Tractive effort Versus Horsepower

[SteelMonsters]

 

Transmission Efficiency

The measure how efficiently the mechanical energy of the diesel engine is converted into electrical energy through the traction motors. The transmission efficiency values are assumed at CTE. Typical values per technology are:

	Transmission Efficiency
AC/AC	92%
AC/DC	87%
DC/DC	83.8%

The AC/AC value seems about what I would expect. What suprises me is that using DC doesn't cause a larger drop in efficiency. I've always thought that a DC motor or generator could only hope to get up to about the DC/DC range percentage. I thought that a DC gen, motor control, and a DC motor would cause the efficiency to drop further than that.

[MStLfan]

 

If you want to present data on outdated locomotives that we are getting rid of as fast as economically possible, more power to you. All I’m saying is if you want to post outdated information from 12 years ago please state it as such.

I don't mind seeing data on older locomotives, it is just as fascinating. But please do state for which locomotive the data is.

Thanks.

Greetings,

Marc Immeker

[oltmannd]

 

Oltmannd and timz:

First, “we” are not GE. I have never said that I work for GE. If you follow my posts, it is pretty obvious what railroad I work for (short of giving you my employee number) based on the model designations alone.

Second, Oltmannd, the data I use is based on actual performance data from our CW44ACs, not GE’s published generic data.

However, since it is obvious that you and timz don’t have any real data on the CW44AC, I will play your game and use GE’s generic data.

Let’s look at your cute little dissertation of GE’s “Transmission Efficiency”.  To quote GE’s definition:

Transmission Efficiency

The measure how efficiently the mechanical energy of the diesel engine is converted into electrical energy through the traction motors. The transmission efficiency values are assumed at CTE. Typical values per technology are:

	Transmission Efficiency
AC/AC	92%
AC/DC	87%
DC/DC	83.8%

Note: “The transmission efficiency values are assumed at CTE.”

Let’s look at how GE defines CTE:

CTE

Continuous tractive effort. Pound force applied to the rear coupler to pull a train. A number that relates to a tractive effort on a DC motor locomotive that the traction motor can obtain indefinitely without overheating. This is usually specified in a speed. CTE is non applicable for an AC traction motor, which use TE only.

Notice:  “force applied to the rear coupler to pull a train”

The last time I looked, for the power to reach the rear coupler, it must go through the axle gears and wheel bearings first. Therefore, GE's definition of Transmission Efficiency at CTE includes ALL losses to the coupler, does it not? Maybe Oltmannd with his “28 years of experience” knows a magical way the power gets to the rear coupler bypassing the axle gears and bearings, but I don’t.

Oltmannd, If you really have 28 years experience, why did you choose to ignore the rest of GE’s data? The point you used was at a very high current draw. Everybody who actually works in this field knows that electric based locomotives are not as efficient at very high current draws.

Let’s look at the rest of the data in table form for GE's 4,390 Traction HP rating:

140,000 lbs TE       10.5mph             89.3% efficiency         3,920 rail hp

130,000 lbs TE       11.5mph             90.8% efficiency         3,986 rail hp

120,000 lbs TE       12.5mph             91.1% efficiency         3,999 rail hp

110,000 lbs TE       13.5mph             90.2% efficiency         3,959 rail hp

100,000 lbs TE       14.9mph             90.5%  efficiency        3,972 rail hp

90,000 lbs TE         17 mph               92.9% efficiency         4,078 rail hp

80,000 lbs TE         19 mph               92.3% efficiency         4,052 rail hp

70,000 lbs TE       21.5 mph              91.4% efficiency         4,013 rail hp

60,000 lbs TE       25.5 mph              92.9% efficiency         4,078 rail hp

50,000 lbs TE       30.5 mph              92.6% efficiency         4,065 rail hp

40,000 lbs TE       37.5  mph             91.1% efficiency         3,999 rail hp

30,000 lbs TE       50.5  mph             92.0% efficiency         4,039 rail hp

20,000 lbs TE       74   mph               90.0% efficiency         3,951 rail hp

At any speed above 11 MPH, the CW44AC operates above 90% efficiency, with a maximum efficiency at 93%.

375 x 0.93 = 349

349 is 11% greater than 315

I don’t know anybody in the industry who thinks an 11% improvement is trivial.

Our test also show that GE's paper rating of 4,390 Traction HP generally underestimates the true power of the 16 cylinder FDL in these locomotives.

Last, my problem with your first post is you threw the 308 number out without any reference to what locomotives it applies to. Railfans who are unknowledgeable about current locomotive performance will look at that and assume it applies to all locomotives.

If you want to present data on outdated locomotives that we are getting rid of as fast as economically possible, more power to you. All I’m saying is if you want to post outdated information from 12 years ago please state it as such.

NOW I know who you work for.   My condolences.  You're the same guys I see mixing AC and DC locomotives willy-nilly all over the place. Why you buying all those AC units only to castrate them by mixing them with DC so much of the time?  Might as well just throw capital money out the window.   If your new NS mgt can't straighten things ou

[oltmannd]

 

Transmission Efficiency

The measure how efficiently the mechanical energy of the diesel engine is converted into electrical energy through the traction motors. The transmission efficiency values are assumed at CTE. Typical values per technology are:

	Transmission Efficiency
AC/AC	92%
AC/DC	87%
DC/DC	83.8%

The AC/AC value seems about what I would expect. What suprises me is that using DC doesn't cause a larger drop in efficiency. I've always thought that a DC motor or generator could only hope to get up to about the DC/DC range percentage. I thought that a DC gen, motor control, and a DC motor would cause the efficiency to drop further than that.

The only real difference between a DC main gen and an AC main gen that would effect transmission efficiency is commutation.  The diodes are more efficient than a commutator with carbon brushes, but not that much more.  One of the main reasons for the advent of the AC main gen was to be able to push the DC voltage higher.  The DC main gens would flash if you pushed the voltage up too high.  As engine HP rose, the need was for higher DC voltage so that the locomotive could develop full HP at high speed without resorting to multiple stages of field shunting.

I'm not certain where GE got their DC/DC numbers from.  Perhaps their U25B - or maybe EMD's GP30/35.  A DC/DC GP38 or GP15 has a main generator efficiency nearly equal to a similar aged AC/DC 40 series and everything from the main gen to the rails is the same.

[oltmannd]

 

 

If you want to present data on outdated locomotives that we are getting rid of as fast as economically possible, more power to you. All I’m saying is if you want to post outdated information from 12 years ago please state it as such.

You don't mean all those old, trashed EMD SD40s you guys rent back from anybody and everybody at twice what it cost you to own them, do you?  You have more of them rolling around on your property than any other North American class one.  I can't remember the last train of yours I saw without a leaser or some other begged, borrowed or stolen unit in it.

What is the avg age of your fleet (INCLUDING all those leasers).  I'll bet it's over 12 years old!

[oltmannd]

Kwality in Motion:

http://www.railpictures.net/viewphoto.php?id=158941

At least the two lead units are in good condition

http://www.railpictures.net/viewphoto.php?id=140097

Nice.  A 4000 HP AC on a flatland van train.  Good use of capital. 

http://www.railpictures.net/viewphoto.php?id=158945

Really scraping the bottom of the barrel for leasers:

http://www.railpictures.net/viewphoto.php?id=109746

For really time sensitive chemical freight:

http://www.railpictures.net/viewphoto.php?id=153335

Fore really, really time sensitive perishible freight:

http://www.railpictures.net/viewphoto.php?id=142018

(hope they fix that leader they broke before they give it back!)

OK.  I've had my fun. 

Now back to your regularly scheduled forum

[JSGreen]

It seems pretty clear, given all the data posted here, that the AC units are more effecient and pull better.  Other than the old Ford/Chevy debate, the deciding factor on which behemoth to buy must then be cost...it they cost the same, one assumes you would buy the highest effeciency for the  same dollars. 

I know that pricing structures are probably not constant, that everybody pays different prices based on the number of units ordered and other little factors, but can someone illustrate what the price differential is for otherwise equilivent AC and DC units? 

[BigJim]

      All of this mathmatical mumbo-jumbo can be tossed out the cab window when the least amount of dew or frost or grease gets on the rail! You should see the horsepower drop on the screen when the wheels can't get any traction. And the bad thing is, it's not getting any better. Each new year, each new unit version is getting progressively worse at holding the rail.

      So you number crunchers can debate this crap all you want. When you decide to get real, come on out where the action is and see how they pull (and hold back - DB) in the Wide Wide World of Railroading!

   

[oltmannd]

      All of this mathmatical mumbo-jumbo can be tossed out the cab window when the least amount of dew or frost or grease gets on the rail! You should see the horsepower drop on the screen when the wheels can't get any traction. And the bad thing is, it's not getting any better. Each new year, each new unit version is getting progressively worse at holding the rail.

      So you number crunchers can debate this crap all you want. When you decide to get real, come on out where the action is and see how they pull (and hold back - DB) in the Wide Wide World of Railroading!

   

This is exactly the kind of thing I meant when I used the "engineeringese"  1 -1/2 significant digits way back on page one.  You put it very suscinctly!

I think we'll let that other road spend all their money dotting i's and crossing t's since that seems to interest them more than actually running the RR.  They are a smart bunch.  Always have been.  But they are disfunctional.

[Anonymous]

If rail was a linear gear and wheels were a bull gear, all the wheel slip number crunching would disappear.... That is tractive effort, torque delivered to the rail. Horsepower is dissipated energy.

[oltmannd]

It seems pretty clear, given all the data posted here, that the AC units are more effecient and pull better.  Other than the old Ford/Chevy debate, the deciding factor on which behemoth to buy must then be cost...it they cost the same, one assumes you would buy the highest effeciency for the  same dollars. 

I know that pricing structures are probably not constant, that everybody pays different prices based on the number of units ordered and other little factors, but can someone illustrate what the price differential is for otherwise equilivent AC and DC units? 

Before you do anything, you have to match the locomotive to the intended service.  And, that will entail a whole bunch of things such routes, train sizes, schedule requirements, etc.  You also have to figure out if you are going to segregate your fleet by service demand (e.g. schedule vs. drag ala BNSF) and whether or not you plan on deploying the new locomotives similar to those they will replace or whether there is new technology that will allow you to do things differently (e.g. DPU).

Let's say I have a simple RR.  I run 70 car, 7,000 ton trains over a route that has a 2% ruling grade and requires 1.2 HP/ton to make schedule reliably.  What kind and how many locomotives would I need to run this train?  To get the train over the grade, figure 20#/ton/% grade (nit pickers need not apply)  So, ideally, I need a locomotive that has 40# TE at minimum continous speed (or the all-weather adhesion limited TE for an AC) for every 1.2HP

40/1.2 = 33

Looking at a few possible locos:

GP40-2  51000/3000 = 17

SD40-2  83000/3000 = 28

SD45    83000/3600 = 23

SD60    100000/3800 = 26

Dash 9  117000/4400 = 27

AC4400 147000/4400 = 33

AC6000 147000/6000 = 24

Looks like the AC4400 has the best balance of HP and TE for my needs.  How many would I need for my train?  I need 20 x 2 x 7,000 = 280,000# TE to get the train over the ruling grade.  So, I'd need 2 of them.  If my fleet was SD60s, I could replace 3 for 2.  If my current fleet was SD40-2s, I could get 4 for 2.  I could also go with 2 AC6000s but I'd be buying HP I didn't need - along with the fuel costs that go with higher HP/ton.  4400 HP per unit gets me 1.25 HP/ton. 

But, I want to look at DC units, too.  I'd need 3 Dash 9s to move the same train, but I'd have plenty of extra TE which might mean a day or two a year I won't stall due to lousy rail conditons or if one unit was "sick".  Also, since I don't need all that HP per unit, I might decide to see about the "dialed down" 4000 HP Dash 9s that NS purchases.  Might be worth some extra reliabilty?  I'd have to have a talk with NS's VP Mechanical about this.

Now I go to the builder with my specs and get some prices on AC and DC units with my RR's particulars.

While the builders are working on their bids, I try to figure out three more things so that I can figure out the life cycle cost for each beast. 

One is maintenance and overhaul cost.  If I already own some of these, or their cousins, I use my own history.  If not, I try to get some facts and figures from someone who does.  If a new model, I guess and pray!  This is where you factor in the lower traction motor maintenance and overhaul costs.

Two is fuel cost.  I can either get this by running some train simulations or by using published or test results for specific fuel consumption (lbs fuel per net traction HP-hr, this is the only efficiency number a RR really cares about in any detail!  You want this one down to a 1/2% or so since you'll burn 400,000 gal/year or so.) and calculate based on equal work for what I'm replacing plus idle fuel.  If a new model, I might borrow the builder's demo units or one from a road that has purchased some and do some static and over the road tests.

Third is the replacement ratio.  I have to figure in availability here as well as the straight 3 for 2 train replacement ratio - I might only have to buy 19 new ones to replace 30 old ones, for example.  I figure out each of the costs over time, calculate the net present value of these costs, add them to the purchase price (in net present value if financing is involved) and whichever number is lower is the winner.

I might also do some sensitivity analysis "what ifs".  As in "what if I'm wrong about maintenance costs?" or "what if the new model can't meet it's promised availablity?" or "what if my guess about the future cost of money is wrong?"

And then, I might just ask the CMO which model makes him least nervous!

[timz]

I know for a fact we are getting 4100 rail hp out of our CW44ACs except at extremely slow speeds at full power. Even then they only drop down to 3900 rail hp.

We are getting 4100 rail hp out of our CW44ACs down to what speed?

[JSGreen]

thanks, Don, (oldtmannd) for an inclusive answer about the COST of locomotives.  Clearly  purchasing units based only on purchase price is short sighted at best.  But I am still curious, what are the prices of AC vs DC units?

[oltmannd]

thanks, Don, (oldtmannd) for an inclusive answer about the COST of locomotives.  Clearly  purchasing units based only on purchase price is short sighted at best.  But I am still curious, what are the prices of AC vs DC units?

There are some old threads where people have posted some prices.  Probably worth doing  a search.  I really don't remember exactly what was posted, but I think they are somewhere around $1.5M for a DC and $2M for an AC.

[JSGreen]

Thanks....thats the kind of rough comparison I was looking for.  I suspected that if the prices were the same, the trend would be toward AC...but the (ballpark) 30% increase makes it a more complex issue...

[BigJim]

If rail was a linear gear and wheels were a bull gear, all the wheel slip number crunching would disappear

The problem here is that much of the extra pulling power comes from the limited wheel "creep".

I suspected that if the prices were the same, the trend would be toward AC...but the (ballpark) 30% increase makes it a more complex issue...

NS did a test on the AC units of both EMD and GE. Under wet conditions they didn't pull enough extra cars to make them worth the extra BIG BUCKS that they cost.