Electrification Isolations

[Aictos]

One for those who deal with the electrification side of engineering on UK railways but I've got a few questions I like to know the answer to:

1. On ex Midland region routes that are paired by use, can you for example turn off the power supply to one pair of lines between any two locations during a engineering blockade and still run electric services on the other pair of lines?

As a example, let's say the slow lines between Leagrave and Harpenden are closed to all services, could Thameslink still run a amended service over the fast lines between those two locations?

2. I've heard of isolating straps being used but not sure how, do they put up a pair at my each end of the isolation needed?

How does it work when lines are paired by direction eg the ECML?

Would appreciate answers to the questions.

 

[Dan17H]

One for those who deal with the electrification side of engineering on UK railways but I've got a few questions I like to know the answer to:

1. On ex Midland region routes that are paired by use, can you for example turn off the power supply to one pair of lines between any two locations during a engineering blockade and still run electric services on the other pair of lines?

As a example, let's say the slow lines between Leagrave and Harpenden are closed to all services, could Thameslink still run a amended service over the fast lines between those two locations?

2. I've heard of isolating straps being used but not sure how, do they put up a pair at my each end of the isolation needed?

How does it work when lines are paired by direction eg the ECML?

Would appreciate answers to the questions.

In answer to question 2, I assume your referring to DC areas.

No, generally they are placed at the end of the Worksite, not the isolation. As its the job of the Level A to provide the straps for protection and not the ECRO (he just switches it off) there could also be additional straps throughout a Worksite in places near to Substations or TP huts, or other places as decided by the Isolation Planner.

Earthing straps are being phased out in DC areas in place of NSCD (Negative Short Circuit Device). Thus removing the need for staff to access track to place the straps.

 

[The Planner]

One for those who deal with the electrification side of engineering on UK railways but I've got a few questions I like to know the answer to:

1. On ex Midland region routes that are paired by use, can you for example turn off the power supply to one pair of lines between any two locations during a engineering blockade and still run electric services on the other pair of lines?

As a example, let's say the slow lines between Leagrave and Harpenden are closed to all services, could Thameslink still run a amended service over the fast lines between those two locations?

2. I've heard of isolating straps being used but not sure how, do they put up a pair at my each end of the isolation needed?

How does it work when lines are paired by direction eg the ECML?

Would appreciate answers to the questions.

You would be surprised at how flexible switching can be (though not everywhere). It is done all the time on the WCML for example.

 

[Aictos]

I should have stated with question 2 I was referring to OHL but your answer has been unintentionally informative.

I remember a few years ago travelling to Stevenage on the first London bound FCC on a Sunday morning on a Class 317 and the driver losing power between St Neots and Sandy eventually having to coast into Sandy station. The reason was a overnight isolation still had a isolating strap in place that the engineers forgot to remove meaning we unexpectedly drove though a dead area of OHL

As to @The Planner is that only possible on lines that are U D U D and not U U D D?

 

[John Webb]

One for those who deal with the electrification side of engineering on UK railways but I've got a few questions I like to know the answer to:

1. On ex Midland region routes that are paired by use, can you for example turn off the power supply to one pair of lines between any two locations during a engineering blockade and still run electric services on the other pair of lines?

As a example, let's say the slow lines between Leagrave and Harpenden are closed to all services, could Thameslink still run a amended service over the fast lines between those two locations?

2. I've heard of isolating straps being used but not sure how, do they put up a pair at my each end of the isolation needed?

How does it work when lines are paired by direction eg the ECML?

Would appreciate answers to the questions.

Yes to Q1. Can't answer Q2.

 

[Highlandspring]

One for those who deal with the electrification side of engineering on UK railways but I've got a few questions I like to know the answer to:

1. On ex Midland region routes that are paired by use, can you for example turn off the power supply to one pair of lines between any two locations during a engineering blockade and still run electric services on the other pair of lines?

As a example, let's say the slow lines between Leagrave and Harpenden are closed to all services, could Thameslink still run a amended service over the fast lines between those two locations?

2. I've heard of isolating straps being used but not sure how, do they put up a pair at my each end of the isolation needed?

How does it work when lines are paired by direction eg the ECML?

Would appreciate answers to the questions.

1. They'll all be on separate electrical subsections so yes you can.

2. The simplified version of this is that for 25kV overhead electrification 'earths' are placed to protect the sections from inadvertent re-energisation (whether that's by the breakers closing or a pantograph bridging a section insulator) and also to prevent induced voltage from adjacent live equipment on other lines or high voltage transmission lines which cross the track. The earths are placed to connect the overhead line equipment to Designated Earthing Points (DEPs) in accordance with a plan worked out beforehand. It'll be more than just one at each end of the isolated section but it's really a 'how long is a piece of string' question.

A 'strap' is a third rail electrification term for an earth but I know almost nothing about third rail so can't tell you how they're used.

 

[Aictos]

Thanks all for the answers so far.

 

[Dan17H]

I should have stated with question 2 I was referring to OHL but your answer has been unintentionally informative.

I remember a few years ago travelling to Stevenage on the first London bound FCC on a Sunday morning on a Class 317 and the driver losing power between St Neots and Sandy eventually having to coast into Sandy station. The reason was a overnight isolation still had a isolating strap in place that the engineers forgot to remove meaning we unexpectedly drove though a dead area of OHL

As to @The Planner is that only possible on lines that are U D U D and not U U D D?

That's mental, I'm suprised it got that far, as soon as the ECO would have tried to reenergise the section the breakers should of tripped and he should of spotted that? I've seen first hand on DC sites what happens when a strap is accidentally left in place and they energise, you get a mighty bang and it blows a hole in the web of the running and 3rd rails.

 

[O L Leigh]

I think a more correct term would be temporary bond. They’re basically a length of blue cable with a clamp at each end which are applied as described above by @Highlandspring. Where lines blockages are also taken I have started seeing a blue flashing light in the 4 foot along with possession and worksite limit boards. I presume that this is in some way connected as either a reminder/proof of isolation.

You can see all these arrangements for yourselves currently at Brum New St while the platforms are resignalled.

 

[59CosG95]

I think a more correct term would be temporary bond. They’re basically a length of blue cable with a clamp at each end which are applied as described above by @Highlandspring. Where lines blockages are also taken I have started seeing a blue flashing light in the 4 foot along with possession and worksite limit boards. I presume that this is in some way connected as either a reminder/proof of isolation.

You can see all these arrangements for yourselves currently at Brum New St while the platforms are resignalled.

Common practice with the temp bonds is to use blue bonds for construction purposes, and orange ones for maintenance purposes (think long term vs short term). Blue flashing isolation markers can also be suspended from the OLE, depending on which product you use (these tend to be favoured where the OLE is isolated but the lines below are open for worksite plant/train movements).

 

[edwin_m]

One of the few good things about headspans is that the isolation options are very visible, by the insulators in the horizontal cable. I believe the MML ones have one insulator in the middle so a pair of tracks are isolated together, but someone with a view of this or a photo is welcome to correct me.

 

[Aictos]

That's mental, I'm suprised it got that far, as soon as the ECO would have tried to reenergise the section the breakers should of tripped and he should of spotted that? I've seen first hand on DC sites what happens when a strap is accidentally left in place and they energise, you get a mighty bang and it blows a hole in the web of the running and 3rd rails.

Well we limped into the platform at a very slow speed because we were coasting but we managed to make it with all 8 carriages fuly platformed.

Think the isolation was half way between St Neots and Sandy as we left St Neots with no issues at all.

As to isolating on OHL guys, if the track layout is U U D D can you isolate the fast lines in the middle while letting traffic pass on the slows or would it be a total isolation covering all 4 lines?

 

[59CosG95]

One of the few good things about headspans is that the isolation options are very visible, by the insulators in the horizontal cable. I believe the MML ones have one insulator in the middle so a pair of tracks are isolated together, but someone with a view of this or a photo is welcome to correct me.

Close but no cigar! The MML has an insulator between each track, true, but at the centre of each headspan, there were a pair of triple dish insulators (now replaced by polymeric ones) with a dropper wire from the middle cross span wire to the lower cross span wire. Why the arrangement was exclusive to the MML I don't quite know; it certainly didn't make it to the ECML north of Hitchin.

 

[edwin_m]

Close but no cigar! The MML has an insulator between each track, true, but at the centre of each headspan, there were a pair of triple dish insulators (now replaced by polymeric ones) with a dropper wire from the middle cross span wire to the lower cross span wire. Why the arrangement was exclusive to the MML I don't quite know; it certainly didn't make it to the ECML north of Hitchin.

Thanks for clarifying. I remember the prominent central ones, which probably made me forget that there were others off to the sides.

 

[Nicholas Lewis]

That's mental, I'm suprised it got that far, as soon as the ECO would have tried to reenergise the section the breakers should of tripped and he should of spotted that? I've seen first hand on DC sites what happens when a strap is accidentally left in place and they energise, you get a mighty bang and it blows a hole in the web of the running and 3rd rails.

More likely an overhead line switch left open (Hookswitch in Southern DC areas).

You only get serious damage to rails from straps not properly secured. When we did isolation checks if strap could be kicked off with your boot it hadn't been put on properly. This results in poor contact being made which would lead to arcing and damage but more importantly it may fail to trip the circuit breaker.

 

[Highlandspring]

As to isolating on OHL guys, if the track layout is U U D D can you isolate the fast lines in the middle while letting traffic pass on the slows or would it be a total isolation covering all 4 lines?

I can't tell you the precise situation on the Midland Main Line without looking at the isolation diagrams, but typically each individual running line on a multi-track railway is a seperate electrical section so each line (or combination of lines) can be isolated if required. It does depend on the feeding arrangements though.

 

[Aictos]

I can't tell you the precise situation on the Midland Main Line without looking at the isolation diagrams, but typically each individual running line on a multi-track railway is a seperate electrical section so each line (or combination of lines) can be isolated if required. It does depend on the feeding arrangements though.

Oh didn't know that, I thought it was more the case of either done by pairs or groups eg pair of two tracks or group of 4 tracks.

 

[Dan17H]

More likely an overhead line switch left open (Hookswitch in Southern DC areas).

You only get serious damage to rails from straps not properly secured. When we did isolation checks if strap could be kicked off with your boot it hadn't been put on properly. This results in poor contact being made which would lead to arcing and damage but more importantly it may fail to trip the circuit breaker.

I've seen a train bridge a gap before and blow holes in both rails, years ago in Hoo Jnc.

 

[Nicholas Lewis]

I've seen a train bridge a gap before and blow holes in both rails, years ago in Hoo Jnc.

Incorrectly fitted straps.

Your supposed to wire brush the webs of the rails before applying the straps only ever done on the training section in the yard in most cases.

 

[Falcon1200]

I can't tell you the precise situation on the Midland Main Line without looking at the isolation diagrams, but typically each individual running line on a multi-track railway is a seperate electrical section so each line (or combination of lines) can be isolated if required. It does depend on the feeding arrangements though.

Indeed, although nowadays the OLE often requires to be isolated on any adjacent lines to that being worked on, for staff safety.

It might be worth mentioning that the isolations discussed here have been planned work; The situation when the power is switched off in an emergency, for example if a member of public decides to climb up a mast, is very different; The power will be off between the nearest neutral sections, meaning that a large area is affected, causing huge disruption. If such an incident occurred at say Neilston, the power would be off right to Glasgow Central, and on the WCML towards Newton (therefore affecting not just services at Central itself but the Argyle Line too).

 

[edwin_m]

Indeed, although nowadays the OLE often requires to be isolated on any adjacent lines to that being worked on, for staff safety.

It might be worth mentioning that the isolations discussed here have been planned work; The situation when the power is switched off in an emergency, for example if a member of public decides to climb up a mast, is very different; The power will be off between the nearest neutral sections, meaning that a large area is affected, causing huge disruption. If such an incident occurred at say Neilston, the power would be off right to Glasgow Central, and on the WCML towards Newton (therefore affecting not just services at Central itself but the Argyle Line too).

However it's possible to shorten the isolation once the location of the emergency is clear and there are people available to do the work, effectively converting it into the sort of isolation that is used for engineering work. The latest electrification schemes have isolation and earthing switches that can be worked remotely - this helps with staff safety but perhaps also allows an isolation to be shortened more quickly.

 

[Falcon1200]

Indeed, and where isolation and earthing switches are provided they are a great benefit, but otherwise.... Getting staff to site and erecting earths and carrying out manual switching can take a while, during which time every electric train, and most if not all other trains in the area too, are at a stand !

 

[Dan17H]

Incorrectly fitted straps.

Your supposed to wire brush the webs of the rails before applying the straps only ever done on the training section in the yard in most cases.

I've been Level A/B for years and correctly fitted straps can cause damage to the rails, as I've seen first hand. Some don't wire brush the webs, but most do.