Every now and then something makes me rethink about this and welcome others to discuss.
In our beloved transit forum I saw
New Russian tram
http://cs.trains.com/trn/f/742/p/230921/2583849.aspx#2583849
narig01Did some looking and found this on the R1http://www.railwaygazette.com/news/single-view/view/russia-one-tram-prototype-revealed.htmlRgds IGN
"Regenerated braking energy could be used to heat the entrance areas to prevent icing"
Maybe great for countries with Russia's 2 month summers and 10 month winters, although I notice the article also says the cars are air conditioned.
But that started me to wonder again what's the best way to use regenerative braking once you've regenerated it? I've always remembered that one pumps the electricity back into the wires so that a braking train can help an accelerating train.
I've heard, and it makes sense to me, that one gets nothing if there's no accelerating train nearby to take advantage of that regenerated power. That's probably not a problem on a transit line with 5 minute headways, but many railroads, even my hometown SEPTA, might have 30 minute rush hour and hourly or worse headways.
Speaking of SEPTA, I had heard about a flywheel arrangement to get around the problem of nobody nearby to use the power.
http://www.scientificamerican.com/article/braking-trains-coupling-with-energy-storage-for-big-electricity-savings/
says they opted for batteries instead, but the article also discusses the pros and cons of battery vs flywheel
if no other train is ready to tap into that power, it is essentially lost ... Andrew Gillespie, SEPTA’s chief engineer... helped install a 1.5-megawatt bank of lithium ion batteries (pdf) at the Letterly substation in Philadelphia, which was among the first attempts in the world to marry regenerative braking and grid-ready energy storage
if no other train is ready to tap into that power, it is essentially lost
...
Andrew Gillespie, SEPTA’s chief engineer... helped install a 1.5-megawatt bank of lithium ion batteries (pdf) at the Letterly substation in Philadelphia, which was among the first attempts in the world to marry regenerative braking and grid-ready energy storage
Trains tend to make a lot of energy braking in a very short time, and it makes sense that a flywheel might be able to capture that better than a battery.
The article also discusses
Supercapacitors have a much higher energy density than batteries, meaning they can charge and discharge extremely quickly; this is useful to meet quick spikes in electricity demand on the rail system. They also can cycle millions of times without degrading whereas batteries have shelf lives on the order of tens of thousands of cycles.
goes on to say SEPTA's next substation will use batteries and supercapacitors, based on results from the pilot installation.
Comments section leads off with a time marches sideways "build the stations higher than the rest of the line", something that early New York elevateds, and if I remember correctly, Montreal subway. This way the grade down from the station helps the train accelarate, and the grade up to the next station helps the train stop.
Patrick Boylan
Free yacht rides, 27' sailboat, zip code 19114 Delaware River, get great Delair bridge photos from the river. Send me a private message
Regenerative braking is both simple and very complicated. Back to basics that many will already know.
1. The Milwaukee electrification is a good start. MKE bought 3 phase AC from utilities. That current operated a 3 phase motor / generator unit that turned a DC generator / motor unit providing 3000 volts DC to the CAT. The MKE train motors picked up the 3000V and used it to power the traction motors lowering the CAT 3000V. If other motors were in the circuit they would also pull the voltage to below 3000V. Any time the CAT line voltage was below 3000V a load controller at the power station would try to provide 3000V up to its load limit.
2. The traction motors when in regeneration would provide some higher voltage (3000 + ) to the CAT Another train needing power would take the excess voltage and apply it to its train and the power station load controller would make up the difference. If no other train in circuit the higher voltage would turn the power station DC generator into a motor that would in turn have the 3 phase motor become a generator. That generated power would return to the utility raising its line voltage which would cause the Utility's generator load controller to allow line voltage to return to its nominal.
3. Have no idea what the +/- values of the voltages were ?
4. That is basically how present day DC systems work, If CAT is DC. Now of course motor generator sets are blasé.
5. AC CAT is a different breed. At first it was the same motor generator power station set up with no regeneration. Later the PRR built rotary converters that internally turned 60 HZ into the 25Hz used. But they were not able to return power to the utility ( that includes HV PRR as a utility ). So as some rolling stock on the PRR side became regenerative capable if no other unit needed power in that circuit the voltage would increase to ~12,600V. Nominal Amtrak 25Hz CAT is now 12,000V up from 11,500. If line voltage 12,600V or higher then dynamic braking takes place. It is required for all regenerating units ( EMUs Motors ).
6. The three phase 60Hz current had a problem at first as the single phase CAT would unbalance the utility system. Now there are special 3 phase input transformers that can provide single phase that keeps the 3 phase balanced both directions.
7. Amtrak has slowly converted their rotary converters and solid state frequency converters so they can move power back to the utility lines., Don't ask how.
8.. NJT, MNRR, and maybe some locations on SEPTA have now installed systems to return power to utilities as well.
9. Have only spotty information as to exactly what features of ALP-44s, -45s, 46s, AEM-7s, HHP-8s have.as well as EMUs Know Silverliner-Vs & M-8s have full regeneration.
10 The ACS-64s have a very interesting set up. Regeneration will first supply current to its 2 HEP packs and other auxiliaries. Excess of those demands will provide some higher voltage to the CAT up to the ~12,600V limit. If other power demands do not limit below the 12,600 then regeneration defaults to dynamic braking.
thank you blue streak 1. Do you, or does anybody else care to lend their knowledge about cost-benefit of using regenerative for hotel power, the ACS-64s very interesting set up regeneration first its 2 HEP packs and other auxiliaries, as well as the fancy Russian tram's proposal to keep the doorways ice free?
A little knowledge messes me up. I thought that electricity is a fluid, but with regenerative fed back into the overhead wires AND hotel power drawing from the overhead wires don't we have a single pantograph per car, or train, that simultaneously feeds braking power back into the wires AND draws hotel power from the wires? Where else do fluids flow 2 directions at the same time?
gardendance thank you blue streak 1. A little knowledge messes me up. I thought that electricity is a fluid, but with regenerative fed back into the overhead wires AND hotel power drawing from the overhead wires don't we have a single pantograph per car, or train, that simultaneously feeds braking power back into the wires AND draws hotel power from the wires? Where else do fluids flow 2 directions at the same time?
thank you blue streak 1.
Obviously I titled this thread wrong. I bet I'd have gotten lots more responses if it was "time for regenerative braking to step up" or "goodbye regenerative braking".
So moral of the story seems to be that it's all a bit more complicated than just having the motors act as generators and magically supply all of a train's or railroad's electrical needs. Electric flow may not act the same as water flow, and I certainly wasn't trying to contradict your answer, but I'm grateful you're stepping up where noone else has yet.
For an aside, on my sailboat I've killed engine batteries because standard operating is to run the engine for only long enough to get out of the mooring field and put up the sails, usually less than 10 minutes, reverse when I return home. Consequently over the course of the season the batteries get frequent starting demand, but very little charging. Add in forgetting to turn off a light coming home Sundays, and voila drained battery the following Saturday.
I bought a 15 watt solar panel which I set out when I leave the boat, so I get some assurance that the batteries get trickle charged when not in use. I wonder what the wiring, and current flow must be on more permanent installations where the solar panels are always connected to the batteries.
Another solar aside, in New Jersey over the past couple of years via government subsidy the utilities have mounted solar panels on what seems to be every roadside utility pole. I don't see very many solar panels on railroad poles, I now wonder why didn't, or if, my state's railroads participate, but perhaps their poles aren't wired to the power grid the same as highway poles.
gardendance [snipped - PDN] . . . I wonder what the wiring, and current flow must be on more permanent installations where the solar panels are always connected to the batteries. Another solar aside, in New Jersey over the past couple of years via government subsidy the utilities have mounted solar panels on what seems to be every roadside utility pole. I don't see very many solar panels on railroad poles, I now wonder why didn't, or if, my state's railroads participate, but perhaps their poles aren't wired to the power grid the same as highway poles.
Over here, NS has several rail lubricators that are solar-powered, even though commercial power is nearby. I've also seen some signals that are solar-powered up in the remote Lehigh River Gorge. Other users are on a case-by-case basis - some billboards, USGS stream monitoring gages, etc. Recently I've even seen a new college campus near Mt. Pocono with 3 parking lots with solar panels over the parking rows (poorly done, IMHO, but that's another story).
- Paul North.
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