on conventional locomotives (in the UK at least), to limit max power (to prevent damage to turbo or the like), a quick fix used to be disconnecting microswitches configured for that maximum throttle position (8 or 9). Is this something that can safely be done for modern freight locomotives i.e. SD70ACe and the likes which are EM2000 controlled.
The Amtrak P42 locomotives were equipped with a switch that would limit only the lead locomotive in a consist to notch 7 (the purpose was unexplained in the orientation video, but it would reduce engine noise and vibration in the cab during acceleration and high-speed operation).
It was my understanding that restricting a ‘whole consist’ to notch 7 or notch 5 was handled strictly with engineer discipline rather than engine governor restriction. Jeff Hergert or others with firsthand experience with ‘notch-restriction’ policies will hopefully comment here. It’s an interesting question how AAR 8-notch on older locomotives with Woodward-governor solenoid-actuated MU would have the 8th notch inhibited.
Some other locomotives other than Amtrak’s had a switch to limit the lead loco to notch 7. It was useful when conditions caused wheel slip. It allowed trailing units to provide full power in notch 8 while the lead unit cleaned the rail and was less likely to slip under reduced power.
Mark Vinski
I think the limiting the engine to notch 7 was a GE thing. I remember it on the GE DC engines. Never saw it on an EMD engine.
Remote engines in distributed power consists can be set up in the DP linking process for CTE, controlled tractive effort. It’s used more in the mountains. I believe it controls power output at various throttle notches rather than limiting the throttle to a specific notch. I’ve never had to use it, always full tractive effort in my territory.
Jeff
thank you all for comments thus far. The consist we operate has no DP setup, just good old pneumatic (26L braking) controlling 130 cars with three to four power units at the front which are multiple unit connected. One particular type of power unit (amongst the three types we run), has turbochargers on their way out and i was trying to preserve the wear/tear until we get turbo stock. So instead of driver keeping all head end units at N6 or N7, why not only limit the one that has aged turbo instead of losing the Tractive effort/horsepower on all three/four units.
Hope i am making sense, at least in what i am trying to achieve!
Seems to me the practical thing – if this is a governed engine – would be to adjust either the governor settings on the particular unit(s) with issues (so the engine sees less peak fuel feed in a given MU notch or DP excitation) or fiddle with the excitation so the engine loads less, or slower, for a given commanded speed. Lower exhaust mass flow for a given intake back-pressure would keep the turbine from producing as much load on the bearings.
Depending on the engine type, you could rig a small wastegate that opens to relieve high boost at notch 7 or 8 and cut back fueling on the affected unit; the problem with that is that you’ll have the same issue with prompt excitation that Alco engines do, and the engine would not hold rpm against load.
You would need to let the motive-power department know the amount of derating for consist make-up purposes.