Here are the major problems I see with a flywheel.
Power transmission.
A) There would have to be a motor to turn the electric energy into work to rotate the flywheel.
B) There would have to be a generator to convert the engery in the flywheel into electrical energy. Alternative, there would have to be a complex mechanical or hydraulic power transmission system to deliver power to the wheels.
Safety, this would probably have to be a large flywheel turning at high speeds. If it does come apart there will be shrapnel flying. However, thick steel and/or concrete used for weight may provide the necesary protection.
Coriolis effect, the bearings will need to take a large torque.
In conclusion, this is something that can be done. However, calculations, and probably test, will need to be performed to determine if this is economically feasible.
My rough recollection was that about one third more power was available in dynamic braking than in traction, since it was based on motor limits, not on the prime mover.
Paul, that’s an idea I had been wondering about for a long time. You have the savings in reduced fuel consumption, need for fewer diesel units (albeit probably more expensive with the modifications), and the expense of the cantenary is restricted to the major grades.
When the GN and Milwaukee were still running electrics and diesels together, I wonder if this option was even technically available to motive power engineers in the 1950’s and 1970’s?
A better solution is the idea of “the compatibles”. Electric and diesel locomotives designed to either work singly or as pairs, with the electric being the “road-slug” for the diesel when off wire, and the diesel being the “road slug” for the electric when under catenary (or over third rail, probably centered Lional Like, just in tunnels and the approach overlaps to avoid clearance problems). Jumper cables between, just like between a diesel and a road slug, except that the cables are the steady traction power and control is via conventional train-line multiple unit controls.
If Harrisburg (Enola) - Pittsburgh (Conway?) and Council-Bluffs - Sacramento were proved good freight electrification lines, such power could still run through beyond the limits ofo the wire.
You’re correct, you caught me ! I gave the #s for a single grid set. The actual firgures are a bit higher. Max grid current is 700 amps, therefor since a pair of motors are connected in series to a pair of grids the formula is as follows: 1.72 grid ohms Times 700 grid amps =1204 grid volts. 1204 grid volts times 700 grid amps = 842800 watts. divideby efficiency factor of 700 = 1204 horsepower times 3 sets of motor/ grids= 3612 total braking horsepower.
I couldn’t sleep last night because that original figure seemed too low, I simply forgot how many wheels an SD40 had.
Randy
I recall reading about some B&O (?) locos that were “specially ballasted” for some heavy haul service - on a grade as I recall. Think I’ve seen other similar examples, but it does prove the point.
Concrete for ballast always seems like such a good idea, until you try it.
A short story.
When Conrail was rebuilding NJTs GP40Ps, the rearragement of equipment meant that some ballast was needed in the front to keep the weight distribution even front to rear. Us engineering types calculated how much and where to put it. We told Juniata to weld some steel below the front walkway - there’s room there above the draft arrangement and between the frame rails. The local mgt at Juniata thought that was a lot of trouble - so they decided to fill that area with concrete instead. This caused three problems. First, that area was not water tight and the concrete oozed out. Second, once they go it to stay put - it didn’t weigh enough to fix the imbalance. And third, they had to chip it all out and weld in steel - like we told’em in the first place! Juniata is like that…
This has actually been studied, well 20 years ago or so, anyway. From memory, the biggest issues were the economics and safety.
You’d use a motor/generator to spin the flywheel up and to reclaim the energy. In this era of computer controlled, high power semiconductors (GTOs et. al.), this would not pose any engineering problems.
The torque reaction to change in angular momentum (gyroscope effect) could be minimized by mounting the flywheel horizontally. You’d have no reaction to hoziontal curves, only change in grade or locomotive carbody roll. If this was still a problem, a pair of flywheels rotating in opposite directions at the same speed could be used. They would cancel each other out.
I like the idea of partial electrification. Altho not in a form of electric-desel mutual slugging :).
What I envision - all diesels being fitted with machinery to share power - effectively slug each other (and for example - keep engines warm without the need for idling). This way when an engine of one unit dies - the train will not lose traction - less stalls.
But - the system benefits mostly in difficult streches of the railroad, where diesels are not powerful enough, or artifically ventilated tunnels were drilled (Moffat or Cascade tunnles come to mind).
On such stretches a powerful electrics would be provided to lead the train through - and would power the diesels - which could idle/be shut down (depending on the length of the stretch).
Since difficult railroad = mountains then such electrics could use dynamic brakes to power up other trains. If there was no train to power, then farms of flywheels (or small hydro plants) would be powered (energy from which would be used was climbing up) and if that fails - then the energy would be dumped through resistor grids.
I thought that CSX has fairly recently ordered GE’s…either Dash Nines, or AC4400’s with extra ballast in them for heavy-haul service. Dave Williams http://groups.yahoo.com/group/nsaltoonajohnstown
Sounds like the way my teenage sons drive - ma***he throttle - slam on the brakes - and idle to watch the girls.
On a more serious note, the Active Power flywheel energy storage system encloses the flywheel in an evacuated chamber. This allows them to use a smaller flywheel at much higher RPM. Thus the directional issues should be minimized. The flywheel uses composite materials and is designed so the the first failure mode is delamination. Thus in the rare event that it does self destruct - it turns into something more like a feather duster as the layers separate - rather than shrapnel.
I know that there has been research on use of flywheels in city transit in Europe but do not the the current status. That leads me to believe that the initial applications were not economically successful. Still it sounds like an interesting area for potential research.
Composite flywheels in vacuum are a fantasic technology that almost works.
the problem isn’t the rotors or the motors, or even the vacuum. it’s the bearings. supporting 20 lbs rotating at 250kRPM is hard enough without vibration and shock to deal with. magnetic levitation bearing technology sshows promise, but are particularly sensitive to orientation changes.
if anyone has ever played with a conventional steel gyroscope toy, you may have encountered a mode where a sharp jolt or several well-timed nudges can get the whole assembly to wobble violently around its center of mass at something near the fundamental rotational speed of the rotor. (try it sometime with a bike wheel)
when a power-storage flywheel gets into that mode, the forces are usually sufficient to destroy the rotor. As Dldlance points out, the composite sort usually don’t get far outside their containers, but there’s still all that energy being released as heat, noise and vibration-- something akin to dynamite exploding inside the can; it happens about that fast-- a memorable experience, according to a co-worker. Even though the rotor is contained, the energy has to go somewhere. . . I’m not saying the problem is unsolvable, just that it hasn’t been solved for mobile applications yet.
Wire hybrid: Neat idea, and workable with todays’ technologies, but (as MWH likes to explain) capital intensive. (Though once the initial investment is in place, the incremental cost to add trains is attractive. Any government policy makers in the house? Here’s a place where throwing money at a problem might do some good.)
It also moves a portion of the emissions produced moving goods over hills to large, fixed places where they can be more effectively mitigated, and allows the USA’s HUGE stocks of coal to be directly used as a primary power source to transportation.
Another advantage (from a railroad point of view) is all those diesels that are idling to stay warm could earn money
The FRA and the US DOE have had a program to develop a flywheel energy storage unit for locomotive use for a number of years now. Last I read this was proceeding forward and the flywheel system had been built and tested in stationary applications. It’s supposed to be mounted in an old Bombardier LRC body and mated to a Bombardier HST 5,000 HP “Jettrain” locomotive. I’ve also read that several freight railroads have studied the concept for use with conventional diesel engines…
Stationary flywheels work well - we have a client with several in service in Europe and are looking at additional installations. But as crazytechie says - getting them to work reliably in transport service is another thing. I will watch those experiments with great interest (from a distance.)
crazytechie: I hadn’t considered sending the electricity to the power grid before. You could set up a caternary system that only receives power from the locomotives, just on stretches with heavy dynamic brake use, and where your locomotives will be idling for extended periods. Transmitting the electricity from the braking-heavy areas shouldn’t be much of a problem with modern voltage converters and whatnot. I’m not really sure how the power grid would handle spikes in power like that, so I don’t really know if that would be an issue.
This way you don’t have to worry about scheduling to make sure that you’ve always got a train going uphill whenever you’ve got another locomotive using the brakes.
that’s the beauty of being grid-connected: when a locomotive goes into dynamic and starts pumping power into the system, all the other gensets’ load-sensing regulators back off a smidge. The national grid has several TW installed, and runs close to capacity. Even figuring a dozen trains each with 4 or 5 locomotives each dumping 0.75MW into the grid, that adds up to 42MW-- about what a single modern Aeroderivitive natural-gas fueled peaker set puts out; peanuts to the grid as a whole.
the big question is what an unpredictable +/- 42MW, (envelope) semi-chaotic swing would do to local line conditions; It might be smart to insulate the rail grid from the consumer grid with a series of storage stations; small pump/generate hydro, superconducting loops or a flywheel farm could absorb the shocks both outgoing and incoming. At the same time you could frequency convert so rail could run on a more convienient frequency. (DC, 25Hz, 400 Hz have all been suggested as possible substitutes)
Out here in Kalifornia, we’re trying to corner the market on those Aeroderivitive plants to keep from having blackouts again. There really are a lot of those going in, and they’re designed to be fast response-- something like 90 seconds from ‘secured’ to full output, and even faster to regulate to local line conditions. So even without “buffer” stations between the RR and the consumer, I think the grid would be OK, assuming proper frequency stabilization.
OK – so I ran some numbers on using dynamic braking to generate power to the grid. I used the grade from Soldier Summit down to Thistle Junction in UT (ex DRGW) as an example. That grade drops about 2000 feet of elevation in about 27 track miles for an average grade of -1.4%. It has good access to the grid with power generating stations at Helper and Price.
If we make the following assumptions:
8 trains per day
4 locomotives per train (2 lead + 2DPU is common practice for the climb from Helper to Soldier Summit)
Average downhill speed 25 mph (a train covers that stretch in about 1 hour)
Max braking power of about 2.5 MW per locomotive (per Randy’s corrected numbers)
No efficiency losses
cost of catenary about $1 million per mile ($27 million)
average revenue $0.4 per KWhr
That stretch would generate about $1.1 million per year in gross power revenue. Assuming no maintenance costs and neglected the cost of adapting the locomotives, payback is almost 25 years.
Ok, since we’re in scribble-on-envelope mode here, i spliced in a few of my own numbers:
(and using your simplifiying assumption of 100% electrical efficiency)
-off-road Diesel Fuel, Delivered to the property: $1.00/ Gallon
-prime movers produce roughly 14hp/hr per gallon in notch 8 (that’s a number out of the air based on aircraft numbers that are 15 years old; modify to suit)
-8 trains down implies 8 trains up the same grade, same time at max power (might be a bit of a stretch, but we’re playing here. Up time seems like it would be longer than down.)
-neglecting costs of converting the locomotives (might be reasonable as the locomotives could be used on many ‘wire-hybrid’ grades)
-assuming free maintenance of wires and connections (emphatically NOT valid, but again, we’re playing with numbers here)
-50% power gets recycled in moving trains up-grade, also ‘billed’ at $0.04/KwH
I come up with just shy of $2k/day in avoided cost of diesel, which, when added to your numbers gives an ‘accelerated’ payback of 15 years or so.
On the face of it, I agree: that’s not a terribly tempting investment, even at today’s low interest rates. (which i see we’ve neglected)
I predict, however, that the rate of increase in the cost of grid power will be lower than the rate of increase of diesel fuel; particularly with the available sources of low-sulphur crude shrinking and the EPA already thinking about Tier III. So that improves the return on investment a bit.
Then some improvement in traffic control might be feasable, based on someone’s “micro-block” suggestion, and might get more trains over the hill (up and down) which would bring the payoff horizon closer still.
the question becomes one of “when does the payoff horizon get close enough?” I submit that we (as a nation) are going to be increasingly in competition with China and the pacific rim nations for all mineral resources, not just oil; and that the longer we
The hill that I chose is interesting because some of the coal mines are at the top of the hill. So over the stretch of track we are looking at the major traffic pattern is empties up and load down.
I agree with your assessment, crazytechie, this is just close enough to reality to be worth further consideration. The wire maintenance costs may be a killer in the long-term but for the first ten years, they ought to be reasonable. Snow might be an issue here.
Intelligent thinking. Goes along with upgrading the power companies transmission lines and better electric power for the future. Tunnels would not have to enlarged if DC 750 volt center Lional style third rail was used in the tunnels, a pefectly feasible option. I’d stick with the same 25,000 or 20,000 volt 60-cyle AC for catenary even if the power company’s transmission lines are dc, for reasons of safety and easy voltage boost or cut. But the two prime candidates for electrification in my view are Omaha - Ogden and Harrisburg - Pittsburgh. Traffic density.