on Sat, Aug 30, 2003 at 02:19:39AM -0700, Paul Johnson (baloo@ursine.ca) wrote:
> On Sat, Aug 30, 2003 at 01:44:43AM +0200, Arnt Karlsen wrote:
> > ..2 reason diesel-electric locomotives are popular; they are
> > about as clean as your average power utility, and they dont
> > put heavy loads on the power grids.
>
> Nope, and nope. Diesel electrics are popular because they give the
> most bang for the buck. Vastly more efficient than gasoline engines
> and mechanical transmissions (it's 2003, why can't I get a diesel
> electric car?, with fewer moving parts than the steam engines it
> replaced. This makes them dirt cheap and bloody reliable. The
> railroads really couldn't give a damn about how much electric they're
> using since they're not having to string thousands apon thousands of
> miles of overhead lines (another costly expense railroads don't bother
> with unless they can get economic benefit from the typically heavier
> and faster trains that electrified lines run).
Electric traction offers a few benefits:
- Quieter.
- Less (near zero) right-of-way (RoW) pollution.
- Better high-speed performance.
- Fewer ventilation issues for tunnels or enclosed operations (e.g.:
RR terminals).
- Ability to power all axels.
This last provides several benefits. One is to reduce the amount of
slam between cars as the train accelerates or decellerates.
Ordinarially, cars pack into the locomotive as the train slows, and
start moving incrementally as the train starts (incidentally
distributing the startup load). More significantly though, for long
trains, is the elimination of the stringlining problem. This is the
result of having all your motive force at one end of a long line of
cars, while drag is distributed through the train. On a long curve (or
series of curves), the tendency is for the string to straighten out.
This has resulted in several derailments in mountainous regions,
notabily Dunsmuir in northern California (near Mt. Shasta, just south of
the Oregon border).
Downsides of electrification are notably the cost of electrifying the
RoW, and aquisition of stock.
Also, back in my intern days at SMUD, I recall that the city's light
rail system operated in power blocks seperated (though not fully
independent of) the city grid, largely because of the acceleration and
deceleration power draws and surges.
Peace.
--
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