What is Neutral Section, please?

[SwiftsOnSea]

May I ask, what is Neutral section?

What is the purpose of it?

Is it dangerous?
Is it dangerous to pass through at 100mph?

Is it possible not having it without issues?

 

[swt_passenger]

It isn’t dangerous. They can be passed at whatever the line speed is. They isolate adjacent electrical sections from each other that are fed from different mains phases, so they cannot be avoided.

(In simple terms the railway takes a 3 phase supply from the grid, but any section of overhead only uses one phase. To balance the load successive sections have to use a different phase.)

 

[DarloRich]

May I ask, what is Neutral section?

What is the purpose of it?

Is it dangerous?
Is it dangerous to pass through at 100mph?

Is it possible not having it without issues?

It isn't an issue or danger of any kind. Don't worry about it. Someone more technical can explain the purpose in much greater detail than I can.

 

[pdeaves]

swt_passenger has the gist of it right, though I will add that there is always something on which the pantograph acts. Modern neutral sections are (effectively) a shortish bit of wire not connected to a power supply. It can be quite complex working through a mass of wires above the railway to determine which bit connects where!
A list of neutral sections is available here: http://www.railwaycodes.org.uk/electrification/neutral.shtm

 

[edwin_m]

SwiftsOnSea, welcome to the forum! To add to what people have said above...

There is a small risk of a train with only one pantograph being stranded if it stops with it in a neutral section. However the neutral sections should be positioned where the trains pass by at a reasonable speed except in emergency (so not close to stations or signals), and a train can roll quite a long way without power.

There is also the possibility of damage if the train is drawing power as it passes into the neutral section. But drivers know where they are and there are signs to remind them, and there is also a system to shut off and restore power automatically as the train passes.

 

[GRALISTAIR]

SwiftsOnSea, welcome to the forum! .

+1 LIKEWISE - welcome

 

[Elecman]

It isn’t dangerous. They can be passed at whatever the line speed is. They isolate adjacent electrical sections from each other that are fed from different mains phases, so they cannot be avoided.

(In simple terms the railway takes a 3 phase supply from the grid, but any section of overhead only uses one phase. To balance the load successive sections have to use a different phase.)

Not quite the ra8lway takes 2 phases of the National Grid supply and it is then transformed to 25 KV. Adjacent feeder stations are on different arrangements of which 2 phases are used so 1 station is say L1 and L2 , the next one may be L2 and L3 and the one after woukd be L1 and L3 to try and balance the loading across the Grid system as a whole

 

[swt_passenger]

Not quite the ra8lway takes 2 phases of the National Grid supply and it is then transformed to 25 KV. Adjacent feeder stations are on different arrangements of which 2 phases are used so 1 station is say L1 and L2 , the next one may be L2 and L3 and the one after woukd be L1 and L3 to try and balance the loading across the Grid system as a whole

That’s why I wrote ‘In simple terms’ in my reply. There’s a risk of over complicating a reply, especially if someone has no prior knowledge of power distribution terminology...

 

[Esker-pades]

The purpose is to split up long railway lines into manageable chunks. That way there isn't too great a power draw on one particular bit of the national grid. It also means that an incident in, for example, Carlisle, doesn't mean the WCML has to close at Lichfield, only the electrical bits around Carlisle are affected.

 

[Bald Rick]

The purpose is to split up long railway lines into manageable chunks. That way there isn't too great a power draw on one particular bit of the national grid. It also means that an incident in, for example, Carlisle, doesn't mean the WCML has to close at Lichfield, only the electrical bits around Carlisle are affected.

It’s not this.

If Lichfield was fed from Carlisle, there would be rather less than 25kV available. It’s about power phases as describe above. There are section insulators much more frequently than neutral sections to deal with incidents.

 

[Esker-pades]

It’s not this.

If Lichfield was fed from Carlisle, there would be rather less than 25kV available. It’s about power phases as describe above. There are section insulators much more frequently than neutral sections to deal with incidents.

I apologise for my misinformation. Thanks for clearing it up.

 

[Bookd]

I seem to think that the same issue applied to trams an trolleybuses; if obliged by traffic to stop in a neutral section the vehicle would be stranded there.

 

[WatcherZero]

Think of its like removing a domino from the line so that when a one or more fall the entire line doesn't fall down.

 

[edwin_m]

I seem to think that the same issue applied to trams an trolleybuses; if obliged by traffic to stop in a neutral section the vehicle would be stranded there.

Trams and trolleybuses use low voltage DC, where generally all the substations feed in parallel and there is no need for neutral sections. I guess trolleybuses would have to have very short neutral sections at junctions to prevent the positive and negative wires shorting together.

 

[pdeaves]

Trams and trolleybuses use low voltage DC, where generally all the substations feed in parallel and there is no need for neutral sections. I guess trolleybuses would have to have very short neutral sections at junctions to prevent the positive and negative wires shorting together.

Or maybe so one section can be switched off for maintenance? You don't want people working on one bit and a passing pantograph touches, even momentarily, live and 'dead' sections at the same time (thus making both bits live briefly).

 

[LAX54]

Or maybe so one section can be switched off for maintenance? You don't want people working on one bit and a passing pantograph touches, even momentarily, live and 'dead' sections at the same time (thus making both bits live briefly).

The dead section will be earthed, so if it did happen (not unknown) yes it would liven up momentarily, and someone would or could get hurt, but would also earth / short out straight away, with an almighty flash and a bang! but would also need more than one pan raised. But of course this should never happen, and is more lilkely with part sections, and not neutrals.

 

[Joseph_Locke]

The other item in the OP's list was

Is it dangerous to pass through at 100mph?

No. SNCF's TGV, the Japanese Shinkansen (and the proposed UK HS2) will all do it regularly at 200mph and over (357.16 mph is the TGV record)

 

[edwin_m]

Or maybe so one section can be switched off for maintenance? You don't want people working on one bit and a passing pantograph touches, even momentarily, live and 'dead' sections at the same time (thus making both bits live briefly).

The dead section will be earthed, so if it did happen (not unknown) yes it would liven up momentarily, and someone would or could get hurt, but would also earth / short out straight away, with an almighty flash and a bang! but would also need more than one pan raised. But of course this should never happen, and is more lilkely with part sections, and not neutrals.

The DC system will be broken up into electrical sections, which can indeed be isolated and earthed for maintenance but in normal operation they are all connected together. Tram OLE is arranged so that when passing from one of these sections to the next the tram does not lose power - for a short period the pantograph is making contact with both sections which would indeed cause a short circuit if the section being driven into is earthed. This also means there is normally no actual "neutral section" where the tram is completely without power. Special arrangements may apply, for example, close to facilities that are particularly prone to electromagnetic interference.

When travelling on a 25kV electric train with a device plugged into the power socket you will often notice the power going off for a few second every few minutes, or you may hear the air conditioning shut down and re-start. This is the neutral sections.

 

[Strat-tastic]

How long are neutral sections?

 

[AM9]

There are at least three types of neutral section.
The first and most common type is usually on low/medium speed lines where it's comp[act design makes siting easier. Pages 20 and 21 of the class 323 driver's manual show both the construction and operation of this type:
http://www.ttweb.co.uk/tra/323tm.pdf
The next type is the predecessor of that type where isolation was provided with vee-shaped bars on either side of the conductor centreline that carried the pantograph over a gap. these were placed in group of four that provided for a a short length of conductor to be grounded. The whole assembly was quite heavy and sensitive to physical instability if traversed at more than quite low speeds. I haven't seen any on running lines for some time but some remain on crossovers where speeds are low for track geometry reasons where they can be accommodated in the restricted length. I can't find any pictures of a complete installation but here is a drawing on a typical vee-shaped insulator:
http://www.indianrailways.gov.in/ra...ACTraction-II-P-I/imagesCh_3/Page_66_fig1.jpg
The third type is usually found on high speed lines. It is a derivative of the termination method of lengths of catenary/conductor wire where a terminating length is run in parallel with the next starting one. In this case there is a short section of OLE so there are two overlaps a few tens of metres apart. The short section can then be grounded when required. Their total length can be from less than 100m to over 400m.

 

[47271]

https://www.railforums.co.uk/threads/caledonian-sleeper-discussion.118802/page-84
Neutral sections can cause problems sometimes, the sleeper ended up stranded near Penrith for a couple of hours just under two years ago.

 

[Supercoss]

The actual ‘dead’ section is only about 15cm long
APC magnets fittedt to sleeper ends prior to and after OHNS turn off trains traction power when APC receiver on train wheelset passes should driver forget to shut off power
( seen here indicated by white diamond)


Aboveexample on Thameslink route at Sandridge,St Albans.

 

[Whistler40145]

I have heard of trains becoming stranded in Neutral Sections, especially EMUs where one pantograph is in the dead section and the others in the live section, usually resulting in another unit being required to rescue the dead unit

 

[mcmad]

There are at least three types of neutral section.
The first and most common type is usually on low/medium speed lines where it's comp[act design makes siting easier. Pages 20 and 21 of the class 323 driver's manual show both the construction and operation of this type:
http://www.ttweb.co.uk/tra/323tm.pdf
The next type is the predecessor of that type where isolation was provided with vee-shaped bars on either side of the conductor centreline that carried the pantograph over a gap. these were placed in group of four that provided for a a short length of conductor to be grounded. The whole assembly was quite heavy and sensitive to physical instability if traversed at more than quite low speeds. I haven't seen any on running lines for some time but some remain on crossovers where speeds are low for track geometry reasons where they can be accommodated in the restricted length. I can't find any pictures of a complete installation but here is a drawing on a typical vee-shaped insulator:
http://www.indianrailways.gov.in/ra...ACTraction-II-P-I/imagesCh_3/Page_66_fig1.jpg
The third type is usually found on high speed lines. It is a derivative of the termination method of lengths of catenary/conductor wire where a terminating length is run in parallel with the next starting one. In this case there is a short section of OLE so there are two overlaps a few tens of metres apart. The short section can then be grounded when required. Their total length can be from less than 100m to over 400m.

There is at least one of the slow speed Vee type installed coming out of the new platform 5/6 at Edinburgh Waverley. It might be seen in the Waverley thread https://www.railforums.co.uk/threads/edinburgh-waverley-station.123351/page-28

 

[thecrofter]

There seems to be some confusion in the thread above between what is a Neutral Section and a Section Insulator. As correctly mentioned, the purpose of a Neutral Section is to separate the different supply phases of the feeders. There is usually (but not always) a Neutral Section at the Feeder Station and one at the mid point between that and the next feeder station along the line. Each electrical section is divided into subsections which can be achieved by using Section Insulators or overlaps in the Overhead Line.

There will not be a Neutral Section in a station area. What will be observed there will be Section Insulators (SIs) which can take many forms depending on their vintage.

 

[DPWH]

Modern trolleybuses in other countries tend to have a battery so that they can drive off-wire when necessary and raise the trolley pole back up later.

 

[AM9]

The actual ‘dead’ section is only about 15cm long
APC magnets fittedt to sleeper ends prior to and after OHNS turn off trains traction power when APC receiver on train wheelset passes should driver forget to shut off power
( seen here indicated by white diamond)
View attachment 58190

Aboveexample on Thameslink route at Sandridge,St Albans.

According to the drivers manual that I linked to:
"Each neutral section is 155 feet long and is split up into the following sections, firstly there is a 100 foot run on, this is from the first APC magnet to the insulated section, secondly there is 15 feet of dead section, which is split in to 5 feet of ceramic insulators then 5 feet of dead section then another 5 feet of ceramic insulators and lastly there is a 40 foot run off, this is from the end of the insulated section to the second APC magnet."
see page 20.
The page also gives instructions on how the driver should recover a train that is stranded at various locations within the overall neutral section.

 

[Elecman]

According to the drivers manual that I linked to:
"Each neutral section is 155 feet long and is split up into the following sections, firstly there is a 100 foot run on, this is from the first APC magnet to the insulated section, secondly there is 15 feet of dead section, which is split in to 5 feet of ceramic insulators then 5 feet of dead section then another 5 feet of ceramic insulators and lastly there is a 40 foot run off, this is from the end of the insulated section to the second APC magnet."
see page 20.
The page also gives instructions on how the driver should recover a train that is stranded at various locations within the overall neutral section.

That sounds like an original 1960s Neutral Section construction,I think modern ones are much shorter

 

[Rick1984]

There is a very slowly speed neutral section on Carstairs curve.

 

[swtandgw]

How long are neutral sections?

Usually very short, with approximately a carriage length or two between APC magnets. Some, such as the Maidenhead OHNS on the GWML, are of the long carrier wire type, which necessitate subsidiary signs underneath the OHLE entrance sign that say "LONG" to signify that the OHNS is longer than the usual OHNS, and is followed by an OHNS sign with a red cross going through them at the exit of the long OHNS.