British railway system is getting another excuse for delays – solar storms

Space weather can wreak havoc on electronic systems, but while most folks focus on protecting datacenters or the power grid, a group of UK researchers are warning that relatively mild solar storms could bork train signaling systems.  Boffins at Lancaster University wrote in a recently published paper that the potential for a …

[Yorick Hunt]

"constructed digital models"

One would assume that they went on to attempt to replicate these results using actual equipment? Or are today's academics really that far detached from reality?

My engineering side suggests that they failed to account for the ubiquitously beefy cast alloy box enveloping such equipment, the fact that said box is invariably well grounded, and that Faraday was no fool.

[Paul Kinsler]

Re: replicate these results using actual equipment?

This isn't anything to do with RF interference: they are talking of significant geomagnetic disturbances, over geographic scales. Space weather events that they consider induce current in all sorts of things, including the ground itself.

[Yorick Hunt]

Re: replicate these results using actual equipment?

Look up "common mode rejection" - if there's sufficient force to create a charge in the earth, that charge will similarly/equally be created in other objects. Potential means nothing when there's no potential difference, otherwise birds would immediately fry when they rest on power lines.

[Anonymous Coward]

Re: replicate these results using actual equipment?

Common mode rejectioon is good for some things. Replication using actual equipment is often good too.

I'm not sure it's good for railway track circuits, or for things which are the wide area equivalent of single turn coils when a coronal mass ejection wants to induce a few thousand amps in the power griid (see e.g. https://en.wikipedia.org/wiki/Carrington_Event#Similar_events).

Haven't had a chance to read the paper yet though.

[cyberdemon]

From the Beeb article

> The Victorians also struggled with the effect of space weather in 1859 when a huge solar eruption caused a geomagnetic storm that interfered with railway signalling and telegraph lines.

That was the "Carrington Event" that you mention

Current UK railway signalling equipment is pretty old, but I don't think much of it dates back to Victorian times. Signals changing from red to green is pretty unlikely. Signals failing altogether, far, far more likely.

However I'm much more worried about the effect of a CME on the world's interconnected electricity grids. HVDC interconnectors could be quite vulnerable to massive common mode current, and they tend to trip offline very easily.

The UK grid operators are also quite worried (search for "blackstart") that without the hulking coal plants with their massive turbine inertia, and with HVDC links and renewables requiring an existing 50Hz grid to sync to before they can supply power, it will be difficult to restart the grid if it does go down completely.

[cyberdemon]

Another part of the grid that could be affected by geomagnetic storms, I reckon, are XLPE-insulated underground cables, whether DC or AC. Overground transmission lines have a spark gap at each insulator, which protects the insulator from overvoltage due to lightning strikes etc, and these are spaced every few hundred metres. Underground cables i think would see just as much magnetic induction(?), but there is nowhere for the energy to go, because they don't have regularly spaced spark gaps, and they could also more easily overheat because they are coated in plastic and buried in a tunnel. Perhaps one of our resident HV power systems engineers could comment here

[damienblackburn]

Wouldn't underground cables be well insulated because they're, well, under the ground? The ground itself would absorb a significant amount of charge before there was enough of a differential for it to have an influence on the cables. AFAIK CMEs, like EMPs, are all direct influence effects and depend upon the object in question being electrically long enough to be able to be influenced. So wouldn't it stand to reason that the literal ground surrounding the cable be a sufficient buffer against direct influence?

[Paul Kinsler]

under the ground

Geomagnetic events are, as the name suggests, magnetic, i.e. not electric (charge). And they can induce currents in the ground itself.

And albeit at a tangent to this subcommenting, it might be worth noting here that solar wind and CME interactions with the magnetosphere/ionosphere/etc are rather excitingly complicated, and all kinds of crazy and/or weird physics goes on up there (and sometimes down here). There is no guarantee that "reasonable assumptions" will be correct, unless perhaps it happens to be ones particular specialism.

[MachDiamond]

"Wouldn't underground cables be well insulated because they're, well, under the ground? "

Just being underground doesn't mean they would be a "ground potential". Even that can be dicey. I recall a recording studio that was sat between two electrical substations that were inducing a ground current between them which caused no end of problems for the studio. It took some time to figure out why they were having problems. I think in the end they moved the studio.

[Ribfeast]

Buried cables aren't safe either.

https://en.wikipedia.org/wiki/Soviet_Project_K_nuclear_tests

[nmcalba]

Re: From the Beeb article

The issue of Black Start and renewables is something that is being addressed.

The 69MW Dersdalloch wind-farm in Scotland has been designed to work as a Black Start source.

From the Scottish Power website :- "The project used ‘grid-forming’ technology called virtual synchronous machines (VSM) to regulate the frequency and voltage of the power from the turbines – essentially forming a stable network island – to keep the electricity system stable and balanced. The technology was then used to integrate that supply with the grid and restore the part of the system that had been blacked out."

[cyberdemon]

Re: From the Beeb article

I have heard that, and I am a little skeptical how a 69MW Wind Farm can jump start the grid when the UK's biggest power station (Drax, 2.6 GW) had issued a warning that they aren't sure if even they are big enough to do it. (or perhaps they are too big?) I'm not sure how it works to synchronise and connect only the generators and disconnect all of the loads, when all power and comms are down.

But nevertheless, I think they really need to organise a full scale test of the Black Start mechanism. Much better to have a little disruption in peacetime, than to wait until we really need it and all the neighbouring grids are down due to a solar flare or enemy action.

[Anonymous Coward]

Re: what are the basic requirements for blackstarting a power grid after a wide-area total outage?

Have a look at https://www.youtube.com/watch?v=uOSnQM1Zu4w - this is a quarter hour video from the Practical Engineering channel from Grady Hillhouse.

He's from 60Hz 120V territory but the principles are similar.

Other "black start" related videos and articles are out there too.

There's rather more to a black start than a couple of GW of independent power from one big power station. Many of the requirements are needed in normal operation too - e.g. synchronisation as islands of supply and demand are reconnected is important too.

Synchronisation used to be the territory of big spinning turbines and magic electromechanical thigns called synchroscopes. Not so much in the 21st century.

In the 21st century the rise of AC->DC->AC power transmission at GW scale (eg various undersea HVDC connections) shows there is now a practical, affordable way of using high power solid state electronics rather than e.g. motor-generator sets or mercury rectifiers or whatever.

Now if you add *control* of the current, voltage, and frequency of the output of those devices, and with some proper understanding and clever control algorithms you can (at least in principle) use it as "synthetic inertia", to behave like a real alternator would, and not just in GW-scale installations.

Anyway, go have a look before the lights go out.

[MachDiamond]

Re: replicate these results using actual equipment?

It could be a good move to convert signaling over to fiber optics as much as possible. It would have the added benefit of reducing the theft of copper cabling. No more long antennas that can pick up disturbances either.

[Jess--]

Re: replicate these results using actual equipment?

I suspect that the miles of steel rail make quite a nice antenna.

as I understand it the most basic (and used) block detection relies on train wheels shorting the left rail to the right rail and it's this basic detection that fails, it doesn't matter what you are using to carry the signal from the sensor to somewhere else when it's the sensor that being tricked.

[Mike 137]

Re: replicate these results using actual equipment?

From the paper, the operational current along the tracks required to energise the relay that signals green seems to be (from graphs, not data) in the order of 80 mA DC, with relay drop out maybe 10 mA below this. Against this, the potential problem seems to be the prospective current induced in an (order of) 1 km section of rail by the solar flair.

[werdsmith]

Re: replicate these results using actual equipment?

But what are the implications for my wireless doorbell?

[David Hicklin]

Re: replicate these results using actual equipment?

> But what are the implications for my wireless doorbell?

The doorbell will be fine but as the internet will be down it won't work anyway

[Richard Tobin]

Re: "constructed digital models"

The "equipment" in question is a block of railway line about a kilometer long, which is rather difficult to enclose in a cast alloy box, especially if you want a train to travel along it.

[Neil 44]

Re: "constructed digital models"

I'm sure, with appropriate negotiation and some funding, they could do a real-world test on one of the heritage railways that have reasonable lengths of line...

(it probably wouldn't be safety critical either as the signals and points are usually controlled by people rather than automation on heritage railways!)

[imanidiot]

Re: "constructed digital models"

As far as I'm aware a lot of heritage lines (the ones not taken over from BR in more recent times excepted) use older interlock systems that rely on mechanical interlocks and things like telegraph and bell links, not relays, for block control. So it might be hard to test this sort of thing on those lines.

[cyberdemon]

Re: "constructed digital models"

> I'm sure, with appropriate negotiation and some funding, they could do a real-world test on one of the heritage railways that have reasonable lengths of line...

How does one arrange a "real-world test" for the effects of a solar storm?

[cookieMonster]

Train or bus??

Check the space weather first!!

[Someone Else]

Re: Train or bus??

Finally, something that might...just might...make the US Space Farce Force useful.

_{...or not...}

[Pascal Monett]

So, let's review

Now, the things that can keep UK trains from running are not only the wrong kind of snow, too much rain, but also too much sun.

Find an excuse for when it's the wrong kind of wind and you can shut the train stations down, guys.

[Magani]

Re: So, let's review

Will no-one think of the leaves?

[DogsPavlova]

Re: So, let's review

I suspect it's because Earth is afflicted with "the wrong kind of sun"....

[Someone Else]

Re: So, let's review

What?!? You mean for all this time, we've been holding it wrong?

[Doctor Syntax]

Re: So, let's review

Add wrong sort of diesel in the signalling generator.

[Bebu]

Re: So, let's review

In the train delaying categories of "wrong kind" - wrong kind of governments have to favourite.

It was claimed il Duce kept the trains running on time but I suspect claiming otherwise would have been positively unhealthy.

The HS2 saga viewed from afar the indecision and changing goals underlines cluelessness of the current crop of clowns.

Wasn't it part of Bloody Stupid's levelling up program?

Personally I would recommend levelling up the whole scurvy crew with a few rounds of chain shot.

[Phil O'Sophical]

Re: So, let's review

The HS2 saga viewed from afar the indecision and changing goals underlines cluelessness of the current crop of clowns.

More likely the incompetence of the Project Manglers in the civil service. HS2 has outlived several sets of clueless clowns in Westminster.

[Stork]

Re: So, let's review

Trains didn’t get more timely under Mussolini. Newspapers were stopped writing about delays.

[Stuart Castle]

Re: So, let's review

"Too much sun" has been an excuse for several years. Hot weather can cause the tracks (and particularly the points) to warp. Particularly if the line is busy, because the trains can heat the tracks quite a lot.

[Anonymous Coward]

Re: So, let's review

It's not so much too hot, as too wide a range. Rail networks cope OK with a spread of about 40ºC, so traditionally the UK network was designed for -10 to +30. Spain, for example, might have used 0 to +40. The UK temperature range nowadays is more like -5 to +35, and it's that 5º upward shift that causes occasional problems.

[Fruit and Nutcase]

Re: So, let's review

The solution is semaphore signalling and steam steam trains

[collinsl]

Engine? We haven't used those in years for most passenger services. Most of them these days are multiple units of one kind or another.

Also, signals are not only there to stop head-on collisions, they also exist to prevent trains going into the back of each other.

[Mr. V. Meldrew]

Tosh!

Complete Tosh!

Lazy so called boffins, looking out of their ivory towers (in this case my much loved Lancaster Uni).

The Uni looks over the West Coast main line. I wonder when they were gazing over the railway that they asked BR...sorry Network Rail... if they could look at the "Relay Room" that is residing by the railway?

They would see Relays. Electromechanical devices with interlocks in robust steel earthed cabinets. The trackside equipment is encased is steel structures, again not electronic.

In what world would a solar flare affect a 243 Tonne train from "shorting" a the section signal out. Yes the line is occupied when the first wheel enters the section rail and remains so until the next section.

Gentlemen of Lancaster uni. Stop looking out of the window.

Mark. Former Signals and Telegraph engineer for British Railways. (S&T.E)

[Steve Davies 3]

Re: Tosh!

Well said.

IMHO, the bits of the network that rely on Radio Transmission such as the RETB (Railway Electronic Token Block) as used on the lines to Phwelli and AFAIK, possibly some parts of the Far North of Scotland Line would be subject to interference from Solar Flares as would be the WiFi connections to the trains.

The safe passage of trains is more likely to suffer from wayward JCB drivers and Cable Thieves. Some stupid idiots dug up some cables near me only to find that they were all fibre optics. Yes, the shielding on the cable said that it was Fibre but they either could not read or decided that it was all fake news. All services were disrupted for three days.

[JulieM]

Re: Tosh!

For some people, disrupting the trains is the primary object of cable theft; being able to make a profit selling anything they stole is just bells and whistles.

[Phil O'Sophical]

Re: Tosh!

Trains are better when they have bells and whistles.

[Mike 137]

Re: Tosh!

"In what world would a solar flare affect a 243 Tonne train from "shorting" a the section signal out

As the paper discusses, the current that keeps the relay closed is pretty small (c. 80 mA) and the relay is at the opposite end of a c. 1 km section from the source that powers it via the rails. Furthermore the difference between the pull in and drop out currents of the relay is only around 10 mA. The magnetic field of the solar flair can induce comparable currents (either in phase or out of phase) with that in the rails, potentially overriding the intended drive current. If the flair induced current is in phase with the current keeping the relay closed (green signal), it may prevent or delay the relay opening when a train "shorts" the section (bearing in mind that the "short" still exhibits resistance) and if it's in antiphase it may (via summation) cause the relay to drop out (red signal) even if there isn't a train shorting the tracks. So not actually tosh at all, but a matter of applied Kirchhoff's Laws.

[munnoch]

Re: Tosh!

I suppose the theoretical failure mode is inducing a current that is equal and opposite to the current that powers the detection circuit making it look like the train isn't there. Which I imagine is so unlikely that its really not something to worry about. If it was then should be easily mitigated by sending a varying signal down and if anything at all comes back then consider the block to be occupied.

[Mark #255]

Re: using varying signals

As you note, sending a varying signal down the track (instead of a static level) allows you to distinguish between <<no train>> and <<train but also interference>>.

Railway signal engineers also had this thought, which is why there are several different types of track circuit which use different frequencies and modulation schemes, none of which suffer from this particular (and known) failure mode that does affect DC track circuits.

[Anonymous Coward]

Re: using varying signals

And do the ancient relay-based systems support this?

You know, because "old is better" has now been claimed in this thread, and it sounds like it really, really isn't.

[Paul Kinsler]

Re: In what world would a solar flare affect a [] train from "shorting" a the section signal out.

I wouldn't imagine it stops the short existing - but presumably it might induce counter- or over-currents across it, in addition to what you normally expect. And so by altering the "short"current, thus also change the measurements, and hence affect the inferences you make regarding whether the short (and by implication the train) is present in some location.

[Yet Another Anonymous coward]

Re: In what world would a solar flare affect a [] train from "shorting" a the section signal out.

Or increases the ground potential between 2 points so that the shorted rail section now looks like it has voltage difference and so isn't connected

[Anonymous Coward]

Re: Tosh!

Former S+TE here too.

Utter tosh, agreed.

Obviously these academics didn't stop to ponder that signalling systems are already well hardened to accept 25kv overhead electrification, with 100's of amps flowing through the rails as a neutral conductor, along with huge levels of EM noise fields. Not to mention fault conditions of 1000's amps flowing and the occasional lightning strike (ok, the latter can cause damage) The relay based DC track circuits they refer to were part of the early electric signalling (not electric traction) and have largely been superceded by more advanced systems in the last 50 years, especially as electrification projects have advanced.

Considering it takes 100's of miles of power or telegraph lines to be affected by solar flares, a few KM of rails, physically in contact with the ground, would be totally unaffected. And it's a so called effect that has never been noted in the past.

[Phil O'Sophical]

Re: Tosh!

I'm reminded of a story about a reverse variant of this. Some years ago the boffins at CERN noticed a small but regular wiggle in some measurements. It wasn't serious, but they couldn't explain it until one day it stopped for a few days, then reappeared.

Looking for more info, they realised that the pause correlated with a French train strike.

It turned out that when a TGV drawing 9MW from an overhead catenary returns it via the rails, the ground currents that are generated were sufficient to perturb the accelerator beams below them.

[Anonymous Coward]

The British 'Train' System

Warning Rant Ahead.

The British 'Train' System does not exist.

It wasn't BT as in British Train... it was BR : British Railways.

Trains run on the Railway. The bits that are fixed make up the railway. ergo... it is not a Train Station. It is a Railway Station.3

We make the same mistake when it comes to Cars and Roads or do we?

Rant over.

[Anonymous Coward]

Re: The British 'Train' System

You mean autos and highways?

;o)

[Anonymous Coward]

Re: The British 'Train' System

Like a "Bus Station?"

[Stork]

Re: The British 'Train' System

Doesn’t station refer to stationary, not moving? As in work station?

[Anonymous Coward]

Re: The British 'Train' System

And trains are made up of a locomotive and carriages, or multiple units. Hence why it is called a train.

An engine is the bit inside the locomotive that produces the motive power. Maybe a diesel engine, or an electric motor, or both. Or an external combustion engine that is built into the fabric of the locomotive such as one powered by steam.

Interestingly, back in the 1980's, when BR added RETB signalling to the West Highland line one of the issues to be overcome was how to fit a radio unit in a steam locomotive cab. Steam loco's were used for special excursion, even in those pre-Harry Potter days, and steam loco's had absolutely no electric systems whatsover, let alone 12V DC to run a a radio unit, or a suitable place to mount it. In fact, the entire train in those days had no electrics.....

Maybe someone with adequate memory can enlighten us as to how electric light was implemented on trains in the days when steam traction was de rigour? Batteries on a wheel driven generator??

[PRR]

Re: The British 'Train' System

> how to fit a radio unit in a steam locomotive

Apparently the Union Pacific's answer when they take Big Boy out is to couple a Diesel to it. The Diesel of course has all the radio and logging needed to run the rails today. With the decline in real rail traffic UP probably has spare Diesels (at least that they can commandeer for scheduled excursions). One could think that if Big Boy stalled on the main line, a Diesel could pull it to a siding. (Actually Big Boy shunted a stalled Diesel freight out of its way once.)

[Ken Moorhouse]

Re: Maybe someone with adequate memory can enlighten us

Sorry, not old enough to remember, but First class passengers in the earliest trains brought their own candles. Later, pots of oil mounted in the roof were used to light carriages. Pullman carriages initially had kerosene lamps with Argand burners. Later, Pullmans had Faure battery cells supplying Edison bulbs. This was superseded by the use of generators, situated in a guards van, which used the wheels below it to provide the oomph. Elsewhere, canisters containing coal gas or compressed oil gas were attached to the underside of carriages.

(Ref: Brian Haresnape "Railway Design Since 1830 Vol 1)

[Phil O'Sophical]

Re: The British 'Train' System

steam loco's had absolutely no electric systems whatsover,

Many did have electric light, at least for headlamps. IIRC they used a steam-driven turbo-alternator fed from the boiler. That would have had very low steam consumption compared to the main driving system.

[imanidiot]

Re: The British 'Train' System

Most locomotives in the later days would have had a steam driven generator. Carriages could have wheel powered generators (and sometimes batteries, sometimes you'd just have no light when stationary) or in some cases steam generators driven from the steam heating circuit (Though I don't know if BR or it's many predecessors ever used this). Some countries also had electrical connectors to have the whole train powered from the locomotive generator (IIRC Germany did this for instance).

[imanidiot]

Re: The British 'Train' System

Interesting point of note btw, the new-built steam locomotiveLNER A1 Peppercorn "Tornado" has a full electrical system, including AWS, TPWS and ERTMS compatible GSM-R radio in the cab. They achieved this by having a battery bank and electronics hidden in the tender.

[This Side Up]

Re: The British 'Train' System

I can't give you a definitive answer, but paraffin lamps were used to illuminate signals, to display headcodes and by guards to signal to the loco crew. Did the crew have any lighting in the cab, other than by opening the fire doors? Some coaches had gas lighting in the ceiling presumably (I don't know) using compressed gas or maybe carbide - not excessively safe either way.

[Anonymous Coward]

Re: The British 'Train' System - light on the subject

A few decades ago, carriages may well have had electric lighting inside. Electricity could come from generators under the carriage floor, belt driven from the carriage wheels. Other options were doubtless available too, as already mentioned.

Maybe there's more info at https://www.railforums.co.uk/threads/internal-lighting-of-heritage-coaches.103377/

Mention of paraffin reminded me that somewhere in this flat I have an old (1960s?) BR guards light, fairly standard for its time, small paraffin lamp in a hand holdable case with a couple of different glass lenses inside so it can be "white", red, or green. Probably.

Never been a BR Signals and Telecom engineer, though did I did once apply and get invited for interview. Didn't get to the interview though, train was late.

BR Telecom had its own national fibre network ages ago, running alongside the tracks from UK, town centre to town centre. Post privatisation, it was sold to Racal Telecom, and then Thales, and who knows where nowadays.

https://en.wikipedia.org/wiki/British_Rail_Telecommunications

[Spherical Cow]

Re: The British 'Train' System

I was once lucky enough to be invited to ride the footplate of a stream locomotive. When we passed through tunnels the only light was from the firebox. Amazing experience!

[Anonymous Coward]

Re: The British 'Train' System

That's got to be the most pointless and wrong rant I've seen so far today.

It's a railway system. It's ALSO a train system. It's also a track system. It's also a transit system. It's also a freight system.

Oh, and 'train station' is actually more correct than 'railway station'. Do railways stop at the station? Nope, trains do. The train becomes stationary. Train station.

[s. pam]

Union storms cause far more damange

The hell with 'lectrical storms, the unions are causing utter chaos on a scale never before seen in mankind by their greedy Marxist behaviours. Regardless of the trains being 'lectric or not, they have destroyed the trains by deliberately ruining millions of hours of human time.

[Anonymous Coward]

Re: Union storms cause far more damange

The greedy capitalists are causing the chaos by not adequately paying workers.

Don't try to blame union workers for problems created by billionaires.

[xyz]

Lol....

Can you just imagine BBC news trying to explain a CME buggering the 8:15 from Croydon in words that the BBC thinks its audience would understand, whilst shoehorning in the phrase Climate Emergency ('cos it's natural playin' up innit) and how if we all used bicycles this would never have happened.

[Ken Moorhouse]

Re: Who remembers the daily cancellations of the 0814 Barnehurst to Blackfriars?

https://www.youtube.com/watch?v=TBPahAoVUyQ

[Big_Boomer]

Pointless waste of time

If we suffer a CME large enough to knock out the Railway Signalling system, then chances are we are all doomed as the Grid will be down, and a great many other electrical/electronic systems will be dead. As for restarting the Grid, that's another reason why we have huge Nuclear Power stations as they have turbines and generators that match or exceed the coal fired station systems.

[Paul Kinsler]

Re: Pointless waste of time

No doubt because of my many sins, I have now attended a number of space weather conferences (the attendees are quite wide ranging - academics, space hardware companies, met services, government labs, the occasional from defence or civil service. As I understand it, although it is not always so easy to get rail companies to take space weather seriously, those who run power grids pay more attention. Those who run Met services (eg the UK Met Office, and its various European and US equivalents, and others around the world) tend to offer space weather predictions; and these even start by measuring current solar activity, and using it to predict the eventual terrestrial consequences. As far as I recall hearing, "Doom" is pretty unlikely, but some might have to react quite nimbly if something Carrington-like seemed to be on the way.

In NZ recently the power networks org even plugged one of their power stations into the ground and had a look to see where the current came out - here's a couple of bits of the abstract for a recent conference presentation:

"A government-funded research program in New Zealand is currently examining the impact of extreme space weather on the country's energy infrastructure. Specifically, we are interested in understanding how geomagnetically induced currents (GICs) affect high voltage power transformers. GICs manifest as quasi-DC currents within the power system and can create issues in the electrical network due to transformer saturation." [...]

"In January 2023, with the assistance of the National Grid operator Transpower, we leveraged New Zealand's high voltage DC (HVDC) transmission link to directly inject current into the ground at the Haywards substation near Wellington, New Zealand. We closely monitored the impact on two 216 MVA, 220/110 kV autotransformers, and one 80 MVA 11/110 kV step up transformer, as well as the associated transmission lines. This testing involved conducting six injection tests over a nine-day period, each lasting between one and two hours. The maximum current injected into the ground reached approximately 612A..."

[Phil O'Sophical]

Re: Pointless waste of time

maximum current injected into the ground reached approximately 612A

Now that's what I call a real experiment. Can you imagine the paperwork if we tried to get permission to do that in the UK?

[Ken Moorhouse]

Legacy Systems

It is extremely unlikely to occur with legacy systems where a feed is placed at one end of a track circuit and a relay is at the other end. The wheel/axle combination of a train short-circuits the feed, depriving the relay of current, de-energising the relay. The London Underground uses 125Hz (older circuits used 33.333Hz) for track circuits (to reject any extraneous 50Hz source interference), and relays are double element vane type, which means that there is a "control" voltage placed on one coil. This has to be the same frequency and compatible phase as the track circuit coil otherwise the relay will not energise, so even if a 'foreign' signal is injected into any part of the circuit, it will fail safe. The Underground uses 600 volts DC for traction, so the need to not give false readings if some of that leaks into the track circuitry is well understood. When a train passes a green signal, the track circuit relay governing the signal drops out, therefore forcing the signal to go red. Interestingly, a further guard is that if the mechanical trainstop (using compressed air controlled by a solenoid) guarding the signal fails and remains down as the train pases, there is a circuit (known as the TQ) which prevents the signal returning to green, even when the train is safely passed. A common cause of such failures was with litter getting lodged in the trainstop arm. This technology has been in use for around a century and is impervious to any EM injection.

The Victoria Line uses a different system with pulsed codes generated mechanically (using pendulums). Detecting equipment uses IIRC passive band-pass filters which work on a goldilocks principle (the detected code has to be within a very tight tolerance otherwise it is ignored. More modern systems I don't know about, as I moved on to other things. But the Signal Engineering profession is totally obsessed (quite rightly) with fail-safe principles, which would include solar storms.

[cyberdemon]

Re: Legacy Systems

Yes indeed, so the worst that can realistically happen to the railways is that all signals would be stuck on red.

Which, in the current era of strikes etc, is pretty much Business As Usual.

[martinusher]

Not if they're designed properly

Railway signalling in the UK has historically been a case of Murphy's Law -- if it can go wrong, it will, and often with disastrous results. The consequence of this is that resilience and fault protection became baked into the systems. Its actually quite fascinating how these systems evolved and the level of detail in even 100+ year old technology, the only potential problem being that people who don't understand the 'why' so see some of the methods and procedures as redundant. (Also, everyone thinks that you need a computer to implement a 'system'......)

As for CMEs themselves they might cause a problem with open air telegraph lines that aren't protected properly but even on heritage railways open air lines, if they even exist, are cosmetic. The effect of the recent CME -- a relatively large one -- was to displace satellites and make H/F communications a bit noisy (and provide a free lightshow for millions).

[cyberdemon]

Re: Not if they're designed properly

It'll make a good excuse though, when they are borked for some other reason.

(Adds 'Coronal Mass Ejaculation' to the BOFH excuse generator)

(autocorrect doing its job admirably there..)

[Anonymous Coward]

new one

New one for me just waiting when our local train company starts using it.

-- Anon because I don't want to give any hints to them.

[Anonymous Coward]

The 8:15 from Surbiton will be delayed today

We are expecting a space leaves storm and minor CME.

We suggest getting the Volvo out.

[This Side Up]

Axle counters

I didn't see one reference to "axle counters" which are gradually replacing track circuits. Are they any less likely to be affected by solar storms?

[Ken Moorhouse]

Re: Are [axle counters] any less likely to be affected by solar storms?

Never experienced axle counters in the field, but the above can be answered by asking how the counting is performed?

If counting is done electronically then the answer is they will be more susceptible to solar storms as pulses can mimic counting, incrementing is fine (from a safety perspective, but not from a passenger's point of view), decrementing is not. False increments will however cause a shut down while non-existent axles have been deemed to be present within the counter, requiring a reset.

How do you perform a reset in case of failure? With track circuits recovery is automatic, but some extremely methodical means of doing an inventory of trains in an axle-controlled area is imperative to safety. Historically, how many crashes on single-track lines have been due to the concurrent issuance of two tokens? (A token is a metaphor for a train that is non-separable into smaller parts). An axle counting solution comes with a similar problem. Single track token issuance and axle count resets are both prone to operator error. Both technologies can take a long time to check if sections are long and every metre checked before the reset can be permitted. This can mean long delays to passengers.

[Anonymous Coward]

Re: Are [axle counters] any less likely to be affected by solar storms?

Ken and other interested parties:

the track circuit vs axle counting vs (something else) question is not a recent one, especially in the era of ETCS?ERTMS.

I don't know what other readers want to see, but I found some interesting reading at

https://www.railengineer.co.uk/ertms-level-3-a-possible-way-forward/ (seems to be free to access)

e.g.

"Level 3 ETCS (the signalling element within ERTMS) is based on a total radio solution. A train’s position is reported back to the RBC (Radio Block Centre) at least every five seconds. This information is based upon the data obtained from a series of track-mounted eurobalises (radio beacons) provided at intervals dependent on the positional accuracy needed (for instance, where a precision stop is required). The position reference obtained is then incremented by accurate train-borne odometry that calculates the distance travelled from the last balise."

Separate mechanisms, some mentioned briefly in the article, can be used to check whether a train has unintentionally separated into pieces.