Loud Crackling and poor acceleration in wet weather

[Deleted]

Upon last night's bucked loads of rain falling, I've noticed an extremely loud cracking noise seemingly coming from the conductor rail. The acceleration is also jittery. Is this a new thing in wet weather or something to do with the condition of the conductor rail or normal? Haven't heard it as badly as lately. Clearly sounds like constant arcing.

[class411]

It's just water interfering with the contact between the conductor rails and the pick-up.

It can be quite spectacular in conditions of freezing fog. (Where the water is in the form of ice crystals on the rail.

ETA: I should add that the reason that the crackling is louder when the rails are wet is down to the electrolysis of the water that is impeding pick-up.

When you pass a current through water it electrolyses it into hydrogen and oxygen (+heat), and, given that there is arcing involved, this is immediately recombined in a mini-explosion. Hence the extra crackling.



ETA -> Edited To Add.

Also, I've just noticed that I said 'louder' here, and then contradicted myself in a later post.

What I meant in this post by 'louder' is that there's more of it. So the instances of noise are more frequent, rather than the level being higher.

[goldenarrow]

Arcing is common place on 3rd / 4th rail open contact railways in damp/wet/frosty conditions. The 1996 stock aren't smoothest pulling away under dry conditions but in the wet, wheel slide protection cutting out the motors once slippage is detected means that trailers and motor cars jostle with each other as the momentum of the aggressive acceleration rate of ATO subsides temporarily.

Below is a an example of arcing from a 1996 stock leaving Finchley Road on the Northbound. Damp conditions, a rail section gap and point work all contributors here.

[jamesb]

Does the arcing mean that more electricity is used in damp/frosty conditions, since it is "wasted" during the process of arcing? Does that mean that the electricity bill goes up when it's raining?!

[class411]

Mar 11, 2019 6:12:52 GMT jamesb said:

Does the arcing mean that more electricity is used in damp/frosty conditions, since it is "wasted" during the process of arcing? Does that mean that the electricity bill goes up when it's raining?!

Yes, but the (relative) amount is minimal.

[Dstock7080]

There are rarely problems with rainwater as it’s a conductor of electricity, as has been said hail, ice and snow are not.

[class411]

Mar 11, 2019 8:42:54 GMT Dstock7080 said:

There are rarely problems with rainwater as it’s a conductor of electricity, as has been said hail, ice and snow are not.

It is a conductor to a degree*, because it is generally very weak nitric acid, but it will still electrolyse, and the resultant hydrogen and oxygen can recombine in tiny explosions.

If you listen carefully to the (electrical) sound made by a train on wet track, it is softer than that made by normal arcing, because the electrolysed hydrogen and oxygen are not contained meaning they ignite with more of a 'flt' or a 'whump' than a 'bang' or crack.

* If it was a good conductor we would have all sorts of problems all over the place. Track circuits would all fail to operate correctly in the rain, for example.

[Colin]

Indeed - I learned on this very forum a few years ago that actually, water is a very poor conductor.

I always struggled with how Network Rail get away with steel rail sleepers worked until I found this out...

Also explains how we get away with carrying water fire extinguishers on our trains. IIRC the water in them is deionised as deionised water is an extremely poor conductor.

[class411]

Mar 11, 2019 13:01:26 GMT Colin said:

Indeed - I learned on this very forum a few years ago that actually, water is a very poor conductor.

I always struggled with how Network Rail get away with steel rail sleepers worked until I found this out...

Also explains how we get away with carrying water fire extinguishers on our trains. IIRC the water in them is deionised as deionised water is an extremely poor conductor.

This is true, but it's worth pointing out that it's dangerous to extrapolate too far from this.

You can't assume that water and electricity are safe because even a very small amount of salt (and this is any salt, not just NaCl) will make the water a conductor, and only a very small current flow can be enough to kill.

[Colin]

Yep, quite right - sorry, I didn't mean to imply it was in any way safe to apply water to live electricity. It absolutely isn't!

To be very clear, anything on fire that involves electricty is only ok to tackle once the electricity is turned off.

[Deleted]

CO2 extinguishers are best for electrical fires but you must always try to isolate the supply first

Halon was great for most fires but it took away all the oxygen so good for fires but not good for anything that requires oxygen including us humans.

[countryman]

Mar 11, 2019 19:54:59 GMT @aetearlscourt said:

CO2 extinguishers are best for electrical fires but you must always try to isolate the supply first

Halon was great for most fires but it took away all the oxygen so good for fires but not good for anything that requires oxygen including us humans.

Dry powder is good, but is messy. But fires make a mess as well!

[vato]

Mar 11, 2019 19:54:59 GMT @aetearlscourt said:

Halon was great for most fires but it took away all the oxygen so good for fires but not good for anything that requires oxygen including us humans.

This is a myth and the same applies to the other gases (e.g. FM200) used to disrupt combustion.

IMHO The scary ones are actually Carbon Dioxide in poorly installed/planned spaces, and Nitrogen (especially when used to prevent fires in normally sealed spaces).