Rail travel disruption continues (BBC News)

[RF News]

Trains continue to be cancelled and delayed because of fallen power cables on the Norwich to London line.

More from BBC News...

[Deathbyteacup]

Just out of curiosity, what causes a train to bring down overhead power lines? General wear and tear?

Seems awfully dangerous to me.

[Foghut]

Originally Posted by Deathbyteacup

Just out of curiosity, what causes a train to bring down overhead power lines? General wear and tear?

The contact wire of the catenary bounces around quite dramatically as the top surface of a train's pantograph (actually carbon strips) pushes up against it. The catenary is stressed at many points by having heavy weights hung from it, and the whole lot is actually quite fragile. If the pantograph causes the contact wire to move further than it's supposed to...then sometimes it all comes down like a house of cards. Don't forget that in addition to vertical excursions there is also "swagger" - IE, the contact wire continuously moves from side to side in relation to the pantograph head, to ensure even wear for the carbons.

Also all pantographs have an Automatic Dropping Device (ADD) which senses when things aren't right. Unfortunately if the pantograph is misplaced and the ADD puts the pan down, this can have the effect of tearing the whole catenary down at the same time. If you're travelling at 100 mph, you've dragged the best part of 1000 yards of OHLE with you by the time you come to a stand. It's a real guilt trip when you look back and see the chaos which your train has just caused !!

Our Driving Policy is to immediately "Drop & Stop" if you're an 8 car and the line light goes out for an unexpected reason, because at high speed having 2 pantographs at a distance of 4 cars apart can occasionally provoke oscillation in the catenary. It's cheaper in the long run to stop and have a look, rather than stop the job entirely.

HTH,
Foggy

[paul miller]

Hi Foggy,
I find that description very interesting, thanks for that.
Has that happened to you many times before.
Paul.

[EuroStar]

Very interesting description - thanks for that, Foggy.

[Foghut]

Originally Posted by paul miller

Has that happened to you many times before.

I've not done it myself, but I've been on another driver's train when it's happened. It's actually quite a worry because there is a slight chance that the fallen structure is still live, so nobody must be allowed near it even though it may wrapped round the train.

Additionally of course arrangements have to be made for all the stranded trains to be evacuated.

And since diesel trains can still run even when the juice is off, you have to try to stop your passengers from detraining themselves before the signaller has assured you that all trains have been stopped.

By the time you eventually get back to the depot and have completed all the reports & interviews you go home feeling you've earnt your money.

[Deathbyteacup]

Originally Posted by Foghut

It's actually quite a worry because there is a slight chance that the fallen structure is still live, so nobody must be allowed near it even though it may wrapped round the train.

Originally Posted by Foghut

you have to try to stop your passengers from detraining themselves before the signaller has assured you that all trains have been stopped.

So can I assume that if the live wire does fall onto the train itself, that the train is designed to act as a sort of faraday cage to protect the people inside, even DMU's / Diesels?

And the power would have to be confirmed off also before evacuation?

Almost thinking twice about riding EMU's now.

[hairyhandedfool]

Originally Posted by Deathbyteacup

So can I assume that if the live wire does fall onto the train itself, that the train is designed to act as a sort of faraday cage to protect the people inside, even DMU's / Diesels?

And the power would have to be confirmed off also before evacuation?

Generally yes, but there may be cases when this is not possible, it is best for the driver/guard to weigh up the options and make a choice.

I doubt they are designed as faraday cages, but in all likelyhood would act as one.

Anything that would not normally come in contact with the OLE could potentially bring it down, the bonnet of a car on a passing freight train for example.

Also, the ADD on 319s is far simpler than you might think. The pantograph is raised by air pressure in a pipe that runs through the pantograph itself. The ADD device is simply a break in the air pipe, should the pantograph rise to far, thereby releasing air pressure and dropping the pantograph. The only other way a pan on a 319 will drop automatically is if the carbon strips on the pantograph are damaged or dislodged, releasing air pressure from the conduit that runs underneath.

Bedford to Harlington on the MML has a speed restriction for Electrics during high winds because of the sway it causes.

[Foghut]

Originally Posted by Deathbyteacup

So can I assume that if the live wire does fall onto the train itself, that the train is designed to act as a sort of faraday cage to protect the people inside, even DMU's / Diesels?

Not as sophisticated as a Farady cage, (which actually keeps out electrostatic fields) but certainly the metal structure of most rail vehicles are earthed.

An example of this was at Kings Cross Thameslink. Because the road bridges over the platforms are low, the height of the catenary over the trackbed is much lower than at most other places. Consequently sometimes if a pidgeon flew between the contact wire and the roof of the PMOS* there was a loud bang and and the pigeon vaporised. Obviously the pigeon had given the traction current a route to earth !

It scared the c**p out of me the first time it happened because it was on the carriage immediately behind me and the sound bounces around the enclosed area of the station. Fortunately a Fitter was waiting there to come 'pass' with me and he calmed down the passengers on the platform before they got a chance to go into headless chicken mode.

*(Pantograph Motor Open Standard - as usual TOCs label their stock differently to what you find in Ian Allan books)

HTH,
Foggy

[G6 UXU]

Morning Foggy, me and the lads where having our usual natter on the bridge at Farington Leyland when a Pendolino going South came past, at the same time a wood pidgeon flew into the overhead live wire and also made a loud bang and vaporised the bird, which resulted in a feathered snow storm. We had never seen that happen before or since. The resident magpies and crows soon shifted the remains. All the best.