Example 1:A GP38-2 has a 2000 HP prime mover diesel engine.What are the horsepower ratings of the electric motors geared to the axle? [4 electric motors; 1 on each axle how much HP?]Example 2:An SD38-2 has a 2000 HP prime mover diesel engine.What are the horsepower ratings of the electric motors geared to the axle? [6 electric motors; 1 on each axle how much HP?]I know the tractive effort of the SD unit would be higher, but with 2 more motors on the axles, does it have more horsepower also?
This Site Might Help You. RE: Diesel locomotive horsepower question? Example 1: A GP38-2 has a 2000 HP prime mover diesel engine. What are the horsepower ratings of the electric motors geared to the axle? [4 electric motors; 1 on each axle how much HP?] Example 2: An SD38-2 has a 2000 HP prime mover diesel engine. What are the horsepower ratings of the
The short answer is, the horsepower is fixed. That is determined by the diesel engine and that can't make more power, it is just divided either by 4 or 6. A 3000 HP GP 40 locomotive pulls considerably more amperage than a 3000 HP SD 40, same horsepower divided by fewer axles, which is of course why the 6 axle pulls so much better at extended low speeds than 4 axles. The total horsepower stays the same, at full throttle the prime mover cant make anymore, your GP-38 will not be able to make any more power than an SD-38, both 2000. Added: At full throttle the main generator is putting out all the power it can, there can be no more load on it, that is fixed, the variable is the number of axles. Avio's figure of 750 HP per axle is absolutely correct, But those 750 HP motors in a 3000 HP locomotive obviously are never making over 500 HP each, there isnt enough power available from the main generator. That is why those motors last so much longer and are able to pull heavier loads, they are never making their maximum power. The amps we see on our meter in a locomotive dash is measured at the number 1 traction motor, not the generator/alternator output. At 10 MPH under maximum throttle a 3000 HP SD-40 (6 axles) pulls around 900 to 1000 amps (per axle), at the same speed a 3000 HP GP-40 (4 axles) locomotive is pulling well over 1200, heat buildup is a factor, short time ratings are soon exceeded and wheel slip is uncontrollable. Good question.
An electric locomotive is just that - electric. A diesel locomotive is in effect a mobile power station, consisting of a large, heavy diesel engine driving an equally-large and heavy generator or alternator to provide power for what is actually an electric locomotive. For the same power output, an electric locomotive is almost half the weight. For higher speeds, higher power output is needed, meaning diesel locomotives need even-bigger engines and generators, which makes the locomotive heavier, which requires a bigger engine and so on. The fact is - with current technology - the diesel locomotive has just about reached the limit of its development with regard to speed.
you must look at the power distribution between 4 and 6 axles as a fraction. you must also realize that at WOT (all 2000 ponies [38-series]) for either an SD or GP, the altenator produces the SAME power output (600amps if i remember correctly?). you are dividing the power available by either 4 or 6. so, you can see here that the GP trac mtrs have more power avail to them. thus why an SD will lug down at low speed longer. takes a bit longer to burn those out because they dont have the power avail to them as a GP. the trac mtrs on GP and SD are the same per class. for interchangability and mass production. so SD trac motors arent smaller. SD's primarily came about as a way to spread the weight out. giving the SD a lighter axle loading than its counterpart GP. for railroads who wanted the high hp, but had light rail. so most everything on a GP38, and SD38 are the same parts. fuel tank, trucks, and frame being the major differences. in essence, both SD and GP 38 series pull the same, they both have the same power output to the trac motors. if either sd or gp trac mtr takes more than it can handle, well, do you smell smoke? you must understand the 'load' is a fixed load. meaning the altenator can only produce so much. basic example: take a 9volt battery. hook 4 xmas bulbs to it. note how well they lite up. now hook 2 more to the chain for a total of 6. notice they all still lite up, but not as bright? thats exactly how it works with traction motors. same power plant in both examples, just a different fraction of power per unit.
