Great Western Main Line electrification - ongoing discussion

[whole diary]

[Red Squirrel]

There are still gaps  . I was in Wiltshire yesterday; I seen em.

[stuving]

By placing the "0" or Neutral point earth connection at the NR^» (Network Rail - home page) end the secondary of the 400/25-0-25kV transformer is electrically isolated from the National Grid earth, there will be a rise in potential on NR infrastructure in the event of a 400kV fault however its is of a lower magnitude.

At Didcot there is sufficient distance between the Grid earth and NR earth for the Grid fault rise of potential to be below the 645V level.

It was all explained to me by an earthing boffin who can quite frankly bore for England on the subject 

I did find a national grid picture that showed that neutral earthed at their transformer, but also showing both stations sitting over the same buried earth mat. That might not reduce the voltage difference enough, and either way there's clearly a problem when you connect that to the earth at the railway feed point. But I know what you mean about earthing experts, even if my encounters with them have been to do with very much higher frequencies. You still see the same effect, that all earths are not equal, voltagewise, but without those scarily high currents.

That's really what struck me most about that site; how small it is. We are used to seeing NG^▸ (Natural Gas)'s big toys in a compound 50 m across in the middle of a field (and so are they). At Kensal Green, those transformers are within 10 m of a public footpath - the canal towpath. Given their standard fault current (into the ground at a single point) is 63kA, and most lightning in this country is below 10 kA, I'd say that looks like a serious safety management problem.

It's all very well to read that these days the experts don't think step voltage (between your two feet, making a current flow up one leg and down the other) is a big risk, because the current has no reason to go near your heart. But you do have to know not to touch the ground with anything but a rubber-soled foot.

Maybe there are signs on the towpath saying "no walking sticks, and don't even think about those walking pole things" - and what about the poor fish?

Here's a picture of the site - the view is about 200 m across. The smaller sheds have shafts in them, as can be seen for the earlier pictures. I do hope they left enough of a raised wall around those shafts to stop the canal ever getting in, even in a serious flood.

[stuving]

Fancy another armchair expedition? This time to hunt for big wormholes across London?

National Grid's London Power Tunnels have got a lot less publicity than Thames Water's supersewer (at least out West of London). But it is still quite impressive - while slim, it is pretty long.

I found this list of the twelve shaft sites, detailed enough that you can plug them into Google Earth and go straight there.

Seagrave Road, Earls Court
Millfields Park, Hackney
Eade Road, Haringey
Seven Sisters Road, Highbury
Lough Road, Islington
Canal Way, Kensal Green
Lodge Road, St. John’s Wood
Royal College Street, St. Pancras
Armoury Way, Wandsworth
Acton Lane, Willesden
Channel Gate Road, Willesden
Riverside Road, Wimbledon
(There's a separate tunnel from Hurst to Eltham.)

You may need to hunt for the site itself, and then you'll then need to wind back time to see the holes; they are now hidden by sheds ("headhouses"). Kensal Green has two shafts (as does Hackney). I think that has to do with the tunneling itself - three tunnels meet there, from Willesden, Hackney, and Wimbledon. And Willesden had two shafts 600 m apart, one of which is now capped.

[CyclingSid]

The comment about earthing at very much higher frequencies reminded me of Army advice. Always jump off the tailgate of a Land Rover with a high power radio installation, in case your undercarriage tries to do an impression of a gold leaf electroscope. Never tried it to see if it was true!

[Electric train]

Fancy another armchair expedition? This time to hunt for big wormholes across London?

National Grid's London Power Tunnels have got a lot less publicity than Thames Water's supersewer (at least out West of London). But it is still quite impressive - while slim, it is pretty long.

I found this list of the twelve shaft sites, detailed enough that you can plug them into Google Earth and go straight there.

Seagrave Road, Earls Court
Millfields Park, Hackney
Eade Road, Haringey
Seven Sisters Road, Highbury
Lough Road, Islington
Canal Way, Kensal Green
Lodge Road, St. John’s Wood
Royal College Street, St. Pancras
Armoury Way, Wandsworth
Acton Lane, Willesden
Channel Gate Road, Willesden
Riverside Road, Wimbledon
(There's a separate tunnel from Hurst to Eltham.)

You may need to hunt for the site itself, and then you'll then need to wind back time to see the holes; they are now hidden by sheds ("headhouses"). Kensal Green has two shafts (as does Hackney). I think that has to do with the tunneling itself - three tunnels meet there, from Willesden, Hackney, and Wimbledon. And Willesden had two shafts 600 m apart, one of which is now capped.

There are quite a few other National Grid tunnels under London that you have not mentioned that I have knowledge of but cannot say where they run between, they are mainly at 275kV a number of them 400kV; UKPN also have a series of cable tunnels at 132, 66kV, there are also some at 33 and 22kV although these tend to be less than 2m in diameter.

The head houses are vital as they contain ventilation fans to keep the cables cool and monitoring equipment

[onthecushions]

I was very surprised to see (Reply#130) the Radley ATS^▸ (Automatic Train Supervision) completed, so far north of Didcot, as I understood that the wires would only reach Appleford for the moment. Presumably the ATS is there to provide the wiring boundary as there won't be much AT demand for the time being, unless Radley becomes an "Oxford South Parkway"!

Curious,

OTC

[IndustryInsider]

I think Radley was one area they were ahead of the game on, so it had been completed before the deferral was announced.

[Electric train]

I think Radley was one area they were ahead of the game on, so it had been completed before the deferral was announced.

This is correct.  GWEP^▸ (Great Western Electrification Program) was unusual in that it got all its Distribution assets ordered and build to time and I believe almost to cost ..................... usually on electrification scheme Distribution is forgotten about until someone says "errrrrrrrrrrrrrrrrrrr where's the 13amp socket to plug the train set into" 

[Thatcham Crossing]

Indeed so, there is some sort of sub-station at Midgham that was built at least a year ago. OHLE metalwork now very close both side of the station, but still not through it yet.

[stuving]

Indeed so, there is some sort of sub-station at Midgham that was built at least a year ago. OHLE metalwork now very close both side of the station, but still not through it yet.

That's one ATS^▸ (Automatic Train Supervision), and Theale has another one. Newbury will get a slightly more up-market one (labelled SATS), but the work seems to have been delayed to fit in with the rebuilding on the adjoining site (the old Sterling Cables factory).

Oddly, when lasted snapped (September), Radley had its transformer while Midgham and Theale had only bare pads. Work flows in mysterious ways.

[onthecushions]

This is correct.  GWEP^▸ (Great Western Electrification Program) was unusual in that it got all its Distribution assets ordered and build to time and I believe almost to cost.

So is the Oxford SATS being built also?

OTC

[paul7575]

I expect the chaps who install switchgear and transformers etc, in the little compounds separate from but near the railway, are chuffed to bits because their work doesn't actually involve using problematic over-hyped equipment such as MPV based modular wiring trains,  and their normal access is by roads or tracks available 24/7 rather than only during railway possessions...

Paul

[Electric train]

Oddly, when lasted snapped (September), Radley had its transformer while Midgham and Theale had only bare pads. Work flows in mysterious ways.

The contractor supplying and the one carrying out the distribution equipment install would have had a programme of works a number of years ago, the changes to the OLE^▸ (Overhead Line Equipment, more often "OHLE") install may have overtaken the original distribution contract, possibly more cost effective to remain on the majority of the distribution install programme

So is the Oxford SATS being built also?

OTC

I believe it could not be built until Oxford Station rebuild had reached a certain stage, its part of the reason why the wires to Oxford were taken out of the current programme, it will go in as part of the CP6^▸ (Control Period 6 - The five year period between 2019 and 2024) electrification to Oxford

[gwr2006]

It doesn't look like Steventon will be ready any time soon and doubtful the high street bridge will even be rebuilt now before December 2018. Loco-haulage anyone?

Apparently they are looking at a temporary solution with a speed limit to achieve the deadline.

NR^» (Network Rail - home page) tweets also suggest they are lowering the track this weekend. So it looks like a combination of lowered track, minimum clearances and reduced speed to allow the gradient of the contact wire to be very steep. 

Any idea what the speed limit might be? I'm sure the villagers will be asking why that can't be a permanent solution as they are so opposed to the bridge being rebuilt. The contact wire will be steep too to obtain the clearance needed at the level crossings.

[ellendune]

It doesn't look like Steventon will be ready any time soon and doubtful the high street bridge will even be rebuilt now before December 2018. Loco-haulage anyone?

Apparently they are looking at a temporary solution with a speed limit to achieve the deadline.

NR^» (Network Rail - home page) tweets also suggest they are lowering the track this weekend. So it looks like a combination of lowered track, minimum clearances and reduced speed to allow the gradient of the contact wire to be very steep. 

Any idea what the speed limit might be? I'm sure the villagers will be asking why that can't be a permanent solution as they are so opposed to the bridge being rebuilt. The contact wire will be steep too to obtain the clearance needed at the level crossings.

Remembered where I found it:

http://www.firstgreatwestern.info/coffeeshop/index.php?topic=5066.msg220937#msg220937

That's all I know