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Author Topic: Great Western Main Line electrification - ongoing discussion  (Read 86356 times)
4064ReadingAbbey
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« Reply #120 on: November 19, 2017, 02:33:48 pm »

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 ...
A better guide is to be found here: http://www.railwaysarchive.co.uk/OLE/.
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« Reply #121 on: November 19, 2017, 05:02:14 pm »

Apparently Bramley Grid supply is going to built in CP6 to the full spec
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CyclingSid
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« Reply #122 on: November 20, 2017, 03:56:34 pm »

A question, from someone who probably does not understand the difference between Network Rail and National Grid supply. You say that Reading has no or unsuitable grid supply. So what is the site to the west of the Reading - Basingstoke line just south of the Kennet & Avon Canal, and probably not far from where Reading Green Park station will be it is known as Reading Power Station, although doesn't look like one to me.

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stuving
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« Reply #123 on: November 20, 2017, 04:50:40 pm »

A question, from someone who probably does not understand the difference between Network Rail and National Grid supply. You say that Reading has no or unsuitable grid supply. So what is the site to the west of the Reading - Basingstoke line just south of the Kennet & Avon Canal, and probably not far from where Reading Green Park station will be it is known as Reading Power Station, although doesn't look like one to me.

That's Burghfield Bulk Supply Point (BSP) - operated by the distribution network operator (DNO) which is Scottish and Southern Electricity Networks (SSEN). It takes in 132 kV from a National Grid Grid Supply Point, but from Fleet GSP, not Bramley, and supplies about 70 MW at 33 kV. One of the next-level substations it supplies is on Burghfield road, converting to 11 kV and supplying up to 9 MW. Oddly, there's another one closer, a few yards south and on the other side of the railway - but it's fed from Thatcham BSP!

Network Rail want too much power to place as a single-phase load on one of these local stations, hence the insistence on taking power direct off the grid. (Though there is a site somewhere on the Crossrail route that draws power from a DNO, though I'm not sure where.)
« Last Edit: November 20, 2017, 05:12:41 pm by stuving » Logged
Thatcham Crossing
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« Reply #124 on: November 20, 2017, 05:11:19 pm »

Looks like there's been some more piling in the Southcote Junction area recently.

The gaps in metalwork between there are Theale are also narrowing slowly but surely.
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broadgage
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« Reply #125 on: November 20, 2017, 05:46:04 pm »

A question, from someone who probably does not understand the difference between Network Rail and National Grid supply. You say that Reading has no or unsuitable grid supply. So what is the site to the west of the Reading - Basingstoke line just south of the Kennet & Avon Canal, and probably not far from where Reading Green Park station will be it is known as Reading Power Station, although doesn't look like one to me.

That's Burghfield Bulk Supply Point (BSP) - operated by the distribution network operator (DNO) which is Scottish and Southern Electricity Networks (SSEN). It takes in 132 kV from a National Grid Grid Supply Point, but from Fleet GSP, not Bramley, and supplies about 70 MW at 33 kV. One of the next-level substations it supplies is on Burghfield road, converting to 11 kV and supplying up to 9 MW. Oddly, there's another one closer, a few yards south and on the other side of the railway - but it's fed from Thatcham BSP!

Network Rail want too much power to place as a single-phase load on one of these local stations, hence the insistence on taking power direct off the grid. (Though there is a site somewhere on the Crossrail route that draws power from a DNO, though I'm not sure where.)

Yes, AC railway traction loads are among the most challenging for a grid system to supply.
Supplying say 20MW for a new industrial and residential area is simple by comparison.
Railway traction demand is intermittent, varying from zero to several dozen MW, from one minute to the next. Supplying a steady or slowly varying load is easy, but a rapidly altering load causes voltage fluctuations to other customers unless supplied at higher voltages where the load is greater and the railway traction load is therefore a smaller percentage.

Or put simply, adding a variable 20MW traction load to a 30MW circuit at 33KV would likely cause excessive voltage fluctuations. Adding the same 20MW traction load to a high voltage grid feeder point with an existing load of 500MW is probably of no consequence.
The fact that AC traction supplies are unavoidably single phase makes it worse.

Decades ago, the inability to supply large, single phase, and intermittent traction loads often resulted in the continuation of steam or diesel power when electrification would otherwise been attractive.

DC traction has the merit that it presents a balanced 3 phase load, but still large and intermittent.
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« Reply #126 on: November 20, 2017, 08:43:08 pm »

DC traction has the merit that it presents a balanced 3 phase load, but still large and intermittent.

DC traction rectifiers produce third, seventh and eleventh harmonic distortion at quit high levels, often NR has its own 33kV transformer at GSP's.  The harmonics are next to impossible to filter out due to the energy levels.  NR in Southeast London is currently building 2 new supply feeders from 2 140MV 275/33kV transformers NR are the sole user of these.

New 25kV electrification and most up grades go for 400kV connection, the single phase loading causes negative phase sequence in the "neutral" of the 3 phase system, when 132kV was the National Grid in the 50, 60, 70s the negative phase sequence could be lived with also train loads were smaller.

Bramley will have been selected by National Grid as their best option that suited NR requirements, based on the space available for switchgear, transformers and distance from the railway; approx. min of 1km is preferred to ensure the Grids rise of earth potential under 400kV (1750V) does not get exported to the railway which has a max rise of earth potential of 645V.  At locations like Kensal Green the earthing point of the 25-0-25 kV has to be moved for the normal place at the transformer to the "0" connection in the NR feeder station, this adds complexity to the protection system.
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Chris from Nailsea
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« Reply #127 on: November 20, 2017, 08:46:11 pm »

Exactly what I was about to say.  Lips sealed

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« Reply #128 on: November 20, 2017, 10:49:34 pm »

Exactly what I was about to say.  Lips sealed

Me too! Lips sealed

But seriously, I am indebted to II, ET, broadgage and others for these snippets. I have some basic understanding of electricity, and if I read their posts on these technical matters often enough, sometimes with a little supplementary reading, the odd scale falls from my eye. Fascinating stuff!
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« Reply #129 on: November 20, 2017, 11:32:52 pm »

At locations like Kensal Green the earthing point of the 25-0-25 kV has to be moved for the normal place at the transformer to the "0" connection in the NR feeder station, this adds complexity to the protection system.

I'm a bit surprised by that. After all, the grid's literally next door - the other side of the fence - and a lot closer to the feeder site than the connection to the railway is.

Google Earth's friends in high places have visited all these OLE sites from Didcot eastwards in the last six months, so if you don't want to go looking for them by train there's an easier way. Some are not finished in the pictures, or indeed in real life, and I'm not sure Westbourne Park has even been started. But here are Didcot and Reading. Pretty, aren't they?

Didcot has two ATs, and a load of switchgear. Next door there's a bit more switchgear at the end of the input cables (buried) from the two 400/50 kV transformers at the grid end. They are in the compound at the old power station, now taking power in from the new station instead. It's not a supply point - Didcot's power is supplied from Cowley, via Drayton.

Reading has three ATs, presumably for each route out (east, west, south). Terminating the input from Bramley will need a new corral - unsurprisingly not built yet. But why is there no space provided for a third AT at Didcot for the line to Oxford? Hmm.

You can also see that vanilla ATSs have one AT each on the GW electrification, but two on the Crossrail
part inwards of Maidenhead. The MPATS at Maidenhead has three - since it is in effect an ATS for the line each side.
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ray951
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« Reply #130 on: November 21, 2017, 10:17:30 am »

Reading has three ATs, presumably for each route out (east, west, south). Terminating the input from Bramley will need a new corral - unsurprisingly not built yet. But why is there no space provided for a third AT at Didcot for the line to Oxford? Hmm.

Could the feed for the Didcot - Oxford line be the electrical substation at Radley?

I have always been of the opinion that unless NR started to dismantle this substation then electrification to Oxford is going to happen, this is probably hopelessly naive.

In other news I notice they have started to put up electrification masts around Didcot East curve.


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stuving
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« Reply #131 on: November 21, 2017, 10:53:07 am »

Could the feed for the Didcot - Oxford line be the electrical substation at Radley?

I have always been of the opinion that unless NR started to dismantle this substation then electrification to Oxford is going to happen, this is probably hopelessly naive.

In other news I notice they have started to put up electrification masts around Didcot East curve.

Radley gets a plain ATS - compare it with the one at Cholsey; it's almost identical. I had not realied that had been, or so it seems, finished. There is also to be a SATS at Oxford, though I can't see that one's been built  and I don't know where it would be if it had been. So, no feed in at either - all the power comes from Didcot (called Foxhall Junction in the planning documents).

I always thought electrification to Oxford looked like a genuine deferral. Assuming that bringing those elements back into the programme is down to NR making a case, they must want that enough to put it top of their CP6 TTD list.
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« Reply #132 on: November 21, 2017, 11:07:42 am »

The SATS at Oxford hasn’t been built yet, but the ATS at Radley looks to be finished.  Oxford’s main problem is the imminent station rebuild, but with the definition of imminent in the railway dictionary being ‘might still be 10 years away’ I think they should just plough on with it.

Signs are still promising - work on Rewley Road sidings is still incorporating provision for easy installation of OLE, and it makes a lot of sense in terms of service patterns, but it does still hang in the balance and the recent confirmation that East-West Rail won’t be electrified initially was another small blow.
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« Reply #133 on: November 21, 2017, 07:32:27 pm »

At locations like Kensal Green the earthing point of the 25-0-25 kV has to be moved for the normal place at the transformer to the "0" connection in the NR feeder station, this adds complexity to the protection system.

I'm a bit surprised by that. After all, the grid's literally next door - the other side of the fence - and a lot closer to the feeder site than the connection to the railway is.

Google Earth's friends in high places have visited all these OLE sites from Didcot eastwards in the last six months, so if you don't want to go looking for them by train there's an easier way. Some are not finished in the pictures, or indeed in real life, and I'm not sure Westbourne Park has even been started. But here are Didcot and Reading. Pretty, aren't they?

Didcot has two ATs, and a load of switchgear. Next door there's a bit more switchgear at the end of the input cables (buried) from the two 400/50 kV transformers at the grid end. They are in the compound at the old power station, now taking power in from the new station instead. It's not a supply point - Didcot's power is supplied from Cowley, via Drayton.

Reading has three ATs, presumably for each route out (east, west, south). Terminating the input from Bramley will need a new corral - unsurprisingly not built yet. But why is there no space provided for a third AT at Didcot for the line to Oxford? Hmm.

You can also see that vanilla ATSs have one AT each on the GW electrification, but two on the Crossrail
part inwards of Maidenhead. The MPATS at Maidenhead has three - since it is in effect an ATS for the line each side.

By placing the "0" or Neutral point earth connection at the NR 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  Grin

Reading has three ATs, presumably for each route out (east, west, south). Terminating the input from Bramley will need a new corral - unsurprisingly not built yet. But why is there no space provided for a third AT at Didcot for the line to Oxford? Hmm.

Could the feed for the Didcot - Oxford line be the electrical substation at Radley?

I have always been of the opinion that unless NR started to dismantle this substation then electrification to Oxford is going to happen, this is probably hopelessly naive.

In other news I notice they have started to put up electrification masts around Didcot East curve.


Didcot Oxford electrification is in CP6 and feeding Oxford from Bramley has already been taken into account
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« Reply #134 on: November 23, 2017, 06:20:52 pm »

Was up on the bridge between Hambrook Lane and Stoke Gifford this afternoon just to the east of Bristol Parkway. Could see that the catenary ironwork has just about reached the bridge, within sight of Parkway. No wires yet though. Can anybody tell me if this means all the basic metal work is now in place all the way back eastwards or are there still gaps?
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