Third rail - becoming a better option for electrification?

[sbf kent]

With the increases effeciency of electric motors, their lighter weight, increased power to weight ratio, potentially backed up by batteries, is third rail becoming a better option for electrifcation than overhead line electrification (OLE) installation. Able to be installed at a lower cost,easier to maintain, less vulnerable to wind related damage, providing both a core supply and a battery charge option, could a third rail be a better, easier, more reslient alternative to OLE. Maybe not for high speed, but for the other parts of the network?

 

[SargeNpton]

25kv AC overhead has numerous technical and financial advantages over 750v DC third rail over its whole life period, which is why just about every main line electric railway worldwide uses it.

In the UK, third rail will only now ever be used for infill in existing areas.

 

[HSTEd]

25kv AC overhead has numerous technical and financial advantages over 750v DC third rail over its whole life period, which is why just about every main line electric railway worldwide uses it.

Even Network Rail now admits that Third Rail is cheaper than 25kV in capital cost terms, and whole lift costings are notoriously wooly because of the assumptions that must be made.

And 25kV prices have increased even further since then (that was a pre coronavirus Kent Route Utilisation Study)

In the UK, third rail will only now ever be used for infill in existing areas.

ORR won't even allow that, which is why the electrification programme has collapsed.

There will be no more third rail electrification in the UK, but there will be precious little new electrification full stop.

 

[yorksrob]

ORR won't even allow that, which is why the electrification programme has collapsed.

There will be no more third rail electrification in the UK, but there will be precious little new electrification full stop.

Not without reform of ORR at any rate.

 

[E27007]

A key disadvantage of third rail is the effect on overnight possessions, work cannot start on the running rails until the juice rail is both switched off and made safe by earthing straps, around a third of the overnight possession period is lost to strapping at the start and end of theline occupation.
Work on the running rails does not require the 25kV OHL to be isolated. The costs of lost of production time mounts over many years, third rail is not a cheap solution in the long-term

 

[HSTEd]

A key disadvantage of third rail is the effect on overnight possessions, work cannot start on the running rails until the juice rail is both switched off and made safe by earthing straps, around a third of the overnight possession period is lost to strapping at the start and end of theline occupation.
Work on the running rails does not require the 25kV OHL to be isolated. The costs of lost of production time mounts over many years, third rail is not a cheap solution in the long-term

In a new build installation there would probably be alternative, faster, ways of confirming that the third rail is isolated.

Just because the Southern Railway practice was a certain way does not mean that it must always be so.
Just as the 33kV trackside feeders that the early schemes had vanished in the later ones.

EDIT:

I very much doubt a modern installation would be using uninsulated hook switches for isolation! Nor would it be relying on field-fixed earthing straps to short out the rail.

 

[John Webb]

With modern electronic devices, is it possible to leave the third rail switched off and only energise it when a train is on any particular stretch of track? This could overcome ORR objections to permanently energised third-rail and also make isolating sections for track maintenance easier?

 

[anthony263]

With modern electronic devices, is it possible to leave the third rail switched off and only energise it when a train is on any particular stretch of track? This could overcome ORR objections to permanently energised third-rail and also make isolating sections for track maintenance easier?

I think that would be the ticket the Industry would need abd should persuade the ORR

 

[12LDA28C]

I think that would be the ticket the Industry would need abd should persuade the ORR

Won't happen.

With modern electronic devices, is it possible to leave the third rail switched off and only energise it when a train is on any particular stretch of track? This could overcome ORR objections to permanently energised third-rail and also make isolating sections for track maintenance easier?

How would that be done exactly and how long would each 'stretch of track' be? 100m? 400m? A signal section? AIUI a specific section can already be isolated for track maintenance / engineering work but I assume that is not such a quick and easy procedure that it could be done and reinstated every few minutes for the passage of a train.

 

[John Webb]

......How would that be done exactly and how long would each 'stretch of track' be? 100m? 400m? A signal section? AIUI a specific section can already be isolated for track maintenance / engineering work but I assume that is not such a quick and easy procedure that it could be done and reinstated every few minutes for the passage of a train.

I would have thought that track circuits could be used as appropriate to switch the power on and off. I've no thoughts about the length of rail that is turned on at any one time, but I would expect that it would need to be several train lengths. But perhaps this discussion is more suited to the speculative section of the Forum?

 

[thomalex]

Exactly my thinking. I’ve lost track of the about of times recently I've heard of overhead lines down.

 

[Western 52]

Isn't 3rd rail more susceptible to issues caused by ice and snow?

 

[swt_passenger]

Won't happen.



How would that be done exactly and how long would each 'stretch of track' be? 100m? 400m? A signal section? AIUI a specific section can already be isolated for track maintenance / engineering work but I assume that is not such a quick and easy procedure that it could be done and reinstated every few minutes for the passage of a train.

The amount of additional switchgear required would be very significant, especially if each track of a busy section had to be independently switched. But the existing DC distribution system design assumes that it is all connected in parallel, and DC regeneration also requires the system to be connected in parallel to improve receptivity. If the third rail itself wasn’t to be live, you’d need a separate high current path running alongside it to provide the same traction current if it couldn’t be passed along the third rail…

 

[NSE]

Isn't 3rd rail more susceptible to issues caused by ice and snow?

Yes, but then:
A) snow and ice is far less frequent than high winds and storms
B) snow and ice can still damage OHLE, it’s been mentioned on here before. Not to the same extend. But it does cause damage.

 

[stuu]

No. Because it's a really stupid, wasteful system to power longer distance trains. The DC system literally burns ~£200m of electricity every year through electrical resistance.

 

[zwk500]

With modern electronic devices, is it possible to leave the third rail switched off and only energise it when a train is on any particular stretch of track? This could overcome ORR objections to permanently energised third-rail and also make isolating sections for track maintenance easier?

This has been proposed several times before on other threads and the answer is that the switchgear would get hammered switching on and off so frequently, as well as the further potential for delay if a fault develops. Many parts of the southern region have trains 2 or 3 minutes apart for substantial portions of each hour. Trains are up to 240m long with very close signal spacing, the length of sections and continuous switching in and out would hammer the system.

 

[Nicholas Lewis]

Not without reform of ORR at any rate.

The ORR doesn't need reforming the Electricity at Work Act needs to exclude Network Rail from being required to comply with regulation 7

Insulation, protection and placing of conductors​

7. All conductors in a system which may give rise to danger shall either–

(a)be suitably covered with insulating material and as necessary protected so as to prevent, so far as is reasonably practicable, danger; or

(b)have such precautions taken in respect of them (including, where appropriate, their being suitably placed) as will prevent, so far as is reasonably practicable, danger

 

[paul1609]

This has been proposed several times before on other threads and the answer is that the switchgear would get hammered switching on and off so frequently, as well as the further potential for delay if a fault develops. Many parts of the southern region have trains 2 or 3 minutes apart for substantial portions of each hour. Trains are up to 240m long with very close signal spacing, the length of sections and continuous switching in and out would hammer the system.

Id suggest in the modern world youd have any physical switch gear on the ac side and leave it permanently energised in day to day running. Youd produce the 750v dc utlising IGBT with a gating suicide. When you need traction current you lift the gating suicide. This has worked in the marine and other high power industrys safely for 40 years. The infil electrification schemes your looking at are pretty lightly trafficed so your probably only looking at a maximum load of around 1.5 MW per section maybe 4 for the Uckfield line? Marshlink could be easily electrified with spare ac capacity available for the last 20 years at Ashford International.

 

[thomalex]

No. Because it's a really stupid, wasteful system to power longer distance trains. The DC system literally burns ~£200m of electricity every year through electrical resistance.

How much does fixing up downed over head lines cost?

 

[yorksrob]

The ORR doesn't need reforming the Electricity at Work Act needs to exclude Network Rail from being required to comply with regulation 7

The act predates the third rail ban by some years surely !

 

[paul1609]

The ORR doesn't need reforming the Electricity at Work Act needs to exclude Network Rail from being required to comply with regulation 7

The Electricity at Work Act came in to force in 1974 so all third rail schemes since then need to be replaced. In fact its probably retrospective so all 3rd rail needs replacing if thats the reason why infill schemes cant be authorised.

 

[Nicholas Lewis]

A key disadvantage of third rail is the effect on overnight possessions, work cannot start on the running rails until the juice rail is both switched off and made safe by earthing straps, around a third of the overnight possession period is lost to strapping at the start and end of theline occupation.
Work on the running rails does not require the 25kV OHL to be isolated. The costs of lost of production time mounts over many years, third rail is not a cheap solution in the long-term

In my experience it didn't eat into time anything like you suggest albeit it did depend on how much strapping resource you threw at so certainly costly. However, there has been vast investment in installing remote controlled short circuiting devices over many routes already and rest of network is to be retrofitted which removes the need for this.

Ultimately though you are correct that almost no activity on third rail is now permitted without full isolation and strapping/short circuit device.

 

[DaleCooper]

Id suggest in the modern world youd have any physical switch gear on the ac side and leave it permanently energised in day to day running. Youd rectify the 750v dc utlising IGBT with a gating suicide. When you need traction current you lift the gating suicide. This has worked in the marine and other high power industrys safely for 40 years. The infil electrification schemes your looking at are pretty lightly trafficed so your probably only looking at a maximum load of around 1.5 MW per section maybe 4 for the Uckfield line? Marshlink could be easily electrified with spare ac capacity available for the last 20 years at Ashford International.

How do you rectify DC?

 

[paul1609]

How do you rectify DC?

Ive edited for you.

 

[Nicholas Lewis]

The Electricity at Work Act came in to force in 1974 so all third rail schemes since then need to be replaced. In fact its probably retrospective so all 3rd rail needs replacing if thats the reason why infill schemes cant be authorised.

EAW came in 1989 it was enabled by the Health & Safety at Work Act 1974.

 

[birchesgreen]

With modern electronic devices, is it possible to leave the third rail switched off and only energise it when a train is on any particular stretch of track? This could overcome ORR objections to permanently energised third-rail and also make isolating sections for track maintenance easier?

There are some light rail systems which use a central third rail which do this The rail is only electrified while the tram is over it.

It uses 11m long segments. Alstom APS, the Dubai metro uses it and some others.

 

[swt_passenger]

There are some light rail systems which use a central third rail which do this The rail is only electrified while the tram is over it.

It uses 11m long segments. Alstom APS, the Dubai metro uses it and some others.

It wouldn’t ever scale up to practical mainline use, with trains of 240m length drawing thousands of amps, I think this has been pointed out in a number of previous threads that mentioned how systems are used with trams.

 

[nwales58]

With modern electronic devices ...

Modern?

Stud contact electrification was in use on a few tramway systems over a century ago. Magnet plus gravity was all it needed. More recently, Alstom's APS is fashionable in France and there are other intermittent supply systems.

In the end, losses favour AC at higer voltages over DC for anything beyond light rail or metro. AC conductors primarily conduct along the edges so no need for the mass of 3rd rail. Put it overhead and most of your insulation gap problems go away.

 

[TSG]

With modern electronic devices, is it possible to leave the third rail switched off and only energise it when a train is on any particular stretch of track? This could overcome ORR objections to permanently energised third-rail and also make isolating sections for track maintenance easier?

That would pretty much guarantee that any advantage in cost and reliability that third rail might have had would evaporate.

The ORR doesn't need reforming the Electricity at Work Act needs to exclude Network Rail from being required to comply with regulation 7

The provision for exemption was written into the regulations. AIUI, the HSE granted BR/Railtrack/NR exactly that. However, the exemption from particular regulations does not change the general duty of care, nor prevent revocation if conditions are not adhered to or excessive risk becomes apparent, nor does it give carte blanche to extend the system.

Exemption certificates​

30.—(1) Subject to paragraph (2), the Health and Safety Executive may, by a certificate in writing, exempt–

(a)any person;

(b)any premises;

(c)any electrical equipment;

(d)any electrical system;

(e)any electrical process;

(f)any activity,

or any class of the above, from any requirement or prohibition imposed by these Regulations and any such exemption may be granted subject to conditions and to a limit of time and may be revoked by a certificate in writing at any time.

(2) The Executive shall not grant any such exemption unless, having regard to the circumstances of the case, and in particular to–

(a)the conditions, if any, which it proposes to attach to the exemption; and

(b)any other requirements imposed by or under any enactment which apply to the case,

it is satisfied that the health and safety of persons who are likely to be affected by the exemption will not be prejudiced in consequence of it.

 

[Nicholas Lewis]

That would pretty much guarantee that any advantage in cost and reliability that third rail might have had would evaporate.


The provision for exemption was written into the regulations. AIUI, the HSE granted BR/Railtrack/NR exactly that. However, the exemption from particular regulations does not change the general duty of care, nor prevent revocation if conditions are not adhered to or excessive risk becomes apparent, nor does it give carte blanche to extend the system.

Yes there was an exemption that Railtrack would never be able to comply with protection against exposed conductors but other elements of the regulations had to be complied with which is why strapping had to be introduced. Oh and which by the way has caused plenty of accidents over the years vs the protection it was supposed to provide. Anyhow at least the Negative Short Circuiting Devices progressively being installed will remove that risk. Separately LUL fought against complying with straps on the basis they discharge entire lines before work can take place but that isn't practical on the NR network.