Thames Valley infrastructure problems causing disruption elsewhere - 2023

[whole diary]

[Electric train]

And, since it seems to be at the foot of the masts that carry traction power connections from the east side of the section break to the Maidenhead MPATS^▸ (Mid Point Auto Transformer Site - electrification), presumably the traction power cables were the source of the fire.

Yes it looks as if that had previously been something larger because of the gap in the troughing. Also I can't help wondering if that is a cable hanging down from the extension on that very blackened middle support and perhaps that made contact with something. Saying that the cable, if that is what it is, in question could be hanging down from there as part of the correct workings of OLE^▸ (Overhead Line Equipment, more often "OHLE"): I don't know.

Dave

The suspected cause is known within NR^» (Network Rail - home page), I'm not at liberty to say what the suspected cause is, it is still subject of a live investigation.

Oooooh how intriguing? Sabotage?

No

Might have contractual implications though

The cables were not the cause of the fire but a victim.

[stuving]

Might have contractual implications though

It'll be embarrassing for someone, too.

[GBM]

The suspected cause is known within NR^» (Network Rail - home page), I'm not at liberty to say what the suspected cause is, it is still subject of a live investigation.

Hopefully earthed 

[1st fan]

And, since it seems to be at the foot of the masts that carry traction power connections from the east side of the section break to the Maidenhead MPATS^▸ (Mid Point Auto Transformer Site - electrification), presumably the traction power cables were the source of the fire.

Yes it looks as if that had previously been something larger because of the gap in the troughing. Also I can't help wondering if that is a cable hanging down from the extension on that very blackened middle support and perhaps that made contact with something. Saying that the cable, if that is what it is, in question could be hanging down from there as part of the correct workings of OLE^▸ (Overhead Line Equipment, more often "OHLE"): I don't know.

Dave

The suspected cause is known within NR^» (Network Rail - home page), I'm not at liberty to say what the suspected cause is, it is still subject of a live investigation.

Oooooh how intriguing? Sabotage?

No

Might have contractual implications though

The cables were not the cause of the fire but a victim.

Nice reply from Network Rail to someone who said fixing the damage had taken too long.

https://twitter.com/David__Brunt/status/1641007491470315520

Network Rail Western
@networkrailwest

29 Mar
⚠️We're sorry for any disruption to your journey this morning as a result of a lineside fire in Maidenhead.

David Brunt
@David__Brunt
Replying to
@networkrailwest
It really took two hours to put out that small fire?
9:20 am · 29 Mar 2023


Network Rail Western
@networkrailwest

16h
Replying to
@David__Brunt
Hi David, at its peak the fire hit 600C. After the fire service put out the flames, the temperature started rising again. Only by 9pm last night had it reduced to a temp that our teams could assess the damage and start repairing/replacing cabling. I hope this helps explain.

[TaplowGreen]

And, since it seems to be at the foot of the masts that carry traction power connections from the east side of the section break to the Maidenhead MPATS^▸ (Mid Point Auto Transformer Site - electrification), presumably the traction power cables were the source of the fire.

Yes it looks as if that had previously been something larger because of the gap in the troughing. Also I can't help wondering if that is a cable hanging down from the extension on that very blackened middle support and perhaps that made contact with something. Saying that the cable, if that is what it is, in question could be hanging down from there as part of the correct workings of OLE^▸ (Overhead Line Equipment, more often "OHLE"): I don't know.

Dave

The suspected cause is known within NR^» (Network Rail - home page), I'm not at liberty to say what the suspected cause is, it is still subject of a live investigation.

Oooooh how intriguing? Sabotage?

No

Might have contractual implications though

The cables were not the cause of the fire but a victim.

Nice reply from Network Rail to someone who said fixing the damage had taken too long.

https://twitter.com/David__Brunt/status/1641007491470315520

Network Rail Western
@networkrailwest

29 Mar
⚠️We're sorry for any disruption to your journey this morning as a result of a lineside fire in Maidenhead.

David Brunt
@David__Brunt
Replying to
@networkrailwest
It really took two hours to put out that small fire?
9:20 am · 29 Mar 2023


Network Rail Western
@networkrailwest

16h
Replying to
@David__Brunt
Hi David, at its peak the fire hit 600C. After the fire service put out the flames, the temperature started rising again. Only by 9pm last night had it reduced to a temp that our teams could assess the damage and start repairing/replacing cabling. I hope this helps explain.

Would have been great if Network Rail/GWR^▸ (Great Western Railway) had put that message (or similar) out proactively.

[Electric train]

Wednesday incident at Maidenhead

The info I have had from a number of sources point to the suspected cause of the fire to have been a fault with the OLE^▸ (Overhead Line Equipment, more often "OHLE") switch or a component / connection associated with the switch arcing.  Molten metal dropping onto the GRP cable trough below casing ignition of the cable sheath.

[stuving]

That is a surprising mechanism, though it can't be the whole story. Surely the protection should have stopped it happening?

I don't have any first-hand experience of arcing at that power level (fortunately), and I wondered why I couldn't find much on the subject. I guess that's because it's just called a fault. But once an arc is established, the voltage across it is very low - under a kV - so the current drawn should trip something, even at the far end of the section. Unless there was something very peculiar about this arc ... or some current-limiting impedance in the circuit ... which has to be reactive or it will dissipate more power than the arc. So as usual, more questions are raised to start with and more investigating is needed.

[Electric train]

That is a surprising mechanism, though it can't be the whole story. Surely the protection should have stopped it happening?

I don't have any first-hand experience of arcing at that power level (fortunately), and I wondered why I couldn't find much on the subject. I guess that's because it's just called a fault. But once an arc is established, the voltage across it is very low - under a kV - so the current drawn should trip something, even at the far end of the section. Unless there was something very peculiar about this arc ... or some current-limiting impedance in the circuit ... which has to be reactive or it will dissipate more power than the arc. So as usual, more questions are raised to start with and more investigating is needed.

Looking at the photos the OLE^▸ (Overhead Line Equipment, more often "OHLE") switch in the area of the fire is purely manual operation, no spring assistance.  Although they are called switches technically they are Isolators (open / close operation only off load) (switches can be operated to  make / break load current)

Arcing is not Voltage dependant, load current and a relatively high impendence will cause arcing due to the Potential Difference between the 2 contacts.  The burning will cause carbonisation which increases the impedance.  It can get to the point where the air becomes Ionized which increases the arcing. 

Temperatures sufficient to melt copper are easily reached in the matter of milliseconds.

The load current on the switch would not be limited to the line it is connected to, Maidenhead being a Mid Point, in the case of this switch the remote end to the feed in from Kensal Green, there is an Intermediate Point at Slough, the circuit breakers and busbar in the Maidenhead Mid Point balance the load across all 4 lines.  At that time of the day there is I suspect a high traction load, 8 and 12 car class 387, 5, 9 and 10 car class 800 and class 345 all starting from stations, checked at signals.

[stuving]

Looking at the photos the OLE^▸ (Overhead Line Equipment, more often "OHLE") switch in the area of the fire is purely manual operation, no spring assistance.  Although they are called switches technically they are Isolators (open / close operation only off load) (switches can be operated to  make / break load current)

Arcing is not Voltage dependant, load current and a relatively high impendence will cause arcing due to the Potential Difference between the 2 contacts.  The burning will cause carbonisation which increases the impedance.  It can get to the point where the air becomes Ionized which increases the arcing. 

Temperatures sufficient to melt copper are easily reached in the matter of milliseconds.

The load current on the switch would not be limited to the line it is connected to, Maidenhead being a Mid Point, in the case of this switch the remote end to the feed in from Kensal Green, there is an Intermediate Point at Slough, the circuit breakers and busbar in the Maidenhead Mid Point balance the load across all 4 lines.  At that time of the day there is I suspect a high traction load, 8 and 12 car class 387, 5, 9 and 10 car class 800 and class 345 all starting from stations, checked at signals.

Thanks for that explanation. I guess it's obvious it would be a series arc, though I understood the really destructive ones develop into a parallel arc. But the question of protection is still there; after all AFDDs are now recommended in domestic installations (18th edition of Wiring Regulations). There are quite a lot of those isolators (opened only for maintenance or during failures) along the section to worry about.

I can see that full protection would be difficult, given that some pantograph arcing is inevitable, and with a choice of parallel paths. You don't want to disconnect a whole section just for occasional pantograph arcing, so something clever would be needed. But I'd guess that clever detection is in place, if only for condition monitoring. Disconnection (of what? where?) might not be feasible in the available time before major damage happens. As usual, it's a compromise.

No doubt someone will be looking at alternatives to GRP conduit covers ...

[Electric train]

Looking at the photos the OLE^▸ (Overhead Line Equipment, more often "OHLE") switch in the area of the fire is purely manual operation, no spring assistance.  Although they are called switches technically they are Isolators (open / close operation only off load) (switches can be operated to  make / break load current)

Arcing is not Voltage dependant, load current and a relatively high impendence will cause arcing due to the Potential Difference between the 2 contacts.  The burning will cause carbonisation which increases the impedance.  It can get to the point where the air becomes Ionized which increases the arcing. 

Temperatures sufficient to melt copper are easily reached in the matter of milliseconds.

The load current on the switch would not be limited to the line it is connected to, Maidenhead being a Mid Point, in the case of this switch the remote end to the feed in from Kensal Green, there is an Intermediate Point at Slough, the circuit breakers and busbar in the Maidenhead Mid Point balance the load across all 4 lines.  At that time of the day there is I suspect a high traction load, 8 and 12 car class 387, 5, 9 and 10 car class 800 and class 345 all starting from stations, checked at signals.

Thanks for that explanation. I guess it's obvious it would be a series arc, though I understood the really destructive ones develop into a parallel arc. But the question of protection is still there; after all AFDDs are now recommended in domestic installations (18th edition of Wiring Regulations). There are quite a lot of those isolators (opened only for maintenance or during failures) along the section to worry about.

I can see that full protection would be difficult, given that some pantograph arcing is inevitable, and with a choice of parallel paths. You don't want to disconnect a whole section just for occasional pantograph arcing, so something clever would be needed. But I'd guess that clever detection is in place, if only for condition monitoring. Disconnection (of what? where?) might not be feasible in the available time before major damage happens. As usual, it's a compromise.

No doubt someone will be looking at alternatives to GRP conduit covers ...

AFDD's are being looked at, the problem is the railways operate a sliding contact current collection system which has many interruptions, building a profile for an arc fault device is challenging. 

The type of protection used on 25kV is Distance Protection, the link has a lot fo tech stuff and sums  ( https://pacbasics.org/fundamentals-of-distance-protection/#:~:text=Zones%20of%20distance%20protection,-Distance%20protection%20uses&text=The%20zone%20and%20time%20grading,respect%20to%20the%20protected%20line. )
Distance Protection is fast form of protection, it can react rapidly to low impedance faults, contact system conductors to traction return and Earth

NR^» (Network Rail - home page) third rail DC^▸ (Direct Current) uses Impedance Protection which is a fast form of protection, this can react rapidly to low impedance faults contact system conductors to traction return, but not so good for Earth faults as these are high impedance, deliberately by design the third rail Neg traction return is not directly bonded to Earth to limit stray DC currents in the Earth.

Both the Distance and Impedance protection systems are not designed for the relatively rare serial arc as found in a burning connection or switch, thermal imaging is used for this periodically however this does need to be done while trains are running, heat is only generated with load current.

I expect the position of GRP trough routes and cables under OLE switches will be reviewed Nationally

[TaplowGreen]

Delays to services between London Paddington and Slough

Due to engineering works not being finished on time between London Paddington and Slough some lines are blocked.

Train services running to and from these stations will be delayed by up to 60 minutes. Disruption is expected until 10:00 02/04.

[Mark A]

A hat tip to the Coffeeshop's map at top left, though it sadly too often looks as though it's been attacked by a three year old with a red crayon and anger issues, it's brilliant at providing an 'At a glance' answer to the question "What parts of the rail network are horked today?"

Also, the 'Via Salisbury' option for Bath and Bristol (and, this weekend, South Wales)... a pity, this weekend, as well as no through services for the past 15 months and no action on the many poor connections at Salisbury, the woes on the GWML^▸ (Great Western Main Line) have conincided with engineering works closing Andover to Salisbury, and today, Bracknell to Reading, and, just in case anyone was thinking of taking the long way round that somehow was a valid through fares routing until a few years ago, Southampton to Salisbury too.

Engineering works aside, I'm wondering if public awareness of travel via Salisbury is receding somewhat.

Mark

[TaplowGreen]

Cancellations to services between Reading and Newbury

Due to a fault with the signalling system between Reading and Newbury fewer trains are able to run.

Train services running to and from these stations may be cancelled or delayed.

Disruption is expected until the end of the day.

[grahame]

The failure of the bridge between Didcot and Oxford was initially posted here on this long thread (as it's an infrastructure issue) - however  it's become clear it merits ite own thread so posts on that bridge, please, to http://www.passenger.chat/27351 - Black Bridge, Nuneham: southern abutment failure

Please continue to post here (as, STOP PRESS, I see Taplow Green has done) with other infrastructure issues

[TaplowGreen]

Cancellations to services between London Paddington and Slough

Due to a points failure between London Paddington and Slough some lines are blocked.

Train services running to and from these stations may be cancelled, delayed or revised. Disruption is expected until 20:45 10/04.