[enhancement] add substations to electrification layer

[c-mammal]

There are quite a few railway substations being added to OpenStreetMap tagged under Power=Substation + Substation=TractionPowerSupply making them visible on OpenInfraMap. Especially in GB there are many for the DC and AC mainline networks. It would be good to have this visualised in some way the electrification layer.

I am aware of the ORM tag railway-power_supply, but this is quite limited because it seems to refer to locations where there are OLE feeder cables, this could be for a wide range of things from simply manually controlled OLE switches or presence of a substation which may or may not be supplying the line. (And also doesn't apply to 3rd rail)

Too Short Want To Read More:

Just so we're on the same page, I understand there to be several distinct kinds of railway substation depending on the genre of system at play:

600-3000V DC OLE or 3rd Rail:

• (AC) Grid Supply Point (GSP): where the railway receives 3-phase HV AC power from a grid supplier (normally 11, 22, 33, 66 kV) to power the DC Railway's Traction Power Network if the railway operates one.
• AC/DC Traction Substation (TSS): steps down HV AC to LV DC supplying the actual OLE/3rd rail. On modern systems the railway may not operate a traction power network and instead every TSS is it's own LV GSP.
• Track Paralleling Hut (TPH): LV conductor rails/OLE circuits are sectioned for use at a junction/depot or just to reduce volt drop

12-15kV AC OLE (16.67hz, 16.7hz or 25hz):
Similar architecture at DC systems (but very technically different) including the part where OLE feeding stations may themselves be grid connections.
Southern Germany, Austria, Switzerland share a 16.67hz traction power grid at 55-132kV, so the locations of GSPs might be quite far away from the railway. (Obviously, it's not really ORM's job to show those power lines).
Worth noting that some (perhaps most?) of the Low-Frequency AC systems use a negative feeder along side the OLE that regularly tops up the contact wire using autotransformers, but these points can be roughly considered a "track paralleling hut" (although that term is very associated with DC railways! So it could instead be "Track Sectioning Cabin")

20-25kV AC OLE (50hz, 60hz)

• Grid Supply Point (GSP) a Grid Operator owned site where 25kV step down transformers are
• These are usually (but not always) right next door to a railway Feeder Station (FS) where the new power is administered to OLE circuits
• Mid-Point Track Sectioning Cabin (MPTSC): because adjacent grid connections are out of phase in (traditional) 25kV electrification, they are seperated by Neutral Sections which may occur on their own, at an FS, or at a 25kV switching station between two FSs (hence midpoint)
• (intermediate) Track Sectioning Cabin (TSC): directly equivalent to TPH

So you could say there are very broadly 3 kinds of substation: a Grid Supply Point (including any traction power stations still out there), a Feeder Station (where that grid power connects to the electrification circuits (if applicable via rectifier and/or step down transformer)) and Track Sectioning Cabin (optionally called TPH on DC lines). If a TSC is actually a mid point in a 25kV system then that is just information contained within the given Name of a substation.

[hiddewie]

Thanks for the issue.

There has been more discussion about rendering power supplies in #302. There is disagreement about the tagging practices and distinguishing between railway-related tagging and power-infrastructure related tagging (although there is overlap).

I am open to improving the electrification rendering, including substations.

My main question for this issue, is if we can get some examples of tagged OSM data using a tagging scheme mentioned above, ideally documented on the wiki, so this can be implemented in the OpenRailwayMap for visualization.

[wolfy1339]

If it's tagged with substation=traction then we can be sure it's related to railways.

https://wiki.openstreetmap.org/wiki/Tag:substation%3Dtraction

[c-mammal]

There's plenty of substation = traction across GB both 25kV AC and 750V DC.
I had a look through #302 and I agree that railway=power_supply is quite unclear. The few times I've seen it used on GB lines it's being put where individual OHNS components are, or where OLE feeder wires are connecting (which is what I thought it was for), but since they've only occurred at Feeder Stations, it definitely seems people are understanding it in some way as a location where new energy is brought to the 25kV OLE. From what I can quickly see of its usage in Germany this is probably not how it's being used there. With regards to OLE feed wires, I'll leave an image here to a "large" example of what I mean.

This is part of a catenary mast perhaps doesn't really need to be tagged because the presence of a switch already implies feed wires.

While we're at it, OHNS tagging is a bit unclear too; it's either railway:main_switch_off=yes and also railway=isolated_track_section.

But back on topic; I'll use this screenshot from OpenInfraMap where all substations are shown to explain.

Sundon is a major transmission substation that supplies the surrounding region; but also contains 2x 400/25kV transformers making it a "GSP"; then there is a brief underground 25kV powerline to the railway-owned site name "Long Meadow Farm" where those two 25kV circuits are distributed onto the OLE circuits and around an OHNS on each of the four lines; this is the "FS". In many other cases, the GSP and FS are even closer to each other than that - but they are always technically separate entities.

For a DC example:

In this case, the part of New Cross 275kV transmission substation where the 275/33 transformers (for rail usage) are located has been tagged differently, these 2x 33kV circuits go to Rotherhithe Switching station which spreads them out across 5x 33kV circuits (not shown), two of which go to South Bermondsey Traction Substation where it's stepped down/rectified to 750V DC. New Cross also supplies around 25 other DC substations. South Bermondsey and the others, I'm proposing, are the "FS"s, while New Cross is the "GSP". (Not entirely sure what Rotherhithe would be though...)

On both systems there are also switching stations for the railway where OLE/Conductor rail circuits can be sectioned but with no new power introduced: these could be "TSC"s

I think this structure should account for how LV DC, 16-25Hz AC, and 25kV AC systems work. Or in other words, those with or without traction power networks. There are also a few limited exceptions out there for 25kV systems where one GSP goes to multiple FSs.

So, I'm suggesting that we have some new tags added within traction substations; perhaps "function = GSP/FS/TSC", and then each of those three is rendered separately in ORM. There is, of course, scope to make even more values for that tag to accurately reflect the terminology for those different systems (DC lines don't really use the word "FS" for example), but those three are about the most efficient structure I could think of.

[c-mammal]

I've thought about it a bit more and revised my tagging proposal.

In the above examples, New Cross 275kV and Sundon 400kV are both tagged substation=high_voltage_transmission and they should remain that way. So, within the other fields inside those substation areas, I'd recommend a new "key" (is that correct?) like substation:traction_GSP = yes.

Further, if something is substation = traction, there should be a new key for traction_function = FS | TSC.

This is better than what I said before because it doesn't require those general use substations to change to traction which would be wrong. And also accounts for when the FS and GSP are completely indistinguishable which is common on tramways (not so much on heavy rail). That would be tagged as follows; power = substation, substation = traction, substation:traction_GSP = yes, traction_function = FS.

[hiddewie]

Thanks for the examples.

Rendering all power = substation with substation = traction seems like a good start.

Then we need additional tagging to identify railway related infrastructure which is not tagged as substation = traction.

The tagging could maybe follow the nested approach used in more railway mapping, like

substation:traction = GSP
substation:traction:function = FS

or some of the other values.

But ideally we have some documented structure on the wiki on how this is tagged, and some tagged OSM data, so we can implement this properly in OpenRailwayMap.

Aside, the proposal in https://wiki.openstreetmap.org/wiki/Proposal:Substation_refinement was also helpful for my understanding of the theory involved with power transmission, and related tagging. Also https://en.wikipedia.org/wiki/Traction_substation, https://wiki.openstreetmap.org/wiki/Tag:power%3Dsubstation and https://wiki.openstreetmap.org/wiki/Key:substation and https://wiki.openstreetmap.org/wiki/Tag%3Asubstation%3Dtraction.

[c-mammal]

Yeah I totally agree that rendering something for all the substation = traction would be a good move.

In terms of substation:traction = GSP, I assume this wouldn't interfere with the designation they already have for substation=transmission/regional distribution etc, tagging as a railway GSP should be an extra attribute to substations that are already primarily something else.

I don't mind adding something to 1.7 of the ORM Tagging Scheme for these new tags. But is there some kind of proposal/arbitration process for this kind of thing - or is it okay to just go ahead and add some new things? Can you implement a tagging scheme while something is still in "proposal"? Clearly, I have no idea how OSM governance works!

Also within ORM tagging scheme I found this intriguing line:

1.16.13 Power sockets next to yard tracks which are used by employees cleaning trains. It is mapped using [railway]=[power_supply]

So railway = power_supply is not only ambiguous but contradicts itself on the same page.

Funny you mention the wikipedia page for traction substation, I wrote pretty 80% of that a few months ago haha