What is the purpose of neutral sections? I understand that they are gaps in the power supply, but why do we need them. Also do diesel trains have to power down to enter them?
-
Our booking engine at tickets.railforums.co.uk (powered by TrainSplit) helps support the running of the forum with every ticket purchase! Find out more and ask any questions/give us feedback in this thread!
Neutral Sections
- Thread starter Huntergreed
- Start date
- Status
Sponsor Post - registered members do not see these adverts; click here to register, or click here to log in
R
RailUK Forums
AlterEgo
Veteran Member
It's so if there's maintenance needed, or a fault, it affected only one short section of line.
Diesel trains don't need to power down of course because they aren't drawing power from the overhead line.
Diesel trains don't need to power down of course because they aren't drawing power from the overhead line.
Let's think about this one for a bit. If there were no neutral sections effectively you would have one, unbroken circuit between (for example) London and Glasgow. This would mean that:
- A train pulling the wire down in Preston would mean trains couldn't run in Wolverhampton
- They would have to shut the entire WCML down to do work anywhere on the line
- There would be a direct connection between power platnts in Scotland and those in southern England - so any phase difference would cause massive problems.
Since diesel trains don't interact with the OHLE in any way, there is no need for them to power down.
That's not quite it.
The railway takes power from the 3 phase national grid but uses single phase power. If it took all it's power from the same phase pair it would put a massive imbalance on the national grid, factory motors would run backwards and the railway would be fined by NG.
so instead we alternate phases - at the first feeder station we take a feed from red-blue, at the next one blue-yellow, and so on. However if these phase pairs are electrically connected things go bang. So midway between the feeder stations you insert insulation into the OLE. That's a neutral section.
The train isn't allowed to draw power through the neutral section since it would pull an arc across the insulation and connect the phase pairs up. So the train switches off before it hits the neutral and then back on again afterwards.
Sent from my HTC One_M8 using Tapatalk
The railway takes power from the 3 phase national grid but uses single phase power. If it took all it's power from the same phase pair it would put a massive imbalance on the national grid, factory motors would run backwards and the railway would be fined by NG.
so instead we alternate phases - at the first feeder station we take a feed from red-blue, at the next one blue-yellow, and so on. However if these phase pairs are electrically connected things go bang. So midway between the feeder stations you insert insulation into the OLE. That's a neutral section.
The train isn't allowed to draw power through the neutral section since it would pull an arc across the insulation and connect the phase pairs up. So the train switches off before it hits the neutral and then back on again afterwards.
Sent from my HTC One_M8 using Tapatalk
In addition to the above, the neutral section is actually grounded, so there are two sets of isolation, one from section a to the grounded neutral section and one from the grounded section to section b. That means that if the on-board auto-isolation (ABB) fails to operate, although the pantograph will draw an arc as it loses power from the first section, the design of the isolator in the OLE reduces tracking (conductive deposits creating a conductive path across the isolation) and and if they do form a complete path, it is only to the grounded neutral section. If it bridged across to the next powered section, it could cause an irregular voltage which might damage trains, insulators or even the feeder points.
An additional benefit of the neutral sections is that lightning discharges to the conductor wire will as a last line of protection, be drawn to ground by the neutral section, thereby limiting any effects to the section that received it.
An additional benefit of the neutral sections is that lightning discharges to the conductor wire will as a last line of protection, be drawn to ground by the neutral section, thereby limiting any effects to the section that received it.
Railsigns
Established Member
- Joined
- 15 Feb 2010
- Messages
- 2,503
Overlaps are provided in the OLE catenary for sectioning purposes.
Neutral sections are there specifically to separate different electrical supplies.
Philip Phlopp
Established Member
- Joined
- 31 May 2015
- Messages
- 3,004
Air Blast Breaker - they drifted towards being called Airblast Breakers (ABs) when ABB (the company) came on the scene.
Neutral sections segregate different power supplies - ie from the different feeder stations that connect to the grid. To enable cross feeding, there is a neutral section roughly half way between each feeder station, and another at the feeder station itself.
Section insulators (SIs) segregate different sections within the same power supply. Typically each track on a route has a section, and they can vary in length. As an example, there are two sections from Kentish Town to City Thameslink, one for each track. There are about another dozen sections fed from the same power supply. Each section has a circuit breaker that will trip (independent of any others) if it detects a problem. So if, for example, there is a problem on the northbound line at St Pancras, the southbound line stays live, as do all lines north of Kentish Town.
Overlaps are simply where each run of OLE meets the next run. On plain line, an OLE length is typically 1km long. This is simply down to physics, ie the weight of the wire and keeping it at the correct tension. There are usually be several lengths of OLE per section.
There can be variations on the above, particularly in complex junction areas.
Section insulators (SIs) segregate different sections within the same power supply. Typically each track on a route has a section, and they can vary in length. As an example, there are two sections from Kentish Town to City Thameslink, one for each track. There are about another dozen sections fed from the same power supply. Each section has a circuit breaker that will trip (independent of any others) if it detects a problem. So if, for example, there is a problem on the northbound line at St Pancras, the southbound line stays live, as do all lines north of Kentish Town.
Overlaps are simply where each run of OLE meets the next run. On plain line, an OLE length is typically 1km long. This is simply down to physics, ie the weight of the wire and keeping it at the correct tension. There are usually be several lengths of OLE per section.
There can be variations on the above, particularly in complex junction areas.
Yes my mistake. I presume that they are still use air blast to suppress arcs rather than a vacuum which seems a bit cumbersome.
Elecman
Established Member
I thought they were all vcbs now?
Learning a lot from the posts on this thread, I didn't know much about OHLE. I was wondering though what the procedure was for powering down for neutral sections?
Do all drivers know exactly where every one is or is there an incab warning of the approaching section? And do different types of traction/train do it automatically or is it totally down to driver input?
Do all drivers know exactly where every one is or is there an incab warning of the approaching section? And do different types of traction/train do it automatically or is it totally down to driver input?
Last edited:
No, in the UK we use permanent magnets mounted on sleeper ends on approach to the neutral section... These trigger an Automatic Power Control (APC) relay on the train bogie which trips the train circuit breaker. Another magnet trips it back in after the neutral section.
Overseas they put more faith in their drivers and rely on them to switch of power based on a sign.
Sent from my HTC One_M8 using Tapatalk
Though, even over here, the location of neutral sections is part of route knowledge. This is so that drivers know to either stop short or coast past to avoid getting stranded.
Elecman
Established Member
Drivers were supposed to run down the tap changer before they hit the APC magnets though
Townsend Hook
Member
There's never any harm in reducing drivers' workloads, the less they need to concentrate on the less likely is they will make a mistake.
Had a look at the SA and count six between Gretna Junction and Glasgow. I thought there would be more.
Thanks for that. Bit short on ohle down here.
I know there is one just south of Carlisle, it delays the acceleration of the units! When can you reapply power? Once the whole train has cleared it or just part of the train?
SpacePhoenix
Established Member
- Joined
- 18 Mar 2014
- Messages
- 5,492
It'll be once the last pantograph of the train has passed through the netrual section.
What's the equivalent (if there is such an equivalent) of a neutral section for 3rd rail - a meter gap in the 3rd rail on all lines?
I understand there is one near Carstairs Junction too
--- old post above --- --- new post below ---
And to add too this for the OP, you'll hear these breakers in various stock. On the 350's there is a very pronounced *thunk* and the air conditioning drops out (the train at this point is running entirely on battery power, so some high voltage draw kit is dropped)
It's a little less pronounced on a Pendolino but can still be heard from what I remember
On another query, I believe all neutral sections are signed on the gantry posts too
--- old post above --- --- new post below ---
And to add too this for the OP, you'll hear these breakers in various stock. On the 350's there is a very pronounced *thunk* and the air conditioning drops out (the train at this point is running entirely on battery power, so some high voltage draw kit is dropped)
It's a little less pronounced on a Pendolino but can still be heard from what I remember
On another query, I believe all neutral sections are signed on the gantry posts too
I had a look at the SA for the southern WCML once and they were about every 13 miles if I remember correctly.
They're often close to major junctions so that one arm of a junction can be isolated leaving the other one live.
Last edited:
Philip Phlopp
Established Member
- Joined
- 31 May 2015
- Messages
- 3,004
You don't need a neutral section on DC - as it's not alternating current, there's nothing to go out of phase.
PermitToTravel
Established Member
The Underground still have gaps in the conductor rail so that sections can be independently isolated. The mainline presumably has these too
DarloRich
Veteran Member
why would a diesel train need to power down for a neutral section of OHLE?
driver9000
Established Member
- Joined
- 13 Jan 2008
- Messages
- 4,244
Harker, Ecclefechan, Murphat, Elvanfoot, Strawfrank (Carstairs South) and Carstairs East.
--- old post above --- --- new post below ---
You can take power once the VCB has closed but on the units I work there is a 20 second delay while the computers check everything is OK before giving traction back to the Driver. The neutral section at Upperby you mention is a pain as well as the two at Carstairs.
--- old post above --- --- new post below ---
VCB on 350s.
--- old post above --- --- new post below ---
Black background sign marks the approach of an OHNS and a white background sign marks the site.
Townsend Hook
Member
Yes, plenty of them.
Yes they do. Isolated sections can be further shortened by the use of local rail-borne switches known as "hook switches".
And non-isolated sections can be shorted by pretty much anything metallic!
- Status