Section neutral signs

[robertclark125]

On some of the Video125 Drivers Eye View DVDs, we see the trains operating on overhead wires. And there are some sections that are neutral sections, with a black and white sign. Here, the driver must shut off power. However, when does the driver know the section is ended? I didn't see any signs.

 

[ralphchadkirk]

Taking a guess here, but probably when the driver gets his line light back.

 

[driver9000]

The neutral section is only a few long (the actual dead section in the contact wire is around 10ft or so) and can also be identified by the APC inductors mounted on the sleeper ends. As the train passes over the first inductor the VCB opens and the line light goes out, on passing the second inductor the VCB closes again and the line light is restored meaning power can be taken again. The White background sign marks the approach to a neutral section while the black background sign marks the site.

 

[rail-britain]

Depends on the locomotive or multiple unit, but usually the driver learns to listen for specific sounds as the power is lost and then resumes once the neutral section has been exited
Once the power has resumed then normal control continues

The only difference would be when driving in a DVT, as consideration has to be given to the length of the train between the cab and loco at the rear
I knew many Edinburgh based drivers when driving IC225 sets that would enter on full power northbound unlike southbound where the power had to be removed before entering

Equally, I also remember working a northbound service on the WCML and the loco failed just as we entered the neutral section at Carstairs, completely blocking all routes
This made it even more of a challenge to source a locomotive, as the two spare locos sitting at Carstairs could not assist, so the spare was sent from Edinburgh

 

[TDK]

Depends on the locomotive or multiple unit, but usually the driver learns to listen for specific sounds as the power is lost and then resumes once the neutral section has been exited
Once the power has resumed then normal control continues

The only difference would be when driving in a DVT, as consideration has to be given to the length of the train between the cab and loco at the rear
I knew many Edinburgh based drivers when driving IC225 sets that would enter on full power northbound unlike southbound where the power had to be removed before entering

Equally, I also remember working a northbound service on the WCML and the loco failed just as we entered the neutral section at Carstairs, completely blocking all routes
This made it even more of a challenge to source a locomotive, as the two spare locos sitting at Carstairs could not assist, so the spare was sent from Edinburgh

350's are a pain as it takes 14 seconds for the power to come back in, this is poor if you are braking for a station.

 

[es373]

Neutral sections separate each phase so you do not bridge them. You usually have this -

----contact wire 1st phase------||||||||------contact wire 2nd phase--------------

The |||||||'s are insulators and also there would be arc horns to dissipate any arcing and skids to allow the pantograph smooth movement.
Most stock have Automatic Power Control (i think). In a nut shell, its a little reed switch on the bogie which when a magnet passes over - it actuates which tells the VCB to open thus to not let any voltage in until the train passes another APC beacon to signify to the VCB to close.

It's my understanding of it anyway.

 

[DaveNewcastle]

The only difference would be when driving in a DVT, as consideration has to be given to the length of the train between the cab and loco at the rear
I knew many Edinburgh based drivers when driving IC225 sets that would enter on full power northbound unlike southbound where the power had to be removed before entering

or the other way round? (loco is at the north/country end)

Equally, I also remember working a northbound service on the WCML and the loco failed just as we entered the neutral section at Carstairs, completely blocking all routes

I recall that the arrangement at Carstairs is quite exceptional - some routes involve passing through 2 closely spaced neutral sections where it is common to coast all the way between them both (I don't know if that is a matter of driving style or whether there are no 'restore contact' magnets within the short intermediate section.

Neutral sections separate each phase . . . . .

That is very often true, but not necessarily; they may merely be separately supplied, separately protected and separately isolated sections of track.

 

[rail-britain]

I recall that the arrangement at Carstairs is quite exceptional - some routes involve passing through 2 closely spaced neutral sections where it is common to coast all the way between them both

That is correct, there are two neutral sections, due to the triangle

Edinburgh - Carlisle you pass through both, with a short powered section between them
Drivers don't normally apply power in this short powered section, but the electrics can be heard briefly restoring and then switching off again
Glasgow - Carlisle you pass through one
Edinburgh - Glasgow you pass through one

I find it amazing that a Class 91 has never stalled, as far as I am aware, when passing through at 15mph

 

[es373]

Agree to disagree Dave with all due respect.

Yes it will be a separate supply (from a different building, obviously) but speaking on terms of the contact wire, it has to be isolated from a separate phase. If its not then you'll have a massive trip of OHL section, not to mention the burn out of booster transformers, damage to rolling stock and possibly sensitive signalling equipment lineside.

So it is the main reason why there are neutral sections on lines.

Or am I misunderstanding what you're saying?

 

[Whistler40145]

Is it correct that Class 90s on-board computer automatically detects each Neutral Section, so the Driver doesn't have to shutoff power?

 

[driver9000]

I find it amazing that a Class 91 has never stalled, as far as I am aware, when passing through at 15mph

As long as the loco keeps rolling it shouldn't stall between APC inductors. Coming to a stand with the pan head on the actual dead section would be difficult to as given its short length although I'm sure some have managed it (like gapping a DC unit with all shoes off the rail). There used to be special instructions for resetting the VCB if the train stopped between inductors but I'm sure these were withdrawn a long time ago.
--- old post above --- --- new post below ---

Is it correct that Class 90s on-board computer automatically detects each Neutral Section, so the Driver doesn't have to shutoff power?

That is the job of the APC inductors. Even older tap changer fitted locos such as the class 86 were fitted with APC and you could see the receiver on the bogie frame which resembled an AWS receiver. The Driver was required to run down the tap and shut off before approaching the neutral section to reduce arcing and a jolt as the power was lost. I believe it's the Thyristor control system on locomotives such as the 90 which enables Drivers to keep the handle open when passing through neutral sections although power is still lost when the VCB opens and the Thyristor will automatically run down and run back up again when power is restored. I'm told that it is still considered good practice to shut off on approach to a neutral section when driving AC traction.

 

[DaveNewcastle]

I'm puzzled as to what we're disagreeing about here.

Agree to disagree Dave with all due respect.

You correctly stated that a neutral section would be placed between 2 powered sections which were fed from different phases of the supply. I responded with "That is very often true, but not necessarily", pointing out that a neutral section may also be installed for other reasons, such as to create a section which may seperately isolated. Two adacent sections could be fed from the same phase of the supply.

It would be wrong to claim that :

So it is the main reason why there are neutral sections on lines.

In fact, even if the supply was generated on only a single phase, there would still be several reasons to isolate sections and therefore the need to instal 'neutral sections' at their interfaces.
The example at Carstairs illustrates this, there being 4 (or more?) powered sections (but only 3 phases), therefore 2 (or more) of them will be in-phase.

Or am I misunderstanding what you're saying?

I fear so.

Edinburgh - Glasgow you pass through one

I was under the impression that there were also 2 closely spaced neutrals on that curve too, (with a powered section between them, although most 91's seem to be coasting through it.)

 

[ChrisCooper]

APC was actually initially designed for when the AC overhead system was dual voltage with some 6.25kV in built up areas and 25kV elsewhere. As well as shutting off and re-applying power automatically for the neutral sections, the APC would also sence the voltage of the section being entered and automatically switch over to the correct voltage. At least that was in theory, the 303s which passed through a number of voltage changes had a tendancy not to switch correctly and if entering a 25kV section when still set up for 6.25kV it could be nasty, including at least one rectifier explosion that killed the guard (as the cooling oil tank was in the guards compartment). The 303s were modified after that to prevent wrong voltage being dangerous (including replacing the old mercury arc rectifiers with silicone ones which didn't need the big tank of oil), and over time the 6.25kV sections were removed, the last being on the LTS lines (as the entire route was 6.25kV it didn't matter so much). The end of 6.25kV also coincided with delivery of new stock in many cases which could be simplified by being 25kV only. The last dual voltage locos were the 85s, the 86s being 25kV only. The last 25kV units were the 312/1s for the Great Eastern route, although the 312/0s for the Great Northern were 25kV only, leading to a swap when the 312/0s were withdrawn from the GN as by that time the GE was 25kV only (converted in time to prevent the 315s having to be dual voltage) so the GN 312s allowed the original GE 312s to be moved to LTS which was still at that time 6.25kV.

I presume 1500v lines used to have neutral or dead sections too. They are on tram lines, normally at and between feeder stations as on 25kV railways. Trams can't take power through deads, although the breakers remain closed so auxiliary is still on, but with the lower voltage arcing is only a problem if the current is very high. On modern systems the dead section is marked by a diamond shaped sign (standard tram sign) with a horizontal bar. On older systems drivers just had to learn where they are. I presume those on 1500v railway lines were the same, at and between feeders and unmarked with route knowledge telling drivers where they were (although they are fairly visable too).

Multi-wire electrification systems have the best dead sections as at junctions or crossovers the seperate voltages or phases have to cross each other. Trolleybuses have arrangements so the live and the return are kept seperate, and similar arrangements are also found on 3 phase systems on the continent where 2 out of phase wires supply power along with the running rails. Powering through these can often trip the supply as it can draw an arc between the live and return or the different phases. Usually one route will be live, the other dead. In most cases at a junction the turning route will be live and the straight route dead as those going straight will be faster so can coast through easier.

 

[MacCookie]

I was under the impression that there were also 2 closely spaced neutrals on that curve too, (with a powered section between them, although most 91's seem to be coasting through it.)

There's one on the Carstairs Curve (between Carstairs East Junc and Carstairs Station Junc), one in each direction on Carstairs South Curve (just north of Carstairs South Junc) and one in each direction on the WCML (just south of Carstairs South Junc).

Edit: There's also one on the Through Siding.

Ewan

 

[Barrett M95]

For TGV drivers, on LGV, if it is a straight neutral section, everything is done by TVM - advance warning of the neutral section is given in the TVM display, the breaker is opened before and closed after - no intervention from the driver is needed. Although it is not good practice for a driver to motor through on full power without backing off, it is possible to do so and *should* cause no harm. If they are driving multiple TGV's or a Eurostar with two pans raised, each power car with pan raised is done separately as it arrives at the section.

If it is a change of either voltage or configuration (LGV to French Classic for example - which are both 25kV, but require different pan settings), the driver must back off the power to "0", open the breakers, drop the pan(s), coast through the changover area (which may or may not include a neutral section), reconfigure their desk controls, and raise the pan(s), finally closing the breaker when given permission to do so. Unike the above scenario though, the whole train is done at the same time. This can be done at line speed.

TGV's and non-North of London Eurostar sets do not have APC receivers.

 

[Whistler40145]

Are there any differences with double headed electric locos at Neutral Sections?

 

[es373]

Are there any differences with double headed electric locos at Neutral Sections?

As long as its got APC or driver notches down to off and release, I can't see it being a problem. Unless of course I am wrong.

 

[ChrisCooper]

For TGV drivers, on LGV, if it is a straight neutral section, everything is done by TVM - advance warning of the neutral section is given in the TVM display, the breaker is opened before and closed after - no intervention from the driver is needed. Although it is not good practice for a driver to motor through on full power without backing off, it is possible to do so and *should* cause no harm. If they are driving multiple TGV's or a Eurostar with two pans raised, each power car with pan raised is done separately as it arrives at the section.

If it is a change of either voltage or configuration (LGV to French Classic for example - which are both 25kV, but require different pan settings), the driver must back off the power to "0", open the breakers, drop the pan(s), coast through the changover area (which may or may not include a neutral section), reconfigure their desk controls, and raise the pan(s), finally closing the breaker when given permission to do so. Unike the above scenario though, the whole train is done at the same time. This can be done at line speed.

TGV's and non-North of London Eurostar sets do not have APC receivers.

What happens at Neutral sections where TVM is not provided? Do drivers operate the breakers manually as at changeover points? What about when NOL sets were running on the UK network, I presume the driver had to manually operate the breakers then too?

Regarding double heading, the APC will operate on each loco seperatly, so the driver will shut off power and then will see the line and breaker lights flash twice as each loco passes the neutral section before reapplying power. The same happens with units in multiple.

 

[es373]

What happens at Neutral sections where TVM is not provided? Do drivers operate the breakers manually as at changeover points? What about when NOL sets were running on the UK network, I presume the driver had to manually operate the breakers then too?

Regarding double heading, the APC will operate on each loco seperatly, so the driver will shut off power and then will see the line and breaker lights flash twice as each loco passes the neutral section before reapplying power. The same happens with units in multiple.

NoL's have APC. Drivers just shut off over neutral sections so I'm told