Ohle damage etc

[Whistler40145]

What happens to the power supply in the event of damage or a complete dewirement?

 

[thecrofter]

It trips out

 

[edwin_m]

What happens to the power supply in the event of damage or a complete dewirement?

If the live OLE touches the ground, a train, or any earthed parts of the OLE it will shut down within a fraction of a second, at least on 25kV. The controllers will normally try to restore it after a few seconds in case it is a transient problem such as a vapourising pigeon, but if it cuts out immediately after 2 (?) attempts they will leave it isolated until they find out what the problem is.

It's possible, but unlikely, that the wires are left hanging close to the ground but haven't actually touched anything so they are still live.

Lower supply voltages have lower fault currents so it is possible the power might not shut down if there is not a low-resistance path to earth. This can result in fires.

 

[ComUtoR]

The controllers will normally try to restore it after a few seconds in case it is a transient problem such as a vapourising pigeon, but if it cuts out immediately after 2 (?) attempts they will leave it isolated until they find out what the problem is.

I was taught. If the current trips then they immediately try to reinstate. If it trips again then they wait for a minute, then reinstate. If it trips again, its left alone and investigated further.

Not sure how accurate that is nowadays.

 

[Whistler40145]

Thanks all for your great replies

 

[DY444]

It's possible, but unlikely, that the wires are left hanging close to the ground but haven't actually touched anything so they are still live.

Happened not too long ago and a Virgin driver was injured having received an electric shock whilst inspecting for ole damage on foot and not seeing the hanging wire in the failing light.

 

[edwin_m]

Happened not too long ago and a Virgin driver was injured having received an electric shock whilst inspecting for ole damage on foot and not seeing the hanging wire in the failing light.

Indeed it did, here's the report:

http://www.railwaysarchive.co.uk/docsummary.php?docID=4863

He had stopped his train having seen damaged overhead power supply wires ahead of it. Following a call to the signaller, he left his train and came close to, or made contact with, an electrically live wire which had broken and was low hanging. The train driver suffered serious injuries.

This accident occurred because one of the overhead wires had broken, was hanging down and was electrically live. Two previous trains had come into contact with this hanging wire and consequently tripped the power supply circuit breakers. Each time the circuit breakers had been reset by the Electrical Control Operators in accordance with procedures to make the overhead wires electrically live again.

However repeating the search (electric shock caused by defective OLE) with a start date of 1950 doesn't bring up any other reports, so I think we can conclude this is a rare occurrence. Railways Archive's accident report search is so much more useful than RAIB's!

 

[ChiefPlanner]

After the tripping out , it gets isolated and earthed and repaired.

 

[LAX54]

If the live OLE touches the ground, a train, or any earthed parts of the OLE it will shut down within a fraction of a second, at least on 25kV. The controllers will normally try to restore it after a few seconds in case it is a transient problem such as a vapourising pigeon, but if it cuts out immediately after 2 (?) attempts they will leave it isolated until they find out what the problem is.

It's possible, but unlikely, that the wires are left hanging close to the ground but haven't actually touched anything so they are still live.

Lower supply voltages have lower fault currents so it is possible the power might not shut down if there is not a low-resistance path to earth. This can result in fires.

In our case, and I assume it's national (?) if there is a 'tripping' ECRO will call the SSM at the PSB, advise there has been a tripping on section 123 or whatever, and ask if there are any trains in section, they will then attempt a reset, if it holds a;; well and good, but they will have 3 attempts, then leave it dead pending investigation, if it is 'bird' related, it normally resets on the first go.
If it does not, there are also other options to go though if there is a train in the section.

 

[Sean Emmett]

However repeating the search (electric shock caused by defective OLE) with a start date of 1950 doesn't bring up any other reports, so I think we can conclude this is a rare occurrence. Railways Archive's accident report search is so much more useful than RAIB's!

There was an incident at St Pancras Intl in 2009 when live 25kv ohle fell onto the platform.

 

[Nym]

I was taught. If the current trips then they immediately try to reinstate. If it trips again then they wait for a minute, then reinstate. If it trips again, its left alone and investigated further.

Not sure how accurate that is nowadays.

All well and good until you put a controller on a panel with auto-reclose and the wires get livened up again many more than twice...

 

[snowball]

This one may be of interest:

https://www.gov.uk/raib-reports/overhead-line-failure-at-st-pancras-international

 

[LAX54]

We had a trip this morning, Romford called to advise 342 tripped,(Col-Man: DM) enquired if anything in the section, which there was not, advised me attempting re-close, followed by 'all alive'
When we are about to have a problem you can hear down the phone, the alarms sounding when they try to liven up again,

 

[edwin_m]

There was an incident at St Pancras Intl in 2009 when live 25kv ohle fell onto the platform.

Report linked in #12. No injuries so not included in my search. There were several failings in procedure IIRC.