Re: [Wildly OT] Locomotive transmissions [was: Re: OT: Debian Mailinglist server slow?]
On Monday 01 September 2003 08:28, Pigeon wrote:
> > > I don't normally disagree with you Pigeon ;), but here I do. If
> > > hydraulics had proved reliable, and cheaper, or significantly better in
> > > any way, d'you think they wouldn't have been more widely adopted by
> > > now? They were certainly tried in enough areas.
>
> So was the 68000, and look what a POS chip PCs ended up using... it is
> all too common for non-technical considerations to result in a
> technically suboptimal solution becoming the most widely used method.
> So we get VHS for VCRs, telescopic forks for motorcycle front
> suspensions, Windoze, incandescent light bulbs...
I *knew* you'd say that. Or rather, I thought you'd say "So's Linux, and
look at the crap everyone else uses".
But the case isn't the same. In the case of the PC (which uses the Intel
chip), or MS Windows, there's a strong motive for everyine to use the same,
whether for interoperability or just because, as a new user, they just use
what's being marketed and have no idea whether there are better ways to do
it.
I assume the people who buy diesel locomotives aren't as ignorant as
first-time computer buyers, and evaluate the technical merits in rather more
depth, including comparing running costs.
(Incidentally, I quite agree, the 68000 chip (or the Acorn RISC chip) are
both way superior to Intel's ad-hoc box of complications.)
>
> > > > Diesel-hydraulics are in many ways a much better idea than the
> > > > diesel-electric - simpler, more reliable, lighter, no need for
> > > > complex high-power electrical control gear, inherently good
> > > > resistance to wheel slip and transmission overheating which makes
> > > > them good choices for heavy freight trains and/or heavily graded
> > > > routes. The reasons they're not more widely used are
> > > > historical/political rather than technical.
> > >
> > > You're not a Great Western enthusiast by any chance? <vbeg>
> > > Me - Southern. ;)
>
> Certainly as far as technical developments are concerned. As for the
> more general view, I'm both Western and Midland - coming from "border
> territory"!
Then we'll *never* agree, will we? ;)
> > > Well, automatic cars all have hydraulic torque-convertor transmission.
> > > It works fine for low powers (by which I mean, up to a few hundred
> > > HP). It doesn't seem to work so well for high powers. Hence OK
> > > for railcars, not (apparently) for locomotives at higher powers.
>
> I admit that my main knowledge is of British traction, but it has to
> be said that the hydraulic transmissions were about the only bits of
> the British hydraulics that didn't fail - even the crappily-built
> British licensed clones of German-designed transmissions. (I'm
> excluding overheating due to (often silly) failures of parts in the
> cooling systems.) German and American hydraulics seem to have been
> similar.
Well, it seems to be an odd an unfortunate coincidence then, that all the
reliable hydraulic systems happened to be hooked up to unreliable
mechanicals. ;)
> > > And *also*, in places like Switzerland (or New Zealand), where there
> > > are long continuous grades, regenerative braking can put a lot of power
> > > back into the grid and save on train brake blocks. I believe some
> > > US diesel-electrics are equipped with regen braking but they just have
> > > to 'waste' the power produced.
> >
> > Yup, they call it rheostatic braking. Basically, the juice just gets
> > burned off by what amounts to giant oven coils under massive fans (the
> > big fans you see on most American diesel-electrics).
>
> Virgin have just introduced some flashy new diesel units with this
> system... not long ago the waves were breaking over the sea wall at
> Dawlish and shorting out the roof-mounted oven coils. The onboard
> computer detected this, and brought the entire train to a halt.
Never happened to a steam train <vbeg>
> > Portland's MAX
> > uses a similar system of braking to send power back on to the line.
> > My school used to share a (small) substation with the trains, you
> > could tell when a train was slowing down on the line up the street
> > because the lights would get slightly brighter, and if a particularly
> > full train (and thus heavy, requiring full throttle to accellerate
> > reasonably well) would make the lights slightly dimmer.
>
> This effect limits the ability of the London Underground, at least, to
> use regenerative braking - too many trains doing it at once, the
> supply voltage rises too high, and there's a risk of trains under
> power going too fast...
Underground trains don't run very fast, nor does their acceleration or
deceleration last very long, nor do they have long gradients, so regen
braking has less to offer. On some lines though, they put the stations at
the top of 'humps', to assist acceleration and deceleration. But I don't
think there'd be any risk of trains going too fast due to voltage -
that's controlled by the driver.
> > > Incidentally, third-rail works fine for multiple-units, but has
> > > distinct limitations for single-loco trains in any place where there
> > > are, say, a lot of railway crossings. (Or, as in NZ, largely
> > > unfenced tracks in some areas).
>
> Good point, though of less weight in Britain - everything's fenced,
> all new passenger stock is multiple-unit and freight operators prefer
> diesels for greater flexibility.
All new stock? Including high speed trains?
> > > The Southern Railway's early electric locos had a
> > > motor-flywheel-generator set ingeniously wired in series with the
> > > traction motors to overcome the break in traction. But that's DC,
> > > I'm not sure it would work so well on AC.
>
> Given that the technology of the time made a rotary convertor a good
> solution anyway, it was a brilliant idea. It'd work just as well on AC
> or DC. It would still be quite a good solution, though I suspect a
> dirty great bank of batteries that you could also go on/off shed with
> would be preferred.
Apparently it allowed them to make *brief* trips down unpowered sidings to
pick up the odd wagon and presumably go on shed. I imagine batteries would
cost quite a bit more in maintenance and renewals, since lead-acids don't
last very long.
> > > Also of course, 3kV third rail is a bit more dangerous than 600v DC.
>
> Well... 600V DC is considered to be in a pretty dangerous range: much
> below that and you're more able to take it; much over that and it
> tends to throw you off before it does much harm. Third-rail voltages
> tend to make you lock on and fry you. With bottom contact, it'd
> probably be safer than the existing system.
Hmm, I wasn't aware of that.
cr
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