If train touches OLE

[Dave R]

after looking at the recent crash in Belgium what happens if in the event of a crash the train touches the overhead wires or third rail?
I'd assume there is a safety device of some sort to stop the people inside getting fried, if so how does it work?

(obviously not the pantograph or shoegear)

 

[90019]

I'd say the train would act as a faraday cage; so people win the train should be fine.
I think it'll also trip the circuit breakers for the cables, so the power should switch off quickly.

 

[truckman060473]

very interesting question considering the metal wheels on the train are carrying the overhead power back to "neutral or earth". I've often wondered if a train, derailed, on all wheels (unlikely) and still in contact with the overhead lines would be a hazard in that the steel body of the train would tend to be at the voltage of the power lines if power was still being drawn by the train.

 

[CosherB]

You only get a shock if you form part of a circuit - ie the current goes from live, through you, to neutral or ground. If you are in a train that touches the OLE / 3rd rail, the train (assuming it's made of a conductive meaterial such as metal) will provide the circuit between the high voltage source and ground. Even if you touch the train, provided you are inside it there is no potential difference bteween your hand on the bodywork and your feet on the floor - so no shock.

As soon as the train shorts the high voltage to ground, circuit breakers will activate to cut off the current.

 

[truckman060473]

oh yeah, what you said is right for people on board. i have a good understanding of electricity. maybe i should have added that if this was to occur, a rescue worker on the ground (assuming OH line still live) may see a difference in the voltage potential between him and the train body if the train body could not source the OH line voltage safely to ground as would happen in normal circumstances when the wheels are on the rail

 

[90019]

a rescue worker on the ground (assuming OH line still live) may see a difference in the voltage potential between him and the train body if the train body could not source the OH line voltage safely to ground as would happen in normal circumstances when the wheels are on the rail

I think that by the time any recue workers got to the train, the OHL would've shorted out or been switched off.

 

[TheExmoorBeast]

It would blow the circuit breakers within a fraction of a second.

 

[truckman060473]

safety systems would yes, undoubtedly kick in to prevent such an occurrence. it's just what might occur in theory.

 

[Zamracene749]

You would only get a jolt if by some freak of circumstances the train had managed to insulate itself between the wheels and the track( or ground). In almost all circumstances(accident or not) the trains wheels provide a better path to earth than the person touching it, so no shock.

Interesting enough, there were apparently cases with early electrics that used rubber shoick absorbing inserts between the axles and tyres that relied on copper straps to ground the loco- if these perished or broke it was possible to get a bit of a thump from the bodywork!

 

[GB]

Even with the circuit breakers tripped there can still be enough residule current/voltage to do serious injury to rescue workers.

 

[Fincra5]

However the train will be earthed, so that residule current shouldn't exist.

 

[Wyvern]

Electrocution, however, is not the only problem. There is the heating effect of the current passing through the bodywork. It just so happens that I've been reading a report about a 33 kV power line falling on road vehicles in Nigeria apparently on two buses and a number of cars killing a number of people.

SCotland on Sunday

The different reports are a bit mixed.

The most level headed seems to be the local paper This Day on Line paper where it would seem those in the cars at any rate were roasted alive.

 

[90019]

The most level headed seems to be the local paper This Day on Line paper where it would seem those in the cars at any rate were roasted alive.

There's certainly been an interesting translation in that article;

But we are going to spread our tentacles to ensure that we give security to such persons and advise them on the danger of loading under high-tension wire.

 

[Wyvern]

Having said that the breakers on the British system must be extremely fast. Didnt the cable come down recently on the platform at St. Pancras station?

 

[Dolive22]

Manuals I have seen for emergency services imply that emergency services only go trackside having requested and received power off on electrified lines. In any case even if the current hadn't been cut off automatically, wouldn't the signaller have had the power turned off long before the emergency services could respond?

 

[Wyvern]

Manuals I have seen for emergency services imply that emergency services only go trackside having requested and received power off on electrified lines. In any case even if the current hadn't been cut off automatically, wouldn't the signaller have had the power turned off long before the emergency services could respond?

What are you actually writing about here? So far its been about passengers in trains and on platforms.

 

[Dolive22]

oh yeah, what you said is right for people on board. i have a good understanding of electricity. maybe i should have added that if this was to occur, a rescue worker on the ground (assuming OH line still live) may see a difference in the voltage potential between him and the train body if the train body could not source the OH line voltage safely to ground as would happen in normal circumstances when the wheels are on the rail

That what I'm talking about Wyvern. I thought the passenger issue had been settled as them being protected by a faraday cage.

 

[merlodlliw]

About 30 years ago a light aircraft next door to me struck an 11 KV power
line on coming in to land on a field, it got entangled in the wires and both
pilots survived due to it not hitting the ground, one of the three wires had broken and was on the ground, sparking.

As the power had tripped out, the fire brigade waited for the all clear,the electric company (manweb) used earth rods if I recall before the emergency services
removed the two. who survived.

With AC current any change in voltage immediate trips the breakers, as does
an RCD in the house.

DC is of course more dangerous I am told, anyhow on 25KV the power can jump
a couple of feet, before tripping the breakers. You make it as same as possible but its still the unseen killer

 

[Wyvern]

With AC current any change in voltage immediate trips the breakers, as does
an RCD in the house.

The RCD detects a difference in the currents in the Live and Neutral lines. An imbalance would indicate a leakage to earth. Two example would be through someones's body or a puncture in the element of an electric kettle.

In a house, MCBs trip with over current. The same with any other in line circuit breaker. Voltage doesn't have anything to do with it.

 

[CarterUSM]

The Electrical Control Office will turn off the power if requested by signalman, driver or guard in the event of an emergency.

 

[Wyvern]

That what I'm talking about Wyvern. I thought the passenger issue had been settled as them being protected by a faraday cage.

orry I was still thinking about my last post about the heating effect of the current through the vehicle body. Clearly a train body is much bigger than a car and is earthed better through the supply return.
--- old post above --- --- new post below ---

The Electrical Control Office will turn off the power if requested by signalman, driver or guard in the event of an emergency.

One would hope that it would have already tripped. It just needs the signalman or electricity control centre to confirm that it is off and will stay off.

 

[CarterUSM]

Yes of course, I would very much hope so myself! Just in the event that it was necessary.

 

[Greeny]

DC is of course more dangerous I am told, anyhow on 25KV the power can jump
a couple of feet, before tripping the breakers. You make it as same as possible but its still the unseen killer

When I did my live rail training, the instructor told us that AC was actually more dangerous, and likely to hold on to you as when you touch it everything in your body goes into spasms at 50hz and you have no control over it. However, I had no intention of finding out the hard way !.

G

 

[Wyvern]

When I did my live rail training, the instructor told us that AC was actually more dangerous, and likely to hold on to you as when you touch it everything in your body goes into spasms at 50hz and you have no control over it. However, I had no intention of finding out the hard way !.

G

I was told that if you get your hand on a cable etc with AC it tends to spasm shut while with DC it tends to be thrown off. (If I remember rightly - I never troubled to put it to the test)

The other suggestion was that a DC flashover tends to be sustained, while AC tends to extinguish as it passes through the null part of the cycle.

There is an accepted safe distance from the 25kV OHL (We had a little green rule book and a ban on aluminium ladders - I don't know if its still the same)

The actual distance it will jump varies with the relative humidity and the earth path.

 

[ralphchadkirk]

They will switch the juice off for anyone with a reason. I have been trained through my heritage railway to get emergency blocks on the adjacent NR territory and the juice switched off.

The emergency services will NOT go on the track unless they have assurance personally from the person who holds the blocks. I have had that confirmed by a friend who works for the Ambulance service.

 

[CarterUSM]

The accepted safe distance from OHLE is 9 feet, though in an emergency you may go as close as 3 feet. If you dare.

 

[Greeny]

The emergency services will NOT go on the track unless they have assurance personally from the person who holds the blocks. I have had that confirmed by a friend who works for the Ambulance service.

Well, most of the time that is correct ........ except where Cheshire Police, and Fire Service are concerned. Complete kn*b-heads in my experience. I once got called to a car train which had lost part of it's roofing at Runcorn. I got there in time to see two Cheshire Coppers climbing up the vehicle ladder to gain access to the roof. So, as there wasn't time to be polite, I shouted to them to get off the train - I won't repeat the words here but you get the drift. Their Inspector stormed up to me wanting to know who the hell I was so I told him. Then he told me that neither he, nor his men, needed the likes of me to look out for their safety. So I invited him to climb back up there again, just as the wind got up and blew the roof open and it hit the OLE. Guess what ? ........ It was the closest I ever got to seeing a Copper smack his boss.

G

 

[GB]

Their Inspector stormed up to me wanting to know who the hell I was so I told him. Then he told me that neither he, nor his men, needed the likes of me to look out for their safety

FFS, what a complete knobber!:roll:

 

[TheExmoorBeast]

The accepted safe distance from OHLE is 9 feet, though in an emergency you may go as close as 3 feet. If you dare.

Having seen the sparking from AC locos & units (particularly at Farringdon when they make the AC/DC changeover) in the past, I think I'd rather be chicken than dead. You don't normally get a second chance with HT electricity.

I know what it's like to get a "belt" off the normal 240v AC household system, when I grabbed a faulty cable, didn't it bloody well hurt! Something I don't intend to repeat.

 

[merlodlliw]

In a house, MCBs trip with over current. The same with any other in line circuit breaker. Voltage doesn't have anything to do with it.[/QUOTE]

agree with your point, I was just comparing.
--- old post above --- --- new post below ---

When I did my live rail training, the instructor told us that AC was actually more dangerous, and likely to hold on to you as when you touch it everything in your body goes into spasms at 50hz and you have no control over it. However, I had no intention of finding out the hard way !.

G

Not always true, I have known people to be thrown several feet by an AC current, with DC which is what TVs etc rectify to, its usually good bye.
However both are the unseen killers.