Amtrak Locomotive Question

[wcfan4ever]

Ok, I have never ridden an Amtrak train or even really waited for one to go by. The only time I happen to see an Amtrak right in front of me is when I go to La Crosse, WI for railfanning by the depot.

Ok, why does, or at least it seems like, Amtrak keep the locomotives running wide open once that train is stopped? Is is for power for the passenger cars? Do they do it so they can climb speed once they leave the station? Any help would be greatfull.

[zardoz]

wcfan-
As you surmised, the engine is running at full speed to provide power for the coaches.

To leave the throttle open to facilitate quicker acceleration is not effective (especially on a passenger train), as the engine speed will increase quickly enough to keep up with the demands of the load regulator (which goes to minimum field when the throttle is in idle, except in a yard/switching locomotive). If the throttle were advanced manually from the cab, the load regulator would also respond to the throttle position; this would quickly cause amperage to build.

[jchnhtfd]

if recollection serves, it was the F40's that ran at a constant speed for HEP -- I think the later ones have separate systems for HEP and don't run the prime mover at constant speed?

[zardoz]

Yes, the F40PH units did run at a constant rpm (900 or so) when providing electricity for the coaches. The units also had a "standby" mode (400 or so rpm), where electricity would be generated for the coaches only, but not the traction motors. "Standby" essentially turned the locomotive into a "power car".

How the Amtrak units function I am now uncertain as well; however, I do not recall ever seeing seperate exhaust stacks on the rear of the locomotive for the auxiliary power engine.

[wcfan4ever]

Thanks, it has always bothered me about that every time I had seen an Amtrak pass. I figured it was to supply power but was never really sure enough to stop thinking about it.

[Anonymous]

It can still be used as motive power by being controled by the load regulator

[Anonymous]

When the locomotive is in "standby" mode, the engine runs at 720 rpm (instead of 900). In this case, HEP power is drawn form the traction alternator (instead of the HEP alternator). The HEP generator needs 900 rpm to produce 60Hz, the traction alternator has more poles, so it just needs 720 for 60Hz.

Anyway, in a locomotive consist, only one locomotive is needed to provide HEP power, others just run in "Freight mode" at variable engine speeds.

The F59 has an independent HEP engine (a smaller CAT V12), so the prime mover works just like in a freight loco.

fgr

[oltmannd]

There is a gearbox between the prime mover and the HEP gen on the F40s (which has been a trouble spot).

Not sure exactly how the GEs function, whether there are additional windings on the main generator or whether there is a shaft driven alt off the back end of the diesel.

[Anonymous]

GE's tap off the main gen.