The threads on energy and the SP runaway (an others) have got me thinking about dynamic braking. In mountain railroading with a heavy train - such as a coal train, what percentage of time on the downhill grade is dynamic braking in use? I suspect that the answer depends on the locomotive model and whether is is AC or DC.
dd
What I thought the question was going to be was how much (ie wattage) power was generated, and thus had to be dissipated by the grids. But the original question is a good one, too.
On the electric roads, that power was put back into the system, often helping power another train up hill elsewhere.
If you want to know how much power thats easy, On an SD40 the power expressed in watts is about 522900 watts in braking.
Randy
so if I were thinking in terms of dynamic brakes solely as a power generating device - it has the capability of about 1/2 megawatt at full load?
dd
right – or, very VERY roughly (before Randy jumps on me) about 600 horsepower…
Is there anyway that the Power could be banked in Batterys so it is not waisted?
As I thought - my subject question what is the horsepower equivalent of a dynamic braking system has been easily answered. Thanks to the smart people who participate in this furm.
However, my second question - how much of the time is it used - is also a part of the power equation.
Based on the information thus far, the collective dynamic braking systems of the continent’s railroads represent a batch of small, randomly intermittent generators, operating in generally remote locations, and often in economically less rewarding time periods.
Hard to make the argument that its worth doing anything with other than just braking.
Comments?
dd
The duty cycle of a locomotive is really terrible from a productivity standpoint. A locomotive spends the bulk of it’s lifetime in idle ! Other duty cycles depend on the specific railroad. If you were to compare the N&W and the IC the N&W would be the harder working engine of the two, both up hill and down. The IC didn’t even have dynamic brake equipment until recently.
Randy
It would be difficult to find space for batterys that will be big enough to absorb 500,000 watts of power.
Randy
Except that there is technology known as energy storage systems, such as batteries, flywheels, etc. The idea being that you store the energy generated during braking and then use it during power demands, thus saving fuel. It is irrelevant whether the power is generated out in the boonies, or on an intermittent basis, it would be stored as it is generated. The question then is whether these systems would be more of a problem to deal with than the value of the stored energy itself.
Yes let’s look at alternative energy storage technologies:
Battery - as Randy pointed out it is hard to find space for 500,000 watt/hours of batteries. That’s about 2,000 Die Hards - of course there are denser battery technologies but even at double the storage density that is still 1,000 Die Hard equivelents.
Flywheel - this one has real possibilities. One of the major manufacturers of flywheel storage devices is based here in Austin and I have been fortunate enough to see their prototype but 500,000 watts is still a tall order for flywheels. In addition, the complexities of having 2 generators in a locomotive would add at lea
Also… the engines burn the fuel by keeping the cylinder hot. No need for a spark. With so much power availible to DRIVE the traction motors, batteries would be kind of irrevelant. Once the power quits or goes down and you suddenly need the battery for something… there is no power being dynamically generated.
Regarding energy storage, a while back someone mentioned super capacitors being developed by Siemens. Anyone know anything about this energy storage technology?
Besides flywheels, fuel cells are another alternative energy storage device. The power being stored is usually used to separate water into hydrogen and oxygen which can then be re-burned to produce energy when needed. I don’t know if fuel cells would be lighter than batteries but they are more effcient storage devices.
One of the dings on battery storage is, I think, not really applicable. Modern diesel locomotives have a fair amount of “dead space” down low. It is my understanding that much of this space is filled with concrete (heavy & cheap) in order to boost the locomotive’s weight. If so, some of that space can be used for batteries instead, without any loss of tractive effort.
Plus, they would probably be lead-acid batteries. How much energy would be wasted hauling all of these around all the time? It would not be worth it.
If a railroad has a SD40-2 that was always hauling heavy trains around at low speeds the added weight might not be detrimental. However, I am sure any large railroad that this would be applicable to (and probably EMD & GE) have investigated this and found that this is not worth the cost.
In regards to the concrete, perhaps you are thinking about slugs.
Something else that I should point out that tractive effort is limited by three factors. How much power can be delivered to the wheels, the weight of the locomotive, and the coefficient of kinetic friction between the locomotive wheels and the rails. The more a locomotive weights for a given coefficient of kinetic friction, the more tractive effort it has, assuming there is enough power available to increase the tractive effort. Hopefully that was clearer than mud.
Correct me if i’m wrong, but slugs are ususally the victims of “ballasting” as a way to replace the mass of the prime mover, generator and associated systems. So, in places where slugs are used to put power-on-rail for hill climbs, mass is a good thing and the entire fuel tank volume is available for use. In that scenario, a battery storage system makes a lot of sense. Back of the envelope (15lbs/ gallon, incl. cables, blowers, etc.), a fuel tank would hold about 1/2 the batteriessomeone (forget who) cites above. Using his energy numbers, and applying the electric-car rule-of-thumb 80% total system efficiency, that’s a little more than 500HP-hours put on the rail, or about 45 gallons of diesel fuel (at 0.5lb/HP-hr) that could be re-used per slug, per charge cycle. If you don’t deep-deep-cycle the cells too often, you could get something like 2000+ cycles out of a good set of vibration-resistant batteries.
Figuring a 50% depth-of discharge limit, that’s about $45k in fuel savings alone, (California prices to the tourist line I sometimes wrench for) which about pays for the batteries and labor to swap them. (lead-acid recycles, so disposal is essentially free)
I’ll let someone else speak to the maintenance requirements of locomotive electricals, but batteries are pretty simple beasts; as long as you don’t let them get too hot or too cold and add water every week or or so, they’re fine.
The biggest wrinkle I can see is that you can safely draw a higher energy rate out of lead-acid than you can put back in. Some sort of electrolyte cooling could help, but any engineered cooling you add to the battery system hurts cost and reliability.
which brings us to:
Flywheels can be designed for much better charge and discharge rate curves and aren’t inherently cycle-life-limited like batteries. They do better on a mass-energy density basis, but really lose out on volume-energy density.
They DO add another wrinkle, in that highly stressed rotors d
My thinking on this is partial electrification. Use Diesel locomotives, but put pantographs or perhaps 3rd rail shoes on them in the manner of the FL9s (these days the LIRR DM-whatevers and the Metro North P32ACs). Run Diesel in the flatlands but run electric in what would be the helper districts and take advantage of regenerative braking and all of that.
With all of that fancy wheel slip control, they are wanting to put 6000 HP in a single C-C locomotive, and they want to use those high HP locomotives on coal trains. Put in maybe a 2000-3000 HP Diesel, adequate for the flatlands, electrify the ruling grades, and the same locomotives can put out 6000 HP or more under wire because the electrical equipment can handle it, but it is hard getting a reliable rail Diesel for 6000 HP. You would get the fuel economy advantage of regenerative braking and coal or nuclear-supplied electricity to lift trains up the hill, and you can put in a smaller Diesel and get better fuel economy on the flatlands.
I suppose wires had been looked at for the Wyoming coal trains and found wanting, but the electronic power conversion equipment for the high HP ACs had come into being after the studies making perhaps a Diesel/wire hybrid more attractive. My thinking is that a Diesel/wire hybrid makes more sense in mainline railroad applications than a Diesel/battery or Diesel/flywheel hybrid.
I have checked the power meter logs on the Oakway SD60s on the BNSF several times. The three highest use positions are Run 8, Idle and Dynamic braking but I don’t remember the particular order. Idle was way up there. Throttle 1-7 were negligible.
Flywheels have one major problem on a locomotive. They do not like to change directioins which may cause serious problems going around curves. Flywheels also work the best when they have a larger diameter and relatively speaking locomotive carbodies are sort of narrow for the weights involved.
The newest diesels can produce far more dynamic braking horsepower than locomotive horsepower. Those traction motors have way more capacity than the diesels that feed them.