Heath and Stratford was kept. I want to believe it was for N-2 redundancy of the Bethnal Green ring, but there's little firm information about how the GE post conversion was fed from any contemporary articles that I could find. Here's an image of how I propose the 33kV changed in isolation which shows a little clearer how circuits could have been diverted.
And this is based off what we know about the present day UKPN infrastructure in the area which I'll draw out here (the Dagenham Dock substation mentioned used to supply the District Line as its electrification was built my the Midland Railway not an LU precursor):
LT&S
As well as being integrated with the Bethnal Green ring, the LT&S mixed voltage electrification also drew from Fleethall grid connection at Prittlewell to Scott transformers at Southend Central and to a secondary single phase connection at Shoeburyness that could use either of the 33kV circuits to Southend Central via a switch. Perhaps this facility was useful for 'operational reasons'. Leigh TSC could also step-down the 25kV west of here for added security of supply for the 6.25kV section within Southend. This overall arrangement is quite interesting because it has both lines at Southend connected together which was not an ability retained when the lines went to full 25kV. I wonder if it could be useful.
The LT&S scheme opened with it's own electrical control room at Pitsea bordering with Romford at Woodgrange Park and Bow Curve. At some point Pitsea was merged into Romford probably in 1984 or '86. Romford opened in 1960 with the AC conversion replacing Chadwell Heath which only operated the DC system.
North East London ("Chenford")
This is unusually very well attested in an article in the Railway Gazette (vol 113, issue 21, 18th Nov 1960, page 396). Most of the details are fairly explanatory on the drawing. The integration of "Bridport Rd substation" is a bit unclear as no such substation exists today. Also worth noting that Walthamstow power station closed in 1968 with today's Exeter Rd 66/11kV at the site, ultimately fed from Hackney 275/66kV. It is also interesting to see that Rye House was originally fed from a 33kV source (albeit the switchboard of a coal power station) and was a measly 5 MVA. Today it's fed at 132kV with a capacity of 27 MVA. Bishop's Stortford is the most mysterious as it was apparently fed from an 11kV source (I've guessed at a local primary substation) only to be used for a fully outage of Rye House. The grid supply was removed when Northumberland Park FS opened in 1969 for the 25kV electrification of the line via Tottenham Hale. Bishops Stortford was designed to become the midpoint between Rye House and a future feeder for extension of wiring to Cambridge. In the end a substation at Stansted junction took this role. Finally, it's mentioned that there was a plan to link Hertford East via an interconnector cable to Hertford North on the GN system. This never happened but it's interesting that they thought about it - another situation a little bit like Southend.
(If anyone wants close ups or pdfs, can easily be arranged)
1.5kV DC
Starting out with the 1.5kV DC system. It can summarised thus:
There's pretty good information about the the Liverpool Street/Fenchurch Street to Shenfield section from this article in The Engineer (7th Oct 1949, page 391). The most intriguing feature is the integration of the 33kV feeders with the local area board infrastructure. A substation in Brentwood is mentioned (indeed there is a 33/11 primary there still) as well as circuits from Gidea Park that go to just "EEB Network". It's hard to know exactly where but I've guessed that this would have been Romford Primary Substation. This is because it's right next to the railway, the buildings sort of look a bit 1930s-ish, and Romford would have definitely been a fairly built-up area at the time. The practice of mixing local power infrastructure with railway controlled (or even owned) lines is a bit unusual but maybe it's something that happened in the 1930s sometimes. There are UKPN documents (see here page 8-9) that mention 'finally' getting rid of 33kV powerlines that are carried along the GEML alignment as late as the 2010s. Around the time of Crossrail I think they were finally decommissioned and you can see the replacement routes in the area on openinframap. It's clear that the main grid connection at Chadwell Heath came from Barking power station, but what the 22kV source at Crosswall was I'm not sure, I don't believe there's any 22kV in that part of London these days. There is a very brief mention of 6.3kV distribution lines used for general heating and lighting at railway properties. Very intriguing but not elaborated on at all.
Information on the Chelmsford and Southend extensions is less detailed. There are a few articles however (Chelmsford: The Engineer, vol 201, issue 5238, 15th June 1956, page 684) (Southend: The Engineer, vol 203, issue 5268, 11th Jan 1957, page 68).
Unlike the earlier article, the number of transformers at each substation isn't mentioned and so I've purely guessed. I'm not entirely sure about the EEB connections either but they represent fairly educated guesses.
AC Conversion
The move to 50hz AC in 1960 is where it gets interesting. The map represents ~1962 when the Chenford, LT&S and Colchester schemes had also come about.
Firstly, it is mentioned in several sources that the original 33kV distribution feeders were kept and used to feed the AC lines. The most important source being the papers of the BR Electrification Conference of 1960 (see them here) specifically paper 05 where it mentions that where BR operates 33kV circuits on the GEML, the phase connections were arranged so that sections could be double end fed between adjacent FSs - something never seen again on AC lines here. It then says (and specifically in paper 28) that Scott connected transformers were to be used on the Southend Vic line which I presume allowed Ramsden and Rayleigh to operate as a double end fed section. A Scott transformer can generate evenly balanced 2 phase AC out of a 3 phase input.Briefly I'll mention that Alrewas TSC on the Clacton Test Line briefly had a neutral sections and a 6.25kV transformer to test voltage changeover for the trains. Substations that step down the OLE voltage from 25kV to 6.25kV were sometimes called "sub-feeder stations" on these mixed voltage systems (see Leigh and Cheshunt). But that name was used in Scotland also to refer to substations that received a 25kV feeder cable from another FS.
33kV
The actual number of single phase 6.25kV transformers and their capacities at each FS on the GE, Victoria branch and LT&S is not known (except for Bethnal Green) so I just guessed 2 each.
The matter of the 33kV infrastructure is also quite interesting. It's well attested that the 22kV sourced Crosswall supply was removed at this point and there's good information on the 66/33kV supply point put in at Bethnal Green at this point, although I still haven't found where Stepney substation is (or was). But since the cables already went in the Fenchurch Street direction, they decided to run the LT&S's 6.25kV FS at Gas Factory Jnc off the Bethnal Green supply.
At the Chadwell Heath end, I have a number of speculations to make. I propose that the 4x 33kV feeds from Barking were diverted to a new CEGB/EEB substation at Crowlands which additionally had (or was to soon have) a 132kV presence. Crowlands grid is still there today and later became a 25kV supply point. I say this because there are still some UKPN 33kV lines broadly connecting Crowlands to Barking to this day. This then means that Chadwell Heath would have had some empty bays as the connections to Gidea Park also go to Crowlands (as is known today). UKPN documents also say they operate a large 33kV switching station at Gidea Park with no other voltages present, therefore it seems to me that this was former BR infrastructure that was handed over at this point along with the lineside cables. We also know that the original Shenfield DC substation was not re-used as a new 25kV supply point was put in that also distributed at 6.25kV. Another point of contention is whether or not a link between Chadwell Heath and Stratford was kept. I want to believe it was for N-2 redundancy of the Bethnal Green ring, but there's little firm information about how the GE post conversion was fed from any contemporary articles that I could find. Here's an image of how I propose the 33kV changed in isolation which shows a little clearer how circuits could have been diverted.
And this is based off what we know about the present day UKPN infrastructure in the area which I'll draw out here (the Dagenham Dock substation mentioned used to supply the District Line as its electrification was built my the Midland Railway not an LU precursor):
LT&S
As well as being integrated with the Bethnal Green ring, the LT&S mixed voltage electrification also drew from Fleethall grid connection at Prittlewell to Scott transformers at Southend Central and to a secondary single phase connection at Shoeburyness that could use either of the 33kV circuits to Southend Central via a switch. Perhaps this facility was useful for 'operational reasons'. Leigh TSC could also step-down the 25kV west of here for added security of supply for the 6.25kV section within Southend. This overall arrangement is quite interesting because it has both lines at Southend connected together which was not an ability retained when the lines went to full 25kV. I wonder if it could be useful.
The LT&S scheme opened with it's own electrical control room at Pitsea bordering with Romford at Woodgrange Park and Bow Curve. At some point Pitsea was merged into Romford probably in 1984 or '86. Romford opened in 1960 with the AC conversion replacing Chadwell Heath which only operated the DC system.
North East London ("Chenford")
This is unusually very well attested in an article in the Railway Gazette (vol 113, issue 21, 18th Nov 1960, page 396). Most of the details are fairly explanatory on the drawing. The integration of "Bridport Rd substation" is a bit unclear as no such substation exists today. Also worth noting that Walthamstow power station closed in 1968 with today's Exeter Rd 66/11kV at the site, ultimately fed from Hackney 275/66kV. It is also interesting to see that Rye House was originally fed from a 33kV source (albeit the switchboard of a coal power station) and was a measly 5 MVA. Today it's fed at 132kV with a capacity of 27 MVA. Bishop's Stortford is the most mysterious as it was apparently fed from an 11kV source (I've guessed at a local primary substation) only to be used for a fully outage of Rye House. The grid supply was removed when Northumberland Park FS opened in 1969 for the 25kV electrification of the line via Tottenham Hale. Bishops Stortford was designed to become the midpoint between Rye House and a future feeder for extension of wiring to Cambridge. In the end a substation at Stansted junction took this role. Finally, it's mentioned that there was a plan to link Hertford East via an interconnector cable to Hertford North on the GN system. This never happened but it's interesting that they thought about it - another situation a little bit like Southend.