Voltage conversion Liverpool St-Shenfield 1960

[Taunton]

It was in 1960 that the Liverpool St-Shenfield-Southend route was converted from DC to AC. Although portrayed as 25 Kv, in fact the whole of this route was at the reduced inner suburban voltage of 6.25 Kv until the 1980s, the changeover to 25 Kv was only beyond Shenfield going towards Chelmsford.

What rolling stock was used immediately after the conversion? I've seen it described that the LTS Class 302 were used as they were built before the LTS electrification was completed, and also Class 31-hauled trains to Southend. But I've also seen multiple references to LMR Class 304 units being loaned until the old DC stock was rebuilt to AC, which took many months. I can't see how the Class 304 could be used because they did not have the reduced 6.25 Kv capability, and there was no significant 25Kv section for them to run on. So are these statements wrong?

 

[30907]

No evidence bar Wikipedia, but I'd have thought it highly likely. First generation ac units would have been 6.25kv capable as it was still assumed that urban areas would need it.

 

[AM9]

It was in 1960 that the Liverpool St-Shenfield-Southend route was converted from DC to AC. Although portrayed as 25 Kv, in fact the whole of this route was at the reduced inner suburban voltage of 6.25 Kv until the 1980s, the changeover to 25 Kv was only beyond Shenfield going towards Chelmsford.

What rolling stock was used immediately after the conversion? I've seen it described that the LTS Class 302 were used as they were built before the LTS electrification was completed, and also Class 31-hauled trains to Southend. But I've also seen multiple references to LMR Class 304 units being loaned until the old DC stock was rebuilt to AC, which took many months. I can't see how the Class 304 could be used because they did not have the reduced 6.25 Kv capability, and there was no significant 25Kv section for them to run on. So are these statements wrong?

As I recall it (note all dates are all from memory), the AC feeder infrastructure was installed whilst the DC Shenfield 3 car and Southend 4 car units were still running. They were removed at the point of the power switchover and taken away for modification. A quick switchover was possible as the single disc insulators originally put in with the 1500VDC knitting in 1949 and 1956 were also used for the 6.25kV ac system.*
On the first day of ac operation, services were provided with a mix of AM4s (304s) loaned from the LMR Western lines scheme, some AM2s (302s) from the LTS, AM5s (305s) from the 'West Anglian' lines and (AM8s) 308s that were being delivered for the start of the outer GE services (i.e. beyond Shenfield).
As the ex-DC units were returned to service (now as AM6s and AM7s), these loaned units were returned to their intended lines.
It was a year later when the electrification reached as far as Colchester, Clacton and Walton and in 1962/3, the new timetable was rolled out making the most of the fabulous AM9s (309s), at the time, the fastest electric train service over similar distances in the world.
* In the late 1950s, the GE lines were originally constrained to using 6.25kV owing to the limited loading gauge of the GER infrastructure. Following tests in 1962 and an evaluation of operational minimum clearances under operational conditions, it was decided to reduce the mandated minimum clearance requirements under bridges and other structures for 25kV lines from the UIC values to new BR dimensions. There was also encouragement to move away from the dual voltage scheme after some issues with the quad primaries of the transformers on the dual voltage stock that resulted in some spectacular fires. The conversion took place in the early '70s which mainly involved changing some of the wire supports and fitting conventional multi-disc insulators instead of the single disc ones surviving form the original 1500VDC installation. This also meant that a number of feed points and neutral sections could be removed.

Please note, my memory of all this is generally OK but some dates may be a little out.

 

[306024]

Thanks for that information, all a bit before my time (sorry). Quite remarkable how much rebuilding was necessary on the AM6s, wonder how long that would take for a fleet of 92 units today.

 

[Springs Branch]

Very interesting thread!
I travelled regularly along the West Anglia lines into Liverpool Street in the early 1980s and never realised how much of the route was 6.25 rather than 25kV.

......... The conversion took place in the early '70s which mainly involved changing some of the wire supports and fitting conventional multi-disc insulators instead of the single disc ones surviving form the original 1500VDC installation. This also meant that a number of feed points and neutral sections could be removed.

This reminded me of a related 1500V versus 25kV thing in Manchester.

Wind back the clock to around 1975 and a youthful me travelling for my first visit to Manchester Piccadilly.

I knew part of the station was electrified at 1500V DC and the rest at 25kV AC. "How will I know", I wondered, "how many platforms are wired for DC trains and which ones for AC?".

Easy - the DC lines will have one-pot insulators, and AC lines the bigger multi-disc insulators.

I was surprised to find that all Piccadilly's platforms (1 to 4 included) had the larger 25kV insulators installed even though a Class 506 Hadfield EMU was sitting in Platform 2.
Being a bit young at the time, I thought maybe there was some facility to switch parts of the overhead between DC and AC supplies, requiring the better insulation throughout.

This was the mid-1970s and well before Quail Track Maps and easy access to info via Internet, but eventually I worked out Piccadilly 1 - 4 were the DC lines and Platform 5 upwards the AC, with no overhead connection between them (even though diesel trains could cross between East & LNWR tracks)

Seems surprising that BR bothered replacing the lower voltage overhead on the East side of Piccadilly at a time when Woodhead was still well and truly open (albeit past its heyday) and presumably no plan yet to convert the Glossop line to 25kV. Maybe this was done in the big London Road - Piccadilly rebuild in 1959/60, anticipating future conversion of Woodhead to the new 25kV standard?

 

[table38]

Pre 1958, what is now Platforms 13 and 14 were also 1500v DC for the old MSJ&A trains. Even before the 25kV arrived, the two systems were never connected, although there was a story I heard concerning an unfortunate Class 506 unit that was accidentally routed onto the 25kV lines with predictable consequences!

Back to Liverpool Street dual electrification, there is a fascinating document here which contains the map below.

 

[AM9]

Pre 1958, what is now Platforms 13 and 14 were also 1500v DC for the old MSJ&A trains. Even before the 25kV arrived, the two systems were never connected, although there was a story I heard concerning an unfortunate Class 506 unit that was accidentally routed onto the 25kV lines with predictable consequences!

Back to Liverpool Street dual electrification, there is a fascinating document here which contains the map below.

Thanks for that link, the report was really interesting. I remember one saturday morning when unit 518 went into meltdown between Brentwood and Harold Wood in the early '70s. Clearly not every failure mode had been fixed.

This bad experience and the changes to the gauge clearance requirements acted as pushes toward converting 6.25 to 25kV as soon as possible.
In case you haven't seen it, I stumbled across this interesting document:

http://www.railwaysarchive.co.uk/documents/BRB_Elec002.pdf

Here you can see how the reduced clearances saved a lot of bridge raising. It also mentions a second easement that allows the use of glass fibre suspension arms with twin conductor wires. I note that these are much in use on the MML where the Midland Railway's loading gauge was not that generous.
Another point about the GE lines that were originally DC is that the original wires were still in use until quite recently. They are easily recognised by their heavier wire gauge and that they are of compound catenary design which is not used on new wiring. Is that so for the Manchester, Glossop and Hyde lines?

 

[table38]

They are easily recognised by their heavier wire gauge and that they are of compound catenary design which is not used on new wiring. Is that so for the Manchester, Glossop and Hyde lines?

Yes, and they are all a funny verdigris colour (like the Statue of Liberty!). I believe all they did in 1984 was to change the insulators (and the feeders of course!)

-- edit --

There's an old thread on here about Manchester conversion here: http://www.railforums.co.uk/showthread.php?t=49760

 

[Taunton]

Thanks to all.

Can anyone provide any positive evidence that the LMR 304s had 6.25 Kv capability, because I believe not.

I travelled regularly along the West Anglia lines into Liverpool Street in the early 1980s and never realised how much of the route was 6.25 rather than 25kV

The voltage changeover points were at Cheshunt on the Bishops Stortford line, beyond Shenfield on the Chelmsford line (but not to Southend which remained 6.25 all the way), and just beyond Barking on both the Upminster and the Tilbury LTS lines. It follows that all the second class-only units, both the sliding door ones on Shenfield and the BR standard slam door ones on Chingford/Enfield, never got onto the 25Kv under normal circumstances, although they were of course capable of doing so and did indeed do so on odd occasions. It was the automatic 25/6.25 changeover equipment (done by trackside magnets like AWS ramps but just outside the running rails) that was the root cause of the transformer explosions in the early days of the AC electrification, by connecting up the wrong voltage. The different classes had equipment by various electrical manufacturers, it was not all of them that got the basic design wrong.

During the power shortages of the 1970s the voltage available fell on some sections, some of the 25 Kv was found to be as low as 17 Kv, and there were concerns that the automatic changeover equipment might operate and change down to 6.25, with dire consequences.

I think the Liverpool Street lines are unique in having had three different voltages over time, all the while keeping the original overhead.

Regarding the 1500v systems at Manchester (probably still London Road when they were both present), the Altrincham line, although jointly owned, was seen as an LMS electrification project, whereas the Glossop-Sheffield line was designed by the LNER and opened under BR while it was still Eastern Region. So no, they weren't going to touch!