MichaelSol wrote:I have posted TE graphs for your perusal, and offered you the fairly straightforward TE equation that you can play with with any numbers you want. Why do you want me to answer this question? What's your point?
What's your point?
n012944 wrote: I didn't say that it had nothing to do with profitability, it just has very little to do with it. There are many reasons for the NS and CN operating ratio, and locomotive choice is but a very small reason.
I didn't say that it had nothing to do with profitability, it just has very little to do with it. There are many reasons for the NS and CN operating ratio, and locomotive choice is but a very small reason.
If a railroad earns a 7% return, and motive power accounts for 25% of a railroad's operating expenses, and AC ( or sticking with DC) can provide a mere 5% improvement in overall motive power expenses -- only 1.25% of all operating expenses -- it goes right to the bottom line and that changes that railroad's profitability by 1.25%, from 7% to 8.25%.
A single management decision that could produce that kind of a change in profitability is a very large reason, not a small one, as it would represent an 18% increase in profitability over your competitor who did not make that decision.
In the real world, that's not small.
timz wrote: MichaelSol wrote:I have posted TE graphs for your perusal, and offered you the fairly straightforward TE equation that you can play with with any numbers you want. Why do you want me to answer this question? What's your point?The fairly straightforward TE equation says the AC (or any other 4400 hp locomotive) will produce 16,000,000 lb of TE at 0.1 mph. And 160,000,000 lb at 0.01 mph. In other words, we can't expect the formula to "work" in that speed range. And it doesn't at 2 mph, either. There is no chance that a single six-axle AC will maintain 2.5 mph (or any other mph greater than zero) with a train that brings eight SD40-2s down to 11 mph.
Well, you've been playing a game here, the usual stuff that comes up on these threads. If you disagree, just simply say so like a grown-up, get it off your chest, and cut out the little "gotcha" string of posts. There are professional ways of approaching these things and pretending you can't do your own math isn't one of them. You didn't need me to do your math for you. I know what the equation says. So do you.
Some of the early AC tests marvelled at how single units could pull heavy trains at, literally, inches per hour, obviously without the software limitations. But, you've got it all figured out. It "can't work". On an unregulated, hypothetical AC or DC locomotive -- and my example was clearly identified as a hypothetical -- what do you think the TE is at 2.5 mph? Why do you think the forumula is in error? What is your formula for the TE on that relevant range? What tests are you relying on? Where is the study that says the curve is in error over part of its range? Is it in error on the high end too? There's not much TE left there. Why?
I think you do just want to argue. Good luck.
MichaelSol wrote:Why do you think the formula is in error?
timz wrote: MichaelSol wrote:Why do you think the formula is in error?The formula isn't "in error"-- we just can't use it in this speed range in the "straightforward" way you want to use it. (Which is to say, we can't expect an AC44 to produce 4400 hp in this speed range.) I guess you'll agree an AC44 can't actually produce 160,000,000 lb TE at 0.01 mph-- right? Despite the formula?
You're playing games. This is an interesting thread on an adult topic and just doesn't need this "oh yeah well what about ..." attitude. If you think it is wrong, ditch the attitude, go out, measure it, and come back with your results that show the formula is wrong.
What I will concede is that at 0.01 mph I don't particularly care what you think is actually produced.
MichaelSol wrote:If you disagree, just simply say so like a grown-up, get it off your chest, and cut out the little "gotcha" string of posts. There are professional ways of approaching these things and pretending you can't do your own math isn't one of them.
JayPotter wrote:An AC4400CW with standard software operating under ideal rail conditions will begin to produce 180,000 pounds of TE when its speed falls to 9.78 mph; but TE will not increase as speed continues to drop.
The 9.78 mph figure should actually be approximately 8 mph. The 9.78 mph figure is the speed at which a standard AC4400CW should be able to produce 145,000 pound of TE regardless of rail conditions. If rail conditions are ideal and speed decreases, TE will increase to 180,000 pounds at around 8 mph; but, because of software-imposed limitations, further speed reduction will not produce any increase in TE.
timz wrote: MichaelSol wrote:If you disagree, just simply say so like a grown-up, get it off your chest, and cut out the little "gotcha" string of posts. There are professional ways of approaching these things and pretending you can't do your own math isn't one of them.I unprofessionally and un-grownupedly figured that once you gave the matter a bit more thought you'd see there had to be a flaw in your calculation. Should I give up on that possibility?
It's an industry formula, it's not "my" calculation. There "had" to be a flaw? Well, what is it? You don't like it?
Let's clarify this. I relied on accepted industry formula. You don't "think" or "like" or "accept" the results. That doesn't put the burden on me. It's not my formula to concede one way or the other that there is a "flaw" in it, nor my "job" to defend an accepted approach.
The industry has used the formula for a good number of years without apparently understanding that it is wrong. Why don't you write a paper on how the formula is wrong, and provide the correct formula that the rail industry obviously needs? Then you can play "gotcha" to your heart's content with whoever designed the original formula and forgot to put parameters on it for you. The engineering design puts its own parameters on it, and that no doubt varies with individual designs or even software limitations, as pointed out.
Until then, drop the attitude. I don't need it, the thread doesn't need it, and Trains forums don't need it.
MichaelSol wrote: n012944 wrote: I didn't say that it had nothing to do with profitability, it just has very little to do with it. There are many reasons for the NS and CN operating ratio, and locomotive choice is but a very small reason. If a railroad earns a 7% return, and motive power accounts for 25% of a railroad's operating expenses, and AC ( or sticking with DC) can provide a mere 5% improvement in overall motive power expenses -- only 1.25% of all operating expenses -- it goes right to the bottom line and that changes that railroad's profitability by 1.25%, from 7% to 8.25%. A single management decision that could produce that kind of a change in profitability is a very large reason, not a small one, as it would represent an 18% increase in profitability over your competitor who did not make that decision.In the real world, that's not small.
Lots of what ifs in that argument. BTW please show me a railroad that has 25% of its operating budget tied up in the purchase price of locomotives.
An "expensive model collector"
MichaelSol wrote:It's an industry formula, it's not "my" calculation. There "had" to be a flaw? Well, what is it?
Nobody said there's a flaw in the formula-- the formula is just a slightly-modified restatement of the definition of the horsepower, and can't be far wrong. It's your calculation-- your misuse of the formula-- that's gone off the deep end. When you said
"It takes 8 [SD40-2] locomotives to keep the minimum speed of 11 mph on that [1.2%] grade and curvature....At 2.5 mph, one AC locomotive could still keep the train moving if it didn't slip."
I was naturally incredulous that you could believe such a thing. Now you're demanding test results that disprove your calculation-- as if tests existed that support your calculation. None do, and none ever will. (Unfortunately, no test will ever disprove it either, since nobody would bother arranging such a test. No need.)
I think that I can explain the problem with the TE formula.
When the industry began applying the formula to AC-traction units, the figures stayed basically the same (EMD, for some reason, began to use 323 instead of 375); however it appears to me that the purpose of the formula changed. It ceased being used to compute TE for any speed and began to be used to compute (or maybe a better term would be "illustrate") something called "nominal continuous TE". This is the amount of TE that an AC-traction unit can be relied upon to produce under any rail conditions. In other words, if a railroad wanted to know what dispatching criteria it should apply to a given AC-traction model, the formula could explain that the unit would produce at least X amount of TE and would be moving at Y speed when doing so.
In other words, "nominal continuous speed" is the AC-traction counterpart to the DC-traction "minimum continuous speed". The former means the speed at which an AC-traction unit produces the maximum TE that it can be relied upon to produce, regardless of rail conditions. The latter means the speed which a DC-traction unit must maintain in order to avoid derating because of thermal limitations.
So the formula is basically a carryover from the DC-traction-only era; and it can't be applied as broadly to AC-traction units as it was to DC-traction units.
n012944 wrote: Lots of what ifs in that argument. BTW please show me a railroad that has 25% of its operating budget tied up in the purchase price of locomotives.
What is with some of you people today. Now, this changes the argument considerably. Previously, AC was alleged superior because of a combination of purchase price and lower maintenance -- that the operating benefits -- which goes to a variety of costs -- and maintenance -- which isn't purchase price -- and crew costs -- slower movement of trains -- fuel cost -- outweighs or exacerbates the higher purchase price of the units, but perhaps less, in combination, than the cost of equivalent DC power. All of which goes into the operating ratio.
Now, if the argument is just about purchase price alone. No, I doubt any railroad spends 25% of its operating budget on the purchase price alone, but that wasn't the proposition.
Tell you what, you show me how locomotives -- purchase, finance, maintenance, operating implications -- "have little to do with the profits of said railroads" or any other railroad.
Show how little it is and offer a basis for your contention.
timz wrote: MichaelSol wrote:It's an industry formula, it's not "my" calculation. There "had" to be a flaw? Well, what is it?Nobody said there's a flaw in the formula-- the formula is just a slightly-modified restatement of the definition of the horsepower
Nobody said there's a flaw in the formula-- the formula is just a slightly-modified restatement of the definition of the horsepower
Timz is exactly right - It is based on the definition power (actually drawbar horsepower) derived straight from mechanics.
Power = force x velocity = TE x velocity
In consistent conventional English units
Power = TE in pounds x velocity in ft/sec which yields power in ft-lb/sec.
Express velocity in mph by multiplying by 5280 ft/mile/3600 sec/hr
Convert power in ft-lb/sec to HP by dividing by 550 ft-lb/sec/HP
This results in
HP = TE x V x 5280/(3600 x 550)
or HP =TE x V/375
solving for TE yields
TE=375*HP/V
It represents the IDEAL tractive effort vs speed behavior for a given drawbar horsepower. As others have pointed out it can't be used to characterize actual locomotive tractive effort behavior at low speeds because of the characteristic of derating power below a critical speed to prevent wheel slip and/or traction motor overheating.
Anthony V.
timz wrote: MichaelSol wrote:It's an industry formula, it's not "my" calculation. There "had" to be a flaw? Well, what is it?Nobody said there's a flaw in the formula-- the formula is just a slightly-modified restatement of the definition of the horsepower, and can't be far wrong. It's your calculation-- your misuse of the formula-- that's gone off the deep end. When you said"It takes 8 [SD40-2] locomotives to keep the minimum speed of 11 mph on that [1.2%] grade and curvature....At 2.5 mph, one AC locomotive could still keep the train moving if it didn't slip."I was naturally incredulous that you could believe such a thing. Now you're demanding test results that disprove your calculation-- as if tests existed that support your calculation. None do, and none ever will. (Unfortunately, no test will ever disprove it either, since nobody would bother arranging such a test. No need.)
"Misuse," "incredulous," "deep end". Wow! It took you what, how many posts to finally get it off your chest?
Why didn't you just disagree?
The fact is TE is a measure. As TE drops off, does it take more locomotive hp to supply the same TE? Yes, it does.
All the way across the curve.
Whether a locomotive not limited by its software can generate the same or more TE than several locomotives at five or six times the speed is not remarkable. I did not invent the TE curve, nor "misuse" it nor go off "the deep end" by using it within the published range of its use.
And you should be no more "incredulous" about it at two miles an hour compared to 11, or 12 miles an hour compared to 70, particularly when I said it "could" generate the TE if it didn't "slip" -- i.e. didn't have the weight to keep the wheels down or didn't fly apart from the stress.
And there is no reasonable basis to dispute it at 2 miles an hour, as at 12, or 20, or 40.
However, as many posts now suggest, you could have stated it in one post, instead of making it a little playground game by pretending you couldn't do the math yourself, and stringing this along for whatever people like you get out of this stuff.
AnthonyV wrote: Timz is exactly right -...TE=375*HP/V
Timz is exactly right -
...
Actually, you're dead wrong. He didn't say that. I did. Exactly in that form. Indeed, he claimed it was my "calculation," and refused to take any credit for it at all.
My reason for offering the equation is that it is the basis of the conversation and explains the TE curves, which I also posted.
If there is some point in jumping in to belabor the obvious, please explain that point.
As I pointed out as well, slip and overheating are the problems at low speeds, and notwithstanding my "example" specifically designed to show the TE advantages of AC at slow speeds compared to DC which doesn't operate well at low speeds because of overheating, and I specifically referenced the slip making the slowest speeds unlikely, however, by simply ignoring what I said, this is degenerating into the usual dogs chasing their tails trying to make something out of it.
If someone wants to show that overheating is a problem for DC at slower speeds, or that slip (or software restrictions) might make high TE unlikely at very slow speeds, well have at it. I've already said it. If someone wants to actually read what I said, it's already there. Somebody wants to play games if they want to suggest I did not qualify those remarks.
However, the high TE available at low speeds offers AC a comparative, not a total, advantage over the DC motors. And I stand by the statements. The point was to suggest how much of an advantage is gained by operating below 11 mph, or wherever a DC motor might overheat to the point that it shuts down. And that is because TE is higher at slower speeds, and the TE curve is relatively steep below 10 mph.
Timz and Anthony V. can play games with that all next week or all eternity for all I care, since that seems to be the point, the only point, of what are becoming neverending posts on the topic and somewhat symptomatic of certain posters attempting to misrepresent an "example" to prove some elusive point that is apparently personal.
MichaelSol wrote: AnthonyV wrote: Timz is exactly right -...TE=375*HP/VActually, you're dead wrong. He didn't say that. I stated that equation. Indeed, he claimed it was my "calculation," and refused to take any credit for it at all. My reason for offering the equation is that it is the basis of the conversation and explains the TE curves, which I also posted.If there is some point in jumping in to belabor the obvious, please explain that point.As I pointed out as well, slip and overheating are the problems at low speeds, and notwithstanding my "example" specifically designed to show the TE advantages of AC at slow speeds compared to DC which doesn't operate well at low speeds because of overheating, and I specifically referenced the slip making the slowest speeds unlikely, however, by simply ignoring what I said, this is degenerating into the usual dogs chasing their tails trying to make something out of it. If someone wants to show that overheating is a problem for DC at slower speeds, or that slip (or software restrictions) might make high TE unlikely at very slow speeds, well have at it. I've already said it. If someone wants to actually read what I said, it's already there. Somebody wants to play games if they want to suggest I did not qualify those remarks. However, the high TE available at low speeds offers AC a comparative, not a total, advantage over the DC motors. And I stand by the statements. The point was to suggest how much of an advantage is gained by operating below 11 mph, or wherever a DC motor might overheat to the point that it shuts down. And that is because TE is higher at slower speeds, and the TE curve is relatively steep below 10 mph.Timz and Anthony V. can play games with that all next week or all eternity for all I care, since that seems to be the point, the only point, of what are becoming neverending posts on the topic and somewhat symptomatic of certain posters attempting to misrepresent an "example" to prove some elusive point that is apparently personal.
Actually, you're dead wrong. He didn't say that. I stated that equation. Indeed, he claimed it was my "calculation," and refused to take any credit for it at all.
It is pointless to use the idealized TE equation as you did - it doesn't apply.
AnthonyV wrote: It is pointless to use the idealized TE equation as you did - it doesn't apply.
And how do you actually know this?
Please, be specific: why does the TE equation accepted by the industry give the wrong results at 2.5 mph? How about 4 mph? What about 6? Where do you think the curve misrepresents reality, and why that specific point? Given the misrepresentations you make above, even about who posted the TE equation, I expect you to give a specific answer. Particularly since I am relying on an accepted methodology, and you are the one objecting to it. Ball's in your court: what is wrong with the standard TE curve generated by the rail industry and generally agreed on by it? Again, be specific. You could break new ground here and show the industry has been wrong for ... how many years?
Indeed, you laboriously derived the equation to show why it is correct ["timz is correct"] and identical to the one I posted, yet you say the results obtained by that same equation are wrong, but didn't offer that "timz is wrong" based on that same equation using an actual number -- in this case 2.5 mph.
Well, which is it? Why bother to go through all that math, and then say it isn't correct? Why bother to triumphantly announce how the equation is derived, then argue that it doesn't work with some numbers, but works with others? Is your derivation wrong? Give us all the benefit of deriving the correct equation instead. Why do you refuse to do that?
And since I used it as an "example" of why AC has advantages below 10 mph, what is your current investment in this conversation? Do you disagree that AC has those advantages? Or that the example, idealized or otherwise, represents those advantages? Or are you trying to claim something else?
If I had the time, I would go back and find an early AC test, in which the locomotive was chugging up the grade, grossly overloaded, at a few inches at a time. The "test" that timz claims hasn't, can't, be done, was actually done, and ... probably many times. Are there mechanical or engineering limits? You betcha. That's not the curve's fault, and doesn't change it one bit. Recall, that was a "hypothetical" and plainly identified as such.
But, that tells me what he thinks he knows.
The TE was in fact measured at the rate representing an extremely slow speed. It may have been reported in Modern Railroads, it may have even been in Trains. However, if I took the time to find it, I know exactly what you would do with it -- you would change the subject, and pretend that something else was said. There is no point in wasting the time with characters that are here just to argue -- particularly when they misrepresent statements, and even contradict themselves, to do so.
Another thread ....
The key words seem to be "if it doesn't slip." If I were to say also, "and if it doesn't overheat," then the same curve would apply to the DC motors. With both caveats in place, both motors would achieve the same TE at equivalent speeds.
I think we should all agree that it will slip at those low speeds and we should get back to the key questions, which I think are:
Why, in current locomotive practice, do AC traction motors appear to have better low-speed performance than DC traction motors?
Why, in the face of all the information in previous posts indicating that AC traction and control is better than DC, do some railroads continue to buy and use locomotives with DC motors?
Why is cooling an issue? It seems that designers should be able to provide whatever cooling DC motors need.
Why have designers of locomotives with DC motors not provided slip control independently to each axle, which appears to be common, if not universal, practice among locomotives with AC motors?
Most of this discussion has been about low-speed performance. How do the two approaches compare at medium and high speeds?
How do they compare in dynamic braking?
I have spent several hours without success trying to find some illuminating information. I think there must be something we haven't discussed yet. Otherwise, it seems that no one should be buying DC motors.
cordon wrote:Why have designers of locomotives with DC motors not provided slip control independently to each axle, which appears to be common, if not universal, practice among locomotives with AC motors?
I suspect -- but don't really know -- that configuring DC-traction units with single-axle control wouldn't be cost effective; however U.S. Patent 6,634,303 does relate to that concept.
EMD AC-traction units do not have single-axle control either. That's a GE-only feature.
cordon wrote:The key words seem to be "if it doesn't slip." If I were to say also, "and if it doesn't overheat," then the same curve would apply to the DC motors. With both caveats in place, both motors would achieve the same TE at equivalent speeds.I think we should all agree that it will slip at those low speeds and we should get back to the key questions, which I think are: Why, in current locomotive practice, do AC traction motors appear to have better low-speed performance than DC traction motors? Why, in the face of all the information in previous posts indicating that AC traction and control is better than DC, do some railroads continue to buy and use locomotives with DC motors?Why is cooling an issue? It seems that designers should be able to provide whatever cooling DC motors need. Why have designers of locomotives with DC motors not provided slip control independently to each axle, which appears to be common, if not universal, practice among locomotives with AC motors?Most of this discussion has been about low-speed performance. How do the two approaches compare at medium and high speeds?How do they compare in dynamic braking? I have spent several hours without success trying to find some illuminating information. I think there must be something we haven't discussed yet. Otherwise, it seems that no one should be buying DC motors.
cordon wrote:How do they compare in dynamic braking? ...Why is cooling an issue? It seems that designers should be able to provide whatever cooling DC motors need. Why have designers of locomotives with DC motors not provided slip control independently to each axle, which appears to be common, if not universal, practice among locomotives with AC motors?
How do they compare in dynamic braking? ...
It might have been another thread, but I believe somewhere above in this thread a statement was made that Dynamic Braking on AC units is actually effective down to slower speeds than DC units. I dont recall reading anything about amount of breaking effort...I would guess it is at least as effective as DC, since you can change the control voltages to increase or decrease the amount of effort...
Individual axle control and cooling are possible, just send money. The relative simplicity of the DC control system is part of why they are less expensive. If you start adding complexity in order to acheive the advantage of the AC units, the cost will go up.
Didnt SP have Tunnel Motors in order to get cooling air to the traction motors in tunnels? If it were wildly successfull, wouldnt it have appeared in other and later generation DC units? So getting cooling air to the DC traction motors may not be an inexpensive proposition...it would be tough to get big fans and duct work down to the motors, and a refrigeration system adds complexity and cost.
And when you spend that money, you may find that the new DC units which exhibit the same slow speed pulling characteristics as the AC units are just as expensive...
Without getting into formulae or curves, my own understanding of the situation (and I have an SB and SM degrees from MIT and worked for a short time for EMD IN 1952) is that AC motors can provide higher continuous low-speed tractive effort by handling higher current because the nature of the current is not continuous, the coils and their insulation are not subject to steady heat but to intermittant heat. The statement that dc motors could be supplied with all the cooling necessary would be correct if there were actually liguid cooling associated with the motors, but the motor mechanical features are pretty much unchanged from Frank Sprague's original Richmond, Virginia, streetcars (1886-7), with one side of the motor suspended from the truck frame and the other side supported by the gear or gears meshing with gear or gears on the axle. These motors are "self ventilating" with built-in fans, and no external cooling is provided on the typical locomotive. So obviously, the amount of cooling air supplied is directly dependent on the speed of revolution of the motor. Supplimentary fans are employed, but there is still a limitation on the amount of air that can be blown passed the motor case and be effective, since heat transfer through the metal from the coil isn't instantanous or perfect.
Three phase motors have non-continous current in the coils, but the nature of sine waves and thus the nature of three phase power is that the power of the motor is continuous, with the peak power of one phases occuring when the other two combine at a minimum. So you don't get the AC motor sound that was familiar to all who rode Pennsy and New Haven commuter trains or GG-1'S and New Haven electrics, other than the Jets and ex-Virginians which had dc motors.
There is one other advantage of ac three-phase non-synchronouos hysterisis motors: No carbon brushes to wear out and require replacement.
...Dave: Do I understand you correctly, stating a traction motor has no external cooling fans....? I personally don't know but thought they were set up with high speed fans to provide cooling air thru duct work to keep temps under control....??
Quentin
http://www.conrailcorp.com/mssd80mac.html
Here is an interesting article about Conrails SD80MACs. There is an interesting part explaining how the AC locomotives will save the company money.
The first graphic in that link is pretty interesting, it detailed some data collection that was envisioned as part of the test....would love to see that!
Technology Review (Cambridge, Mass.), March 2002 v105 i2 p74(5)
Digital rail-road: An injection of computing power is turning trains into smart machines for precisely controlled hauling of heavy loads.
By Don Phillips.
No one had intended to make railroad history on May 5,1998. It's just that there was a shortage of locomotives in Phippsburg, CO. Instead of the usual five locomotives, only four were available to pull a 108-car coal train up Union Pacific Railroad's steep Toponas grade on the western slope of the Rocky Mountains. What followed is, among locomotive builders, legendary.
The locomotives were brand new General Electric behemoths with a twist: their traction motors operated on alternating current rather than direct current. Climbing the Toponas grade that day, the trains slowed to a barely perceptible six meters per minute. No self-respecting engineer would have tried such a foolhardy trick with conventional direct-current motors: wheels would have slipped, the train would have stalled, and the motors themselves would have been fried like an egg. But none of those things happened. Indeed, later investigation showed that the locomotives had been producing more pulling power than was thought possible at that speed. This feat of strength initiated a radical transformation of railroading--a revolution that stems directly from advances in information technology.
[excerpt]...
Now, the speed measured here was 0.22 mph -- substantially less than the 2.5 mph that for some reason became an issue here. Well, apparently these locomotives can move at that speed -- this train was moving at that speed because that's where it could develop enough tractive effort to keep moving. It could not go faster because, according to the standard TE curve, the locomotives would have lost tractive effort, it's tractive effort would have fallen below that necessary to overcome the resistance of journals, flange, grade and curvature -- and the train would have stalled.
The train had to operate at 0.22 mph because that is the point on the TE curve where it could develop enough TE to move.
It was neither "pointless" nor "idealized" on that particular day.
MichaelSol wrote: Technology Review (Cambridge, Mass.), March 2002 v105 i2 p74(5) Digital rail-road: An injection of computing power is turning trains into smart machines for precisely controlled hauling of heavy loads. By Don Phillips. No one had intended to make railroad history on May 5,1998. It's just that there was a shortage of locomotives in Phippsburg, CO. Instead of the usual five locomotives, only four were available to pull a 108-car coal train up Union Pacific Railroad's steep Toponas grade on the western slope of the Rocky Mountains. What followed is, among locomotive builders, legendary. The locomotives were brand new General Electric behemoths with a twist: their traction motors operated on alternating current rather than direct current. Climbing the Toponas grade that day, the trains slowed to a barely perceptible six meters per minute. No self-respecting engineer would have tried such a foolhardy trick with conventional direct-current motors: wheels would have slipped, the train would have stalled, and the motors themselves would have been fried like an egg. But none of those things happened. Indeed, later investigation showed that the locomotives had been producing more pulling power than was thought possible at that speed. This feat of strength initiated a radical transformation of railroading--a revolution that stems directly from advances in information technology. [excerpt]...Now, the speed measured here was 0.22 mph -- substantially less than the 2.5 mph that for some reason became an issue here. Well, apparently these locomotives can move at that speed -- this train was moving at that speed because that's where it could develop enough tractive effort to keep moving. It could not go faster because, according to the standard TE curve, the locomotives would have lost tractive effort, it's tractive effort would have fallen below that necessary to overcome the resistance of journals, flange, grade and curvature -- and the train would have stallThe train had to operate at 0.22 mph because that is the point on the TE curve where it could develop enough TE to move. It was neither "pointless" nor "idealized" on that particular day.
Now, the speed measured here was 0.22 mph -- substantially less than the 2.5 mph that for some reason became an issue here. Well, apparently these locomotives can move at that speed -- this train was moving at that speed because that's where it could develop enough tractive effort to keep moving. It could not go faster because, according to the standard TE curve, the locomotives would have lost tractive effort, it's tractive effort would have fallen below that necessary to overcome the resistance of journals, flange, grade and curvature -- and the train would have stall
I notice you have not presented any data for tractive effort actually produced by these locomotives at these speeds.
Your assertion that the idealized formula applies indicates that you believe each locomotive (assuming 4,400 hp each) was producing 7,500,000 lb of tractive effort at 0.22 mph.
Also, the formula predicts an infinite starting tractive effort (i.e., at 0 mph).
You better get on the phone with GE because they are under the false assumption that their Evolution AC locomotive produces a starting tractive effort of about 180,000 lb and a maximum continuous tractive effort around 166,000 lb.
AnthonyV wrote:I notice you have not presented any data for tractive effort actually produced by these locomotives at these speeds.
Each of the units would have been producing 180,000-or-less pounds of TE. The extent to which those TE levels approached 180,000 pounds would have depended on the levels of adhesion that rail conditions allowed the units to produce.
AnthonyV wrote: I notice you have not presented any data for tractive effort actually produced by these locomotives at these speeds.
Anthony, you are going to "notice" things until you turn blue. And not answer a single question posed to you in the earlier post. Let's look at this: "Your assertion that the idealized formula applies indicates that you believe each locomotive (assuming 4,400 hp each) was producing 7,500,000 lb of tractive effort at 0.22 mph."
First, we would need to know how much TE was necessary to move the train. We would need to know the resistance: the grade, the curvature, and the tonnage of the train. The article does not provide that information, and so I can't generate the numbers. But, I do ask that you cease saying that I am making "an assertion." I pointed out that a generally accepted TE curve exists. I didn't create it. Get that through your head. I also applied the TE curve to a "hypothetical" AC locomotive to show the potential of AC traction motors -- and immediately qualified that hypothetical as unlikely. Get that through your head.
I don't "believe" each locomotive was producing 7.5 million lbs of TE. I don't even particularly care what each locomotive was producing. This bizarre argument has already gone on far too long, and is representative of what is wrong with these forums.
I believe that the locomotives were producing enough to move the train. TE is indeed a function of speed. After I posted the accepted formula, you then spent the time to undertake a derivation, arrived at exactly the same formula, pronounced that it vindicated timz -- "timz is right" -- and then denounced the results of the formula you had just arrived at. What was that all about?
I really don't follow the contradictions in whatever it is you are getting at, but you are making a career out of it, just as you did with the Brown thread and several others. The TE curve has long been accepted by the industry. You don't like the results. You can't seem to explain why. I do accept that more tractive effort is generated at lower speeds, and that this provides an advantage for AC. I am not going to lose sleep over the fact that the principle underlying the curve is a sound one, and I will leave it to better engineers to come up with a better equation if there is one.
You haven't.
The equation is clearly purely physics. There are mechanical limitations as Jay Potter pointed out. I pointed out that I doubted a single unit would produce the curve TE because of "slip" which was my inarticulate description of whatever happens when a machine reaches the point that it cannot physically produce the work product predicted by theory. I should have included drawbars yanked and door handles flying off to boot, had I realized at the time that my hypothetical had to be rigorously defined in case someone decided it was worth 20 or 30 posts to nitpick. For some reason you can't seem to accept that I distinguished what the curve predicted from what would happen in the real world, and I did so in the single reference that I made to a low speed use of the TE curve -- as a cautionary about that end of the curve.
I think it was an intentional misreading, allowing you to continue these endless nitpicking sessions of self-contradictory posts. That's the problem with guys playing "gotcha" -- they don't read too well.
"You better get on the phone with GE because they are under the false assumption that their Evolution AC locomotive produces a starting tractive effort of about 180,000 lb and a maximum continuous tractive effort around 166,000 lb."
Get on the phone yourself. I understand the GEVO is software limited. Place the limitation on the TE curve and you can have any starting tractive effort you want if the machine will support it. Pick a spot. The question you might as is why there is a software limitation.
Because those motors want to generate more TE than the physical framework will safely permit. DC motors tried to do the same thing and overheated -- and shut down or burned up. Might be because those motors want to follow that curve. Ya think? So GEVO has a software limitation. Does that mean the curve is wrong? No. It means that engineers cannot economically harness the lower end of that curve nor is there a particular need to.
However, since I already pretty much said that in my initial post on the topic, these endless efforts of yours to prove the curve wrong are misguided. The technology simply can't/hasn't/doesn't need to reach the TE potential offered by low speed operation. The advantage of the AC motor is that it exploits the low speed TE in a fashion that the DC motors could not. And as the TE curve shows, there is an enormous potential there to exploit.
Now, there must be something you can put your good mind to that is more productive than beating a horse that was already dead -- because the remark concerning the single unit AC locomotive had already been qualified at the outset as improbable, but offered an intriguing insight into the possibilities of AC compared with DC traction motors.
Our community is FREE to join. To participate you must either login or register for an account.