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| Are trains Faraday cages? + surges, what happens? 26/01/2010 at 12:17 #607 | |
razgriz33
42 posts |
Well it happens to aircraft quite frequently and they protected because they are faraday cages. im talking about lightning strikes. So is a train protected by a Faraday cage? i would hope passenger trains are at least, it is highly unlikely that a lightning strike would strike a train but beleive it or not all cars are faraday cages, even your microwave. I thought i would ask and also raise awareness that they even exist. some of you may have thought the rubber in cars stop lightning strikes in their tracks. well no rubber actually turns into a big conductor at the levells of lightning so the faraday cage is important. I suppose an EMU or a electric loco would just get some kind of safety thing with the electric systems if a lightning bolt struck the ohle or 3rd rail. any ideas? which leads me onto my next question what happens in the event of an electric surge in the system? Are there massive cuircuit breakers on the trains that keep it protected? I'd like to know and spread the knowledge at the same time, any replies would be appreciated - ta for those of you that do not know what a faraday cage is, please bear with the low quality: (it is a very good explanation) Log in to reply |
| Are trains Faraday cages? + surges, what happens? 26/01/2010 at 12:17 #6204 | |
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razgriz33
42 posts |
Well it happens to aircraft quite frequently and they protected because they are faraday cages. im talking about lightning strikes. So is a train protected by a Faraday cage? i would hope passenger trains are at least, it is highly unlikely that a lightning strike would strike a train but beleive it or not all cars are faraday cages, even your microwave. I thought i would ask and also raise awareness that they even exist. some of you may have thought the rubber in cars stop lightning strikes in their tracks. well no rubber actually turns into a big conductor at the levells of lightning so the faraday cage is important. I suppose an EMU or a electric loco would just get some kind of safety thing with the electric systems if a lightning bolt struck the ohle or 3rd rail. any ideas? which leads me onto my next question what happens in the event of an electric surge in the system? Are there massive cuircuit breakers on the trains that keep it protected? I'd like to know and spread the knowledge at the same time, any replies would be appreciated - ta for those of you that do not know what a faraday cage is, please bear with the low quality: (it is a very good explanation) Log in to reply |
| Are trains Faraday cages? + surges, what happens? 26/01/2010 at 12:40 #6205 | |
Peter Bennet
5402 posts 
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I can't answer your question as such but I can tell you that I have been on a train that was struck by lightning. It was back in the mid '80s on the Nene Valley Railway (behind 55022/D9000 as it happens). There was an almighty bang and some scorch marks on the roof of the MK1- but I think that was that. Peter I identify as half man half biscuit - crumbs! Log in to reply |
| Are trains Faraday cages? + surges, what happens? 26/01/2010 at 13:17 #6208 | |
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clive
2789 posts |
Actually, neither a train nor a car is a Faraday cage, because it isn't spherical and has large holes in the metal. Nevertheless, in the case of a strike most, if not all, of the current will take the easy route through the metal rather than trying to go through the high-resistance interior. But this is no different in principle to the lightning conductors on the top of buildings, which aren't Faraday cages either. Log in to reply |
| Are trains Faraday cages? + surges, what happens? 26/01/2010 at 13:21 #6209 | |
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razgriz33
42 posts |
clive said:Actually, neither a train nor a car is a Faraday cage, because it isn't spherical and has large holes in the metal.ahh very interesting, thanks for the responses so far Log in to reply |
| Are trains Faraday cages? + surges, what happens? 26/01/2010 at 13:39 #6213 | |
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bill_gensheet
1413 posts |
This is being used by some TOC to enforce the 'mobile free' coaches by improving the Faraday effect through making the windows conductive and joining this to the body. Not that that will carry lightning impulses. There is no requirement for a Farady cage to be spherical, any closed 'perfect' conductive surface will work just as well, generally up the frequency where the gaps are 10 - 25% of a wavelength. Bill Log in to reply |
| Are trains Faraday cages? + surges, what happens? 26/01/2010 at 23:24 #6224 | |
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razgriz33
42 posts |
again very interesting, i bet the japanese are interested in the mobile free coaches you mentioned. (I hear that they think it's incredibly rude to use your phone on the train) now if only we could stop chavs playing rubbish loudly in the quiet coaches. still the question stands what happens if a fault, surge or something of a failure nature occured in an electrified track setup? ohle or otherwise Log in to reply |
| Are trains Faraday cages? + surges, what happens? 27/01/2010 at 14:01 #6241 | |
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bill_gensheet
1413 posts |
At various points (trackside and on train) you will have flashover devices so that an excess voltage will break down the gap (often air) and get to ground that way. Similarly an OHLE failure onto the roof will find its way to the ground through the chassis and wheels, toasting bearings and bits of rubber if required. That kind of fault will also pop out the circuit breakers in the supply side preventing any further flow. You see this in the public supply when it is windy, snowy or there are a lot of geese flying about [1]. Brief dips and so on as a fault occurs, then if it isn't on your bit it comes back up again. If it is your part that is faulted, the breakers will have a couple of goes at closing again (ie the goose is cooked, the tree has passed by) and then give up and you've got a power cut. 3rd rail must be a bit trickier as very high current is quite normal [1]. From my parents area, they had a lot of problems with geese flying into the lines, and also cows rubbing on the poles and pushing them into trees. One time the power cut phone line got a bit overwrought and said 'geese rubbing up agianst the poles and cows flying into them' Bill Log in to reply |
| Are trains Faraday cages? + surges, what happens? 27/01/2010 at 16:29 #6242 | |
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razgriz33
42 posts |
RE: [1] hilarious!!! Thanks a bunch for the info Bill. That'l do me for a happy chappy. and also not forgetting thanks to clive and peter Log in to reply |
| Are trains Faraday cages? + surges, what happens? 27/01/2010 at 18:18 #6243 | |
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Quizman
276 posts |
This article is not funny but I couldn't help smiling - talk about being in the wrong place at the wrong time..... http://www.sptimes.com/2006/07/10/Hillsborough/Lightning_survivor__c.shtml Log in to reply |