GWML Electification

[D854_Tiger]

Would it be too much to ask if there are any here that could comment on what the official position is on the delays and cost overruns of the GW electrification.

 

it would help those of us that do not have an intimate relationship with the project to better understand why it all seems to be going belly up.

[Zomboid]

Recently rebuilt when it became the Overground but it was 3rd/4th rail before the rebuild, which involved only a couple of short stretches of new build to create the through route.

Regards

I'd describe Shoreditch to Highbury is more than a "short stretch". OK it's not an inter city main line, but it is proof that it is possible to build a brand new route with 3rd rail electrification under the current legislation. And hence, legally speaking at least, an AC/DC changeover within Reading station is possible. Technically would be a different matter, and the lack of any reason to have one is the real obstacle.

Anyway that's way off topic.

[D854_Tiger]

I'd describe Shoreditch to Highbury is more than a "short stretch". OK it's not an inter city main line, but it is proof that it is possible to build a brand new route with 3rd rail electrification under the current legislation. And hence, legally speaking at least, an AC/DC changeover within Reading station is possible. Technically would be a different matter, and the lack of any reason to have one is the real obstacle.

Anyway that's way off topic.

 

I believe, for a while, there was talk from Network Rail that as power renewals fell due they would endeavour to replace third rail with overhead 25kv and part of the LSW main line was mentioned as a potential candidate.

 

Whether that is still the case .....

[phil-b259]

The problem with that is that new 3rd rail would have to be installed, which isn't allowed anymore, only renewals of existing 3rd rail is allowed. Then the Junctions and multitude of shunt moves on the Southern lines makes the change over there undesirable as well. 

 

Simon

 

3rd rail installation is still permitted for small scale adjustments - typically extra sidings, depots or layout modifications but the extension of it into the ex GWR platforms would still be permissible under such provisions (as would the the addition of 3rd rail a short way up the Reading line out of Basingstoke if that were easier / cheaper than fitting OHLE to the SWT platforms).

 

However with Reading and the gradients involved, providing there is sufficient clearances it would be more sensible to extend the OHLE onto the Southern line for a short distance rather than the other way round, thus keeping the GWR sections of the station free of 3rd rail. Given the Electrostars (and pretty much every post privatisation dual voltage EMU) is capable of on the move changeovers this would not prove a problem

[phil-b259]

I believe, for a while, there was talk from Network Rail that as power renewals fell due they would endeavour to replace third rail with overhead 25kv and part of the LSW main line was mentioned as a potential candidate.

 

Whether that is still the case .....

 

This proposal came up before NR actually started electrifying things and the many problems it has subsequently faced have made the DfT abandon any further schemes.

 

Thus while I think there is still a general "we would like to do his one day" mentality within NR, it is recognised that due to the aforementioned electrification problems such a proposal is not going to happen for several decades. Consequently while things like bridge reconstruction (driven by the bridge condition itself) will continue to make passive provision for OHLE, any 3rd rail traction supply equipment will be renewed on a like for like basis.

[Edwin_m]

I'd describe Shoreditch to Highbury is more than a "short stretch". OK it's not an inter city main line, but it is proof that it is possible to build a brand new route with 3rd rail electrification under the current legislation. And hence, legally speaking at least, an AC/DC changeover within Reading station is possible. Technically would be a different matter, and the lack of any reason to have one is the real obstacle.

Anyway that's way off topic.

 

Pretty sure Shoreditch to Highbury was done before the latest ORR policy appeared.  Most of it must also be amongst the safest areas for track workers, because there are walkways on both sides of the former four-track viaduct. 

 

Had the current policy applied at the time then I think they would have struggled to justify third rail north of Shoreditch.  Adjoining an existing 25kV section it would probably not have needed a new feeder station, which is one of the main costs of 25kV.  The structures on the four-track section already have 25kV on the north side and the only over-structures on the re-opened section were built for the project and no doubt have 25kV clearance anyway.  While the trains are single-voltage, others of the same class are also equipped for AC so extending this to the whole fleet would be relatively inexpensive.  Thus, to my mind, there is nothing that would have rendered the use of OLE "grossly disproportionate" which is now ORR's threshold for allowing third rail instead. 

Edited July 27, 2017 by Edwin_m

[Grovenor]

I'd describe Shoreditch to Highbury is more than a "short stretch". OK it's not an inter city main line, but it is proof that it is possible to build a brand new route with 3rd rail electrification under the current legislation. And hence, legally speaking at least, an AC/DC changeover within Reading station is possible. Technically would be a different matter, and the lack of any reason to have one is the real obstacle.

Anyway that's way off topic.

But Shoreditch to Highbury is not the brand new build, the NLL into Broad Street was 3rd/4th rail and rebuilt (albeit) after quite a long closure). The new build is just the 500 m through Shoreditch from Pedey Street to Batemans Row.

Regards

[phil-b259]

Pretty sure Shoreditch to Highbury was done before the latest ORR policy appeared.  Most of it must also be amongst the safest areas for track workers, because there are walkways on both sides of the former four-track viaduct. 

 

Nope, the ELL extension was authorised after the current ORR guidance was formulated (though much of the planning took place before that) - however the ORR were being practical. Not only was the line an extension of a current 3rd / 4th rail scheme, but most of the rebuilt line was up on viaducts llacked any foot crossings, didn't have platform ramps and was heavily fenced in with palasade fencing where there was any chance of potential trespass. It also benifted from being a TfL driven project and as far as I am awere were TfL to propose a surface Underground extension then the ORR would not insist on OHL instead of conductor rail.

[Zomboid]

But Shoreditch to Highbury is not the brand new build, the NLL into Broad Street was 3rd/4th rail and rebuilt (albeit) after quite a long closure). The new build is just the 500 m through Shoreditch from Pedey Street to Batemans Row.

Regards

Whilst that's true, it's a bit of a stretch to call it a renewal or anything other than a new build. It just happens to be on the route of an old line.

 

And yes, there are conditions around the ELL which means the ORR permitted it to use 3rd rail. It simply proves that such conditions do exist, and new build 3rd rail isn't completely off the table. If and when it actually happens, the Croxley link will be 4 rail as well. Implementing those conditions on the national network may be impossible in a lot of cases, but if (for example, and I realise it's not actually imminent...) Bentley to Bordon were to be reopened, it would get a 3rd rail, not OLE.

[Edwin_m]

The ORR policy document referring to "grossly disproportionate" is undated (poor) but a footnote makes reference to 2012 documents.  So it must be later than that date, by which time the ELL extension had been open to Dalston for several years and was just opening to Highbury & Islington. 

 

It is of course possible that the policy existed in unwritten form (even poorer!) prior to 2012.  I recall doing a web search in around 2005 for the oft-quoted HMRI (as it was) "policy" only to allow third rail as an extension of an existing system and finding no primary source (it was mentioned in evidence to Parliament on the Crossrail Bill when someone asked why the western part of Crossrail couldn't be third rail).  This former "policy" is less stringent than what is now set out. 

 

http://www.orr.gov.uk/__data/assets/pdf_file/0017/17621/dc-electrification-policy-statement.pdf

[rodent279]

IEP seen belting westward this morning through Cholsey, as I passed on a London bound HST, at 0945.

[The Stationmaster]

The biggest question mark over dual system, ie AC + DC, track is the conflict between the floating negative return adopted by the DC system, and the Earthed return adopted by AC. Euston - Camden has had dual electrification for decades, ever since the North London/Watford DC lines were converted from 4th rail, and the world hasn't ended, and there are changeover sections working successfully on the West London Line and at Cheriton, without complication. In comparison, the transfer section at Highbury has remained out of use due to complications, and the present day arrangements between Blackfriars and Farringdon are complex to the point of being a potential reliability problem once the full Thameslink service starts, involving changeover of both positive and negative in order to avoid connecting the two system's negatives. You could be forgiven for thinking that people have forgotten how we used to do things and why.

 

Signalling was the other potential complication, at least when everything had to be done by track circuits, as they needed impedance bonds that could sort out 50Hz traction current, DC traction current and the AC track circuit frequencies, not that this was insoluble. However, the development of axle counter systems has rather avoided the problem. I would presume that the whole of the GW side of Reading is now on axle counter as part of the general resignalling of the main line, but it is not at all beyond the bound of practicality to introduce local axle counter blocks as an emulation of track circuits on the Southern side.

 

Jim

 

The whole of Reading is axle counter, certainly in the station area AFAIK

[The Stationmaster]

Govt does at least seem to be continuing to be wholly capable of double speak with private cars having to go electric in 2040 while trains aren't being allowed to go electric with schemes already underway (or which were underway).

 

In the meanwhile work continues between Reading and Newbury with further structures appearing and some already provided with registration arms - overall work seems to be to the pattern we know and love with one part of the job not finished on a particular stretch before the next part, or the one after it, or even the one after that, has been started on the same stretch.  However both of the main workbases looked pretty bare of component supplies.

 

Reading is looking increasingly 'electrified' with all platform lines done and most catenary in place east of the station (see below) although clearly - as has been the case elsewhere) a lot of detail work remains to be done.  At Twyford one mast on the Up Relief side remains 'missing' (it is lying on the ground nearby) but the Reliefs are now wired through the station and it looked earlier this week as if the 25kv feeder route might be in course of construction on the Down Main side.

 

(click on a picture to enlarge it)

 

Reading east end 180717

 

 

Twyford looking west 260717

 

 

Twyford looking east 260717, the wooden panel in the tarmac at extreme left covers the foundation for the missing mast - presumably there will be no lead-off of the ohle onto the branch?

 

 

 

[Banger Blue]

The whole of Reading is axle counter, certainly in the station area AFAIK

The whole of Reading (including the depot) is Axle Counter and certainly as far as, if not already including Didcot Parkway Station area.

[jim.snowdon]

And so, I would expect, will the DC lines into Reading once the Feltham resignalling project is completed (sometime). In any case, it is entirely feasible to convert the Reading end of the line to axle counter and still interface it with the existing relay interlockings. The tricky bit is arranging the tractin negatives so as not to create a significant stray current problem, and that will be determined by such factors as where the AC section is in relation to the DC substation and how the OLE can be earthed separately from the running rail (as is done on the Paddington approaches).

 

Jim

[rodent279]

And so, I would expect, will the DC lines into Reading once the Feltham resignalling project is completed (sometime). In any case, it is entirely feasible to convert the Reading end of the line to axle counter and still interface it with the existing relay interlockings. The tricky bit is arranging the tractin negatives so as not to create a significant stray current problem, and that will be determined by such factors as where the AC section is in relation to the DC substation and how the OLE can be earthed separately from the running rail (as is done on the Paddington approaches).

 

Jim

 

If it's an all axle counter area, what is the problem with stray earth currents? Is it just a matter of making sure ntohing becomes live that shouldn't, or that electrolytic corrosion is minimised, or can stray earth currents still interfere with axle counters? Or do you still have a small number of track circuits?

Edited July 30, 2017 by rodent279

[Edwin_m]

If it's an all axle counter area, what is the problem with stray earth currents? Is it just a matter of making sure ntohing becomes live that shouldn't, or that electrolytic corrosion is minimised, or can stray earth currents still interfere with axle counters? Or do you still have a small number of track circuits?

 

DC railways are generally kept insulated from earth because of the risk of stray currents (the insulation is not perfect which prevents people getting electric shocks when climbing on trains etc).  AC railways don't cause stray current corrosion and everything is earthed, due to protection against passengers or staff encountering dangerous voltages I think.  So areas of dual electrification need some compromise between these rather

[Southernman46]

The AC/DC problem will be lessened at Reading as the DC traction substation is immediately adjacent to the section giving a fairly low attenuation on the traction return - beef up the negative return (i.e. reinforcing cables at S&C etc.) to sort that, the track down to Reading Spur Jn is relatively new and the rail pads etc non-leaky - new insulators on the +ve side etc ..... all reduces the problem relating to the mis-matched traction systems - there are also systems that can be fitted to the negative return that monitor relative -ve return & earth voltages and alarm or even trip the DC system feed HSCB's should a serious issue occur - don't know if that is being done though.
 

EDIT - in fact aren't the AC & DC lines at Reading going to entirely separate from each other ?? (in traction terms - not physically) so that there will be no dual traction fitted sections areas unlike the old NLL (that really was a head scratching scenario) - makes things even easier - just the DC leakage to earth to worry about then ...................

 

Related trivia fact ........... Reading UK Power Network Grid site is a 33kV intake point for the SR traction system and the cable (feeder 219 ISTR) runs in the Down GWML cess - we trialled some of the original "Project Mercury" GRP trunking on the route back in the day (1984 ???) - crikey it was shite and not fit for purpose - back to concrete then  .....  was the 1st time I got to play on the track with those nasty fast 125 trains  

Edited July 31, 2017 by Southernman46

[david.hill64]

If it's an all axle counter area, what is the problem with stray earth currents? Is it just a matter of making sure ntohing becomes live that shouldn't, or that electrolytic corrosion is minimised, or can stray earth currents still interfere with axle counters? Or do you still have a small number of track circuits?

Technically this is a complex topic, but to add to what Edwin and Jim have said so far, I'll offer the following.

 

Electric railways, AC or DC, provide one source of electricity (wire or rail) and usually use the running rails to provide the return current path. The enlightened exceptions include London Underground where the 4th rail is provided.

 

If you let the DC electricity leak out of the running rails into the earth, it will corrode any metal structures (viaduct reinforcements, tunnel linings, gas mains etc) in the vicinity. This is generally considered a 'bad thing' for obvious reasons. AC doesn't do this so you don't have to be so careful about the return path. I am not an expert on main line third rail systems, but in DC metros there are two approaches adopted for getting the return current back safely to the feeder stations which are likely to be about 2-3km apart. You can either ensure that the running rails are nominally insulated from the track bed with rubber pads under the foot of the rail and ensuring that any metallic fastenings are insulated from the rails or you can be less strict about that and install a current collection mat (basically steel mesh) in the track support system and connect this and the rails to the negative pole at the feeder station.

 

There will be a voltage in the rails arising from the return current. This may be in the order of 100V. These voltages and currents can interfere with track circuits (hence the development of 'traction immune' circuits), but generally have no effect on axle counters. You do not require track circuits in areas where there are axle counters. Generally speaking it is not a good idea to duplicate train (vacancy) detection systems: if they give conflicting results who do you believe? In modern communications based train control systems where train location information is sent by the train itself, the presence of a secondary detection (axle counter or track circuit) system gives rise to interesting arguments about which to believe when they differ - clearly the safe option is to believe whichever system says 'occupied' but this is a off-topic.

 

The fact that rails will have a voltage in them, and that metallic structures in the vicinity of the railway will have voltages induced in them from the traction supply leads to the possibility of electric shocks so there are standards governing 'step and touch' potentials. You want to avoid the situation where it is possible for a person to touch (or step between) two (metallic) structures at different potentials. In an AC-only railway this is easy to control: you just bond all surrounding metallic structures to the running rails and these are essentially at earth potential. (let's forget about booster transformers and auto transformers systems but essentially still have the same bonding principles).

 

For DC it is more complicated: as the running rails are nominally isolated from earth then trains themselves can be at a non-zero potential when at a station. If the station is at earth then there is a possibility of electric shocks as people board the train. For this reason the platforms of metros are usually electrically isolated from earth and platform screen doors bonded to the running rail. On the main line it means that objects such as point machines have to be bonded to the running rail and insulated from earth and any metallic lineside structure that is earthed must be about 2m from the nearest running rail. DC metro systems also have over voltage trip devices so that if rail voltage gets above 120V the system will short circuit to earth.

 

The problem is reconciling the two fundamentally different approaches for AC and DC in mixed systems. As Jim says, it can be done but it requires thought.

[Zomboid]

EDIT - in fact aren't the AC & DC lines at Reading going to entirely separate from each other ?? (in traction terms - not physically) so that there will be no dual traction fitted sections areas unlike the old NLL (that really was a head scratching scenario) - makes things even easier - just the DC leakage to earth to worry about then ...................

 

Related trivia fact ........... Reading UK Power Network Grid site is a 33kV intake point for the SR traction system and the cable (feeder 219 ISTR) runs in the Down GWML cess - we trialled some of the original "Project Mercury" GRP trunking on the route back in the day (1984 ???) - crikey it was shite and not fit for purpose - back to concrete then ..... was the 1st time I got to play on the track with those nasty fast 125 trains

I invented this AC/DC changeover thing when I mentioned that 387s are dual voltage and could therefore run onto the southern if a changeover was provided. As far as I know the systems are not actually going to be electrically linked, so I guess the only consideration should be whether any of the DC lines are within the OLE drop zone, if not they shouldn't need earthing.

[corneliuslundie]

Dual systems were done years ago of course in some of the platforms at Euston.

Jonathan

[jamie92208]

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

[The Stationmaster]

The whole of Reading (including the depot) is Axle Counter and certainly as far as, if not already including Didcot Parkway Station area.

 

Has the Didcot area now been converted?  Orignally axle counters were not provided on the former Swindon B control area as it was a straight swap from control at Swindon B, which was of course electronic interlocking, to control by TVSC (I think the signal numbers at Didcot still reflect that although I must admit I haven't checked them recently and there have been some alterations).  The former Swindon A area, i.e. the original Swindon panel, has changed over to full TVSC interlocking and control so also has changed to axle counters.  That apart everything east of Moreton Cutting all the way to Stockley Bridge was axle counter equipped, including the branch lines, by last December and of course by then all the former relay interlockings had gone (not necessarily physically but in operational terms as TVSC took over full electronic control and the interim control of existing relay interlockings ended - easily traced from the changes to signal numbering).  

 

in simplistic terms it would appear that all areas which have gone onto new TVSC interlocking are equipped with axle counters but when previous electronic interlockings have gone onto control from Didcot the previous track circuiting has remained (i.e Slough New and Swindon B control areas).

 

As far as Reading SR is concerned the information is in two separate Appendixes (appendices?) but New Jcn to Reading Spur Jcn is axle counter so I expect that everything west of Reading Spur Jcn and into the station will also be axle counters.

[rodent279]

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

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.

Edited July 31, 2017 by rodent279

[Geoff Endacott]

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

 

Geoff Endacott