Tractive effort Versus Horsepower

[cpbloom]

Hello!

Is there a formula to convert horsepower to tractive effort and vice-versa, or are they incompatible

[oltmannd]

TE is a force. HP is power. They are not "convertible" but related by speed.

Force x distance = energy

energy/time = power

so, power = force x distance / time

since distance/ time = speed

power = force * speed

For an typical DC locomotive:  HP = TE (lbf) x speed (mph)/308

where 308 is a factor that accounts for std English mearement and locomotive transmission efficiency.  For an AC, use 315 - they have slightly higher transmission efficiency. 

 

[MStLfan]

Oltmannd

At home (I am at work right now) I have an old ALCO catalogue with ratings of locomotives in both HP and CV.

If I remember correctly CV (french?) means also horsepower but with a different (continental european?) horse for measurement.

I what way does the equation change if CV is substituted?

greetings,

Marc Immeker

[oltmannd]

Oltmannd

At home (I am at work right now) I have an old ALCO catalogue with ratings of locomotives in both HP and CV.

If I remember correctly CV (french?) means also horsepower but with a different (continental european?) horse for measurement.

I what way does the equation change if CV is substituted?

greetings,

Marc Immeker

CV?  I've never heard of that term, but that probably just makes me ignorant - or forgetful!

[MStLfan]

I think it is short for cheval which means horse in french.

See these links:

http://en.wikipedia.org/wiki/Citro%C3%ABn_2CV

http://en.wikipedia.org/wiki/Tax_horsepower

greetings,

Marc Immeker

[M636C]

Firstly, for those not used to formulae, the relationship between tractive effort and horsepower expressed in Oltmannd's posting could be expressed as:

Tractive effort determines how much a locomotive can haul.

For a given tractive effort, increased horsepower allows an increased speed with other things remaining the same.

So if we look at an AC6000 compared to an AC4400, assuming the weight, traction motors and gear ratio are all the same, they are likely to haul the same load over a given grade but the AC6000 would move the train faster.

CV is not just "cheval" (horse) but "cheval vapeur" (steam horse)

A CV is equal to 736 watts, a HP is equal to 746 watts. English speaking horses are very slightly stronger than French speaking horses.

M636C

[MStLfan]

Thanks M636C,

I was looking for that missing link for some time!

Now, which horse is prettier?

greetings,

Marc Immeker

[M636C]

Thanks M636C,

I was looking for that missing link for some time!

Now, which horse is prettier?

greetings,

Marc Immeker

The French horses spend much more time worrying about looking prettier, but in fact they just eat better food. The English horses think they are much superior to the French horses, and don't realise how bad their food is!

M636C

[oltmannd]

Thanks M636C,

I was looking for that missing link for some time!

Now, which horse is prettier?

greetings,

Marc Immeker

The French horses spend much more time worrying about looking prettier, but in fact they just eat better food. The English horses think they are much superior to the French horses, and don't realise how bad their food is!

M636C

It's all that heavy cream in French cooking that slows'em down!

[timz]

A "horsepower" is defined as 550 foot-pounds per second; as I recall a CV is defined as 75 "kilogram"-meters per second, where "kilogram" means the weight of a kilogram. So that makes a CV equal to 0.98632 horsepower.    At a given power output a locomotive's tractive effort is inversely proportional to its speed, and obviously that can't forever continue to be true as speed decreases. Even aside from adhesion limitations, the transmission can only produce so much TE, and a locomotive's actual capability at 1 mph, or 5 mph, or 10 mph isn't that well known-- by us fans at least.

[Anonymous]

TE is a force. HP is power. They are not "convertible" but related by speed.

Force x distance = energy

energy/time = power

so, power = force x distance / time

since distance/ time = speed

power = force * speed

For an typical DC locomotive:  HP = TE (lbf) x speed (mph)/308

where 308 is a factor that accounts for std English mearement and locomotive transmission efficiency.  For an AC, use 315 - they have slightly higher transmission efficiency. 

 

Good advice but it would be better just to use 375 times whatever efficiency a specific locomotive has instead of using a generic 375xeff number.
No two locomotives have identical efficiency.

[Anonymous]

Also, when playing with steamers, things are sort of reverse...

in the most simplified theory, steamers have constant TE

so instead of starting with HP and calculating TE at a given speed, you start with TE and calculate HP at a given speed.
As a result of that equation, their HP rises as their speed rises

But in reality its never that simple and linear of course. That's just a rough illustration of the difference between electric and steamer physics

[trainfan1221]

Basically, things are reversed with steam as per one book I have.  A diesel is more about moving any train it has the power to start, whereas a steamer is about being able to actually start any train it is capable of moving.  At least that's what I have read.  A GP40 and GP38, despite having 1000 difference in horsepower, can both move multi-thousand ton trains by themselves in the right conditions, provided it can actually get the train started.  The difference in horsepower relates largely to speed, a lone 38 will move a ten thousand ton freight, as will a lone GP40.  But the GP40 will move it faster.  Yard switchers can pull a whole train behind them, don't expect to set any speed records though.

[broncoman]

A CV is equal to 736 watts, a HP is equal to 746 watts. English speaking horses are very slightly stronger than French speaking horses.

M636C

Peter, 

You are a pretty brave guy opening up a can of worms like that.  Its a good thing there aren't too many French guys on the forum!  (Not that I disagree with the statement)



Dave

[billbtrain]

Tractive Effort decreases with speed.Correct?And Horse Power is governed by the engine's RPMs(I.E.:an SD40-2 is rated at 3000HP at 900RPM).Given that a locomotive is not operating at maximum RPMs in throttle notches 1 or 2 when starting a train,how would these factors be included in the equation?

Have a good one.

Bill B

[CSSHEGEWISCH]

Diesel engine horsepower is usually measured at maximum RPM (notch 8). 

[timz]

Given that a locomotive is not operating at maximum RPMs in throttle notches 1 or 2 when starting a train...

Remember the formula-- TE times speed, divided by 375, equals horsepower. In other words, at zero mph, horsepower at the rail is zero, no matter what the TE is. As long as the wheels aren't turning, the prime mover only has to supply enough power to overcome the electrical resistance in the alternator/generator and traction motors, and that's not much. So the locomotive control system has to be set up so that when you move the throttle to Run 1 a certain fairly-low preset amperage goes to the traction motors.

[oltmannd]

TE is a force. HP is power. They are not "convertible" but related by speed.

Force x distance = energy

energy/time = power

so, power = force x distance / time

since distance/ time = speed

power = force * speed

For an typical DC locomotive:  HP = TE (lbf) x speed (mph)/308

where 308 is a factor that accounts for std English mearement and locomotive transmission efficiency.  For an AC, use 315 - they have slightly higher transmission efficiency. 

 

Good advice but it would be better just to use 375 times whatever efficiency a specific locomotive has instead of using a generic 375xeff number.
No two locomotives have identical efficiency.

True, but railroading is a two significant digit enterprise!  (maybe only 1-1/2 digits....)

[GP40-2]

TE is a force. HP is power. They are not "convertible" but related by speed.

Force x distance = energy

energy/time = power

so, power = force x distance / time

since distance/ time = speed

power = force * speed

For an typical DC locomotive:  HP = TE (lbf) x speed (mph)/308

where 308 is a factor that accounts for std English mearement and locomotive transmission efficiency.  For an AC, use 315 - they have slightly higher transmission efficiency. 

 

Good advice but it would be better just to use 375 times whatever efficiency a specific locomotive has instead of using a generic 375xeff number.
No two locomotives have identical efficiency.

Sound advice from wildrails. The newest locomotives are much more efficient than older models.

In case anyone is wondering, the outdated 308 factor came from the first generation diesels with DC main generators and DC traction motors. Locomotives such as the F7 and GP7 had electrical systems that were around 82% efficient in converting the traction HP from the diesel to rail HP.

375 x 0.82 = 308

Using the 308 factor when calculating the rail HP of a new locomotive such as the GEVO or new SD70 is just plain wrong.

The advent of using AC alternators with DC traction motors (so called second generation diesels) elevated electrical efficiency up to 88%.

Current generation locomotives have electrical efficiency well into the 92%+ range.

[cpbloom]

Thank you all for your answers/comments.  

[oltmannd]

TE is a force. HP is power. They are not "convertible" but related by speed.

Force x distance = energy

energy/time = power

so, power = force x distance / time

since distance/ time = speed

power = force * speed

For an typical DC locomotive:  HP = TE (lbf) x speed (mph)/308

where 308 is a factor that accounts for std English mearement and locomotive transmission efficiency.  For an AC, use 315 - they have slightly higher transmission efficiency. 

 

Good advice but it would be better just to use 375 times whatever efficiency a specific locomotive has instead of using a generic 375xeff number.
No two locomotives have identical efficiency.

Sound advice from wildrails. The newest locomotives are much more efficient than older models.

In case anyone is wondering, the outdated 308 factor came from the first generation diesels with DC main generators and DC traction motors. Locomotives such as the F7 and GP7 had electrical systems that were around 82% efficient in converting the traction HP from the diesel to rail HP.

375 x 0.82 = 308

Using the 308 factor when calculating the rail HP of a new locomotive such as the GEVO or new SD70 is just plain wrong.

The advent of using AC alternators with DC traction motors (so called second generation diesels) elevated electrical efficiency up to 88%.

Current generation locomotives have electrical efficiency well into the 92%+ range.

You guys are splitting hairs, and misleading these guys all in one fell swoop!

308 is EMD's published number for Dash 2s. 

315 is their published number for 70MACs.

You gotta include gear set efficiency and other mechanical losses between the wires in to the TM and the railhead.

I've done dyanometer car tests on Dash 2s, 50 series, and SD60MACs and can tell you that EMDs numbers are solid. 

[trainboyH16-44]

Tractive Effort decreases with speed.Correct?

I don't believe so. Tractive effort is governed by how much power you can get down to the rail through the wheels, and it's governed by weight, mostly.

[beaulieu]

Tractive Effort decreases with speed.Correct?

I don't believe so. Tractive effort is governed by how much power you can get down to the rail through the wheels, and it's governed by weight, mostly.

No, he is correct T.E. falls with speed if you have a constant horsepower locomotive, which a diesel locomotive is. Once you exceed the continuous rated speed of the locomotive, the tractive effort will begin falling.

[GP40-2]

TE is a force. HP is power. They are not "convertible" but related by speed.

Force x distance = energy

energy/time = power

so, power = force x distance / time

since distance/ time = speed

power = force * speed

For an typical DC locomotive:  HP = TE (lbf) x speed (mph)/308

where 308 is a factor that accounts for std English mearement and locomotive transmission efficiency.  For an AC, use 315 - they have slightly higher transmission efficiency. 

 

Good advice but it would be better just to use 375 times whatever efficiency a specific locomotive has instead of using a generic 375xeff number.
No two locomotives have identical efficiency.

Sound advice from wildrails. The newest locomotives are much more efficient than older models.

In case anyone is wondering, the outdated 308 factor came from the first generation diesels with DC main generators and DC traction motors. Locomotives such as the F7 and GP7 had electrical systems that were around 82% efficient in converting the traction HP from the diesel to rail HP.

375 x 0.82 = 308

Using the 308 factor when calculating the rail HP of a new locomotive such as the GEVO or new SD70 is just plain wrong.

The advent of using AC alternators with DC traction motors (so called second generation diesels) elevated electrical efficiency up to 88%.

Current generation locomotives have electrical efficiency well into the 92%+ range.

You guys are splitting hairs, and misleading these guys all in one fell swoop!

308 is EMD's published number for Dash 2s. 

315 is their published number for 70MACs.

You gotta include gear set efficiency and other mechanical losses between the wires in to the TM and the railhead.

I've done dyanometer car tests on Dash 2s, 50 series, and SD60MACs and can tell you that EMDs numbers are solid. 

Sorry guy. I have 27 years experience with this stuff. The 308 number you keep professing is EMDs data for DC-DC locomotives only. Their published numbers for Dash 2s is in the 87% - 88% range. That includes ALL losses to the rail.

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.

If you are claiming that an SD70MAC/Ace is only a 315 efficiency, no wonder GE is cleaning up on the market.

BETTER YET:

Enough of this I said, you said stuff.

Here's a challenge to you: Contact GE and tell them about your 82% effeciency theory for their new locomotives. After they are done laughing at you, please report back to us.

GE Transportation Systems
2901 East Lake Road
Building 9-119
Erie, PA 16531

I'd give you their email, but they don't want us to give it out to railfans.

[oltmannd]

TE is a force. HP is power. They are not "convertible" but related by speed.

Force x distance = energy

energy/time = power

so, power = force x distance / time

since distance/ time = speed

power = force * speed

For an typical DC locomotive:  HP = TE (lbf) x speed (mph)/308

where 308 is a factor that accounts for std English mearement and locomotive transmission efficiency.  For an AC, use 315 - they have slightly higher transmission efficiency. 

 

Good advice but it would be better just to use 375 times whatever efficiency a specific locomotive has instead of using a generic 375xeff number.
No two locomotives have identical efficiency.

Sound advice from wildrails. The newest locomotives are much more efficient than older models.

In case anyone is wondering, the outdated 308 factor came from the first generation diesels with DC main generators and DC traction motors. Locomotives such as the F7 and GP7 had electrical systems that were around 82% efficient in converting the traction HP from the diesel to rail HP.

375 x 0.82 = 308

Using the 308 factor when calculating the rail HP of a new locomotive such as the GEVO or new SD70 is just plain wrong.

The advent of using AC alternators with DC traction motors (so called second generation diesels) elevated electrical efficiency up to 88%.

Current generation locomotives have electrical efficiency well into the 92%+ range.

You guys are splitting hairs, and misleading these guys all in one fell swoop!

308 is EMD's published number for Dash 2s. 

315 is their published number for 70MACs.

You gotta include gear set efficiency and other mechanical losses between the wires in to the TM and the railhead.

I've done dyanometer car tests on Dash 2s, 50 series, and SD60MACs and can tell you that EMDs numbers are solid. 

Sorry guy. I have 27 years experience with this stuff. The 308 number you keep professing is EMDs data for DC-DC locomotives only. Their published numbers for Dash 2s is in the 87% - 88% range. That includes ALL losses to the rail.

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.

If you are claiming that an SD70MAC/Ace is only a 315 efficiency, no wonder GE is cleaning up on the market.

BETTER YET:

Enough of this I said, you said stuff.

Here's a challenge to you: Contact GE and tell them about your 82% effeciency theory for their new locomotives. After they are done laughing at you, please report back to us.

GE Transportation Systems
2901 East Lake Road
Building 9-119
Erie, PA 16531

I'd give you their email, but they don't want us to give it out to railfans.

What you "know" doesn't match builder published numbers.

Let's look at some actual numbers from GE and EMD.

First, the 308 and 315 were from EMD for Dash 2 and Siemens equipped SD70MACs, not GEVOs and ACes.  It's what they quote in their 1994 locomotive application guide.

Second, here are some builder published numbers for shaft to DC conversion:

NTHP/THP for an SD40-2 = 93.85% (AR10)

NTHP/THP for an SD60 = 93.88% (AR11)

NTHP/THP for B36-7 (CHEC) = 94.40% (GTA24)

NTHP/THP for a GP30 = 93.83% (D22)

From the cables out of the gen/rectifiers into the switch gear to the rail is nearly identical on all these locomotives, no?  So if 308 is good for 1st gen, it's good for Dash 2's and 60 series (and Dash 7s, and Dash 8s). 

Third, from an actual test of 3 SD60MACs on Conrail:

TE (actual) = 375,000

THP (rated) = 12000

speed (actual) = 10.0 mph

Conditions were pretty close to AAR std - just a bit warmer, fair day, 1500' elevation, so barometer was close to std.

375000 x 10.0/12000 = 312.5 (within 1% 315 - how about that!)

Fourth, from GE's web page for AC4400(https://www.getransportation.com/general/locoanalyzer/displayjpg.asp?type=AC4400_TE.gif)

TE = 145000#

speed 9.81 mph

THP = 4390 HP (shaft HP into the traction alt. for traction)

145000 * 9.81/4390 = 324 (about 3% better than "315")

324/375 = 86% from engine shaft into generator to rail - by GE's own numbers.

BTW - I never claimed 82% for a GEVO - I claimed it for a Dash2 (and Dash 7)

Single % efficiency improvements are very valuable for the fuel savings they generate and their contibution to the ROI for purchase.  However, they are nearly meaningless in calculating locomotive performance.

Fifth, from GEs own web page:

"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. "

Note that IT DOES NOT INCLUDE MECHANICAL LOSSES FROM THE MOTOR SHAFT TO THE RAIL such as the gear set and axle brearings (as you have been asserting - maybe you should read your own company's literature?).

The notion that the avg railfan (or even the avg railroader) needs to apply actual transmission efficiency to 375 in order to understand the realtionship between speed, HP and TE is ridiculous.  And, that was what the original poster wanted to know! 

And finally:

Take the "GE - know it all" chip off your shoulder!  You're starting to sound like the EMD LaGrange "know it alls" from the 1970s!  (their field service engineers weren't nearly so arrogant)...And that's not a good thing!  Just look where it got them!  The RRs aren't exactly thrilled to death with the product out of Erie - it's just better than that out of London, these days.

And, I have 28 years, so there!

 

 

 

 

 

 

[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" being GE? Do the railroads get 4100 rail hp out of their units too?

A C44 puts out 4100 rail hp down to what speed? And 3900 down to what speed?

[JSGreen]

anybody else read the disclaimers on the chart which the link points too? Pretty amusing....

By the way, the link to the GE locomotive site was a great resouorce.  Thanks for posting it!

[Anonymous]

The tonnage an engine will move doesn't totally depend on its prime movers HP, but the efficiency of the generator, traction motors, and other things. For example, a 4000HP PM(prime mover) won't be any better than having a 2000HP PM if the TMs can only exert X amount of force. Having more power wouldn't help- more powerful traction motors and/or generator would be needed to actually use all of that power.

[oltmannd]

The tonnage an engine will move doesn't totally depend on its prime movers HP, but the efficiency of the generator, traction motors, and other things. For example, a 4000HP PM(prime mover) won't be any better than having a 2000HP PM if the TMs can only exert X amount of force. Having more power wouldn't help- more powerful traction motors and/or generator would be needed to actually use all of that power.

You're talking about a balanced locomotive design fit to the application.  That's a whole 'nuther can of worms!

[GP40-2]

 

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.