What exactly does how fast a locomotive loads have to do with anything?
I think what im asking is what does the loading do?
It is the Locomotive equivilent to when you step on the accelerator how fast does the car respond. When you advance the throttle a fast loading locomotive will immediately accelerate, a slow loading locomotive will accelerate slowly. Normally a locomotive designed as a switch engine loads quickly so as to kick a freight car, while road locomotives accelerate slower so that the greater tractive effort they produce won’t pull out a drawbar.
It’s the rate at which the excitation to the main generator increases. It’s part of the design of the locomotive.
There are a couple of factors that determine what loading rate is the best. One is the rate at which the diesel engine can accomodate more load. If you try to load up the main gen. faster than the engine can accomodate it, you’ll bog the engine down - too much fuel for the air supply. EMD’s either with blowers or gear drive turbo can accomodate rather fast loading and can go from no load idle to full load and speed (engine RPM, not track speed) in about 25 seconds. A GE will load much more slowly in order to let the turbo get up to speed to supply enough air. In fact, it has three loading rates. If you start from no load idle and wipe the throttle to N8, it will load very slowly for about 30 seconds, then the loading rate will increase to a medium rate for the next 30 seconds. Finally, the loading rate will be almost EMD-ish for the last 20 to 30 seconds.
If you have GP40 and a B36 in the same consist and wipe the throttle from idle to N8 - the GP40 will be giving you all 3000 HP 25 seconds or so while the GE is still thinking about getting up to 1000 HP.
The second factor is train handling. An EMD with a blower is capable of loading so fast that it can make for lousy train handling. EMD used to put a loading rate switch in some of their locomotives that would give you the fast loading rate for kicking cars and then allow you a slower rate for operating a road train.
Don – clearest explanation of the hows and whys I’ve seen yet. Thanks!
“how quick ya can get the power to the wheels…”
Adrianspeeder
Don, I remember seeing that switch on SWs. I think it was a “forestalling,” switch. The unit wouldn’t start to load until the diesel was good and wound up.
Oh, thanks guys. I was wondering because I was working with a NW5 and it kept loading erratically.
don i almost agreed with everything you said the faster loading engines make train handling much easier not harder that is why GE engines suck they wont load you haft to break all the rules to get them to do what 1 good emd will do.
Iron ken series forestalling had nothing to do with how fast a unit would load .forestalling was /is a device when used limits power to keep from burning up traction motors. if you used the unit in road service with big units as power you must set this feature up so power is limited to notch 7 ( or at least i was told this by the mechanical forces ) because these units ( yard switchers) would burn the traction motor up . i never used them i just dragged them along for the ride.
Oops, thanks Wabash.
I’ve learned a lot on this one… so now I have a question: what controls the rate at which an engine will load? Is it something in the diesel’s governor or fuel control, which controls the rate at which the fuel injection can increase? Or something in the electrical circuitry (maybe in the exciter?) which controls it? Obviously there is something there…
Don? Somebody?