Great Western Main Line electrification - ongoing discussion

[whole diary]

[Electric train]

Incidentally, in that picture the Foxhall Junction ATFS is over on the right, and close to it there is a kind of compost bin halfway up a pole. That is a braking resistor.

These are needed in case there are no trains drawing power when one (or more) are regenerating, so trying to put power back into the supply. However, I don't think this one is sized to do that for very long. IETs^▸ (Intercity Express Train) are required to provide regenerative braking, but to turn this off if the OLE^▸ (Overhead Line Equipment, more often "OHLE") voltage rises above 29 kV. They are allowed 100 ms to do this, so the energy to be dumped is not very large - but the resistor is still needed.

With no resistor the line voltage could rise too fast, so the voltage could still reach a damaging level before the IET reacts. I suspect it is also there to cope if a train "forgets" to turn off its regeneration.

Its not a "breaking resistor" its called a damper but electrically it is a harmonic filter and also helps with power factor correction.   The train regulates the re-gen braking it can only raise to a certain voltage after that the train dumps the energy in to resistors on board the train.

[stuving]

Incidentally, in that picture the Foxhall Junction ATFS is over on the right, and close to it there is a kind of compost bin halfway up a pole. That is a braking resistor.

These are needed in case there are no trains drawing power when one (or more) are regenerating, so trying to put power back into the supply. However, I don't think this one is sized to do that for very long. IETs^▸ (Intercity Express Train) are required to provide regenerative braking, but to turn this off if the OLE^▸ (Overhead Line Equipment, more often "OHLE") voltage rises above 29 kV. They are allowed 100 ms to do this, so the energy to be dumped is not very large - but the resistor is still needed.

With no resistor the line voltage could rise too fast, so the voltage could still reach a damaging level before the IET reacts. I suspect it is also there to cope if a train "forgets" to turn off its regeneration.

Its not a "breaking resistor" its called a damper but electrically it is a harmonic filter and also helps with power factor correction.   The train regulates the re-gen braking it can only raise to a certain voltage after that the train dumps the energy in to resistors on board the train.

OK, I stand corrected on that one. Big lineside resistors are used for both purposes (and probably a few others).

In fact, I recall seeing in one article about the order for 802s that not only did they get higher engine rating (for going up more hills) and bigger fuel tanks (for going further) but also bigger on-board resistors (for going down more hills). In that case the same braking resistors are used with no external power supply, of course. That does suggest that these roof-mounted resistors are sized to provide all the electric braking the train needs without having to send any power off-board as regeneration.

[Electric train]

Incidentally, in that picture the Foxhall Junction ATFS is over on the right, and close to it there is a kind of compost bin halfway up a pole. That is a braking resistor.

These are needed in case there are no trains drawing power when one (or more) are regenerating, so trying to put power back into the supply. However, I don't think this one is sized to do that for very long. IETs^▸ (Intercity Express Train) are required to provide regenerative braking, but to turn this off if the OLE^▸ (Overhead Line Equipment, more often "OHLE") voltage rises above 29 kV. They are allowed 100 ms to do this, so the energy to be dumped is not very large - but the resistor is still needed.

With no resistor the line voltage could rise too fast, so the voltage could still reach a damaging level before the IET reacts. I suspect it is also there to cope if a train "forgets" to turn off its regeneration.

Its not a "breaking resistor" its called a damper but electrically it is a harmonic filter and also helps with power factor correction.   The train regulates the re-gen braking it can only raise to a certain voltage after that the train dumps the energy in to resistors on board the train.

OK, I stand corrected on that one. Big lineside resistors are used for both purposes (and probably a few others).

In fact, I recall seeing in one article about the order for 802s that not only did they get higher engine rating (for going up more hills) and bigger fuel tanks (for going further) but also bigger on-board resistors (for going down more hills). In that case the same braking resistors are used with no external power supply, of course. That does suggest that these roof-mounted resistors are sized to provide all the electric braking the train needs without having to send any power off-board as regeneration.

Those "sheds" as they were called were first installed on the WCML^▸ (West Coast Main Line) in around 2000 for the introduction of the Pendolino's. 

[ellendune]

I saw a lot of knitting in Swindon Station last week though by no means complete.

I also notices some additional switchgear going in at the Dicot feeder is this for the swindon section?

I'm puzzled by that. The ATFS enclosure at Foxhall Junction looked to be fully populated when first built, so where would they put any new bits?

It seems to be a separate enclosure a few metres to the West

I had an opportunity to go and look at this today, and I reckon it's a bunch of isolators or track switches. So that is switchgear in a sense, but not the usual one of protection (circuit breakers). They are usually found on top of OLE^▸ (Overhead Line Equipment, more often "OHLE") structures, next to points, allowing each running track to be isolated in case of a failure while keeping the rest in use. That means they are OLE components, not part of the ATFS.

As a switch connecting across an insulated gap in the conductor/catenary pair, a position close to the gap is preferred as it keeps the 25 kV wires short. The operating rods can run from the side of the track, where operation is either manual or motorised. However, in this case a small copse of stanchions has been built instead of using the OLE supports. That does seem rather odd.

Presumably they will provide isolation of the OLE at the four crossovers west of Foxhall junction itself, and perhaps some more as well (there a ten stanchions with I think one switch each). But how will the 25kV connections get to various places above the track? Such leads from the ATFS call for overheight stanchions both side of the line, and ther's no sign of them yet.

Anyway, here's a picture of the forest...

I went past again today.  There seem to be three enclosures.  The main one at the rear of the Stuving's picture is I believe the feeder.  Then behind that there is another completed smaller enclosure similar to the one being built.   

[ellendune]

I also noticed the wiring in Swindon Station is nearing completion.  On Tuesday the south side of the station had been done and by today most of the north side had been done as well.  Lots of shiny copper wire!

[stuving]

I went past again today.  There seem to be three enclosures.  The main one at the rear of the Stuving's picture is I believe the feeder.  Then behind that there is another completed smaller enclosure similar to the one being built.   

The enclosure behind (i.e. east) of the ATFS is the National Grid's 25 kV substation, which does contain ground-mounted switchgear, plus a tin shed. It is at the end of the buried cable link that starts in their 400 kV substation by the power station, where the two 400/25 kV transformers are.

[martyjon]

I have been watching the wiring work near my residence. It would appear to me that two work compounds near me are being used as training schools for a wiring gang. Both lines have the overhead wires in place for a short stretch but stanchion to stanchion wiring remains to be done. I'm also intrigued by the varying heights of some stanchions, one pair of stanchions has a gantry affixed so that the top side of the gantry and the top of the stanchions are level but he next pair of stanchions has a gantry affixed at the same height with the pair of stanchions protruding above the gantry by a metre or so whilst another stanchion has what looks like a tubular bracket strapped to it to provide an at contact height the copper wire OHL^▸ (Over-Head Line) whilst the stanchion top rises to more than twice the height of the height from the pile cap to the strapped tubular bracket. Weird.

[onthecushions]

While it's not GWML^▸ (Great Western Main Line) electrification, two return journeys were made using the OLE^▸ (Overhead Line Equipment, more often "OHLE") by Pendolino 390 152 "Virgin Knight" from Preston to Blackpool North,  overnight (14/15) without incident.

Well done.

OTC

[TonyK]

While it's not GWML^▸ (Great Western Main Line) electrification, two return journeys were made using the OLE^▸ (Overhead Line Equipment, more often "OHLE") by Pendolino 390 152 "Virgin Knight" from Preston to Blackpool North,  overnight (14/15) without incident.

Well done.

OTC

I'm pleased! For the year up to November last, I made regular trips to Blackpool North, and could see the electrification taking shape from the start. My last trip by rail was just before the long, long closure of the line, and sadly my future trips are likely to be infrequent and accompanied, so by car.

[Thatcham Crossing]

Wires going up through Theale Station when I was there late last night.

[onthecushions]

....and ORR^» (Office of Rail and Road formerly Office of Rail Regulation - about) is reported to have signed off NWEP 3 (Blackpool N) for passenger service operation from Sunday 20/5.

So we needn't expect delays for Swindon etc from them as they can respond within the same week!

Silver linings,

OTC

[ellendune]

So what is happening between Didcot and Chippenham this weekend that they have closed the line for three days?

[Rob on the hill]

So what is happening between Didcot and Chippenham this weekend that they have closed the line for three days?

https://www.networkrail.co.uk/running-the-railway/our-routes/western/great-western-mainline/wiltshire-swindon/

[DidcotPunter]

So what is happening between Didcot and Chippenham this weekend that they have closed the line for three days?

Network Rail (NR^» (Network Rail - home page)) are supposed to be energising the Over-Head Line Equipmnet (OHLE) between Milton Junction (the present limit) and Wantage Road this weekend. There were lots of engineers all over the Over-Head Line Equipment (OHLE) at Challow when I went past on the A417 earlier this morning so they are clearly using the blockade to prepare this section to go live in a few weeks time.

Edit: VickiS - Clarifying Acronyms

[Electric train]

So what is happening between Didcot and Chippenham this weekend that they have closed the line for three days?

NR^» (Network Rail - home page) are supposed to be energising the OLE^▸ (Overhead Line Equipment, more often "OHLE") between Milton Junction (the present limit) and Wantage Road this weekend. There were lots of engineers all over the OLE at Challow when I went past on the A417 earlier this morning so they are clearly using the blockade to prepare this section to go live in a few weeks time.

This is so they can commission the Neutral Sections and associated (electrical) protection and control systems at Foxhall ATFS.