New 3rd Rail (again)

[furnessvale]

I am no fan of 3rd rail, but I wonder if consideration has ever been given to a "only energised when train in section" solution to extensions to the 3rd rail which would otherwise be banned under current regs?

This method has been used for stud contact trams in street running. I appreciate the differences including the fact that studs are only alive UNDER the trams whereas a 3rd rail could be live before and after the train passes.
Just a thought!

 

[jopsuk]

it would be a nightmare of switching.

 

[birchesgreen]

You mean like APS that uses wireless control to only energise the rail while the vehicle is above it?

 

[HSTEd]

Very high performance MOSFET switches would be capable of it with negligible voltage drops (SiC and such).

But it would require a separate trackside insulates busbar to bridge empty sections.
I've thought about it a lot but I don't really no what fraction of signal sections are occupied at any given time so I have no idea what the risk reduction would actually be

 

[XDM]

What is the problem the switching is to solve?
The third rail electrocution statistics prove 750dc is safer than 25kv overhead line. Only 3 days ago man died in Preston by 25 kv ac.

 

[NSEFAN]

Switching on sections only as required for traction power would save some money with reduced energy losses, but would it actually improve safety? Staff would still need to act as if it were always live, unless it has been explicitly switched off (as per the current procedures for possessions and emergencies). Sections are quite short, but possibly long enough such that passengers and staff could mistakenly believe a lack of a train means the conductor is powered down when in fact it is live, creating a false sense of security.

Far better is the bottom-contact system, such as that on the DLR, as it's inherently more difficult to have an accidental electric shock compared to a completely exposed conductor.

 

[HSTEd]

If you don't make a big song and dance in the press about what sections are live only when the train is around, and posted the 'rail is live' signs as now then I doubt it would generate a sense of security.

And essentially all the fatality-weighted-injuries from third rail are tresspassers

 

[NSEFAN]

If you don't make a big song and dance in the press about what sections are live only when the train is around, and posted the 'rail is live' signs as now then I doubt it would generate a sense of security.

And essentially all the fatality-weighted-injuries from third rail are tresspassers

Word inevitably gets around. I'm sure plenty of people already believe that trains are just like giant train sets, and the power is off when the train is stopped. I suppose it would help if all 3rd rail areas were so converted for consistency, but then if you're making that big an infrastructure investment then why not just use off-the-shelf OLE and bi-modal trains?

 

[najaB]

I'm sure plenty of people already believe that trains are just like giant train sets, and the power is off when the train is stopped.

I have heard someone telling their friends that the rail is only live when there's a train coming.

 

[HSTEd]

I suppose it would help if all 3rd rail areas were so converted for consistency, but then if you're making that big an infrastructure investment then why not just use off-the-shelf OLE and bi-modal trains?

But the existing routes are all safe enough as is.
And the cost of this system would probably be not that large since the switches would be a standard component procured in large numbers to a single specification

 

[NSEFAN]

But the existing routes are all safe enough as is.
And the cost of this system would probably be not that large since the switches would be a standard component procured in large numbers to a single specification

That's grandfather rights for you. That said there is a good case, since old installations are now well established and locals are more likely to be fully aware of the risks. For new installations, you can't assume that the locals will understand this and so you legally have to reduce risk to them. If you could close every level crossing and install brand new fencing, then this would help matters, but may be prohibitively expensive.

If this proposed system had very short electrified blocks (maybe limiting exposed conductor to less than a few carriage lengths) then it could be suitable. However limiting to signalling blocks is in my view too long (certainly around here, the blocks between Soton and Fareham last for several stations, so there's no way of seeing or hearing a train is close by).

I see your point about ordering the switches and electrical equipment, but this would require organisation at Network Rail to have a standard design created and have a rolling programme of installation. Again, if you're going to that much effort then you might as well upgrade to 25kV OLE to reduce costs in the long term, and also avoid the bespoke issues surrounding this proposed switching method. No amount of compact, modern power electronics can get you out of the basic maths surrounding power losses due to current when the train is taking power.

 

[jopsuk]

the switching system would be a point of failure. It is added complexity that means another system to maintain that if it fails stops the job.

 

[najaB]

What is the problem the switching is to solve?
The third rail electrocution statistics prove 750dc is safer than 25kv overhead line. Only 3 days ago man died in Preston by 25 kv ac.

Statistics don't (and can't) prove anything.

 

[HSTEd]

If this proposed system had very short electrified blocks (maybe limiting exposed conductor to less than a few carriage lengths) then it could be suitable. However limiting to signalling blocks is in my view too long (certainly around here, the blocks between Soton and Fareham last for several stations, so there's no way of seeing or hearing a train is close by).

Well you can still get a substantial reduction in risks even if the trespasser can't see the train before it goes live. If the rail is only live half the time we would expect only half as many electric shocks.
We could even design the switched out sections live at some lower voltage to remind peole not to touch it in a non dangerous but memorable manner. And also I suppose detect faults that develop before they go live.

I see your point about ordering the switches and electrical equipment, but this would require organisation at Network Rail to have a standard design created and have a rolling programme of installation. Again, if you're going to that much effort then you might as well upgrade to 25kV OLE to reduce costs in the long term, and also avoid the bespoke issues surrounding this proposed switching method. No amount of compact, modern power electronics can get you out of the basic maths surrounding power losses due to current when the train is taking power.

Well the switches would likely cost a few thousand pounds each when procured in the kind of numbers we are talking about, since they would replace most of the DC CBs in an installation done using modern techniques.
They are negligible compared to the enormous costs associated with 25kV, a DC installation has much less red zone working than a 25kV after all.

And the DC loss issue is often overstated and can be mitigated using new technologies

 

[NSEFAN]

And the DC loss issue is often overstated and can be mitigated using new technologies

To which new technologies are you referring? Local batteries/supercaps on the train to absorb regenerative braking energy and release it during acceleration?

Even with 100% efficient power conversion, if the transmission line is unchanged (i.e. still the same old 3rd rail) then losses there are never going to go away unless you either reduce the loss resistance or traction current.

 

[Elecman]

a DC installation has much less red zone working than a 25kV after all.

Red Zone working has nothing to do with any type of electrification

 

[HSTEd]

To which new technologies are you referring? Local batteries/supercaps on the train to absorb regenerative braking energy and release it during acceleration?

To a large degree, simply breaking up the substation capacity into smaller, cooperating, units and scattering it along the right of way - the power grid can provide dispersed supplies along the route an order of magnitude more cheaply than an OLE system as running parallel to the route otuside the boundary fence, or simply using other convenient supplies, requires none of the safety permissions and techniques required to work on the railway.
The on railway property equipment would draw 400V three phase supplies from adjacent pole mount or pad mount unit substations, as is commonly done for sub-megawatt industrial customers.

If you reduce R by supplying as much current as possible to the train from as close as possible then losses drop drastically.

Even with 100% efficient power conversion, if the transmission line is unchanged (i.e. still the same old 3rd rail) then losses there are never going to go away unless you either reduce the loss resistance or traction current.

If the weighted average current distance from the substation to the train is reduced then losses drop drastically.

Red Zone working has nothing to do with any type of electrification

I thought red zone working was a reference to working in areas that required the line to be blocked?
A lot more of the work on DC systems is done away from operational lines.

 

[Mojo]

I thought red zone working was a reference to working in areas that required the line to be blocked?

It means the exact opposite; red zone is working on a line that is still open to traffic.

 

[HSTEd]

It means the exact opposite; red zone is working on a line that is still open to traffic.

Huh, learn something every day.
Is there a term for work that requires the line to be blocked as opposed to work say on a station lift, that would not?

 

[najaB]

Is there a term for work that requires the line to be blocked as opposed to work say on a station lift, that would not?

I'd think that would be the difference between working on/near the line or lineside.

 

[Trackman]

You mean like APS that uses wireless control to only energise the rail while the vehicle is above it?

I was thinking that, but impractical because of speed restriction, like DLR bottom contact max 30mph.
APS has big problems when it rains heavily, and the vehicle has to have a battery back up, so would need new stock too.

Wireless power transfer is coming on leaps and bounds, maybe that will be a solution in the future.

 

[najaB]

Wireless power transfer is coming on leaps and bounds, maybe that will be a solution in the future.

At the power levels required it won't be feasible until we have practical room temperature superconductors.

 

[AM9]

... The on railway property equipment would draw 400V three phase supplies from adjacent pole mount or pad mount unit substations, as is commonly done for sub-megawatt industrial customers. ...

The problem with that is that a traction supply would need to provide between 1 and 3 MW in order to allow a single train to progress without significant operational restictions on acceleration etc.. That load would be intermittent and unpredictable (in supply terms). So if you start drawing such relatively large currents in bursts it would degrade the existing users on the same low voltage circuit. A substation feed for domestic and light commercial distribution is most likely to be fed by an 11kV feed and even a load rapidly changing from near zero to over 1MW would create perturbations on a feeds from the same substation. That's why proportionaltely large variable loads are fed from HV lines and not LV.

 

[swt_passenger]

the switching system would be a point of failure. It is added complexity that means another system to maintain that if it fails stops the job.

And you'd need one every 40m or so, to cope with the shortest trains. And this system would be fitted per track, and at 100 mph line speeds would have to detect the length of train, switch on and switch off during the few seconds for the shortest train to pass. The idea is part way to Dagenham...

 

[HSTEd]

The problem with that is that a traction supply would need to provide between 1 and 3 MW in order to allow a single train to progress without significant operational restictions on acceleration etc.. That load would be intermittent and unpredictable (in supply terms). So if you start drawing such relatively large currents in bursts it would degrade the existing users on the same low voltage circuit.

The advantage of the system I have outlined is that if you wish, you can deliberately trade away a little of the efficeincy you get from dispersed rectifiers [efficiencies up to 98% at the shoe are apparently plausible] to smooth out the perturbations.
[ie. you would apply a normal-condition rate-of-change limit on a substations current output that would cause the substations to spread the load and avoid going from 0-100% load in half a second, current would be pulled along the rail/bus from adjacent substations in the interim]
Loads vary wildly on a lot of circuits as is, when domestic consumption doubles or triples in all electric estates as the storage heaters come in for Economy 7.

A substation feed for domestic and light commercial distribution is most likely to be fed by an 11kV feed and even a load rapidly changing from near zero to over 1MW would create perturbations on a feeds from the same substation. That's why proportionaltely large variable loads are fed from HV lines and not LV.

The substation would only be a few hundred kilowatts, rather than a megawatt. I often, based on the example of Portland Streetcar, propose substations of about 300-500kW.
11kV feeders have been used for conventional third rail electrification (according to the Gibb Report anyway, for East Grinstead), in this case it would be a 11kV unit substation of the type installed for industrial customers, with the leads on the 400V side crossing the railway boundary into the adjacent railway substation.

And you'd need one every 40m or so, to cope with the shortest trains. And this system would be fitted per track, and at 100 mph line speeds would have to detect the length of train, switch on and switch off during the few seconds for the shortest train to pass. The idea is part way to Dagenham...

Why would it be necessary to only liven the rail below the train?
You gain a very large fraction of the risk reduction with far longer sections, if a rail section is only live for 25% of the time, then you would expect far fewer electric shocks (on order of only 25% as many).

The real interesting idea would be, if tresspass electrocutions occur randomly on all lines rather than running lines (so people in stabling sidings etc), then the risk reduction might be very much greater than that, since using this system you would be able to turn off every siding except the one that had a train in it, or a train that you wanted to move.

 

[AM9]

... The substation would only be a few hundred kilowatts, rather than a megawatt. I often, based on the example of Portland Streetcar, propose substations of about 300-500kW.
11kV feeders have been used for conventional third rail electrification (according to the Gibb Report anyway, for East Grinstead), in this case it would be a 11kV unit substation of the type installed for industrial customers, with the leads on the 400V side crossing the railway boundary into the adjacent railway substation. ...

So it wouldn't really be a case of a connection to residential/small commercial distribution supplies, - instead it would need a dedicated 400V connection to an 11kV substation connection immediately adjacent to the railway boundary at each feed point. Are most railways routed adjacent to substations or are we back to providing an 11kV feed from wherever just to allow lots of 400V feed. If say 8-car trains were run, thats a likely load of 2-3MW so these 500kW feeds would need to be evry 500metres at least near any gradients and stations. There'll be substations needed every km, each with their own 11kV feed.
Mmmm, doesn't look cheaper than a single 25kV feed every 20-30miles (or a 50kV AT feed every 40-50miles). And of course it would have a permanently energised 750VDC conductor throughout at ankle height, so would fall foul of modern safety rules for new installations. No chance!

 

[HSTEd]

So it wouldn't really be a case of a connection to residential/small commercial distribution supplies, - instead it would need a dedicated 400V connection to an 11kV substation connection immediately adjacent to the railway boundary at each feed point. Are most railways routed adjacent to substations or are we back to providing an 11kV feed from wherever just to allow lots of 400V feed

As a side effect of the tendency of railways to run where people live, many railways are surprisingly close to 11kV circuits throughout their length, and in either case the cost of wood-pole 11kV circuit is surprisingly low, and is often considered to be something of the order of £50-100/m.
This should be compared to the price of OLE electrification equipment of something like £5000/m for a twin track railway, in addition even if a parallel feeder has to be provided it can be shorter than the railway since it can go between substations in any pattern that is convenient and can go over over obstructions that a railway cannot.

They would be dedicated unit substations yes, however such units are already routinely provided to industrial customers and the DNO will operate hundreds or thousands (or even tens of thousands!) of such units throughout it's service area - this allows for impressive economies of scale thanks to the permitted specialisation of labour and materials.

. If say 8-car trains were run, thats a likely load of 2-3MW so these 500kW feeds would need to be evry 500metres at least near any gradients and stations. There'll be substations needed every km, each with their own 11kV feed.

My working estimate is for 1000kW train units (essentially a single Class 319, as not many unelectrified railways would expect several eight car trains per hour), but I assume substations every kilometre anyway.

Mmmm, doesn't look cheaper than a single 25kV feed every 20-30miles (or a 50kV AT feed every 40-50miles).

Bespoke installations and 400kV circuits (and AT systems apparently almost certainly require 400kV feeds) are enormously expensive!
And since they constitute points of failure you have to provide for redundancy, so any new significant 25kV scheme is likely to require a new feeder station unless it is pure infill or is sufficiently short that the risk of it being taken out is judged acceptable.
The advantage of 400V substations is that they become purely low voltage installations, which means that earthing and control system requirements and such are drastically less onerous, it could literally be a location cabinet sized device beside the track, and produced on a production line by the hundred at surprisingly low cost.

And of course it would have a permanently energised 750VDC conductor throughout at ankle height, so would fall foul of modern safety rules for new installations. No chance!

Who said anything about it having to be permanently energised?
Aluminium is cheap.
Could provide modern low cost semiconductor switches to the conductor rails if you like [as described above], and run the along-line bus inside a concrete trunking beside the track, like those used for signal equipment.

The capital cost would still be so much less than a 25kV installation that I believe a test installation is justified.

 

[AM9]

... My working estimate is for 1000kW train units (essentially a single Class 319, as not many unelectrified railways would expect several eight car trains per hour), but I assume substations every kilometre anyway.

I didn't mention 'several eight car trains an hour', but the fact is that a even single train may require more than 1MW, however infrequently it may pass.

Bespoke installations and 400kV circuits (and AT systems apparently almost certainly require 400kV feeds) are enormously expensive!

And since they constitute points of failure you have to provide for redundancy, so any new significant 25kV scheme is likely to require a new feeder station unless it is pure infill or is sufficiently short that the risk of it being taken out is judged acceptable.

Not all OLE feed points are connected to 400kV, the thread is about lightly used lines so (possibly) a single feed from either connecting NR routes or 275KV, 132KV or even 33KV could be used.

Who said anything about it having to be permanently energised?

It was discussed upthread and I read it as being marginally safer than powering-up only when in use but hardly worth the additional risk of trespassers then assuming that all 3rd rail lines are similarly operated. To a lay person, one railway looks like another, and the type of person willing to trespass wouldn't take much notice of warning notices anyway.

The capital cost would still be so much less than a 25kV installation that I believe a test installation is justified.

Not as much as you are indicating above because lower feed point costs could be made just as easily, and with fewer locations being required. Also 3rd rail is currently off the table for new schemes and likely to remain so unless a really cynical attitude is taken and retrograde safety standards are allowed in the non-EU Britain. MKI human beings won't have changed much in their vulnerabilities and their immunity to 750VDC.