Great Western Main Line electrification - ongoing discussion

[whole diary]

[DidcotPunter]

Class 387 and a Class 800 on AC did test runs on Saturday night between Slough and Didcot.

800 002 has made a number of runs this week between North Pole and Didcot on AC throughout. Passed it yesterday running on the down relief near Twyford while on 800 005 heading towards Padd (on diesel up to Maidenhead!)

[Thatcham Crossing]

On a bustitution last night - Reading to Thatcham just after midnight. Noticed an engineering train at work near Midgham.

Updating my own post - this morning in daylight, quite a lot of metal dangly bits have appeared in the last few days at various points between Aldermaston and Thatcham. Also, some more uprights near to the M4 at Theale, which was one of the remaining gaps with no metalwork.

[stuving]

Class 387 and a Class 800 on AC did test runs on Saturday night between Slough and Didcot.

800 002 has made a number of runs this week between North Pole and Didcot on AC throughout. Passed it yesterday running on the down relief near Twyford while on 800 005 heading towards Padd (on diesel up to Maidenhead!)

There are no more Sunday morning closures, so presumably they can now do all their testing by running trains. I imagine soon they will want to run enough trains to fully load the system, and see what it does.

Or can they? I'm still puzzled about where and how much power can be fed in at Reading ATFS. There is no National Grid site at Reading, and the intended feed from Bramley hasn't been built. (Yet.) Plan B was a longer feeder along the track from Didcot; I'm 99% sure that is not going to happen. So presumably it has a temporary feed from SSEN^» (Scottish and Southern Electricity Networks - website) at 132 kV. Their nearest "bulk supply point" is at the back of their offices in Vastern Road, less than 1 km away, but I doubt that could supply the full rated power of the ATFS.

[IndustryInsider]

Sounds like a question for ‘Electric Train’...

[paul7575]

Surely power isn't 'fed in' from the Grid at Reading ATFS, it comes along the route (ie the traction Over-Head Line Equipment (OHLE) and Auto Transformer Feeder (ATF)) from Didcot. 

AIUI^▸ (as I understand it) Kensal Green feeds as far as Maidenhead MPATS^▸ (Mid Point Auto Transformer Site - electrification), just west of the station.  From the Reading side of the Maidenhead MPATS to (somewhere between Didcot and Thingley) is fed from Didcot.   There are only 4 national grid supply points on the whole route, Kensal Green, Didcot, Thingley (Melksham) and somewhere in Wales.

As described by Electric train here a couple of years ago:  http://www.firstgreatwestern.info/coffeeshop/index.php?topic=15735.msg176211#msg176211

I don't think Bramley is an absolute necessity yet, it is a sort of belt and braces for when Newbury and Basingstoke are added into the whole system.

PS I have now checked the Sep 17 Network Rail (NR^» (Network Rail - home page)) enhancement plan and the "Reading Independent feeder" is about levels of redundancy in the event of failures elsewhere.  It is a separate project for completion during CP6^▸ (Control Period 6 - The five year period between 2019 and 2024) and will either come from Bramley or along the track (separately) from Didcot.

Paul

A MPATS is a "mid point autotransformer feeder site", it is the limits of normal feeding, but there is switchgear to allow cross feeding under reversionary conditions.

Edit: VickiS - Clarifying Acronym

[stuving]

I don't think Bramley is an absolute necessity yet, it is a sort of belt and braces for when Newbury and Basingstoke are added into the whole system.

That's really what I was getting at - the "standard design" does allow for any one feed point to be lost with little or no effect, but how big an issue is it to leave one out and operate permanently in this reversionary mode? And is that no effect, or just a little, or an important power contraint? Didcot-Kensal is significantly further than the normal upper limit of 60 km between feed points, and it's not to be lightly  used.

The Bramley feed point was a late addition, but I think that was based on the realisation that one was needed even if the grid wasn't very helpfully arranged. The full design had an ATFS at Bramley as well as a high-level feeder along the line, but no sooner had that been planned than that stretch of Over Line Equipment (OLE^▸ (Overhead Line Equipment, more often "OHLE")) was deferred and may not be undeferred.

So if the "F" in "Reading ATFS" is silent, as in MPATS^▸ (Mid Point Auto Transformer Site - electrification), the heavily-used section from Reading to Maidenhead is always fed at the end of another section. And when Reading-Newbury is added, that has no feed point, so gets fed the same way..

There is also a loss of feed diversity while the Over Line Equipment (OLE) through Bath and Bristol is missing. Thingley ATFS should feed to Bristol Parkway, and even on to Cardiff, by both routes. There is (or was) to be another high-level feeder along the track from Thingley to an ATFS at Royal Wootton Basset - is there any sign of that? That was explained as needed to feed the line between Wales and Swindon when the B&H^▸ (Berks and Hants - railway line from Reading to Taunton via Westbury) is turned off. You can see the concern over only feeding a main line by power along another line (branch or branch main).

No doubt DfT^» (Department for Transport - about) will now be telling Network Rail (NR^» (Network Rail - home page)) that backup power is another luxury not needed if trains have on-board power at the push of a button. But that logic doesn't hold east of Didcot (or eventually Swindon) and Newbury, where the 387's run.

A MPATS is a "mid point autotransformer feeder site", it is the limits of normal feeding, but there is switchgear to allow cross feeding under reversionary conditions.

"Mid Point Autotransformer Site" does seem to be the standard interpretation, keeping the "F" for Feeder only for sites that feed in external power. Of course "feeder" does, confusingly, have other uses, as in Auto Transformer Feeder (ATF).

Edit: VickiS - Clarifying Acronym

[TonyK]

On my way by car along the M4 twixt Bath and Swindon, I saw actual wires in place around RWB. Fantastic - they are going through with it after all! Not only that, Bristol Temple Meads seems hopeful in CP6^▸ (Control Period 6 - The five year period between 2019 and 2024) after all.

"Mid Point Autotransformer Site" does seem to be the standard interpretation, keeping the "F" for Feeder only for sites that feed in external power. Of course "feeder" does, confusingly, have other uses, as in Auto Transformer Feeder (ATF).

WTF?

Edit: VickiS - Clarifying Acronym

[patch38]

I saw actual wires in place around RWB. Fantastic - they are going through with it after all!

RWB area wiring was never in doubt, was it? Beyond Thingley was where it all got a bit questionable...

[paul7575]

I don't think Bramley is an absolute necessity yet, it is a sort of belt and braces for when Newbury and Basingstoke are added into the whole system.

That's really what I was getting at - the "standard design" does allow for any one feed point to be lost with little or no effect, but how big an issue is it to leave one out and operate permanently in this reversionary mode? And is that no effect, or just a little, or an important power contraint? Didcot-Kensal is significantly further than the normal upper limit of 60 km between feed points, and it's not to be lightly  used.

The whole advantage of the Auto Transformer Feeder (ATF) system is to allow grid feeders as far apart as Kensal and Didcot, isn't it?   Lets say that 60 km is the upper limit of a conventionally fed system - (said to be 40 - 60 km between grid connections in an online resource). 

The addition of the Auto Transformer Feeder (ATF) then allows one of 3 things:
Additional distance been grid feeders for the same power drawn,
Or additional power draw (less volt drop) for the same distance between supply points,
Or a combination of the two.

Paul

Edit: VickiS - Clarifying Acronym

[stuving]

The whole advantage of the ATF system is to allow grid feeders as far apart as Kensal and Didcot, isn't it?   Lets say that 60 km is the upper limit of a conventionally fed system - (said to be 40 - 60 km between grid connections in an online resource). 

The addition of the ATF then allows one of 3 things:
Additional distance been grid feeders for the same power drawn,
Or additional power draw (less volt drop) for the same distance between supply points,
Or a combination of the two.

Paul

You're right, that 60 km was for "classic" systems, so not really the appropriate value. But in the area around Reading I would expect most of the benefit of AT feeding to be used up in the high traffic load, so not available for extra distance (and Kensal-Didcot is 80 km).  However, that's off the end of my thumb - you'd need to do the right sums to really know.

[TonyK]

RWB area wiring was never in doubt, was it? Beyond Thingley was where it all got a bit questionable...

Never was in doubt - I mention it purely as a matter of record of progress.

[Electric train]

Class 387 and a Class 800 on AC did test runs on Saturday night between Slough and Didcot.

800 002 has made a number of runs this week between North Pole and Didcot on AC throughout. Passed it yesterday running on the down relief near Twyford while on 800 005 heading towards Padd (on diesel up to Maidenhead!)

There are no more Sunday morning closures, so presumably they can now do all their testing by running trains. I imagine soon they will want to run enough trains to fully load the system, and see what it does.

Or can they? I'm still puzzled about where and how much power can be fed in at Reading ATFS. There is no National Grid site at Reading, and the intended feed from Bramley hasn't been built. (Yet.) Plan B was a longer feeder along the track from Didcot; I'm 99% sure that is not going to happen. So presumably it has a temporary feed from SSEN^» (Scottish and Southern Electricity Networks - website) at 132 kV. Their nearest "bulk supply point" is at the back of their offices in Vastern Road, less than 1 km away, but I doubt that could supply the full rated power of the ATFS.

I doubt they will fully load the system, sufficient loading will be done to check Vl-Vt (Voltage longitudinal - Voltage transverse) basically the interference on telecoms circuits, and any touch potentials at public areas also to check the stability and direction of the (power) protection.

Reading depot has always been a concern regards power in the event of an all line isolation is required between it and Didcot, I believe feeding has been designed such that Reading can be kept alive from Kensal Green.  As far as I am aware there are no plans to bring in a feed from Reading Grid, it just does not have the capacity, indeed the 33kV feed to Reading third rail substation generally only feeds a couple of subs on the network due to capacity at the Grid.  Even a standby supply would need to be in the order of 10MVA

[grahame]

In answering questions elsewhere I came across http://www.bathnes.gov.uk/sites/default/files/sitedocuments/Planning-and-Building-Control/Planning/nr_a_guide_to_overhead_electrification.pdf ... which is I suspect a general Network Rail guide mirrored by Bath and North East Somerset.   Perhaps already mentioned here in the past - but worth repeating even if it has been as it seems like a useful guide ...

[stuving]

In answering questions elsewhere I came across http://www.bathnes.gov.uk/sites/default/files/sitedocuments/Planning-and-Building-Control/Planning/nr_a_guide_to_overhead_electrification.pdf ... which is I suspect a general Network Rail guide mirrored by Bath and North East Somerset.   Perhaps already mentioned here in the past - but worth repeating even if it has been as it seems like a useful guide ...

Indeed I did, last year: http://www.firstgreatwestern.info/coffeeshop/index.php?topic=5066.msg200603#msg200603

Note that the much-derided (for good reasons) forum search facility seems to work quite well on little-used text strings in a link - even if that string is invisible.

[Chris from Nailsea]

Note that the much-derided (for good reasons) forum search facility seems to work quite well on little-used text strings in a link - even if that string is invisible.

Yes, that's how I still manage to dredge up various historic posts / information - with some determined digging!