Re: mini/microturbines in the railway?
- From: hhc314@xxxxxxxxx
- Date: 28 Sep 2005 10:31:10 -0700
Interesting Bob, but I've forgotton the specific HP figures, only that
typically they ran between something like 1,000 and 8,000 HP depending
on the locomotive's type and size. Normally torque is not cited,
substituting the force that the locomotive is capable of exerting on
it's drawbar for torque (Tractive Effort). The horsepower of the
locomotive is always proportional to its weight, because the "Tractive
Effort" it can develop is limited by the coefficient of friction of a
steel wheel on a smooth steel rail hence gravity comes into play. (This
is why all diesel, diesel-electric, and electrics house massive weights
(usually large blocks of concrete).
Hence the maximum usable horsepower of a locomotive is limited by its
weight, and the weight is limited by the carrying capacity of the track
and roadbed. This is why you often see tandem or triple locomotives
pulling large freight loads, because this way the tractive power effort
is distributed over a greater length of track and roadbed, and why a
single, large locomotive cannot be on conventional 90lb mainline rail.
Power fed to the traction motors is controlled by electronic devices,
not by rheostats. When I worked at GRS, locomotives were still using
thyratrons and ignitron devices (essentially tubes) but no doubt these
were replaced by semiconductor in more recent times. (I left GRS and
railroad/rapid transit work in 1979, and moved on to work in military
systems at another company, so what I am posted is what I remember from
26 years ago and many things have changed over the years.)
Just a side bit, but its the limitations of steel wheels running on
steel rails that limits both the acceleration and braking that a train
(or a transit system) can exhibit. On a subway, for example, at
anything above an acceleration/deceleration rate of 3-miles/hour per
second, the wheels will either spin on the rail (during excess
acceleration attempts, or slide on rail (during Emergency Full Service
Braking). I know, not vital information for anyone not working on the
design of rapid transit and rail systems, but just one of those trivial
fact that many of us can't get out of our heads.
Another useless tidbit of information is that most freight locomotives
cannot simply start pulling a long (say 75 car) train from stop unless
they back-up first. I leave it to the readers to figure out why this
needs to be done, and how it works. (Think World Trade Center
collapse...)
Another curious tidbit, Navy Aegis Cruisers (Bunker Hill is one
example) are powered by twin LM2500 turbine engines burning what is
essentially jet fuel. I have no idea what the maximum horsepower these
engines at full throttle, but they can drive these 10,000-Ton
displacment ships using two props at speeds that would make most
smaller ships hydroplane! The top speed of this class of ship is
classified, but I suspect that 40-knots plus might be a good guess.
Kindest regards, Harry C.
.
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- From: hhc314
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