3 ms·

I'm wondering whether it might become even more cost-effective if it can run off of third-rail electrification (the form factor makes overhead catenary impracti

by dhosek 5y ago

I'm wondering whether it might become even more cost-effective if it can run off of third-rail electrification (the form factor makes overhead catenary impractical). That said, the issue about last-mile rails having been removed is very much a big issue. There was once a rail spur in downtown Chicago along Kinzie Avenue to serve printing plants at the Sun-Times and Tribune which is no longer maintained, although I'm not sure if there's a good use case for it even with these sorts of cars (IIRC it originally ran to loading docks off the river in an area that's now luxury condos). I remember a few years back going for a run nearby and watching workers tear up the rails from another rail spur off the Illinois Central¹ tracks. ⸻⸻⸻ 1. Like many a Chicagoan, I have a tendency to refer to things by long-superseded names that no longer apply. I honestly could not tell you the name of the current owner of that right of way.

bluGill 5y ago
Third rail cannot deliver nearly as much power as overhead for voltage reasons. It might work for short lines where you don't need speed, but not for mainline
- Symbiote 5y ago
  It mostly-works and is used in South East England (including South London + some bits), both for passenger and freight trains. The top speed is about 160km/h. I don't know if the maximum weight or length of a freight train is reduced vs. overhead catenary. However, it's more expensive to maintain and more dangerous to staff and the public. There's a very, very long term policy aim to convert everything to overhead catenary.
  - iggldiggl 5y ago
    It might sort of work, but it's still less than ideal: - A Class 92 in DC mode is limited to 4 MW, whereas on AC it can output 5 MW (and other, more modern four-axle electric locos manage 6.4 MW), and even that 4 MW capability already required significant infrastructure upgrades (I think they basically had to double the number of substations along the designated freight corridors between the Channel Tunnel and London) - Anecdotally, even with just passenger trains on some heavily trafficked sections of route they're running into the problem that the current draw becomes so high that it becomes hard to distinguish between regular operations and an earth fault (and building even more substations isn't cheap, and if you compare it with the amount of substations you'd require for high voltage AC…) - At switches and crossings you get unavoidable gaps in the third rail, and especially at the complex track layouts around some of the larger stations those can occasionally combine into gaps of substantial length. Multiple units with distributed traction (which have dominated passenger traffic on the Southern Region for a long time) can handle those better because there are pickup shoes distributed along the whole length of the unit, plus possibly a traction power bus connecting those pickup shoes together (at least within a single three-/four-/five-car unit). So all in all it's relatively unlikely that a multiple unit will find itself completely off the traction supply ("gapped"). With a freight train powered by a single locomotive on the hand, power supply to the locomotive will always be interrupted by anything but the very smallest gap in the third rail, which means that the tractive effort gets interrupted on each of those occasions (and to avoid jerking the couplings you want to turn off and re-apply power smoothly, and especially the former will make driving more complicated), you need to power the loco's auxiliary systems through all those interruptions, and if the train comes to an unscheduled stand within a junction (whether due to a technical fault, external influences like trespassers, a driver error, or whatever…) there is a much higher risk that the train ends up gapped and will then cause quite a bit of delay until you can somehow get it going again (if you're very lucky the track gradient might get the train rolling again, otherwise you either need to connect up some extensions leads up to the loco or else give it a push with another train/loco, all of which takes quite some time to set up).
- dhosek 5y ago
  It works just fine for the “L” here in Chicago. I'm not sure how the convoys would work in terms of power drain, my EE knowledge is pretty much zip, but since this would be for last-mile transportation by and large, I think it would be ok. The biggest concern would be public safety, I imagine.
  - bluGill 5y ago
    For lightweight passenger cars it is okay. Freight is a lot more mass to get moving. Is also means you have a lot more expensive infrastructure costs as the relatively low voltages means more substations
    - dhosek 5y ago
      I guess what I'm thinking is this battery-powered system augmented by third-rail to improve range/time of operation.

by dhosek 5y ago

bluGill 5y ago

Third rail cannot deliver nearly as much power as overhead for voltage reasons. It might work for short lines where you don't need speed, but not for mainline

Symbiote 5y ago
It mostly-works and is used in South East England (including South London + some bits), both for passenger and freight trains. The top speed is about 160km/h. I don't know if the maximum weight or length of a freight train is reduced vs. overhead catenary. However, it's more expensive to maintain and more dangerous to staff and the public. There's a very, very long term policy aim to convert everything to overhead catenary.
- iggldiggl 5y ago
  It might sort of work, but it's still less than ideal: - A Class 92 in DC mode is limited to 4 MW, whereas on AC it can output 5 MW (and other, more modern four-axle electric locos manage 6.4 MW), and even that 4 MW capability already required significant infrastructure upgrades (I think they basically had to double the number of substations along the designated freight corridors between the Channel Tunnel and London) - Anecdotally, even with just passenger trains on some heavily trafficked sections of route they're running into the problem that the current draw becomes so high that it becomes hard to distinguish between regular operations and an earth fault (and building even more substations isn't cheap, and if you compare it with the amount of substations you'd require for high voltage AC…) - At switches and crossings you get unavoidable gaps in the third rail, and especially at the complex track layouts around some of the larger stations those can occasionally combine into gaps of substantial length. Multiple units with distributed traction (which have dominated passenger traffic on the Southern Region for a long time) can handle those better because there are pickup shoes distributed along the whole length of the unit, plus possibly a traction power bus connecting those pickup shoes together (at least within a single three-/four-/five-car unit). So all in all it's relatively unlikely that a multiple unit will find itself completely off the traction supply ("gapped"). With a freight train powered by a single locomotive on the hand, power supply to the locomotive will always be interrupted by anything but the very smallest gap in the third rail, which means that the tractive effort gets interrupted on each of those occasions (and to avoid jerking the couplings you want to turn off and re-apply power smoothly, and especially the former will make driving more complicated), you need to power the loco's auxiliary systems through all those interruptions, and if the train comes to an unscheduled stand within a junction (whether due to a technical fault, external influences like trespassers, a driver error, or whatever…) there is a much higher risk that the train ends up gapped and will then cause quite a bit of delay until you can somehow get it going again (if you're very lucky the track gradient might get the train rolling again, otherwise you either need to connect up some extensions leads up to the loco or else give it a push with another train/loco, all of which takes quite some time to set up).
dhosek 5y ago
It works just fine for the “L” here in Chicago. I'm not sure how the convoys would work in terms of power drain, my EE knowledge is pretty much zip, but since this would be for last-mile transportation by and large, I think it would be ok. The biggest concern would be public safety, I imagine.
- bluGill 5y ago
  For lightweight passenger cars it is okay. Freight is a lot more mass to get moving. Is also means you have a lot more expensive infrastructure costs as the relatively low voltages means more substations
  - dhosek 5y ago
    I guess what I'm thinking is this battery-powered system augmented by third-rail to improve range/time of operation.