To use an example...an SD40-2 is rated at 3000 hp... how is that figure determined?...and how accurate is it really?
It is the nominal mechanical power coming out of the diesel engine that's eventually headed for the traction motors. You measure it as electrical power out of the main generator, divided by the main generator's efficiency.
On an SD40-2 it will vary with atmospheric pressure and temperature, fuel temperature, fuel specific heat and auxiliary load at the moment (cooling fans, dust bin blower, cab heaters, air compressor...) The engine will consume a fixed volume of fuel at each notch setting.
On a new locomotive with "constant HP" excitation, it will not vary much at all, but the total shaft HP, and volume of fuel, will vary depending on the auxiliary load.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
Don hit it on the head. The key item when talking about North American rail locomotives is that the HP rating is what can be delivered to the traction motors. The air compressor and aux alterntors all drag down the available hp from the prime mover. As a good rule of thumb, EMD would drop about 10% off of the rating. A V16-645E in a SD40-2 is rated at 3000 hp. The same basic prime mover in a stationary power plant is rated at 3,300 hp. European builder usually rate diesels at the actual hp at the crankshaft for rail applications. The KM 'Diesel Hydraulics' of SP fame were rated at 4000 hp by the builder, and at 3600 hp by the railroad.
With the above said, it is possible to adjust the fuel racks so that one gets too much hp out of the engine. It is possible to get 2000 hp out of a rebuilt 567C with 645 power packs in it. Then you better have a cooling system to handle it, and an electrical system that is not going to fry on the output. BN had a 'rebuild' program for old ex-GN GP7 engines(CLRP-1) that boosted the ratings from 1500 hp to 1850 hp - They figured that was about the limit of the existing parts in the locomotive. During testing, they had one of the early ones put out 2200 hp on the load stand. Engine cooling water temp rose very fast as the cooling system could not drain off the heat fast enough.
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
Yes it is the power that CAN be delivered to the traction motors. I think that the builder , like EMD or GE, does the HP rating tests on their own prime movers before shipping them to their customers right. I never gave it a second thought but the compressers etc. would drop off the power a little bit wouldn't thay. hum... Don, wouldn't the turbo make up for some of this power loss? Or is the turbo, if so equipped, blended into this figure? Also for example... The MK 5000's, buitlt by Morris Kanutsin, had 5000 hp. How did that acheive this odd horsepower rating. Was it a turbocharger? Thay had CAT engiens in them, is it beacause of the diffent engine builder?
The road to to success is always under construction. _____________________________________________________________________________ When the going gets tough, the tough use duct tape.
According to "howstuffworks.com" James Watt (1736-1819) in the U.K. set the measure of one horsepower as equaling 33,000 foot-pounds per minute...in other words, the mine ponies he was working with should be able to lift 330 lbs of coal 100 feet in one minute. Actually the average horse did 22,000 foot-pounds per minute, he increased it 50% apparently figuring they could do that once with maximum effort.
It also translates to 746 watts of electricity, so a horse on a treadmill hooked up to a generator could produce a steady flow of 746 watts.
A 645E3 (turbo) is a 3300 HP engine in notch 8 .Parasitic loads include , cooling fans (30hp each) Air compressor (80-100 hp) Aux gen (30-40 hp) engine driven pumps (50-70 hp) If you graph the wattage you can actually see the bumps when cooling fans start, aircompressor loads and cab heaters are turned on even.
The first time I loadboxed an SDL-39 I thought there was something wrong with the engine, the first time a cooling fan started I lost 90 HP, 30 of which didn't come back . Took me a while to figure that one out , that little 12 cylinder engine was trying to keep up.
UlrichTo use an example...an SD40-2 is rated at 3000 hp... how is that figure determined?...and how accurate is it really?
Great answers above from Randy and Don. But what I thought you were saying, is "how" is that determined. The manufacturer determines it empirically for a given design. It load-boxes the engine, and, under a given set of conditions such as Don describes, the engines is physically demonstrated as producing that horsepower.
Is it accurate? Yes, within the manufacturer-defined upper and lower limits. The manufacturer is warranteeing to the purchaser, that if the engine is operated under a given set of parameters, it will when it rolls out the factory door produce the claimed horsepower, minimum. The manufacturer also provides the different horsepower outputs under different parameters, too, such as lower atmospheric pressure (higher altitude), higher or lower temperature, different fuel BTUs, and so forth. Those different parameters may be incorporated into the warranty too.
Over time horsepower output may decline due to mechanical condition of the engine and the transmission and auxiliaries. A tired SD40-2 may be producing something significantly less than 3,000 hp (at the flywheel after deduction for parasitic loads), but still burning the same amount of fuel, just wasting the difference as half-burned soot, or wasting some of its output on parasitic loads that have increased due to their own mechanical wear or insulation leakage.
In reality, the manufacturer doesn't produce a design, figure out what it will do, and go straight to market. It's a highly iterative process with thousands of hours of load-box time on various test engines, shooting for an ideal mix between fuel efficiency, manufacturing cost, reliability, maintenance cost, market need, market assessment, and so forth. The state of the technology informs the manufacturer what is possible, the state of the market informs the manufacturer what is economical.
RWM
jrbernierthe HP rating is what can be delivered to the traction motors.
So what it boils down to is that when we say a locomotive has say, 3000 horse power is that some of that energy is going o run electrical componets compressers etc once it it is turned into electrical energy in the alternator. So it really isn't exerting 3000 hp on the rail head by the time it is returned to mechanical energy in the traction motor. It's what 10% less I think someone said.
timz jrbernierthe HP rating is what can be delivered to the traction motors.It's what can be delivered to the main alternator/generator for traction. Whatever losses occur in the main generator are subtracted from the 3000 hp for an SD40-2, leaving 2800 (or whatever it is) to be delivered to the traction motors.
I thought that the losses are accounted for? With your example of the SD40-2, the 645 prime mover is actually producing approx.3200 "shaft horsepower" and the manufacturers power rating accounts for "parasitic load" i.e the power needed to operate the auxiliaries and the generator losses. Therefore the 3,000 HP rating is actually maximum power at the rail....
"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock
Start with about 3250 horsepower at the engine crankshaft
Subtract 250 horsepower for the traction motor blower, air compressor, and auxiliary alternator (which supplies power for the radiator fans etc)-- this quantity will of course depend on how many fans are running, but the plan is to end up with 3000 hp after those loads are subtracted.
That 3000 hp enters the main alternator/generator; neither it nor the traction motors are 100% efficient, so maybe 2600? horsepower appears at the motor pinions. The gears subtract some small amount, so 2500 hp at the rail is as good a guess as any for an SD40-2 in good condition, at speeds above, say, 15 mph. They're known to do better than that, but it's far more common for them to do worse.
Perfect!
timz Start with about 3250 horsepower at the engine crankshaft Subtract 250 horsepower for the traction motor blower, air compressor, and auxiliary alternator (which supplies power for the radiator fans etc)-- this quantity will of course depend on how many fans are running, but the plan is to end up with 3000 hp after those loads are subtracted. That 3000 hp enters the main alternator/generator; neither it nor the traction motors are 100% efficient, so maybe 2600? horsepower appears at the motor pinions. The gears subtract some small amount, so 2500 hp at the rail is as good a guess as any for an SD40-2 in good condition, at speeds above, say, 15 mph. They're known to do better than that, but it's far more common for them to do worse.
So now let's up the anty. Say we have our good freind the ES44DC, lets keep it DC for simplicity's sake. Now our computer systems are more advanced. So that's evan less power going to the rail right? The cooling systems, compressers,electronic systems are bigger. So that would subtract like what 450 hp? Just curious. Plese correct me if I said anyhting wrong or improper about anything.
Sort of , but not really..... All things being equal, the parasictic load would increase in direct proportion the the engine HP so it would be a wash, but...
The ES44DC would have proportionally lower parasitic and auxiliary loads than an SD40-2. Both EMD and GE reduced the avg parasitic and auxiliary load since the Dash2 and Dash7s in order to improve fuel economy.
The best example is the traction motor blower. Both EMD and GE used a mechanically driven blower to cool the traction motors. At notch 8 engine speed these suckers consume about 125 HP. Since you only need maximum airflow at low speeds, you are wasting a lot of HP at all other times. Both EMD and GE now use motor driven blowers with solid state motor controllers driven from an onboard computer to match the cooling air flow to the demand and minimize the HP going to the traction motor blowers.
Since your ES44DC is has "constant HP" exictation, the traction HP will remain constant, but the total shaft HP of the diesel will vary with the parasitic and auxiliary load. (Think about a car going 60 mph on the level with the AC turned on. When the compressor clutch engages, you have to step on the gas a bit harder to cover that auxiliary load and keep going 60). On SD40-2s and older, the shaft HP would remain constant and the traction HP would vary with the parasitic and auxiliary load.
Don,
Don't take this personal by any means but I really don't understand a word you just said. I am, however, eager to learn. If you have time, do you could explain to me some of the terms you just talked about in youre last post? I would be gratefull!
My e-mail... mackjs01@sbcglobal.net If you feel like it or have time. Thanks!
I believe that the 16 cylinder 645 had closer to 3300 hp, I had read that several times and it would make sense so that the 3000hp was delivered to the rail. I guess a number of conditions can vary this, but I believe that is how it works. Here's a good example, the DD40AX had two engines and was rated at 6600hp. Therefore the engines had to be at least 3300 if not more. If anyone can add to this it would be appreciated.
Allow me to reference a non-railroad related vehicle. The world's largest dump truck, the " Terex Titan" had an EMD locomotive engine in it, and it was supposedly rated for 3300hp. It also used traction motors, so basically it was a diesel locomotive in dump truck form. Well, along with a few other differences.
I think the DD40 was a 960 RPM engine . Like the 50 series with the 645F. I think the SHP was 3650.
trainfan1221I believe that the 16 cylinder 645 had closer to 3300 hp, I had read that several times and it would make sense so that the 3000hp was delivered to the rail.
An SD40-2 with 62:15 gearing was officially rated at 83,100 lb TE at 11.1 mph, which is 2460 rail horsepower. It can hope to do a little better than that at higher speeds, but 3000 is out of the question if the engine is set to load normally.
timz trainfan1221I believe that the 16 cylinder 645 had closer to 3300 hp, I had read that several times and it would make sense so that the 3000hp was delivered to the rail. To repeat: the prime mover on an SD/GP40-2 is supposed to produce a total of around 3250-3300 hp, of which somewhere around 2500 can be delivered to the rail. An SD40-2 with 62:15 gearing was officially rated at 83,100 lb TE at 11.1 mph, which is 2460 rail horsepower. It can hope to do a little better than that at higher speeds, but 3000 is out of the question if the engine is set to load normally.
To repeat: the prime mover on an SD/GP40-2 is supposed to produce a total of around 3250-3300 hp, of which somewhere around 2500 can be delivered to the rail.
As well as the DDA 40X mentioned above there were a number of HEP equipped locomotives, some F40PH-2 and the original F40C units that were said to be rated at 3200 HP.
I've always assumed that these locomotives (which had to run at constant RPM when supplying HEP) ran at 900 rpm to ensure a constant 60 Hz power frequency.
So were these units truly 3200 HP into the alternator(s) or was the 3200 HP the rating before auxiliaries were deducted?
M636C
Before. The best I've ever gotten from an F-40 is 3000 HP. Subtract 1147 HP if the HEP is running.
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