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Author Topic: Great Western Main Line electrification - ongoing discussion  (Read 239939 times)
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« Reply #1140 on: August 07, 2022, 04:56:21 pm »

Alas, the article has hidden behind a paywall. Presumably Tranche 0 should be first?

To quote my son, who tends to be rather direct: Yes, that's how numbers work!

I am again indebted.

I can access the MR (Midland Railway) article intermittently - sometimes the paywall blocks it, sometimes it doesn't.

So far, no good. I'll try on my phone when it has some electrification of its own.

The article refers to Tranch 0 as the 'Hendy tail' - schemes removed from GWEP (Great Western Electrification Program) following the review of the CP5 (Control Period 5 - the five year period between 2014 and 2019) enhancements by Network Rail Chair Sir Peter Hendy:

The strategy notes that electrification from Chippenham to Bristol can utilise spare capacity in the feeder station at Thingley and could cut journey times by up to 2.5 minutes. On Filton bank (Bristol Parkway to Temple Meads), the potential for South Wales to Bristol EMUs (Electric Multiple Unit) is noted, as are the environmental benefits of decarbonisation in an urbanised area.

Labelling this 'Tranch 0' does sort of imply that it should have happened already. MR says the NR» (Network Rail - home page) report describes these schemes as ‘mature’, with power supply in place and signalling immunised in readiness for electrification.

Is the shaving of 2.5 mins off journey times really a key selling point though? I would have thought the environmental benefits would be an easier sell...

I agree entirely, especially with Bristol's new clean air zone in operation. That said, whilst I can manage the extra 2.5 minutes when travelling from 'Nam to Temple Meads wityhout noticing, that sort of margin could be significant in terms of schedules for other services.
« Last Edit: August 07, 2022, 06:30:33 pm by TonyK » Logged

Now, please!
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« Reply #1141 on: August 07, 2022, 06:17:38 pm »

The re-signalling of the ECML (East Coast Main Line) has been in development for a number of years, projects like the dive under at Peterborough, Kings Cross remodelling even the Hitchin flyover are all part of the bigger plan.   The ECML was re-signalled South of Hitchin in the early 1970's for the Electrification the rest of the ECML re-signalling follow fairly quickly after that, so it is at the end of its life.   There are lot of issues with the existing signalling equipment, wire insulation degradation, silver migration in relays and general obsolescence  

What's "silver migration in relays"?

When an electrical circuit with inductance (a coil for instance), is broken, the current drops suddenly. The inductance therefore tries to oppose this by producing a large inverse voltage. This is sufficient to cause a spark across opening contacts. At such high energies small particles of the (silver alloy) metal surface are transferred with the spark. You can see this also in a traditional car ignition system. Over years of frequent operation even highly rated railway relay contacts therefore start to lose their initial shape, producing some resistance between them when closed.

ISTR (I seem to recall/remember) that railway policy was to replace them every 21 years but condition monitoring was not used, so heavily used ones were not changed any more often than lightly used ones. Modern practice is to use more solid state devices and to use strategies such as "Zero volt/current switching" in ac circuits.

Our esteemed ET member could give a clearer more precise description.


Not certain that this is correct. Contact wear in relays is undoubtedly a problem as described above, it may be reduced in various ways.
SILVER MIGRATION is however a different phenomena. It is an electrolytic process whereby in the presence of traces of moisture, silver is dissolved to form ions, which then migrate under under an electric field, and form metallic silver in some place other than the original location of the original silver contact.
This can result in maloperation, and in extreme cases even in a wrong side failure of signaling.

Silver migration is the result of a DC (Direct Current) voltage, it wont occur on AC circuits.
It may be reduced by physically larger equipment with greater clearances, and by excluding damp.
It may be eliminated by not using silver contacts.

Contact wear from sparking has been known about since the very beginning of the electrical age, well over 100 years ago.

Silver migration was not recognised until the 1950s, and not fully understood until some years after that.

Railway signaling schemes that use miniature relays are vulnerable.

Silver migration is an electrolysis process where the sliver plating on the relay contacts migrates from contact to the other contact this increases the electrical resistance of the contacts due to oxidisation, can lead to burning of the contact faces all this has can lead to wrong side failures.


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« Reply #1142 on: August 07, 2022, 06:41:31 pm »

I promised that ET would have the final and best word!

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« Reply #1143 on: August 10, 2022, 03:39:18 pm »

This Wales and Western Regional Traction Decarbonisation Strategy is now available on that link, but only if you are logged on as a user of RailUKForums. It was liberated by a rather rapid FoI request.
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« Reply #1144 on: August 10, 2022, 04:10:59 pm »

Surely FOI (Freedom of Information) requests ,make documents PUBLIC? Not to be restricted to just some members of the public?
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« Reply #1145 on: August 10, 2022, 04:47:14 pm »

This Wales and Western Regional Traction Decarbonisation Strategy is now available on that link, but only if you are logged on as a user of RailUKForums. It was liberated by a rather rapid FoI request.

Surely FOI (Freedom of Information) requests ,make documents PUBLIC? Not to be restricted to just some members of the public?

Hmmm ... we do similar on the Coffee Shop.  Our achieve holds around 1,000 indexed .pdf files (and others that need indexing) but only 100 are whitelisted.  It's not that the other 900 are not out there in public - it's just that with the complexity of copyrights, etc, I only authorise something in public from a web site I manage if I'm certain that I'm allowed to.

Edit - you fill find lots of Decarbonisation Strategy stuff in our members archive -
« Last Edit: August 10, 2022, 05:29:15 pm by grahame » Logged

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