Great Western Main Line electrification - ongoing discussion

[whole diary]

[Electric train]

I've noticed they've got wires up at the Stoke Gifford depot, just seem to be single wires, not the full catenary.

Depots use what is called a "trolley wire" system it is just a single wire usually fixed tension.  The trolley wire is used in depots because of the low speeds in depots; it is simpler system and requires less maintenance than catenary system

[TonyK]

As the trains are supposed to enter under diesel power, the reduced standard seems acceptable.

[DidcotPunter]

I thought they were supposed to use electric power at Stoke Gifford? Anyway the trolley wire OLE^▸ (Overhead Line Equipment, more often "OHLE") is also installed at the Reading Depot and is pretty standard at electrified depots elsewhere where speeds are low and a simpler system will suffice.

[Tim]

Are electric trains in depots ever able to move under electric power supplied from a plugged in cable (ie with the pan down)?  or would such a system be too low power to work?

[grahame]

Are electric trains in depots ever able to move under electric power supplied from a plugged in cable

Errrrrrrr ... isn't that a bit difficult?   As the train moves away from the socket, it pulls the plug out, and to move any great distance there are going to need to be some very long cables.    As a layman, it sounds reasonable for turning wheels to get another bit to the top for attention, but not for relocating trains.

[paul7575]

Are electric trains in depots ever able to move under electric power supplied from a plugged in cable

Errrrrrrr ... isn't that a bit difficult?   As the train moves away from the socket, it pulls the plug out, and to move any great distance there are going to need to be some very long cables.    As a layman, it sounds reasonable for turning wheels to get another bit to the top for attention, but not for relocating trains.

DC^▸ (Direct Current) third rail, and LU fourth rail, systems do not normally extend through shed maintenance roads, at the speeds the trains enter they run until nearly 'off the end' of the external DC and then get plugged into a shore traction power system that is fed by cables from trolleys at roof level, that trolley can then move with the train.  But the trains only need to move the last few yards using this power, and on leaving they only have to move until the first shoe is in contact with the normal third rail outside the shed. On most current DC units the main risk to personnel is that the pick up shoes are always live throughout the train when ever there is traction power on, the shoes have fuses but are not individually switched.

You cannot safely provide 25kV down a portable plug and socket system though, so I think in AC sheds the solution is just to run in and then isolate the OHLE^▸ (Over-Head Line Equipment (electrification via catenary)) prior to roof access, using key access systems.  Sometimes the depot power is supplied through a conductor bar system that can be moved out of the way to give better roof access.

Paul

[stuving]

Errrrrrrr ... isn't that a bit difficult?   As the train moves away from the socket, it pulls the plug out, and to move any great distance there are going to need to be some very long cables. 

Well, it can be done if you put your mind to it. Not long ago, when this country had an iron ore industry, there was a huge Ransomes and Rapier electric walking dragline (called "Sundew" - the biggest in the world in its day) that was powered via a long cable from a fixed substation. I came across it as an example on a management course - it was more memorable than the rest of the course. The project we looked at was its famous cross-country walk in 1974 to get 13 miles to a new quarry near Corby.

Anyway, I can't find its power rating just now, but its cable (11 kV?) needed a Scammel tractor to drag it around the quarry, or across the fields, following the dragline.

[broadgage]

Are electric trains in depots ever able to move under electric power supplied from a plugged in cable (ie with the pan down)?  or would such a system be too low power to work?

I do not see why it could not be done, but AFAIK^▸ ('as far as I know') it never is these days. The length of cable would be limited by cost and weight, it would be a trip hazard if at floor level, and the risk of mishap if driving beyond the limit of cable length.
If a standard industrial supply was used, say 400 volts 3 phase, then a converter on the train would be needed thereby adding weight and complexity.

IIRC^▸ ('if I recall/remember/read correctly') a plug in trailing cable WAS used in the distant past to power DC^▸ (Direct Current) EMUs^▸ (Electric Multiple Unit) in depots, but not these days. I think that the voltage was a then fairly standard 250 volts DC, sufficient to power 750 volt DC traction equipment at much reduced power.

[Electric train]

Are electric trains in depots ever able to move under electric power supplied from a plugged in cable

Errrrrrrr ... isn't that a bit difficult?   As the train moves away from the socket, it pulls the plug out, and to move any great distance there are going to need to be some very long cables.    As a layman, it sounds reasonable for turning wheels to get another bit to the top for attention, but not for relocating trains.

All third rail traction maintenance sheds have a 750V dc trolley wire system (note this is different to the 25kV discussed above) with a cable with a plug that goes into the unit, the unit is then able to creep out of the shed, it is not normally required to enter the shed.  The trolley wire can also be used to power the unit to aid fault finding.  Once the unit is sufficiently out of the shed and the shoes are on the con rail the plug can be removed. For long units 8s and 12s two trolley wire cable are plugged in.  The trolley wire has contactor which has an inter-lock key that is part of the depot safety system (de-railers and signals etc)

Modern dc traction maintenance sheds have the running rails earthed to the depots main earth terminal this is to ensure there is no greater than 25V touch potential; the normal main line dc the running rails are earth free (they are earthy but not directly connected to the general mass of the earth) this means all modern sheds need their own dedicated rectifiers dc switchgear and a switched buffer zone on the shed approach road.

For 25kV maintenance sheds most if not all roads are wired at 25kV.  There is a dedicated switch for each road which isolates the 25kV and applies an earth to the OLE^▸ (Overhead Line Equipment, more often "OHLE") on that road, the OLE switch has an inter-lock key that is part of the depot safety system (de-railers and signals etc) releases gates to access platforms, overhead hoists etc

[Cruithne3753]

I've noticed they've got wires up at the Stoke Gifford depot, just seem to be single wires, not the full catenary.

Depots use what is called a "trolley wire" system it is just a single wire usually fixed tension.  The trolley wire is used in depots because of the low speeds in depots; it is simpler system and requires less maintenance than catenary system

From where I am (I work at the NHS blood centre just to the West of the new depot) it looks like it's on the curve just South of Patchway... part of the main line?

[Electric train]

I've noticed they've got wires up at the Stoke Gifford depot, just seem to be single wires, not the full catenary.

Depots use what is called a "trolley wire" system it is just a single wire usually fixed tension.  The trolley wire is used in depots because of the low speeds in depots; it is simpler system and requires less maintenance than catenary system

From where I am (I work at the NHS blood centre just to the West of the new depot) it looks like it's on the curve just South of Patchway... part of the main line?

Depots have things called head shunts these will often run parallel to the main running lines, it could also be one of the depot reception roads both these are low speed so can use simple OLE^▸ (Overhead Line Equipment, more often "OHLE") system such as a trolley wire

[Tim]

Wow.  Thanks for everyone's input.  Rather typical of this forum, ask a simple question and learn more than you imagined.

Thanks

[grahame]

http://www.networkrailmediacentre.co.uk/news/residents-invited-to-drop-in-event-to-find-out-more-about-electrification-of-the-great-western-main-line-through-pilning?

Residents invited to drop-in event to find out more about electrification of the Great Western Main Line through Pilning

Pilning residents are invited to attend a drop-in event to find out more about the work taking place in their area to prepare the Great Western Main Line for the arrival of a new fleet of electric trains.

The event will take place between 3.30pm and 6.30pm on Thursday, December 17 at the Mafeking Hall, Redwick Road, Pilning. Members of the Network Rail project team will be on hand throughout to explain the plans and to answer any questions.

[rower40]

Does this mean there'll be piling in Pilning?

(Will they be using Tubular steel in Oldfield Park?)

[Bmblbzzz]

   Curiously enough, someone was talking about you, Rower, when one Ursus maritimus stopped us all near a railway bridge somewhere in the Greater West Midlands Conurbation.


As for Pilning, it's ironic that a place with two trains a weeks gets an electrification event, but it's just the sort of place that would have a Mafeking Hall. Goes with the Indian Orthodox Church! In a way...