GWML Electification

[Northroader]

Looking out of the window on the stretch Westerleigh to Bristol Parkway this week, overbridges (not many) and signalling cable troughs all look about there, but most of this stretch is on high embankments and viaducts, and it's hard to detect any work at all on the mast foundations. The hitachi depot west of BPW looks ready, fully wired, but there'll be a long wait before any sets get there under their own steam, so to speak.

[HillsideDepot]

Looking out of the window on the stretch Westerleigh to Bristol Parkway this week, overbridges (not many) and signalling cable troughs all look about there, but most of this stretch is on high embankments and viaducts, and it's hard to detect any work at all on the mast foundations. The hitachi depot west of BPW looks ready, fully wired, but there'll be a long wait before any sets get there under their own steam, so to speak.

Strange you should say that, as I've just looked at the NR website which has been updated today with this weekend's work plan:

 

Hullavington - Westerleigh Jn

 

Saturday 27th August 2016

02.00am - 11.00am

2.00pm - 11.00pm

Local Authority: Wiltshire and South Gloucestershire

 

Sunday 28th August 2016

02.00am - 11.00am

2.00pm - 11.00pm

Local Authority: Wiltshire and South Gloucestershire

 

I might pop out for a look, although I have also just visited the Met Office website too!

 

[modfather]

Looking out of the window on the stretch Westerleigh to Bristol Parkway this week, overbridges (not many) and signalling cable troughs all look about there, but most of this stretch is on high embankments and viaducts, and it's hard to detect any work at all on the mast foundations. The hitachi depot west of BPW looks ready, fully wired, but there'll be a long wait before any sets get there under their own steam, so to speak.

They currently run under diesel. I believe they are short of a substation.

[brian daniels]

I have been looking at the overhead between Didcot and Reading and I wonder if someone can help me. What is the wire for that dangles from the insulator at the top of each up-right? I see that it is not a continuous wire at the moment like the contact wire. There are a couple of gaps and at a few over bridges it just ends in a curl of wire waiting to be fed under the bridges.

[RJS1977]

I was wondering the same thing having spent nearly 12 hours at Cholsey station last weekend!

[St. Simon]

Hi,

 

I don't know the answer (helpful I know), but if its on the Relief lines side of the formation, then it may not need to be continuous as the Reliefs at the moment are yet to be energised as far as I'm aware.

 

Simon

[The Stationmaster]

I have assumed - probably totally incorrectly - that it is some sort of return or (current) balancing wire as it is suspended from insulators.  There are also high voltage cables in new metal troughing in places as well.

 

I noticed today that although the Reliefs between Scours Lane and Purley Marina are now wired they are various bits which I would describe as 'jury rigged' to structures in the vicinity of Tilehurst East Jcn - readily identifiable in some cases from the bits of blue or orange plastic wrapped around them.

[The Stationmaster]

Hi,

 

I don't know the answer (helpful I know), but if its on the Relief lines side of the formation, then it may not need to be continuous as the Reliefs at the moment are yet to be energised as far as I'm aware.

 

Simon

This wire wasn't continuous on the Main Lines side even when they were first being energised Simon - several gaps in it.

[lmsforever]

The haphazard way this job seems to be carried out is causing problems for the new timetable using bi mode units with only a top speed of 100mph on diesel it will be hopping from the wires to non electric all the way so passengers are going to be inconvienced.

[St. Simon]

This wire wasn't continuous on the Main Lines side even when they were first being energised Simon - several gaps in it.

 

Okay, ignore me then (you probably were anyway, I would!)

 

Simon

Edited August 31, 2016 by St. Simon

[brian daniels]

This insulated wire is on the mainline side. I was just wondering that it was supposed to have been energized a while back but without this wire "wired up" what is it there for?

[nightstar.train]

If you look at this document linked above

 

http://www.bathnes.gov.uk/sites/default/files/sitedocuments/Planning-and-Building-Control/Planning/nr_a_guide_to_overhead_electrification.pdf

That wire seems to be something to do with the auto transformer feed. I think it's basically a 25kv bus line to supply the sections. It allows the project to use fewer transformers from the grid, which is a big saving.

[Titan]

If you look at this document linked above

 

 

That wire seems to be something to do with the auto transformer feed. I think it's basically a 25kv bus line to supply the sections. It allows the project to use fewer transformers from the grid, which is a big saving.

 

It is actually quite clever, it is 25Kv, but it is 180 degrees out of phase with the contact wire. This effectively makes it a 50Kv system, with a resultant increase in power available, and/or increase in the distance apart feeder stations can be, which means you need fewer of them. You still only need 25Kv clearance to earth and 25kv insulators, but you must have 50Kv clearance from this cable to any other live part of the OLE. However getting 25Kv clearance to earth under bridges is a bit more tricky compared to the tensioned OLE, so they tend to be run as heavily insulated cables in troughing under bridges. They also in theory perform the same function as the return conductor in reducing inductance/interferance in the signalling cables. However modern traction and signalling systems tend to be much better in this respect compared to 1960's technology, so it is likely that existing return conductor systems may be removed as they will no longer be necessary.

 

One other innovation that will become common place in the future is invertor feeder stations. It has always been a bit awkward in that the railway imposes a heavy single phase demand on a three phase national grid. They try to mitigate this by having adjacent feeder stations on different phases, but it is far from ideal. With an invertor feeder station you can take load from each phase evenly, rectify it to dc and then invert it to single phase AC. Not only does this eliminate asymmetric loading on the national grid, but all feeder stations can output on the same phase as each other eliminating the need for neutral sections, since the output phasing is independent of the input. I think they also make regenerative braking feeding back in to the grid easier as well.

Edited August 31, 2016 by Titan

[Edwin_m]

If posts on other forums are to be believed, some of the North West electrification was energised before the AT wire was completed.  This suggests it is possible to run the system without it, though presumably not supplying full power.

[Zomboid]

That's called the autotransformer feeder. Titan's explanation is about right. Return conductor systems with Booster transformers suffer higher losses because they increase the impedance of the system, so if satisfactory immunisation can be achieved without them then that is better all round.

 

There are no inverter feeder stations on GW though, all the connections are via conventional 400 or 275kV SGTs. The benefit of inverters is that the load is balanced across all the phases so the connection can be at a lower voltage, potentially as low as 33kV, which is a much cheaper connection, but so far there are none in this country, and GW isn't going to change that.

[The Stationmaster]

If posts on other forums are to be believed, some of the North West electrification was energised before the AT wire was completed.  This suggests it is possible to run the system without it, though presumably not supplying full power.

 

The same has happened on the GWML where that cable was not in place all the way between Reading and Didcot when Class 800 trial running on electric power began.

 

In relation to the explanation given above by 'Titan' regarding the use of cable instead of an overhead conductor this is the cable troughing in course of installation at Tilehurst

 

 

Another interesting feature which I had never noticed before, seen here below the footbridge at Tilehurst, is what appears to be some sort of insulated sleeving applied to the catenary and earth wires where they pass under the footbridge.  This week I have also noticed that it is in place under some of the electrification structure girders at Tilehurst East Junction. (click on the pic to enlarge it for a better view)

 

Edited September 1, 2016 by The Stationmaster

[Titan]

 

Another interesting feature which I had never noticed before, seen here below the footbridge at Tilehurst, is what appears to be some sort of insulated sleeving applied to the catenary and earth wires where they pass under the footbridge.  This week I have also noticed that it is in place under some of the electrification structure girders at Tilehurst East Junction. (click on the pic to enlarge it for a better view)

 

 

It is just mitigation where clearances are tight. The insulation is not thick enough to provide full 25Kv protection, but the idea is that small air gap + some insulation reduces the flashover risk to earth compared to having no additional insulation at all. Quite why the contractors have decided to put insulation on the earth wire too I have no idea...

[Vanders]

Quite why the contractors have decided to put insulation on the earth wire too I have no idea...

"Put insulating sleeves on the wires going under the bridge"

"Okay boss"

...and lo'

[RJS1977]

What effect is a pantograph going to have on the sleeving? I would imagine that it would be more prone to wear than the wires themselves.

 

Alternatively there's the possibility the sleeving could get dragged/pushed along out of position by the pan if the wire contracts at a greater rate than the sleeving in cold weather.

[Grovenor]

There isn't any sleeving on the contact wire.

Regards

[RJS1977]

There isn't any sleeving on the contact wire.

Regards

Oops - you're right - I saw the two bits of sleeving close together and thought one was on the top and one on the contact wire, but now I realise it's an overlap section and they're both on the top wire. Makes more sense.

[St. Simon]

Hi,

 

In relation to the sleeving, I attended a meeting during summer last year about a totally seperate project on Western where the OLE design team were present. During this meeting we discussed clearance for the OLE. They revealed that the standards had changed in summer last year to increase the clearance required in and around station areas.

 

I presume at this time the bridges for Tilehurst etc were probably still in the design stage, or maybe early construction phase, so the change in clearance requirements may have delayed the installation and the sleeving may be a way of getting around a change in standards quickly and effectively. 

 

Of course, I can only guess at it, but that might explain the sleeving

 

Simon

[RJS1977]

I seem to remember hearing a rumour that Tilehurst footbridge was built lower than it should have been, with insufficient clearance for the OHLE. Was it rebuilt, or is the sleeving the workaround for this?

[Great Western]

Class 800 sets 800002 and 800004 carried out three nights of testing this week between North Pole and Bristol Temple Meads.

 

Virgin coloured 002 standards on Platform 9 at Temple Meads, on Friday 02nd September 2016.

[talisman56]

Class 800 sets 800002 and 800004 carried out three nights of testing this week between North Pole and Bristol Temple Meads.

 

Virgin coloured 002 standards on Platform 9 at Temple Meads, on Friday 02nd September 2016.

 

The Graffiti 'Artists' have been at the new stock already...