What engineering work does electrification entail?

[MadMac]

Quoting @najaB from the Levenmouth thread:

“And, for completeness, the problem isn't that the UK network is old, but that it has a very restrictive structures guage. Almost any electrification project requires rebuilding bridges, reboring tunnels and/or altering buildings. That's the expensive bit”.

Another big-ticket item is signalling. Taking Fife as an example, the vast majority is relay-based from the late 70s-early 80s. That in itself isn’t a problem, but the plain line track circuits (train detection) are audio frequency and are incompatible with AC electrification, so they all have to be changed. That takes design, installation and testing, none of which come cheap if you can get the resources. Insulated joints will need to be added to separate the sections, again expensive and time-consuming. Costs add up pretty quickly!

Anyone care to add items to the shopping basket?

 

[zwk500]

Adding in the connection to the power grid isn't cheap either. A short branch might get away within existing power capacity but anything too long will need it's own feed.

 

[Railsigns]

Another big-ticket item is signalling. Taking Fife as an example, the vast majority is relay-based from the late 70s-early 80s. That in itself isn’t a problem, but the plain line track circuits (train detection) are audio frequency and are incompatible with AC electrification, so they all have to be changed. That takes design, installation and testing, none of which come cheap if you can get the resources. Insulated joints will need to be added to separate the sections, again expensive and time-consuming.

When the line is next resignalled, train detection will most likely be by axle counters, so the cost of installing insulated joints is at least avoided.

 

[Tim M]

Quoting @najaB from the Levenmouth thread:

“That in itself isn’t a problem, but the plain line track circuits (train detection) are audio frequency and are incompatible with AC electrification, so they all have to be changed.”

Audio frequency Jointless Track Circuits have been used under 25kV traction systems for many decades, however it will depend on the type of equipment installed. If Reed based, please replace (I was involved with these in the 1980’s), but I would expect with suitable changes to accommodate the traction return TI21 and more recent variants should be compatible. This should avoid the need for extra insulated rail joints. As someone else has said axle counters could be used to directly replace track circuits, eliminating insulated rail joints.

On the subject of relays, immune style are required for trackside circuits. Using Westinghouse styles as an example QNA1 rather than QN1 would be required, the ‘A’ means ‘immune’. It would be relatively easy to swap out, new plugboards would be needed, but no changes to wiring would be involved. As said above, this all takes design, installation and testing resources.

On the subject of signals, protection for staff working close to the overhead line needs to be considered, gantries (being very expensive) might need replacement. However modern lightweight signal posts are a potential alternative. The whole subject of earth bonding is outside my area of expertise, maybe others can comment.

This all assumes that there are no changes to track layout or signal spacing, where Resignalling might be the better option.

 

[alxndr]

Any remaining non-AC immune point operating equipment, such as the HW1000 would need replacing, although conversion to the newer HW2000 is relatively straightforward.

 

[LBMPSB]

The whole subject of earth bonding is outside my area of expertise, maybe others can comment.

I notice at my local station, which is OHL, all metal structures, lamposts, shelters etc are bonded to earth. It is a subject I am not up on, but I would guess it would also include lineside structures and then buildings and structurea outside the railway boundary but close to the railway might also need earthing, bearing in mind some buildings are alongside the cess in many locations.

 

[alxndr]

I notice at my local station, which is OHL, all metal structures, lamposts, shelters etc are bonded to earth. It is a subject I am not up on, but I would guess it would also include lineside structures and then buildings and structurea outside the railway boundary but close to the railway might also need earthing, bearing in mind some buildings are alongside the cess in many locations.

Not my area of expertise either, but as I understand it, all metal structures must be bonded to the traction return rail within a specified distance of the overhead line equipment unless adequately earthed. This is to reduce the risk of sufficient voltage being induced in the metal structure to cause a hazardous voltage difference between the structure and the ground.

Similarly, if metal objects are less than 2.5m apart (considered to be within "arms reach") then they should be bonded so that one cannot become at a different potential voltage to the other.

 

[Hellzapoppin]

Cables over a certain length need to be sheath gapped, I can't remember if that's 2.5 or 5k in length but that includes any redundant cables.

 

[Annetts key]

Another big-ticket item is signalling. Taking Fife as an example, the vast majority is relay-based from the late 70s-early 80s. That in itself isn’t a problem, but the plain line track circuits (train detection) are audio frequency and are incompatible with AC electrification, so they all have to be changed. That takes design, installation and testing, none of which come cheap if you can get the resources. Insulated joints will need to be added to separate the sections, again expensive and time-consuming. Costs add up pretty quickly!

As others have said, modern audio frequency track circuits (digital TI21 type for example, which is the current version) are compatible (with additional equipment) with OHL. Digital TI21 type can replace existing TI21 type. And in many places, Network Rail are having to replace ASTER U / SF15 audio frequency track circuits anyway, as spares are no longer available. They are being replaced with digital TI21 in many areas.

Where conventional track circuits are in use, such as at junctions or other places where audio frequency track circuits are undesirable, it depends on the type that are fitted.

Any conventional track circuits that are double rail (IRJs in both rails) will need converting so that the traction return current has a low resistance return path. If the track circuit equipment is not an AC immune type, it will need changing to an AC immune type.

From a signalling point of view, after track circuits, the biggest issue with existing signalling relay interlocking installations is the line circuits. That is, the circuits that travel along the fixed line-side cables along the length of the railway. To prevent the induced voltage from the OHL from becoming too great, relays used as isolators/repeaters are needed every so many km. Each added relay increases the time delay of the circuit. This means any final interlocking circuit has to be carefully studied to determine if the increased time delay will cause unsafe operation.

Telecommunications cables and systems will also need investigating in case they need alterations. Induced voltage may be a problem here also.

 

[59CosG95]

I notice at my local station, which is OHL, all metal structures, lamposts, shelters etc are bonded to earth. It is a subject I am not up on, but I would guess it would also include lineside structures and then buildings and structurea outside the railway boundary but close to the railway might also need earthing, bearing in mind some buildings are alongside the cess in many locations.

Lampposts (normally referred to as Lighting Columns in the trade) need to have positions taken into account as well when OLE masts are being installed; most station lampposts can be folded down for maintenance, but OLE masts can't be placed in such a way that lampposts get folded 'onto' them.

 

[Annetts key]

Same applies with the 'bendy' fold down signals. You have to be careful that OHL structures are not placed in the area where these are lowered into.

 

[59CosG95]

Adding in the connection to the power grid isn't cheap either. A short branch might get away within existing power capacity but anything too long will need it's own feed.

To add to this; yes, it's a point mentioned time and time again in the existing threads, but the lead times for grid connections are fairly large, with outages planned months (and sometimes years) in advance.

 

[Bald Rick]

Essentially, almost anything. For example I‘m aware of electrification works that have required major embankment strengthening to cope with the piles for the masts. pr complete replacemtn of telecoms kit to mitigate interference.

 

[themiller]

Normally, it’s an opportunity to resolve niggles like low speed crossovers, 95lb bullhead rails on wooden sleepers, sub optimal track alignment, bridges nearing end of life removal of redundant assets, etc., etc., etc. Not essential but saving having to return to the same site in the near future.

 

[Snow1964]

If got to span lots of tracks, or plenty of junctions then need gantries closer together, the wires run in straight sections, so tighter the curves, the shorter the wire spans to approximately follow the curve.

Take a look at this photo when there were still short quadruple lead junctions at Bethnal Green to understand the extra equipment.

https://www.londonreconnections.com/wp-content/uploads/22.jpg

 

[The Planner]

Normally, it’s an opportunity to resolve niggles like low speed crossovers, 95lb bullhead rails on wooden sleepers, sub optimal track alignment, bridges nearing end of life removal of redundant assets, etc., etc., etc. Not essential but saving having to return to the same site in the near future.

Only if that is in the scope. Ideally you would do that at the same time, but normally the electrification project won't be funded for those enhancements.

 

[eldomtom2]

Normally, it’s an opportunity to resolve niggles like low speed crossovers, 95lb bullhead rails on wooden sleepers, sub optimal track alignment, bridges nearing end of life removal of redundant assets, etc., etc., etc. Not essential but saving having to return to the same site in the near future.

Only if that is in the scope. Ideally you would do that at the same time, but normally the electrification project won't be funded for those enhancements.

And of course, too many "nice to haves" risks ballooning the cost...

 

[Bald Rick]

Normally, it’s an opportunity to resolve niggles like low speed crossovers, 95lb bullhead rails on wooden sleepers, sub optimal track alignment, bridges nearing end of life removal of redundant assets, etc., etc., etc. Not essential but saving having to return to the same site in the near future.

None of that would be in an electrificarion budget. It might be delivered under the same project, and contractors, but it woudl be accounted for differently.

 

[Ken H]

Do you have to consider non railway utilities close by. Water/sewage in metal pipes, gas, electricity, telecoms. Do they need earth bonding? What about abandoned utility routes?

There is also the interaction between different systems. TfL 4 rail insulated return, 3rd rail, fake 4 rail where 1 rail is earthed and 25Kv. And trams. I think there are corrosion issues with different systems close together.

 

[plugwash]

AIUI Having both low voltage DC and high voltage AC on the same track is problematic, because high voltage AC requires very solid bonding to avoid dangers from induced voltages, but low voltage DC ideally wants more control of the current return path to avoid corrosion. There are some small bits of track with both but it's generally something to be avoided.

I would assume that having them in diffferent parts of the same station is less of a problem. It's certainly something one sees at many of the London terminals and in places like Manchester and Newcastle.

 

[Bald Rick]

avoided.

I would assume that having them in diffferent parts of the same station is less of a problem. It's certainly something one sees at many of the London terminals and in places like Manchester and Newcastle.

One London terminal.

The LU system is completely bonded away from the running rails (except in a handful of places where tracks are shared with 3rd rail stock).

The issue is return currents, which are naturally much higher on DC than AC. Because of this it needs to have a specific return system, whereas AC can just return via earth. In shared areas, the DC will find it easier to get to earth, thence you have several thousand amps heading to earth which can burn out all manner of things and interfere with signalling.

The key issue is the size of the DC return current and how often / how long it is produced. 4 trains an hour from a London overground train between Euston and Camden isn’t a major problem; 20 trains an hour of Class 700s in the Thameslink core very much is.