Future of Third Rail

[Ken H]

With 4th rail, traction current is returned via the fourth rail. With 3rd rail, the traction current is returned through the running rails which is also shared with track circuit currents which can require special bonding, depending on type of track circuit.

On shared track the centre juice rail is electrically bonded to the other juice rail. That rail is then at full voltage. And the current in it will double compared to 'proper' 4th rail.

 

[tomuk]

On shared track the centre juice rail is electrically bonded to the other juice rail. That rail is then at full voltage. And the current in it will double compared to 'proper' 4th rail.

No it isn't the centre 'juice' rail is bonded to the running rails at 0v or earth. The outer 'juice' rail is +750V nominal.

 

[Ken H]

No it isn't the centre 'juice' rail is bonded to the running rails at 0v or earth. The outer 'juice' rail is +750V nominal.

Doh. Sorry

 

[snowball]

On shared track the centre juice rail is electrically bonded to the other juice rail. That rail is then at full voltage. And the current in it will double compared to 'proper' 4th rail.

That would mean zero volts input to the train. Rather, it's as tomuk says.

 

[Pigeon]

Remember the District was originally the Metropolitan District and was a child of the Metroplitan Railway. But the best laid plans and all that and the district ended up in the Yerkes Underground group.
The district electrified at the Yerkes standard but the Met wanted a different system for their lines, including the northern bit of the circle. They wanted some sort of overhead system but arbitration meant they had to install the Yerkes standard system. But not standard enough to stop the shoes falling off the narrower juice rails the Met installed!

Ganz three-phase system. I guess that would have been 2 parallel overhead wires for two of the phases and the third one on the running rails. I also guess that the point of the idea was to take advantage of the more efficient and elegant methods of speed control that were possible with three-phase induction motors as opposed to DC ones. Which would have been dead interesting and neat, and it's a great shame they didn't do it.

 

[Ken H]

Ganz three-phase system. I guess that would have been 2 parallel overhead wires for two of the phases and the third one on the running rails. I also guess that the point of the idea was to take advantage of the more efficient and elegant methods of speed control that were possible with three-phase induction motors as opposed to DC ones. Which would have been dead interesting and neat, and it's a great shame they didn't do it.

Thanks. I half remembered the ganz thing.

 

[61653 HTAFC]

Merseyrail DC requires (at present) buffer stops at its limits - fine for internal travel but a hindrance to expansion or integrated travel outside the region, which the local economy needs.

Surely this isn't actually a requirement, otherwise there'd have to be buffers (and no connection) at Ellesmere Port and Chester in addition to Ormskirk and Kirkby?

 

[Greybeard33]

The recent PWI presentation by Nigel Wheeler, Senior E&P Programme Manager, Southern Region, Network Rail, was quite bullish about the future of third rail.

He indicated that new third rail, with risk mitigation measures such as switched sections in station areas, is currently the front runner for decarbonisation of the Uckfield line. While the "sweet spot" for the North Downs line will most likely be a combination of battery trains with short sections of new third rail.

 

[zwk500]

The recent PWI presentation by Nigel Wheeler, Senior E&P Programme Manager, Southern Region, Network Rail, was quite bullish about the future of third rail.

He indicated that new third rail, with risk mitigation measures such as switched sections in station areas, is currently the front runner for decarbonisation of the Uckfield line. While the "sweet spot" for the North Downs line will most likely be a combination of battery trains with short sections of new third rail.

I remain sceptical the costs of the switched sections will be sufficiently low enough to justify installation while satisfying the ORR that the risks are kept low enough to meet the safety case. But the recent RSSB report did give a clearer picture of the risk management approaches so with a bit of thought and application I could easily be proved wrong.

 

[Greybeard33]

I remain sceptical the costs of the switched sections will be sufficiently low enough to justify installation while satisfying the ORR that the risks are kept low enough to meet the safety case. But the recent RSSB report did give a clearer picture of the risk management approaches so with a bit of thought and application I could easily be proved wrong.

The presentation emphasised that the switched sections would be very simple, e.g treadles that energise the whole length of conductor rail through the station whenever there is a train in section. So not eliminating the risk of passengers or trespassers coming into contact with the live rail, but reducing the risk by reducing the exposure time. Of course, electrocution is not the only risk to a person who is on the track when a train is approaching!

Alternatively the trains would be equipped with small traction batteries and the juice would only be switched on if a train became stranded in the station.

He said that the ORR and RSSB are involved in the risk assessments.

 

[zwk500]

The presentation emphasised that the switched sections would be very simple, e.g treadles that energise the whole length of conductor rail through the station whenever there is a train in section. So not eliminating the risk of passengers or trespassers coming into contact with the live rail, but reducing the risk by reducing the exposure time. Of course, electrocution is not the only risk to a person who is on the track when a train is approaching!

Alternatively the trains would be equipped with small traction batteries and the juice would only be switched on if a train became stranded in the station.

He said that the ORR and RSSB are involved in the risk assessments.

We've seen before that simple ideas are presented at conferences and then when the real world hits them they're a lot more complicated than they were meant to be.

I'm not saying it won't happen, I'm just measuring my expectations

 

[tomuk]

We've seen before that simple ideas are presented at conferences and then when the real world hits them they're a lot more complicated than they were meant to be.

I'm not saying it won't happen, I'm just measuring my expectations

Take a look at the overlapping interlocks required for VivaRail's rapid charging rails to make it safe. This is in the context of a pair of rails a couple of feet long in the four foot the train making it difficult to touch them when live.

 

[MarkyT]

The presentation emphasised that the switched sections would be very simple, e.g treadles that energise the whole length of conductor rail through the station whenever there is a train in section. So not eliminating the risk of passengers or trespassers coming into contact with the live rail, but reducing the risk by reducing the exposure time. Of course, electrocution is not the only risk a person who is on the track when a train is approaching!

Alternatively the trains would be equipped with small traction batteries and the juice would only be switched on if a train became stranded in the station.

He said that the ORR and RSSB are involved in the risk assessments.

I'd expect an emphasis on the prevention and detection of trespass and other accidental ingress. Stations are one area where this is a risk, as are level crossings. Improvements and maintenance of fencing could be looked at generally. At higher risk potential ingress locations, some additional sensors might be incorporated, activating alarms and perhaps automatic power shutoff. Some finer-grained quick-switching facilities might also be made available for maintenance staff protection on the lineside. As to the switching itself, this need not be ruinously complex or expensive in an all-new installation, with additional switchgear incorporated in the original design. I still think a modest-sized battery onboard is best, with platform areas then able to be devoid of conductors completely for most through stations, and 3rd rail present only at termini or other locations with long layovers, and then only briefly switched on when required for stationary charging and pull away. The battery option also permits longer gaps through junctions and either side of any remaining level crossings. While in this scenario the majority of the simple plain line between stations would be equipped with 3rd rail, the battery option could also help address the parallel running risks between Eridge station and Birchden Junction, where the Spa Valley Railway runs closely alongside the national rail single line for about a mile. With batteries onboard, the Southern Uckfield subfleet could cope with a long gap from just south of Eridge station to just north of Birchden Junction. How the new 3rd rail is supplied from the electrical grid is an area where some innovation might allow the feeders to be connected to local the local DNO network in a number of places rather than requiring an extension of the railway's own high voltage distribution system in a traditional Southern Region configuration. The single line limits peak loading and the new feeder locations might themselves incorporate some peak-levelling storage capability.

 

[zwk500]

I'd expect an emphasis on the prevention and detection of trespass and other accidental ingress. Stations are one area where this is a risk, as are level crossings. Improvements and maintenance of fencing could be looked at generally. At higher risk potential ingress locations, some additional sensors might be incorporated, activating alarms and perhaps automatic power shutoff. Some finer-grained quick-switching facilities might also be made available for maintenance staff protection on the lineside. As to the switching itself, this need not be ruinously complex or expensive in an all-new installation, with additional switchgear incorporated in the original design. I still think a modest-sized battery onboard is best, with platform areas then able to be devoid of conductors completely for most through stations, and 3rd rail present only at termini or other locations with long layovers, and then only briefly switched on when required for stationary charging and pull away. The battery option also permits longer gaps through junctions and either side of any remaining level crossings. While in this scenario the majority of the simple plain line between stations would be equipped with 3rd rail, the battery option could also help address the parallel running risks between Eridge station and Birchden Junction, where the Spa Valley Railway runs closely alongside the national rail single line for about a mile. With batteries onboard, the Southern Uckfield subfleet could cope with a long gap from just south of Eridge station to just north of Birchden Junction. How the new 3rd rail is supplied from the electrical grid is an area where some innovation might allow the feeders to be connected to local the local DNO network in a number of places rather than requiring an extension of the railway's own high voltage distribution system in a traditional Southern Region configuration. The single line limits peak loading and the new feeder locations might themselves incorporate some peak-levelling storage capability.

Tbh I can see them ending up with just full traction batteries and a top-up length of switchable third rail at Uckfield.

 

[HSTEd]

How the new 3rd rail is supplied from the electrical grid is an area where some innovation might allow the feeders to be connected to local the local DNO network in a number of places rather than requiring an extension of the railway's own high voltage distribution system in a traditional Southern Region configuration. The single line limits peak loading and the new feeder locations might themselves incorporate some peak-levelling storage capability.

Well that is how all the 80s and 90s third rail projects were done.

Even 11kV systems are tapped to support third rail in the more modern installations.

 

[MarkyT]

Tbh I can see them ending up with just full traction batteries and a top-up length of switchable third rail at Uckfield.

When you consider the resistance losses in third rail installations I tend to agree, although some extension of the conductors under these new principles for a distance beyond Hurst Green might be beneficial for range nonetheless.

 

[zwk500]

When you consider the resistance losses in third rail installations I tend to agree, although some extension of the conductors under these new principles for a distance beyond Hurst Green might be beneficial for range nonetheless.

Agreed, extend the 3rd rail past the junction so that trains can accelerate away on the juice and if they have to stand on the Up they can start charging sooner, but then it drops out probably at the first tricky bridge or tunnel.

 

[Greybeard33]

Tbh I can see them ending up with just full traction batteries and a top-up length of switchable third rail at Uckfield.

The presenter said that full battery operation is impractical for the Uckfield line, because 12-car battery trains would need too much charging current from the third rail while on the main line. 3/4-car battery trains on the N Downs line would be ok.

 

[zwk500]

The presenter said that full battery operation is impractical for the Uckfield line, because 12-car battery trains would need too much charging current from the third rail while on the main line. 3/4-car battery trains on the N Downs line would be ok.

I've heard both sides of that from different people at NR.

 

[MarkyT]

Agreed, extend the 3rd rail past the junction so that trains can accelerate away on the juice and if they have to stand on the Up they can start charging sooner, but then it drops out probably at the first tricky bridge or tunnel.

Although 3rd rail is a lot less tricky to get through such structures than any overhead system. I'd take it to just onto the single line beyond Hever, a distance of just over six miles, so any non-battery-equipped or insufficiently-charged train might make it thus far and be able to reverse via the double to single turnout.

 

[zwk500]

Although 3rd rail is a lot less tricky to get through such structures than any overhead system. I'd take it to just onto the single line beyond Hever, a distance of just over six miles, so any non-battery-equipped or insufficiently-charged train might make it thus far and be able to reverse via the double to single turnout.

There's a crossover at Hurst Green to allow emergency reversals. The issue with tunnels particularly is the need to isolate the third rail if staff have to go inside for any reason, which is potentially disruptive if the isolation also affects the East Grinstead branch. I'd personally not take the third rail beyond Edenbridge tunnel, and may not ever taken it as far as that.

 

[MarkyT]

There's a crossover at Hurst Green to allow emergency reversals. The issue with tunnels particularly is the need to isolate the third rail if staff have to go inside for any reason, which is potentially disruptive if the isolation also affects the East Grinstead branch. I'd personally not take the third rail beyond Edenbridge tunnel, and may not ever taken it as far as that.

That's what I was suggesting regarding finer-grained isolation facilities for this sort of scenario, probably easier to incorporate at more reasonable cost in a new installation.

The presenter said that full battery operation is impractical for the Uckfield line, because 12-car battery trains would need too much charging current from the third rail while on the main line. 3/4-car battery trains on the N Downs line would be ok.

I wonder if any further strengthening of the power supplies on the mainline could help with this issue.

 

[zwk500]

That's what I was suggesting regarding finer-grained isolation facilities for this sort of scenario, probably easier to incorporate at more reasonable cost in a new installation.

True, although it'd be cheaper to just add in a short 1-2Km extension that is wired in with the rest of the juice rails.

I wonder if any further strengthening of the power supplies on the mainline could help with this issue.

@Bald Rick has commented on the power supply from London Bridge to Hurst Green before, IIRC.

 

[Bald Rick]

The presenter said that full battery operation is impractical for the Uckfield line, because 12-car battery trains would need too much charging current from the third rail while on the main line. 3/4-car battery trains on the N Downs line would be ok.

Thats a common held opinion by some power engineers. All the evidence I have seen suggests that it was an opinion for several years ago that is taken as read, and needs properly assessing.

 

[PGAT]

The presenter said that full battery operation is impractical for the Uckfield line, because 12-car battery trains would need too much charging current from the third rail while on the main line. 3/4-car battery trains on the N Downs line would be ok.

But trains don’t even exceed 8 cars right now

 

[zwk500]

But trains don’t even exceed 8 cars right now

Uckfield line trains were running as 10-car Turbostars pre-covid, which is 230m long. Fair bet to assume that 8x20m Batterystar wouldn't quite be enough.

 

[tomuk]

Or we could stop messing about and just put the third rail down with some better fencing and trespass measure and maybe some more granular isolation for trackside staff. Job done. o messing with the stock, or coming up with byzantine failsafe switching mechanisms to de-energise sections sections track when trains are present.

 

[PGAT]

Or we could stop messing about and just put the third rail down with some better fencing and trespass measure and maybe some more granular isolation for trackside staff. Job done. o messing with the stock, or coming up with byzantine failsafe switching mechanisms to de-energise sections sections track when trains are present.

If only it were that easy

 

[tomuk]

If only it were that easy

It is that easy. It is in place today for approx 2000km or railway not to mention the Underground.

 

[Dr Hoo]

It is that easy. It is in place today for approx 2000km or railway not to mention the Underground.

Have you ever had an experienced third rail maintenance colleague electrocuted right next to you, fundamentally because of awkward isolation and earthing procedures?

I have. It's not nice. Especially within a few weeks of attending the Coroner's inquest into the electrocution of nine-year-old schoolboy who had got onto the track through a gap in the fence created by rail staff to create a short cut to a depot.