Freight over 3rd rail

[norbitonflyer]

This is probably a bonkers idea, but would it be feasible to boost the power at selected places by installing a second third rail on the other side? Or would this fry the running rails?

Not sure that would actually have any effect - both rails would be at 750V, and any limitations on current draw would not be in the live rail but in the internal resistances elsewhere in the circuit (substation or loco).

 

[hwl]

What challenge is that? What would be the point when 750V is clearly inadequate for anything other than metro operations.

Much of the 3rd rail network has been upgraded in place so it isn't as bad as it used to be. The available power for a train varies between 0.75 and 1.5 Class 66s (based on electrical power available to traction motors).

A modern loco would be much more efficient.

Not sure that would actually have any effect - both rails would be at 750V, and any limitations on current draw would not be in the live rail but in the internal resistances elsewhere in the circuit (substation or loco).

The resistance of the running return rail also has significant effect hence using the heaviest section rail, CWR and audio frequency track circuits or axle counters will help.

 

[Carlisle]

Is there actually that many flows though? .

If it’s possible to design something also capable of hauling freightliner sized trains for reasonable distances on unelectrified lines then yes, if it isn’t, probably not, until more electrification has been completed

 

[73128]

At a recent virtual meeting about class 93 speaker advised that 750dc was originally in plans but had to be taken out because of space and weight constraints.

There's a good piece by Ian Walmsley in the current Modern Railways. Not about Class 73s or third rail but the issue of electric freight haulage, timings and multiple modes. The upcoming class 93 is already tri mode - if it became a quad mode it would gobble up all southern freight at a canter.

 

[popeter45]

750V DC was entirely adequate for freights to / from the Channel Tunnel, hauled by class 92s.

they had to specally upgrade curtain routes for these (same as the 373's) and the second they could they moved these over to HS1 so they could use the OHEL it has

 

[zwk500]

they had to specally upgrade curtain routes for these (same as the 373's) and the second they could they moved these over to HS1 so they could use the OHEL it has

Having to upgrade the power supply doesn't mean that 750V DC third rail is useless for freight though, just that the total draw on the section was expected to be more than the system supplied (because it had been installed 30+ years ago). It happens with OLE lines as well when services are upgraded. The freights moved onto HS1 for access to Ripple Lane and to avoid congestion in South London rather than being desperate to use the OLE.

750V DC is perfectly fine to haul freight on - it's operational and economic concerns preventing greater use of electric traction (as it is under OLE).

 

[D365]

I wouldn't necessarily call a lot of routes in 3rd rail land metro operations (although plenty in London are)

Exactly my point. Third rail is not ideal for those inter-urban routes, especially when freight comes into the picture.

Having to upgrade the power supply doesn't mean that 750V DC third rail is useless for freight though, just that the total draw on the section was expected to be more than the system supplied (because it had been installed 30+ years ago). It happens with OLE lines as well when services are upgraded.

The difference is that boosting the DC supply is far more costly. The need for a far greater number of substations and associated land costs. Never said that third rail freight is impossible. What I'm saying is that, in comparison to 25kV AC, it isn't ideal.

If we're going to entice freight operators to switch to electric haulage, offering performance "equivalent to a Class 66" isn't exactly a great carrot.

 

[zwk500]

What I'm saying is that, in comparison to 25kV AC, it isn't ideal.

Totally agree on that point.

If we're going to entice freight operators to switch to electric haulage, offering performance "equivalent to a Class 66" isn't exactly a great carrot.

Tbh you don't need to entice freight operators, they're fairly keen to use electric traction. But you do need it to make economic and operational sense for them. 'equivalent to a Class 66' is actually fair enough, but 'need a new loco' or 'needs loco change en-route' is not.

 

[hooverboy]

At a recent virtual meeting about class 93 speaker advised that 750dc was originally in plans but had to be taken out because of space and weight constraints.

Perhaps this is yet another reason why some form of lightweight,low RA DC/AC/Hybrid loco would be very useful on the network.

A short wheelbase bo-bo weighing in at 75 tonnes ish and 16-17m long,with a reduced traction pack from the proposed 93 would be just the ticket.

650-700kW traction motor*4

2.5MW capable on AC or 750VDC - a reduction on cl93 4MW rating, but still comparable to single class 86 or 2*CL73.

Caterpillar c32B triple turbo engine(1400Hp approx) +600kW battery,maybe solid state if the technology is sufficiently developed. That gives cl 31/33 performance at the very least in diesel only mode, considerably more when you add in traction control and battery assistance.

 

[zwk500]

Perhaps this is yet another reason why some form of lightweight,low RA DC/AC/Hybrid loco would be very useful on the network.

A short wheelbase bo-bo weighing in at 75 tonnes ish and 16-17m long,with a reduced traction pack from the proposed 93 would be just the ticket.

650-700kW traction motor*4

2.5MW capable on AC or 750VDC - a reduction on cl93 4MW rating, but still comparable to single class 86 or 2*CL73.

Caterpillar c32B triple turbo engine(1400Hp approx) +600kW battery,maybe solid state if the technology is sufficiently developed. That gives cl 31/33 performance at the very least in diesel only mode, considerably more when you add in traction control and battery assistance.

This is quite a specialised design, which will increases costs and restricts potential orders. Most of the freight in 3rd rail area is Aggregates, which needs tractive effort and grip as well as raw power, so a lightweight 4-axle loco could pose issues.

The sense I've got from other threads (which may be very wrong) is that to fit within the UK loading gauge it tends to be a choice of Dual voltage or bi-mode (at least to keep within a reasonable cost). If it can be managed, what might be more feasible is a Dual-Voltage loco with last-mile batteries. The batteries would be smaller and more space-efficient than a diesel engine, allowing the 2 sets of electrical equipment to be accommodated. This would be combined with infill electrification in the London area.

 

[randyrippley]

This is probably a bonkers idea, but would it be feasible to boost the power at selected places by installing a second third rail on the other side? Or would this fry the running rails?

Or emulate the London underground with a 4th centre rail at -750V while the normal third rail remains at +750V?
The running rails would be a common return for both

 

[Nicholas Lewis]

Or emulate the London underground with a 4th centre rail at -750V while the normal third rail remains at +750V?
The running rails would be a common return for both

LU is nominally 450V on third rail and -200V on fourth rail and is done to ensure current is kept in the traction circuit and doesn't escape and cause electrolysis issues with the tunnel linings ie erode them!

The real limit with third rail is managing the high currents at the interface with the shoegear and that circulating in the power cables and traction return paths and in particular not saturating track circuits so they don't become unreliable with unnecessary right side failures when infrastructure is compromised by broken rails, blown block joints and damaged cables. A move to axle counters could potentially liberate a higher current level although that would increase losses further. Class 92's on DC aren't lightweights with 5400hp available so not sure we need anything more and many routes have much higher conductor rail index since the power reinforcement works that have been undertaken.

 

[43096]

This is quite a specialised design, which will increases costs and restricts potential orders. Most of the freight in 3rd rail area is Aggregates, which needs tractive effort and grip as well as raw power, so a lightweight 4-axle loco could pose issues.

The sense I've got from other threads (which may be very wrong) is that to fit within the UK loading gauge it tends to be a choice of Dual voltage or bi-mode (at least to keep within a reasonable cost). If it can be managed, what might be more feasible is a Dual-Voltage loco with last-mile batteries. The batteries would be smaller and more space-efficient than a diesel engine, allowing the 2 sets of electrical equipment to be accommodated. This would be combined with infill electrification in the London area.

What the freight operators will want is a loco that is flexible: i.e. it can haul various train weights, at up to 75mph and that can be easily re-deployed as traffic is won and lost (so is go-anywhere). Such locos are far more attractive for leasing companies, too, as the residual value is higher because they are more easily re-leased. Class 66 is a good example.

 

[zwk500]

What the freight operators will want is a loco that is flexible: i.e. it can haul various train weights, at up to 75mph and that can be easily re-deployed as traffic is won and lost (so is go-anywhere). Such locos are far more attractive for leasing companies, too, as the residual value is higher because they are more easily re-leased. Class 66 is a good example.

Totally agree