4 ms·

Yes. https://tfl.gov.uk/corporate/transparency/freedom-of-information/foi-request-detail?referenceId=FOI-3010-2223 https://tfl.gov.uk/corporate/transparency/fr

Yes. https://tfl.gov.uk/corporate/transparency/freedom-of-information/foi-request-detail?referenceId=FOI-3010-2223 https://tfl.gov.uk/corporate/transparency/freedom-of-informa...

altairprime 1y ago
> If the line is unreceptive, braking energy is dissipated in on-board resistors How many watts are dumped into onboard heat-generating resistors on the trains in the most heat-affected lines per week? Should regenerative braking be disabled in aboveground trains when heat impacts reach uncomfortable levels in belowground tunnels? > Regenerated braking energy is transmitted to the London Underground high voltage distribution network If regenerative braking oversupply is inducing higher temperatures belowground through on-train resistors, then only an operational change to aboveground mode would be required to minimize that induced heating during times of thermal need. (Obviously longer-term solutions with non-zero capital expenditure exist that could be pursued in parallel.)
- cranky908canuck 1y ago
  To me, 'disable abovegound regen' feels like not likely to solve the problem, just from a feeling that those systems are not that closely coupled. Otherwise, it seems easy to just keep on doing regen and set up (maybe not even need to: run a cable up to) aboveground dissipation grids. I will guess that the limit is how much regen current can be passed back from the train into the supply system through the power supply rails / pickup shoes. If I were making (confess, yes, untrained outsider) suggestions, I'd add water tanks to the trains, use the resistive braking to heat the water (not ambient air) during the trip, then change out the now-hot water for cold at the destination layover points. Not thinking this is a particularly creative solution, sounds like the "pull trains full of ice" already noted. Also this is off-the-cuff, so welcoming critiques! Speculate: district level heating (wikipedia entry: https://en.wikipedia.org/wiki/District_heating https://en.wikipedia.org/wiki/District_heating) using heat pumps to draw out the tunnel heat; not sure if that is too complex altogether, maybe it would work as a longterm maintenance process but not as a 'fix the current problem' one...?
- avianlyric 1y ago
  > Should regenerative braking be disabled in aboveground trains when heat impacts reach uncomfortable levels in belowground tunnels? It’s not that simple. You can’t just treat the entire line as some kind of perfect conductor that allows to you move unlimited amounts of energy around. In reality there’s issues with both the conductive capabilities of the lines themselves, but there’s also the simple problem that train lines aren’t generally electrically connected end-to-end for a few reasons. 1. You don’t want trains pulling power down more of the line than necessary, when it’s more efficient to draw power from other parts of the high voltage grid. 2. You don’t want a single track fault to cause your entire line to be forced to disconnect completely. 3. You don’t want your line to accidentally become a power carrier for electrical grid, just because the two ends of your line a physically located far enough apart that they experience different grid conditions. As a result most train lines are broken up into electrically isolated segments, each with its own distinct power supply. So you could turn of regen on overground trains, but unless they happen to be sharing a section of track with underground trains, it doesn’t create any additional capacity to dump breaking energy into.
  - altairprime 1y ago
    Even with isolated segments, the measurements performed with Southern found 10% of regenerative power was turned into heat as the line voltage was already at max threshold from other trains; if that holds true today, then there’s still opportunity to consider optimizations for ensuring that 10% is weighted towards aboveground rather than below. https://railknowledgebank.com/Presto/content/GetDoc.axd?ctID=MTk4MTRjNDUtNWQ0My00OTBmLTllYWUtZWFjM2U2OTE0ZDY3&rID=MTE4&pID=Nzkx&attchmnt=True&uSesDM=False&rIdx=MjU2Ng==&rCFU= https://railknowledgebank.com/Presto/content/GetDoc.axd?ctID... Also: > A super capacitor is being used in a substation by Docklands Light Rail in London, UK So at least they were considering what to do about this fifteen years ago. I wonder if they've made progress?
    - avianlyric 1y ago
      How exactly are you going to “weight” that 10%? Each segment is independent, you can’t “weight” the voltages, because that would require the ability to move power between track segments, which you can’t do, because then they wouldn’t be track segments anymore. Additionally you’re making the assumption that line voltages are stable and constant, and can be tweaked as needed. They’re not, they’re some of the most noisy, electrically unpleasant power systems in the world, with voltage bouncing up and down as trains accelerate and decelerate, consuming up to a MW each under peak load. Power distribution companies hate providing power to train systems because you need so much infrastructure to handle the noise and prevent the train line from seriously degrading the local power grid. The substation that connect train lines to the power grid are constantly having their switchgear trip in and out as the huge spikes in demand cause the equipment to momentary disconnect to protect downstream equipment. So creating headroom for extra regenerative breaking isn’t a simple thing to do. When each train can instantly consume as much power as 10 households all maxing out their power supply, electrical systems stop behaving anything like “normal”.

Yes. https://tfl.gov.uk/corporate/transparency/freedom-of-information/foi-request-detail?referenceId=FOI-3010-2223 https://tfl.gov.uk/corporate/transparency/freedom-of-informa...

altairprime 1y ago

> If the line is unreceptive, braking energy is dissipated in on-board resistors How many watts are dumped into onboard heat-generating resistors on the trains in the most heat-affected lines per week? Should regenerative braking be disabled in aboveground trains when heat impacts reach uncomfortable levels in belowground tunnels? > Regenerated braking energy is transmitted to the London Underground high voltage distribution network If regenerative braking oversupply is inducing higher temperatures belowground through on-train resistors, then only an operational change to aboveground mode would be required to minimize that induced heating during times of thermal need. (Obviously longer-term solutions with non-zero capital expenditure exist that could be pursued in parallel.)

cranky908canuck 1y ago
To me, 'disable abovegound regen' feels like not likely to solve the problem, just from a feeling that those systems are not that closely coupled. Otherwise, it seems easy to just keep on doing regen and set up (maybe not even need to: run a cable up to) aboveground dissipation grids. I will guess that the limit is how much regen current can be passed back from the train into the supply system through the power supply rails / pickup shoes. If I were making (confess, yes, untrained outsider) suggestions, I'd add water tanks to the trains, use the resistive braking to heat the water (not ambient air) during the trip, then change out the now-hot water for cold at the destination layover points. Not thinking this is a particularly creative solution, sounds like the "pull trains full of ice" already noted. Also this is off-the-cuff, so welcoming critiques! Speculate: district level heating (wikipedia entry: https://en.wikipedia.org/wiki/District_heating https://en.wikipedia.org/wiki/District_heating) using heat pumps to draw out the tunnel heat; not sure if that is too complex altogether, maybe it would work as a longterm maintenance process but not as a 'fix the current problem' one...?
avianlyric 1y ago
> Should regenerative braking be disabled in aboveground trains when heat impacts reach uncomfortable levels in belowground tunnels? It’s not that simple. You can’t just treat the entire line as some kind of perfect conductor that allows to you move unlimited amounts of energy around. In reality there’s issues with both the conductive capabilities of the lines themselves, but there’s also the simple problem that train lines aren’t generally electrically connected end-to-end for a few reasons. 1. You don’t want trains pulling power down more of the line than necessary, when it’s more efficient to draw power from other parts of the high voltage grid. 2. You don’t want a single track fault to cause your entire line to be forced to disconnect completely. 3. You don’t want your line to accidentally become a power carrier for electrical grid, just because the two ends of your line a physically located far enough apart that they experience different grid conditions. As a result most train lines are broken up into electrically isolated segments, each with its own distinct power supply. So you could turn of regen on overground trains, but unless they happen to be sharing a section of track with underground trains, it doesn’t create any additional capacity to dump breaking energy into.
- altairprime 1y ago
  Even with isolated segments, the measurements performed with Southern found 10% of regenerative power was turned into heat as the line voltage was already at max threshold from other trains; if that holds true today, then there’s still opportunity to consider optimizations for ensuring that 10% is weighted towards aboveground rather than below. https://railknowledgebank.com/Presto/content/GetDoc.axd?ctID=MTk4MTRjNDUtNWQ0My00OTBmLTllYWUtZWFjM2U2OTE0ZDY3&rID=MTE4&pID=Nzkx&attchmnt=True&uSesDM=False&rIdx=MjU2Ng==&rCFU= https://railknowledgebank.com/Presto/content/GetDoc.axd?ctID... Also: > A super capacitor is being used in a substation by Docklands Light Rail in London, UK So at least they were considering what to do about this fifteen years ago. I wonder if they've made progress?
  - avianlyric 1y ago
    How exactly are you going to “weight” that 10%? Each segment is independent, you can’t “weight” the voltages, because that would require the ability to move power between track segments, which you can’t do, because then they wouldn’t be track segments anymore. Additionally you’re making the assumption that line voltages are stable and constant, and can be tweaked as needed. They’re not, they’re some of the most noisy, electrically unpleasant power systems in the world, with voltage bouncing up and down as trains accelerate and decelerate, consuming up to a MW each under peak load. Power distribution companies hate providing power to train systems because you need so much infrastructure to handle the noise and prevent the train line from seriously degrading the local power grid. The substation that connect train lines to the power grid are constantly having their switchgear trip in and out as the huge spikes in demand cause the equipment to momentary disconnect to protect downstream equipment. So creating headroom for extra regenerative breaking isn’t a simple thing to do. When each train can instantly consume as much power as 10 households all maxing out their power supply, electrical systems stop behaving anything like “normal”.