Eastern Railroad Discussion > 30T On Her Knees - D&H LAND

September 16, 2020

Train 30T is crawling up Belden Hill at Belden, NY, "on her knees" at a walk at Allen Road crossing.
Power is NS 1007 and 4369.

Lots of noise and a long wait as the sound reverberated through the hills of Upstate New York this afternoon.

Somehow, even though it was loud, it didn't have the drama of the old Alcos and GE's pouring out the smoke !

 



Edited 1 time(s). Last edit at 09/16/20 14:48 by train1275.

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Yeah the new stuff doesn’t sounds as dramatic when it’s pulling hard.
Neat location, that’s an interesting angle at the crossing.
Dan

Posted from iPhone

Probably because of accurate
‘Current limiting’ circuitry.....

At slow speeds the crankshaft HP far exceeds the current handling
capacity of the traction motors.

The motors ‘could be’ severely overheated at slow speeds... so,
the power that controls the density
of the generator’s magnetic ‘field’
is severely reduced.

[ controlling the “excitation field strength” of the generator is a convenient way to control and regulate the locomotive’s power output to the traction motors.
The generator’s excitation field is a modest current flow that is easy to regulate.

The total generator output is a combined result of the magnetic field and Engine RPMs... the magnetic ‘load’ from the straining traction motors actually puts a severe mechanical
‘braking-effect’ on the engine’s crankshaft....

That’s what makes the diesels ‘bark’ —- the reduced ‘load’
at drag speeds, yields a quieter noise out the stack... there’s plenty-enough amps to burn up the traction motors. So, by regulating
the generator’s magnetic field, thus the ‘load’, the designers keep the
current ( primary factor in motor’s heat generation) very restricted
during slow speed, drag operations..]


The reduced load on the crankshaft
allows the engines to rev-up, but there’s reduced & limited power supplied to the traction motors.... thus, very little fuel is burned, but the revs are high...
and there’s not as much noise.

At higher track speeds, the needed voltage is increased and allows the
total ‘electrical load’ on the crank to be increased.... the ‘watts’ in the system increase as a result of doing
more ‘work’ ..

Remember, HP is the ‘rate’ at which
the weight is ‘raised’.... the same mass moved at half the time, reflects a 4-fold increase in power.

So, to prevent burning-out of the traction motors, the current in the power-control circuitry is way-reduced
(to hold down the heat in the motors
hung on the axles..)..

So, you’ll not see today’s diesels very good
at ‘lugging’ against a load...

If you want more power into the train, add more locos to share the load —- radio controlled, maybe.

More traction motors doing the work
gets more force into the drawbars...
again, though, the engine cranks won’t be forced into higher loads with pouring-in of more fuel... the fuel feed will be
limited, per unit—- but more units
necessarily means more fuel consumption —- more cranks are spinning...

Another way to look at it is the fact
that the traction motors are limited
in physical ‘size’.... they are hung from the axles— bigger prime movers have to be held-back because the T/Ms are virtually still the same physical size as those under the SD-9s of decades past... the power
from the engines has expanded...
so it’s easier to burn-up the motors... that’s not a good thing for your ‘warranty’ program, if you’re
a manufacturer..... You’re going to use current limiting to keep yardmasters from adding more cars & overloading your traction motors..

Wes Camp

(See also how engine load affects
Turbocharger air pressure output...)

Posted from iPhone



Edited 3 time(s). Last edit at 09/17/20 06:38 by wcamp1472.

All that goobledegook (no offense) applies to DC motors...but they have never found the breaking point of AC motors used on locomotives...they can take massive currents down to a dead stall....and since they produce maximum torque at stall, they will turn and pull...if they can....even they can't pull unlimited weight but they will happily hold the train on the grade if they can....of course their massive torque means they could just spin....and there's where current limiting might come in, so as to prevent spin although a small amount of creep is allowed as that has been found to improve tractive ability a useful if small amount.