Help on school paper, need info on traction drives

[Maddhatter]

Hi, I am writing a paper for school and I can not find any information on the actual electric motors that are in diesel locomotives. I have been studing the Dash 9 and it uses several GE 752AH traction drives. Can anyone give me any information about this motor or other motors? I am looking for data on the power, current, voltage, and torgue that each motor is rated at. Any information would be appreciated. Also I need info on the AC induction motors that are used on some of the new trains.

Can anyone help?

Thanks for your time

Eric

[Allen Hazen]

Basics.
The traction motors weigh about 3.5 tons each. (Modern diesel locomotives have one motor on each axle.) The 752AH is capable of "soaking up" about 1,000 engine horsepower at useful locomotive speeds (back in the early 1990s GE produced a 4,000 hp freight locomotive, the B40-8W, for the Santa Fe -- I think its motors were a slightly earlier variant of the 752).
You figure out the torque: the power at the rail is about 82% of the engine horsepower, so think of each motor on a B40-8W giving 820hp of output. The motor rotates about 4 times for each rotation of the wheel. The wheel is 40" in diameter. (That,I think, should be enough data. Full power at low speeds overheats the motor, so think of this being at, say, 20mph.)
For current draw, etc: there is a string on the Alco forum of Railroad.net called "PA-1 Traction motors." Early this year it had a long discussion of the evolution of the GE traction motor, and how its capacity increased over time.
Good luck with your essay!

[Maddhatter]

Thanks for the info, this will really help. One more question though, does anyone know if trains compensate for steep grades by them-self or does the engineer have to adjust the speed (power) or the train?

In case you are wondering, I am an electrical engineer at the University of Tennessee, studing hybrid vechiles. Hopefully I will help bring you cleaner running cars and trains.

Thanks again.

[timz]

does anyone know if trains compensate for steep grades by them-self or does the engineer have to adjust the speed (power) or the train?

Compensate for what? The engine is supposed to continue to generate full (i.e. constant) power (above 15-20 mph, anyway), so as the total train drag increases and speed drops, the engine's pull increases until equilibrium is re-established.

[Typewriters]

Timz is right, of course. As a train begins to ascend a grade, the fact that the train itself has to be raised against gravity, considering a constant power output, causes the speed to drop.

Load current will increase as speed decreases, but the output remains the same so that a balance is reached at a new, lower speed.

Naturally, everyone is already hitting the "reply" button as this is a gross oversimplification. For example, on many EMD locomotives, a system called Performance Control was fitted that essentially had the effect of limiting locomotive output to 500 HP per axle in the lower speed range, and used a fixed proportion of power at a given speed in the range wherein power was being modulated.

What, you say? Well, taking the GP-35, which was a four-axle unit rated 2500 HP for traction as an example, we see that 500 HP per axle gives a total of 2000 HP. From a dead standing start, theoretically only 2000 HP would be available (although wheel slip and resulting power modulation on start might well reduce ACTUAL power below this) until you accelerated to a speed of about 12 MPH. At that point, the locomotive's excitation control equipment began to allow horsepower to increase, and it increased in step with speed until a speed of about 18 MPH was reached. At that speed, the full 2500 HP output was available, and naturally was at all speeds above this.

I only mention this because this is NOT as simple as the first explanation given, but begins to reveal the complexities of locomotive control as related specifically to your question. In the case of Performance Control equipped units, then, if a grade drags your speed down below about 18 MPH, you do NOT have a constant power available with which you reach that theoretical "balance speed," but rather less power than "full rated" so that this had to be taken into consideration. The system was originally fitted to the GP-30 and was described as "Drag Duty Performance Control" which was supposed to allow the GP-30 to operate effectively on heavy grades when in multiple with older, lower horsepower units. The idea was to control tractive effort of the units in the low speed range so that they would not, as they say, try to hog the load from the lower powered units -- which would result in constant wheel slip, and either stalling or breaking in two.

Hope that helps in its own (only seemingly) confusing way!

-Will Davis

[Allen Hazen]

Eric - Mad Hatter--
I don't know what to presuppose in answering your questions. If you are an EE student, you probably know lots more than I do about the principles involved, but the wording of your questions suggests you don't know very much about railroad operations.
Adjusting for speed on steep hills...
(1) If a train is going to have to climb a hill, the dispatchers will assign it locomotives powerful enough to climb the hill, and so powerful enough to exceed the speed limit on the level portions of the route. So they won't be running at full power (*) on the level. Adjustment is not automatic: the engineer has to adjust the throttle.
(2) Going downhill is another thing. I assume you know about "dynamic braking" on diesel locomotives? This allows minimization of the use of the air brakes on the train. Works by using the traction motors as generators, with the excess energy traditionally dumped as heat from grids cooled by roof-top (**) fans, though General Electic is supposedly developing a hybrid locomotive on which the dynamic braking energy will be stored in onboard storage batteries: theoretically to be introduced in 2008. ... A neat illustration of the principle of dynamic braking was provided by a woman I met when I was a student in Pittsburgh many years ago. Her normal bike route (to/from work/school) involved a long, fairly gentle but constant grade, hill near the CMU campus. She had found that she could control her speed downhill by switching on her headlight: the light acting as the "grid" to get rid of the energy generated by the wheel-mounted generator!
---
* Most American diesel locomotives have controls with a small number of fixed throttle positions rather than a continuous throttle like an automobile's accelerator. Full power is "notch 8".
** Locomotives you are likely to see are built by two builders: General Electric and Electro-Motive Diesel (the latter recently spun off from General Motors). They have different design philosophies.
Electro-Motive locomotives have a series of fans in circular housings that project above the roof line. The ones near the rear of the locomotive cool the radiator. Dynamic brake cooling fans are near the middle of the locomotive hood on older locomotives. In newer ones they are either just behind the operator's cab or at the extreme rear, and are sunk within the carbody so the fan housing isn't visible from the side. GE has all itsfans internal: the radiators are at the rear end of the locomotive with the fan beneath them. The cooling-air openings for the dynamic brakes (on locomotives built since the mid 1980s, which would cover most of the GE locomotives you are likely to see on mainline trains) are square openings on the side of the hood, just below the roof, a bit behind the operator's cab.