SEPTA (and the Vienna subway) are said to test a pionieering project the pressetext-newsletter reported. Generators attached to the generate electricity while the m.u. are braking entering stations. The electricity is "stored" in batteries.
For me, it sounds strange and I don't see what's new here, except the batteries. You can use an electric motor as a generator, for example, when a locomotive goes down a grade, i.e. the motor is driven by the speed of the locomotive. It is called regenerative braking and has been practiced for about 100 years on electric railroads. And for the case of the SEPTA, it would seem to me more appopriate to give the electricity back into the SEPTA-system, because you most probably have at the same time a slowing and an accelerating m.u. The latter obviously needs energy to accelerate. Batteriex are expensive to operate and maintain and you lose energy, because their efficecy is way below 100 %
Does anyone more on the SEPTA-project?
Regenerative breaking has been around for years. 1912 West Penn interurban cars had it and hand brakes and generative power powered track brakes and no air brakes. The many electric railcars today have a combinations of air, dynamic (electricity to heat) and regenerative braking. When the voltage is already high becuase of light load, the braking-generated power goes to resistor banks and heat, and when the voltage is low because of light load, the braking energy is generative energy and supplies power to be used elsewhere. In some cases, power is returned to the electric company. What is new here is the use of fixed wayside batteries to store energy that cannot be used ether by the railroad or the power company at times of light load. At least what I have read is that they are wayside, but they could be on the vehicle.
Regenerative braking was a feature of straight-electric rail vehicles virtually from the beginning of electric streetcars. The diesel equivalent, dynamic braking, was introduced while most locomotives were still steamers.
This might be new to some technologically challenged journalist who is ignorant of the history of electric traction. It's old news to even this casual railfan.
Chuck
The difference between this and plain-jane regenertive braking is that, as Dave Kepler points out, regen braking defaults to dynamic braking when the there is no ready consumer of the regenerated power (line voltage is too high). The wayside batteries solve this problem by providing a place to store the power. It can be used to accelerate the same train minutes later.
Especially good for off peak when there are few trains on the line and/or they are so far away that most of the regen braking energy would go to line loss.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
tomikawaTT Regenerative braking was a feature of straight-electric rail vehicles virtually from the beginning of electric streetcars. The diesel equivalent, dynamic braking, was introduced while most locomotives were still steamers. This might be new to some technologically challenged journalist who is ignorant of the history of electric traction. It's old news to even this casual railfan. Chuck
To be fair, how many people outside railroading and our hobby are familiar with the concepts of regenerative and dynamic braking? It's not exactly an obvious concept that jumps out and announces itself.
I think the technical advance is to regenerate electricity on an AC overhead system.
It was easy on a 600 V DC system where it was fairly simple. there was only one voltage and no phases to match.
I assume the SEPTA system uses single phase AC about 12 000V now at 60Hz?
The motors on current rolling stock are probably induction motors working on three phase AC at a variable frequency and variable voltage.
So the present system converts the three phase current from the motors acting as generators to 1000 V DC and then it is inverted and phase matched to the voltage on the overhead line. If it is to be stored in batteries, it would be stored as DC either at the intermediate stage on the vehicles but more likely after another conversion trackside.
It has only recently become economical to use rectifiers and inverters in conjunction with batteries to store power, just as three phase motors are enabled by the same equipment.
M636C
I believe they are going to do this on the 600VDC Market St Subway/Frankfort El transit line.
M636C [snip] I assume the SEPTA system uses single phase AC about 12 000V now at 60Hz? [snip]
Actually, 25 HZ - and no indications that its about to change anytime soon.
It was an 11KV system - I've read that the ex-PRR side was uprated to 12KV some years ago, but I don't know if that happened to the ex-RDG side too.
If you guys are nice to me, I'll see if I can find and post the link for a USDOT-sponsored research report from the 1970's or 1980's that proposed and investigated a similar wayside storage system - except that it was based on mechanical flywheels, if I recall correctly. I've accessed and printed portions of it within the last year, so there's a good chance it's still available on-line . . .
- Paul North.
The report would be interesting to read.
AFAIK, Amtrak wanted to change the NEC between NY Penn Station and Washington D.C. to 50 (60?) Hz but didn't do it although 25 Hz is outdated today. Nobody would build that if he had to build from scratch.
Regenerative braking is not new to A.C.-traction either.
martin.knoepfel [snip] AFAIK, Amtrak wanted to change the NEC between NY Penn Station and Washington D.C. to 50 (60?) Hz but didn't do it although 25 Hz is outdated today. Nobody would build that if he had to build from scratch. [snip]
True enough - that's been on the 'wish list' for decades now. However, with the advent of modern control systems, the frequency of the catenary power matters less, as I understand it. The trend of new equipment is to have it capable of operating on either frequency, and also for the input power - again of either frequency - to be first rectified into DC, and then 'chopped' into the variable frequency for the AC motors. However, there are many auxilliary systems - mainly the signal power now - that is also fed off the 25 Hz power supply, and those are in the process of being changed to dual-frequency equipment. In any event, I understand that Amtrak is even now rebuilding the Lamokin frequency converters to still run on 25 Hz with 'Recovery Act' funds, and still has at least one 25 Hz generator at the Safe Harbor Hydro-Electric generating station.
On SEPTA, I believe there is only 1 class left of the early SilverLiners that can't operate on 60 HZ, and those will be retired when the current order of SL-5's is placed into service.
Since you're interested, I'll try to post some of those links later today. A few I retrieved on Friday were close, but not quite right . . .
Paul_D_North_Jr If you guys are nice to me, I'll see if I can find and post the link for a USDOT-sponsored research report from the 1970's or 1980's that proposed and investigated a similar wayside storage system - except that it was based on mechanical flywheels, if I recall correctly. I've accessed and printed portions of it within the last year, so there's a good chance it's still available on-line . . .
This is one that's close, but not quite the one I had in mind - it's from Canada, in 1982 - 1984 . . .
http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4504441
Also not quite right, but considerably more recent, from 2009 -
http://tris.trb.org/view.aspx?id=916509
Closer -
http://www.fta.dot.gov/documents/RFA-D2008-ENR-TRV-TRI_Energy_Storage_for_Rail_Transit_Operation_RFA.pdf
A California company - Pentadyne Power Corp. - that makes flywheel systems, and says it has sold over 1,000 of them since 2004 -
http://www.railway-technology.com/contractors/electrification/pentadyne/
You can also look for yourself - I searched for the phrase "wayside energy storage" plus the word "rail" . . .
I think this is a summary of the article -
http://adsabs.harvard.edu/abs/1979amc..rept.....L
And this is an abstract for it -
http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=5749945
BINGO ! OK, here's the link to "WAYSIDE ENERGY STORAGE STUDY - Volume IV - Dual Mode Locomotive: Preliminary Design Study", Report No. FRA/ORD-78/78, IV, by L. J. Lawson and L. M. Cook, AIResearch Manufacturing Company of California, Torrance, CA 90509, FINAL REPORT - February 1979, for the US DOT and FRA; 58 pgs., approx. 1.55 MB in size
395.0973, Un386ord, 78/78.4; TF - 975 - .A47 - V. 4.
http://www.fra.dot.gov/downloads/Research/ord7878-IV_Wayside_Energy_Storage_Study_Volume_IV.pdf
A companion study for a FLYWHEEL ENERGY STORAGE SWITCHER, Report No. FRA/ ORD-79/ 20.1, April 1979; 346 pgs., approx. 9.10 MB in size, is at -
http://www.fra.dot.gov/downloads/Research/ord7920-1_flywheel_energy_storage_switcher.pdf
The FRA Office of Research and Development webpage where I found these goodies is "Research Reports - Published prior to 2000" at -
http://www.fra.dot.gov/rpd/policy/1717.shtml
Enjoy !
Thanks for the links. Lot of interesting reading-stuff for the next weekend.
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