Great Western Main Line electrification - ongoing discussion

[whole diary]

[John R]

I noticed yesterday that a fair section of the route between Airport Jn and Maidenhead appears to be being wired with two separate stanchions, unconnected by an overall girder.  So, as an example, both up and down relief line wiring are supported solely by the stanchion to the outside of the track. 

It occurred to me that this is likely to look marginally less obtrusive than the design used in the Goring Gap, and could be a possible solution.  There's no obvious reason to me why the spacing of the tracks at the latter location would be unsuitable for this design, and it could be relatively simple to convert.  Am I missing something obvious here, as it it were that obvious, I'm sure it would have been suggested by now.

[IndustryInsider]

Separated structures have usually been used when there's a significant difference in height between the leftmost and rightmost line - not uncommon with the cant required on high speed corners.  Could possibly have been used in more areas between Didcot and Reading but obviously more pulling forces are loaded onto the uprights, so perhaps that's why full ones have been used?  There's also more places with wider gaps between main and relief lines east of Reading which might also have been a factor.

[Electric train]

Technical question. I live by the only (?) fully wired stretch (4 lines) between Burnham and Taplow, which was done at Christmas 2015.

Now we are getting a kind of gibbet being fitted on top of the horizontal arm which holds the hangers (dangly bits) for the wires. Looks like there will be another wire slung between them. What's it for?

From your description that's for the 'Auto Transformer Feeder' or ATF.   

As a modern design the GW^▸ (Great Western) OHLE is actually fed at 50 kV, with two anti phase 25 kV conductors.  So you get a 25 kV - Ov - 25 kV feed where the rails are the Ov line, the contact wire (and its support catenary) is at 25 kV, and your newly observed line is also at 25 kV but anti phase to the contact wire.  So the ATF needs similar insulators to the contact wire, similar clearances from structures, and needs to be positioned where it cannot accidentally touch the contact wire under fault conditions.

It's all a bit complicated electrically, but it all helps make the system far more efficient than the earliest simple 25 kV with traction return down the rails.

The autotransformers themselves are mounted in various track side compounds along the line, how they actually work in terms of detail is above my pay grade, so I think although they should be mentioned as existing, that'll do for now...

Paul

The use of Auto Transformer feeding basically doubles the distance between Grid sites; GWML^▸ (Great Western Main Line) Kensal Green and Didcot approx. 50 miles with the mid point (MPATS^▸ (Mid Point Auto Transformer Site - electrification) at Maidenhead (which has AT's) there are also AT's at West Ealing, Hayes, Slough these are intermediate IATS.

The IATS and MPATS are to manage the return current and to ensure the OLE^▸ (Overhead Line Equipment, more often "OHLE") voltage is constant.  The reason for 50kV is simple Ohms Law I²R

Also the fault levels on AT systems are higher 12kA where as classic 25kV is 6kA.

AT is a more complex system, especially the protection (fuses) scheme and the level of immunisation that has to be done is more complex, however it is more efficient as it reduces the number of Grid Sites which are now at 400kV locations.  Its worth noting that the Kensal Green Grid Lines are in a tunnel 

[Bmblbzzz]

I noticed the other day that something is being constructed or some work is being done on the southeast side of the Foss Way Bridge between Partway and Wootton Bassett. The bridge itself was reconstructed last year, so could it be a grid site? Or is it something else?

http://streetmap.co.uk/map.srf?X=386135&Y=182740&A=Y&Z=120

[IndustryInsider]

Another excellent article from railengineer, this time concerning the Severn Tunnel electrification:

http://www.railengineer.uk/2016/06/02/preparing-for-severn-tunnel-electrification/

[DidcotPunter]

Did a run from Oxford to Reading and back via Didcot so could see progress on completing the test section between Didcot and Tilehurst.

Up and down main lines are fully wired from Scours Lane, Reading to Moreton Cutting east of Didcot, including the crossover between the lines at Tilehurst East Junction. Relief lines are also mostly wired from just east of Tilehurst to Moreton Cutting. There are some wire runs missing through Goring and between South Stoke and Moreton Cutting but these don't look big jobs to complete.

The Didcot station area is still to be wired though there's an earth return wire in place on the main lines through platforms 1 & 2. Most of the small part steelwork is in place and all the main steelwork too from what I could see.

West of the station there is a wire run on the main lines at Foxhall Junction but nothing else wired through to Milton Junction.

The autotransformer stations at Pangbourne and Moulsford are being wired up (presumably the National Grid feeder at Foxhall Junction is too, but I couldn't see that). There's a run of autotransformer feeder wire around Pangbourne but I didn't notice any more in place, though several brackets an insulators have been added to the gantries for it.

So it looks like the test section is nearing completion with just the Didcot area to complete (and presumably the relief lines east of Tilehust to Scours Lane).

[ellendune]

I have seen a lot of lorries carrying electrification large metal parts on the A4361 through Wroughton, both towards Swindon and away from Swindon. Does anyone know where is it going to/from? 

If it were going towards the track west of Swindon it is on the wrong road. If it is coming to Swindon I cannot think where it would be coming from. 

[TonyK]

I have seen a lot of lorries carrying electrification large metal parts on the A4361 through Wroughton, both towards Swindon and away from Swindon. Does anyone know where is it going to/from? 

If it were going towards the track west of Swindon it is on the wrong road. If it is coming to Swindon I cannot think where it would be coming from. 

Are we talking the bases or the all above ground bits?

[Electric train]

Did a run from Oxford to Reading and back via Didcot so could see progress on completing the test section between Didcot and Tilehurst.

Up and down main lines are fully wired from Scours Lane, Reading to Moreton Cutting east of Didcot, including the crossover between the lines at Tilehurst East Junction. Relief lines are also mostly wired from just east of Tilehurst to Moreton Cutting. There are some wire runs missing through Goring and between South Stoke and Moreton Cutting but these don't look big jobs to complete.

The Didcot station area is still to be wired though there's an earth return wire in place on the main lines through platforms 1 & 2. Most of the small part steelwork is in place and all the main steelwork too from what I could see.

West of the station there is a wire run on the main lines at Foxhall Junction but nothing else wired through to Milton Junction.

The autotransformer stations at Pangbourne and Moulsford are being wired up (presumably the National Grid feeder at Foxhall Junction is too, but I couldn't see that). There's a run of autotransformer feeder wire around Pangbourne but I didn't notice any more in place, though several brackets an insulators have been added to the gantries for it.

So it looks like the test section is nearing completion with just the Didcot area to complete (and presumably the relief lines east of Tilehust to Scours Lane).

It is likely the "test track" will be configured as classic 25kV rail return, the Auto Transformers not commissioned they are not required at this stage because there is only likely to be one or two units running intially.  Setting up the OLE^▸ (Overhead Line Equipment, more often "OHLE") protection and control running in classic is a much simpler arrangement and is often done on the UK^▸ (United Kingdom) main lines, the ATF being commissioned at a latter stage

[ellendune]

I have seen a lot of lorries carrying electrification large metal parts on the A4361 through Wroughton, both towards Swindon and away from Swindon. Does anyone know where is it going to/from? 

If it were going towards the track west of Swindon it is on the wrong road. If it is coming to Swindon I cannot think where it would be coming from. 

Are we talking the bases or the all above ground bits?

Above ground bits

[bobm]

Ahead of the wires, the signs are also going up warning trains where they can't go....



Aren't they officially the Chester lines?

[IndustryInsider]

Aren't they officially the Chester lines?

They are indeed.  A mistake?  Or perhaps a (sensible) renaming to coincide with the electrification work?  Anyone know the date of the last Paddington to Chester service via Oxford?  I reckon it might have been as long ago as the 1960s!

[ellendune]

They are indeed.  A mistake?  Or perhaps a (sensible) renaming to coincide with the electrification work?  Anyone know the date of the last Paddington to Chester service via Oxford?  I reckon it might have been as long ago as the 1960s!

I would imagine that they would have used the High Wycombe and Bicester route once that was open so it could have been a lot earlier than that. Though there may have been some rerouting during WCML^▸ (West Coast Main Line) electrification in the 1960's when the London Birmingham express services were all concentrated on the Paddington route.

[Oxonhutch]

According to the WR Sectional Appendix (p. 148 of Mod. WR2; document page 320), the photograph is of 'Chester Line Junction' but the route is now called the Up and Down Oxford.

[paul7575]

According to the WR Sectional Appendix (p. 148 of Mod. WR2; document page 320), the photograph is of 'Chester Line Junction' but the route is now called the Up and Down Oxford.

There are different names for different purposes, the boxes at the top of the page still show the route number GW^▸ (Great Western) 200 as being Didcot to Heyford, but having the engineer's line reference (ELR) of "DCL". 

Whether or not it is hierarchical, I don't know, but sections of line can change name every few miles.  I bet the bridges are all still labelled DCL/x...

Paul