GWML Electification

[Bilbo]

There is a simple solution for the gas main problem - wait for the government to ban gas.

 

Geoff Endacott

 

They'd have to close the House of Commons.

[jim.snowdon]

I remember reading some years ago that there were problems in the Farringdon area from leaky earth's with the 25Kv and the DC south of the river and also the LT lines. IIRC this even caused problems some way away up on the North London Line.

 

Jamie

There were, and from what I can remember about it, being part of LU then and only interested in passing, as it were, was that the key factors were that at Farringdon, the tracks were earthed, as part of the AC system, and at the far end of the section from the DC substation, therefore at the high end of the return voltage drop.

 

Part of the issue is that it is convention with railway AC to treat the Earth and Neutral as the same conductor by connecting every structure to the track. The alternative is to keep the track and earth separate back to the supply point, as I believe is done on the Paddington approaches, where the structures are connected by a separate earth wire (in addition to the return conductors, which are insulated from the structures).

 

Jim

[jjb1970]

I went on an IET/IRSE Railway Electrification Systems course a few years back. There was a lengthy discussion about earthing, and an example was given of a problem with, I think, a gas main in the Manchester area, which corroded to the point of leaking gas, due to some earthing issue on the Manchester - Bury line.

I think it took about 20yrs to manifest itself, so these issues are not always apparent or easily spotted.

 

Pipeline insurance is a bit of a nightmare for that very reason. They're susceptible to all sorts of long trigger issues. Over the years I've been involved in a few pipeline issues and on the whole I'd rather stick to engines, much less stress.

[Zomboid]

Part of the issue is that it is convention with railway AC to treat the Earth and Neutral as the same conductor by connecting every structure to the track. The alternative is to keep the track and earth separate back to the supply point, as I believe is done on the Paddington approaches, where the structures are connected by a separate earth wire (in addition to the return conductors, which are insulated from the structures)

The structures are still usually bonded to the rails, even where earth wires are provided.

It may be different with the LU DC lines parallel from Westbourne Park inwards, but that's a pretty small segment.

[Southernman46]

I remember reading some years ago that there were problems in the Farringdon area from leaky earth's with the 25Kv and the DC south of the river and also the LT lines. IIRC this even caused problems some way away up on the North London Line.

 

Jamie

 

Yes - there was (is ??) a complex contactor arrangement that reconfigured the DC traction system for the passage of each train to prevent the earthed / negative return mixing and causing issues to the surrounding buildings. It was a bit of a Heath Robinson arrangement  - wasn't entirely ideal but it served - the situation was improved by the addition of a second rectifier at Farringdon SS.  The contactors were located on the platforms of the old Snow Hill station just before the market sidings site on the LHS (going N) - would be about 50m off the N platform end of the current City Thameslink station. Spent an awful long time in those tunnels in the 88 - 91 period.

 

Nick Catford took some good photos of the area in 85-86

[jjb1970]

There is a massive earthing grid immediately next door to Farringdon station, with some huge neutral earthing resistors.

[Southernman46]

It has changed an awful lot recently I suspect

[jim.snowdon]

I have, in more recent times, seen the DC arrangements for Blackfriars to Farringdon, and can only say that they are truly complex, to the extent that I sometimes wonder what their reliability will be when the full 24tph service starts.

 

Applying the Thamesling logic, the combined AC/DC installation between Camden and Euston ought not to work at all, or all the structures should have rotted away long ago. Simiilarly the now extinct AC/DC installations at Manchester Piccadilly. The fact that they haven't, and that there seem to be nearly as many variations on the design of AC-DC changeover points as there are locations does leave me wondering if each set of designers had any appreciation for what went before. The laws of physics haven't changed in the last 60 years, although the people trying to apply them have, several times over.

 

Jim

[Southernman46]

I suspect the contactor contacts will disappear pretty quickly - the mechanisms if they haven't been renewed will be approaching end of life having been in service for (flippin heck !!) ............. 30 years - I feel old now

[jim.snowdon]

I'll file it alongside the wisdom of the designers who insisted that, at New Cross, insulated rail joints were provided so as to ensure that the East London Line tracks could not be electrically connected to those of the Souther Region, and then wondered why every time a train passed across them, they got arcing at the joint as the last wheels crossed. It wasn't as if TfL electricity was going to find its way home via a Southern Region substation.

 

Jim

[bigP]

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Edited January 31, 2021 by bigP
Deleted

[rodent279]

Yes - there was (is ??) a complex contactor arrangement that reconfigured the DC traction system for the passage of each train to prevent the earthed / negative return mixing and causing issues to the surrounding buildings. It was a bit of a Heath Robinson arrangement  - wasn't entirely ideal but it served - the situation was improved by the addition of a second rectifier at Farringdon SS.  The contactors were located on the platforms of the old Snow Hill station just before the market sidings site on the LHS (going N) - would be about 50m off the N platform end of the current City Thameslink station. Spent an awful long time in those tunnels in the 88 - 91 period.

 

Nick Catford took some good photos of the area in 85-86

 

Which makes one wonder why Farringdon was chosen as the AC-DC changover point? Why not somewhere like Kentish Town? Or even KX-T station?

 

I have, in more recent times, seen the DC arrangements for Blackfriars to Farringdon, and can only say that they are truly complex, to the extent that I sometimes wonder what their reliability will be when the full 24tph service starts.

 

Applying the Thamesling logic, the combined AC/DC installation between Camden and Euston ought not to work at all, or all the structures should have rotted away long ago. Simiilarly the now extinct AC/DC installations at Manchester Piccadilly. The fact that they haven't, and that there seem to be nearly as many variations on the design of AC-DC changeover points as there are locations does leave me wondering if each set of designers had any appreciation for what went before. The laws of physics haven't changed in the last 60 years, although the people trying to apply them have, several times over.

 

Jim

 

How on earth (pun not intended, but rather good actually!) did they earth the systems in continetal border railway stations, such as Venlo, Monchengladbach etc, where 2, sometimes 3 different systems would meet? Can't think where it is, but I'm sure there is one spot where 1.5kV dc, 3kV dc & 15kV AC meet. The 15kV systems of Switzerland & Austria meet the 3kV DC systems of Italy at a few points, so too do the 15kV AC systems of Germany & 3kV DC systems of Poland. They obviously have ways of making it work.

Edited August 1, 2017 by rodent279

[Southernman46]

Which makes one wonder why Farringdon was chosen as the AC-DC changover point? Why not somewhere like Kentish Town? Or even KX-T station?

 

ISTR that the Farringdon line was already electrified at 25kV (as part of the ECML south end (?) / Bed-Pan (?) - Snow Hill tunnel was still an urban waste land until 1986 ..................

 

War story .......... following the commissioning of a replacement transformer / rectifier at Farringdon SS - the Engineer in charge had omitted to check which tapping the transformer was set at ............... apparently 319's don't like 900+ volts DC        Well at least I managed to get it right at the second attempt ....................

 

Anyway back the chaos that is ..............................

[rodent279]

ISTR that the Farringdon line was already electrified at 25kV (as part of the ECML south end (?) / Bed-Pan (?) - Snow Hill tunnel was still an urban waste land until 1986 ..................

 

War story .......... following the commissioning of a replacement transformer / rectifier at Farringdon SS - the Engineer in charge had omitted to check which tapping the transformer was set at ............... apparently 319's don't like 900+ volts DC        Well at least I managed to get it right at the second attempt ....................

 

Anyway back the chaos that is ..............................

 

I suppose that would have meant extending the DC to Moorgate, but that would not have been rocket surely?

[Trog]

ISTR that the Farringdon line was already electrified at 25kV (as part of the ECML south end (?) / Bed-Pan (?) - Snow Hill tunnel was still an urban waste land until 1986 ..................

 

War story .......... following the commissioning of a replacement transformer / rectifier at Farringdon SS - the Engineer in charge had omitted to check which tapping the transformer was set at ............... apparently 319's don't like 900+ volts DC        Well at least I managed to get it right at the second attempt ....................

 

Anyway back the chaos that is ..............................

 

History of that sort of thing there.....

 

Back in the 1980's our Head Relaying Supervisor was doing some work near the new junction at Farringdon, as the 3rd rail was not commissioned yet there was no isolation. Which did not feel right so he dropped a fish plate over the running and conductor rails, just to be sure to be sure.    BANG.  The fishplate then melted as the erroneous live feed was not through the normal breakers. 

Edited July 31, 2017 by Trog

[Southernman46]

Yes it is possible to create a short-circuit that the traction system will just see a nice juicy load and a rusty fishplate making a "dodgy just enough contact" contact will do nicely ................ bit like my rail measuring wheel did at Farnborough when it slide out of the rubber carrying handle - that took some explaining away. 

 

I am hoping that everybody who now is having / will have to work around the new GWML 25kV will do so without such incident as it is very unforgiving.  For example, most of my former colleagues in the structure examination teams have had their working environment changed completely by the introduction of OHL and also complicated by the the geographical cutbacks, some will have a "some & some" situation which isn't ideal.

Edited August 1, 2017 by Southernman46

[jamie92208]

Yes it is possible to create a short-circuit that the traction system will just see a nice juicy load and a rusty fishplate making a "dodgy just enough contact" contact will do nicely ................ bit like my rail measuring wheel did at Farnborough when it slide out of the rubber carrying handle - that took some explaining away. 

 

I am hoping that everybody who now is having / will have to work around the new GWML 25kV will do so without such incident as it is very unforgiving.  For example, most of my former colleagues in the structure examination teams have had their working environment changed completely by the introduction of OHL and also complicated by the the geographical cutbacks, some will have a "some & some" situation which isn't ideal.

At least you didn't do what happened in Northern Spain some years ago. Part of the Euskotren network was being converted to a higher voltage and sometime before the changeover date an engineer pulled the wrong switch in the control room and fried all the trams that were out on the network at the time.

 

Jamie

[corneliuslundie]

Some years ago I was in Rotterdam (I think) and travelled on a tram which changed from overhead to third rail and vice versa  on the move. I assume it must have been the same voltage etc, but I am sure there have been places where this has happened where the switch is from DC to Ac.

One place where the Swiss and French systems meet is Geneva station, though they may possibly manage to avoid more than one or two points where they actually share a track as the services usually use different platforms.

Jonathan

[Edwin_m]

Not sure about Rotterdam, but one tram line in Amsterdam changes to third rail to share a Metro line. 

[rodent279]

Some years ago I was in Rotterdam (I think) and travelled on a tram which changed from overhead to third rail and vice versa  on the move. I assume it must have been the same voltage etc, but I am sure there have been places where this has happened where the switch is from DC to Ac.

One place where the Swiss and French systems meet is Geneva station, though they may possibly manage to avoid more than one or two points where they actually share a track as the services usually use different platforms.

Jonathan

 

Either Venlo or Monchengladbach must have dual voltage capable OHL, as I remember going to Koln from Hook of Holland. We changed engines at one of the aforementioned stations, and our Dutch loco (unfortunately not an EM2 ) unhooked and disappeared, to be replaced by a DB 15kV electric.

[96701]

It really doesn't matter where there are different contact systems at different voltages and alternating / direct current, physics is still the same, so the same earthing / isolation systems need to exist whether in mainland Europe, UK or anywhere else.

[The Stationmaster]

Some years ago I was in Rotterdam (I think) and travelled on a tram which changed from overhead to third rail and vice versa  on the move. I assume it must have been the same voltage etc, but I am sure there have been places where this has happened where the switch is from DC to Ac.

One place where the Swiss and French systems meet is Geneva station, though they may possibly manage to avoid more than one or two points where they actually share a track as the services usually use different platforms.

Jonathan

 

Geneva is at least in part a 'gare commutable' - i.e. certain platforms can be switched between one electrification system and the other as at - for example - Aachen HbF.  However I believe that in the past (and still?) one platform at Geneva was exclusively SNCF use snfd the catenary was energised on that basis and could not be switched.

[Ron Ron Ron]

Mmmmm?

 

I'm not sure why so much time is being spent discussing changeovers between OHLE AC and third rail DC, or between 25kv and other voltages?

Isn't it rather academic considering non of that is being installed or applied on the GWML, or its branches?

 

 

 

.

[jim.snowdon]

Probably because there isn't very much happening on the GW itself, so we've digressed (as often happens).

 

Jim

[Northroader]

Today I headed west from Swindon, a trip I haven't done for some time. Oddly, it isn't until you get a mile or more west of the station that works are apparent, excepting some of the base tubes. Then there are a good lot of masts up, with gaps here and there, until you reach Wootton Bassett. Through there, no masts, and head off right on the South Wales line. From W.B. to Hullavington, you get a very favourable impression, as I'd say the masts are all in, with double track spans as necessary, but there are none of the bits for support with the insulators. Beyond to Badminton there's masts scattered here and there, but I'd say there are far more gaps than masts. West from here base tubes can be seen here and there, with their little ply covers well weathered, as they've been in getting on for two years in some cases, and there's still big lengths without tubes. A worksite has been readied about a mile west of Chipping Sodbury on the south side, so possibly a big push is coming. Theres a finished substation in the vee at Westerleigh Junction, but no masts anywhere, and Parkway hasn't changed any, except the canopies have been trimmed back. The depot in the triangle looks all ready, and all the wiring up, with one of those Azuma thingys sticking its nose out. Down through Filton to Temple Meads, no electrification works, but contractors are very busy widening the trackbase. Tracks or reserved bus lanes?

I gather the tail end of this month a closure is planned, track-work at Parkway for a new platform, Sodbury tunnel is getting an overhead rail like the Severn Tunnel, and supports are being done in Alderton Tunnel.

Edited August 10, 2017 by Northroader