Really stupid question

Chovies5910 · Posted: Thu Nov 20, 2008 4:25 pm

But what would happen if a bolt of lightning struck the track or the wire thingo's that power the trains Razz

With the huge storm that came over Penrith last night i had alot of time to think ( all Bl**dy night Evil or Very Mad

)

Anthony

wongm · Posted: Thu Nov 20, 2008 4:38 pm

The control system inside the train would not like it if lightning hit the overhead, and would probably blow up in the same way your electronics would if the power line into your house got hit.

Do they have any kind of surge protection to shunt to the ground any lighting hitting the overhead? Or do they hope it just misses and hits the grounded stanchions instead?

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Bwana · Posted: Thu Nov 20, 2008 5:00 pm

I'm fairly sure I've heard of it happennign in the past. Don't know the mechanics of it but generally is a relatively short (~30 min) period of no power to that section. At a guess someone has to go to the substation and reset a circuit breaker.

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Johnmc · Posted: Thu Nov 20, 2008 5:30 pm

I had *roughly* the following conversation with my tutor driver, when I was driving a QR 3900 electric freight loco, during my training:

"If your loco gets struck by lightning, then it would blow up your (loco's) transformer"

"And how bad would that damage the loco?"

"There wouldn't be anything left of it above the floorline. Don't worry, you wouldn't feel a thing."

(I'm fairly sure that I gave my tutor an appropriate look at this point. From what I've heard, mid-train electric locos have been recorded as being hit, with the aforementioned results, but lead locos have missed out, afaik.)

edit:typos

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TE2815 · Posted: Sat Nov 22, 2008 10:28 am

Hitting the track or lineside equipment will affect the signalling system. Just ask Campbelltown, happens there frequently.

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bulldozed · Posted: Sat Nov 22, 2008 8:40 pm

Johnmc · Posted: Sat Nov 22, 2008 10:42 pm

409 · Posted: Sat Nov 22, 2008 11:05 pm

I read in TRAINS magazine a letter that asked the same question some time ago and the response was that the chances of being hit are fairly slim due to the fact that the first metallic point of contact (other then the train) are the rails which are fairly well insulated from the negative electrons that come out of the ground because they are mounted on sleepers which are in turn mounted on ballast. To cut a long answer short then, the very way a railway is constructed helps prevent attack from lightning.

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Oldfart · Posted: Sun Nov 23, 2008 6:32 am

From my knowledge of the behaviour of lightning I suspect a train and possibly even the construction of OHW systems will operate as a Faraday Cage. Wiki has a reasonable article about it; an excerpt includes:

Cars and aircraft function as Faraday cages when struck by lightning. The metal frame and outer skin of the vehicle cause the electrical charge to travel safely away from the occupants. This differs from a popular urban legend that claims that a car's tires cause the lightning strike to reach the ground. However, radio and cellular phone signals can still reach inside the vehicle since their wavelengths are significantly smaller than the windows and other openings in the vehicle's conductive frame.

The role of a car as Faraday cage was demonstrated by Richard Hammond in an episode of the BBC television program Top Gear. At the Siemens High-Voltage Lab in Berlin, Germany, Hammond sat in a car that was being struck by simulated lightning of over 800,000 volts, and reported during the experiment that he felt nothing.

More sensitive devices, like most signaling systems however, will probably be spooked but not necessarily destroyed by the electrical fluctuations from a strike. Because of the Faraday effect it's often relatively non-conductive things like trees, sheep and occasionally people who fare far worse. In aviation the concern is with the greater use of some non-conductive synthetic materials in structures. That enables lightning to strike through, say, a fibreglass light aircraft skin blasting a hole in it to hit metal components inside, instead of hitting and being dissipated by a metal external structure.

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