Great Western Main Line electrification - ongoing discussion

[whole diary]

[EBrown]

I believe slab track is similar to the track inside St. Pancras International?

[BerkshireBugsy]

It's been a while since I have been to st. Pancras but I believe you are right

[paul7575]

The only time I can envisage conrail trough the underpass would be as part of an AC / DC^▸ (Direct Current) interface where a electrical section OHL^▸ (Over-Head Line) overlaps a conrail electrical section.  The ORR^» (Office of Rail and Road formerly Office of Rail Regulation - about) and not keen to extend DC third rail and it is not current NR^» (Network Rail - home page) policy to extend it either.   

I also thought that the underpass would have been the most obvious/logical place to have a short changeover section, and there have been a number of subsequent statements, (including by NR in response to FGW^▸ (First Great Western) as recently as last October) that they intend to allow for AC and DC in the underpass:

{FGW}
25. Paragraph 5.10 Remodelling of East Throat: Network Rail to advise extent of third rail and / or overhead electrification intended or if passive provision provided in the southern underpass;
{NR}
The Up and Down Reading Low Level Line is provided with passive provision for AC & DC electrification with headroom clearances and 3rd Rail sleepers being installed.

http://www.networkrail.co.uk/browse%20documents/network%20code/network%20change/current%20proposals/reading%20redevelopment/nc%20g1%20rsar%20002/train%20operator%20replies/first%20great%20western/reply%20to%20fgw%20stage%20f%20ncn%2003102012.pdf 

However DfT^» (Department for Transport - about) have also said in the GW^▸ (Great Western) franchise ITT^▸ (Invitation to Tender):

"The three new north side platforms and the new dive under at Reading station will be equipped [...] to facilitate third rail electrification."

Which suggests to me tripling the complexity of the power supplies for little operational gain, although I suppose changeover during a planned station call is always going to be better than a stop outside the station; especially where a changeover failure would block a single track.   Swings and roundabouts...

Paul

[Western Explorer]

@Paul7755: "I also thought that the underpass would have been the most obvious/logical place to have a short changeover section, and there have been a number of subsequent statements, (including by NR^» (Network Rail - home page) in response to FGW^▸ (First Great Western) as recently as last October) that they intend to allow for AC and DC^▸ (Direct Current) in the underpass"

It would be preferable to make the changeover in a platform because then there are more options if it fails for any reason. You don't want to have a train stuck in the underpass or needing to reverse out, even though it is bidirectional.

[Network SouthEast]

Aside from disruption risk when changing from AC to DC^▸ (Direct Current) due to rolling stock issues there are two other factors that have not been mentioned by posters yet in respect of changing over at a platform.

1. driver of AC trains forgetting to pan-down when changing over to DC mode, and then either activated the ADD^▸ (Automatic Dropping Device) or worse... hitting a bridge or other object and ripping the pan off.

2. door release other than in a platform - several incidents of this each year, but thankfully no injuries to passengers. Why create an extra risk?

It is possible to change over from AC to DC on the move, as is done by London Overground (but not Southern) on the WLL at North Pole, however it requires a fairly substantial overlap.

As the underpass is only a short distance I really don't see why posters here are making a fuss about DC overlapping with AC. There are plenty of examples on the rail network already where ECOs^▸ (Electrical Control Officer) (and their substations/infrastructure) provide AC and DC supply in the same location.

[paul7575]

@Paul7755: "I also thought that the underpass would have been the most obvious/logical place to have a short changeover section, and there have been a number of subsequent statements, (including by NR^» (Network Rail - home page) in response to FGW^▸ (First Great Western) as recently as last October) that they intend to allow for AC and DC^▸ (Direct Current) in the underpass"

It would be preferable to make the changeover in a platform because then there are more options if it fails for any reason. You don't want to have a train stuck in the underpass or needing to reverse out, even though it is bidirectional

I'm not disagreeing with that point though.  What I went on to suggest is that the costs of having three dual voltage platform areas, is significantly higher than doing it along the length of the underpass - and this might colour their decision.

Having said this it's already been discussed to death once in the main Reading Station thread anyway, so I'll leave it there I think.

Paul

[Electric train]

AC / DC^▸ (Direct Current) change over sections are not short.  They are usually 3 electrical sections which have to longer than the longest train to use the section, note this include non electric traction hauled trains; it can be done with 2 electrical sections which may be the case at Reading as there are 2 rectifiers at Reading to manage the DC return current, at least 1 of these would have to be in service for AC / DC change over, AC will almost certainly need the installation of isolation transformers.

I know the GW^▸ (Great Western) electrification team have looked at the system we installed at Ludgate Cellars system used for the Thameslink change over at Blackfriars this is an extremely expensive and complex contractor system.

The actual change over of power from one to the other is the easy part its the managing the traction return currents that are the problems.  Stray DC cause electrolytic erosion ferrous  items like rebar, bridge steels, cable armours etc (and not just on railway owned land) also track circuits have to be DC immune over a considerable distance; for stray AC this is more an EMC^▸ (ElectroMagnetic Compatibility) issue with telecoms and track circuits but can cause some rise in earth potential under fault conditions on the AC system.

[Chris from Nailsea]

On a lighter note - from First Great Western JourneyCheck:

15:16 Avonmouth to Bristol Temple Meads due 15:50
This train will be cancelled.
This is due to electrical supply problems.
Message Received: 31/12/2012 14:35

 

[chuffed]

Did they find that the pantograph wouldn't fit a 142 ??

[paul7575]

I last went into Reading (from Maidenhead) about three weeks ago by which time track had been laid into P13-15 from the Southern underpass.

Webcams show the rail was delivered through the platforms a little later than that; it only appeared from Sun 16th, and sleepers were being fitted on the 18th and 19th. 

However, the main reason for my looking back to those dates was that you can just see that the sleepers actually used, in P13/14 at least, definitely are fitted with the threaded inserts for third rail insulators. (You need the extreme bottom right view of camera 1/1 at 100% magnification, try about mid-day on the 19th.)

As they are buried in ballast now you can't see that sort of detail any longer.  Seriously though I realise it's still a work in progress and the sleepers will probably reappear during final tamping and lining etc...

Paul

[Western Explorer]

On a lighter note - from First Great Western JourneyCheck:

15:16 Avonmouth to Bristol Temple Meads due 15:50
This train will be cancelled.
This is due to electrical supply problems.
Message Received: 31/12/2012 14:35

 

This was at Reading P16 on 12th December. I was last there on the 14th but sans camera.


Edit note: Quote marks fixed. CfN.

[onthecushions]

Happy New Year everyone.

Might not the ac/dc change-over be simpler on the Wokingham line rather than at Reading, as dual voltage stock is now to be the future for the South Western....

S'pect it's been suggested before,

OTC

[IndustryInsider]

Worth mentioning that preliminary work continues at a pace, with foundation holes dug most of the way from Reading to Oxford for the overhead masts that will be installed by this wonderful electrification train that will soon be with us.

Most of the holes have simply been dug, lined with a strong canvas sack with handles, and then filled in with gravel, soil and ballast.  But at a few locations the foundation post to which the gantry will be attached has also been installed.

[Electric train]

Worth mentioning that preliminary work continues at a pace, with foundation holes dug most of the way from Reading to Oxford for the overhead masts that will be installed by this wonderful electrification train that will soon be with us.

Most of the holes have simply been dug, lined with a strong canvas sack with handles, and then filled in with gravel, soil and ballast.  But at a few locations the foundation post to which the gantry will be attached has also been installed.

In OLE^▸ (Overhead Line Equipment, more often "OHLE") teams gantries are refereed to as Structures, the dig out structure foundations ahead of being filled with concrete is quite normal often they are hand dug.

The first part of the GW^▸ (Great Western) Mainline electrification to be commissioned is Reading Oxford, this will allow driver training. East of Reading relies on Kensal Green feeder station and Crossrail electrifying Stockley to Maidenhead 

[ellendune]

Work is now well under way at the Swindon Electrification Depot.