Third Rail or OHLE freeze

[jopsuk]

Good question. I assume it is loaded somewhere on the network. It is all taken care of by RFF. I would have to refer to them to be sure.

Surely it would have to be on every section, as far as possible from the section feed

 

[captainbigun]

Definitely to OHL heating on the UK 'classic' network. I suspect the legacy feeding arrangements mainly put pay to this, but I also suspect that icing is not a big enough issue often enough to warrant the investment. Cheaper to hire some locos and pay for the pan heads.

Whether the revised AT feeder arrangements which are being introduced will change this, I don't know. It's not featured in any docs I've seen, so suspect not.

86101 doing an East Coast tour this evening.

 

[O L Leigh]

The problem of ice on the overheads is slightly overplayed. Yes there are issues with arcing on the carbons but, as TGV hints, this isn't really the limiting factor. The WA lines, as with many others, run without an ice-breaker in a perfectly satisfactory manner.

The issue, particularly with newer units (hence the issues with Desiros and Pendos on the WCML) is that the ice on the overheads and the effect it has on power transmission can lead to interference that can impact on the train's traction equipment. These are issues that do not affect older units.

Cl379s have a Line Interference Module (LIM) on the roof that monitors the power transmission and, if the interference is too great, will open the main breaker to isolate the train's equipment from the overhead power supply. In normal operation the interference caused by frost on the overheads would result in the breaker opening too frequently. Therefore when the weather is cold drivers are instructed to select Ice Mode on the TCMS which alters the LIM default settings to prevent it interfering too much.

The amount of ice that builds up on the overheads is, on frequently used lines at least, modest. It is simply frost. The wires themselves are below freezing and so the moisture in the air freezes out. The problem is that you never really clear it away because as long as the wires are below freezing and there is moisture in the air, more frost forms.

Yes you can get carbon damage if the arcing becomes particularly serious, but even then you would require a lot of ice to start that off. In fact you can get a large amount of arcing simply where the pan head loses contact with the OLE, far more than frost can generate. While I am not saying that it doesn't happen, I have never yet encountered carbon damage except where the pan had struck an object. In weather like this, on most lines and services, OLE is relatively unaffected.

O L Leigh

 

[captainbigun]

I'd disagree. You should see the state of the pan heads that come of the WC ice breakers....and they aren't left on long. A lot of leading edge damage and that's caused by ice.

 

[apk55]

OHL heating on lines fitted with a +- 25KV system could be done by a tapping on the most distant auto transformer (or some equivlent arangment) to cause a large circulating current.

 

[captainbigun]

I should also add to this discussion that the carbon manafacturers are doing a LOT of work to develop carbons that are less susceptable to failure. One of the biggest issues is bonding failure. The carbon is bonded to it's carrier (with the air gallery beneath), this overheats and fails, I've also seen carbons where holes have been blown into the carrier through arcing.

 

[W230]

Cl379s have a Line Interference Module (LIM) on the roof that monitors the power transmission and, if the interference is too great, will open the main breaker to isolate the train's equipment from the overhead power supply. In normal operation the interference caused by frost on the overheads would result in the breaker opening too frequently. Therefore when the weather is cold drivers are instructed to select Ice Mode on the TCMS which alters the LIM default settings to prevent it interfering too much.

What exaclty is the LIM responsible for during normal running? The reason I ask is that our 377s have this too and get put into ICE mode in weathers such as these we have now. Obviously a "usually" sensitive LIM must be giving some sort of benefit to the unit otherwise it wouldn't be that sensitive in the first place! I'm just not sure what it is it actually does (and i'm still waiting for my 377 traction course... ).

 

[merlodlliw]

reminds me of the Ghost Trains that used to run on 3rd rail in BR Days

 

[TGV]

I'd disagree. You should see the state of the pan heads that come of the WC ice breakers....and they aren't left on long. A lot of leading edge damage and that's caused by ice.

I don't think we're disagreeing that pan heads get damaged. We see the same things you do but whereas pan damage stops 1 in 100 trains (services) for intervention, ballast and ice damage will stop 1 in 20. Rough numbers but they illustrate the point.

Carbon manufacturers (of which there are very few) are, in my experience, very slow to react to any such issues. I've been waiting literally years for an improvement to come through. If they're doing a lot of work for you, perhaps you can send them my way!

Do your trains run with any speed restrictions in similar conditions?

 

[455driver]

reminds me of the Ghost Trains that used to run on 3rd rail in BR Days

They still run.

 

[ainsworth74]

Does anyone have pictures of pan heads that have been chewed up by ice? And preferably another one from before for a comparison.

 

[sarahj]

Dont have any pics to hand, but here is what happens when it goes wrong.

http://www.youtube.com/watch?v=2ocbtg1jlpM


And some third rail sparks

http://www.youtube.com/watch?v=slyRo5lMCPw

And OHLE sparks

http://www.youtube.com/watch?v=fFQNQspI2ek
SJ