2 ms·

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 ma

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”.
- altairprime 1y ago
  These are all valid concerns. My goal was to highlight an opportunity for improvement that does not require capital equipment purchases. As you note, analysis may not reveal any opportunity for improving the regenerative controls. Given their inability to address the problem today, I expected they’d rather investigate a low-odds opportunity than disregard it. I was incorrect; I will raise my minimum-likelihood thresholds at HN in the future. ‘Simple’ was meant only in relation only to all other identified options, that each require non-zero capital expenditure and thus invoke the complexities of capital expenditure. It was not my intent to diminish the intricacies or difficulties of rail electrical engineering with my imprecise use of that adjective and I apologize for the disrespect inflicted.

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”.

altairprime 1y ago
These are all valid concerns. My goal was to highlight an opportunity for improvement that does not require capital equipment purchases. As you note, analysis may not reveal any opportunity for improving the regenerative controls. Given their inability to address the problem today, I expected they’d rather investigate a low-odds opportunity than disregard it. I was incorrect; I will raise my minimum-likelihood thresholds at HN in the future. ‘Simple’ was meant only in relation only to all other identified options, that each require non-zero capital expenditure and thus invoke the complexities of capital expenditure. It was not my intent to diminish the intricacies or difficulties of rail electrical engineering with my imprecise use of that adjective and I apologize for the disrespect inflicted.