Trains and weather
Paul Dormer
Eurostar trains breaking down in the channel tunnel. Reports are saying
that this is because the trains have been travelling through northern
France where the temperature is below freezing and entering the tunnel,
where the temperature is 25C. Condensation is messing up the electrics.
The tunnel's been operating for fifteen years now, and below freezing
temperatures can hardly be uncommon in northern France, so why is this
happening now?
Martha Adams
wrote:
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=====================
I think maybe it's not that simple. News I saw said it was a matter
of snow blowing into the engine's works, and then when the train moved
down into the tunnel, the snow melted there and made trouble. Old
story but larger scale.
Titeotwawki -- Martha Adams [2009 Dec 24]
cryptoguy
> On Sun, 20 Dec 2009 13:51:00 -0000, Paul Dormer <p...@pauldormer.cix.co.uk>
> wrote:
>
> > Also on the matter of weather affecting transport is the odd case of the
> > Eurostar trains breaking down in the channel tunnel. Reports are saying
> > that this is because the trains have been travelling through northern
> > France where the temperature is below freezing and entering the tunnel,
> > where the temperature is 25C. Condensation is messing up the electrics.
>
> > The tunnel's been operating for fifteen years now, and below freezing
> > temperatures can hardly be uncommon in northern France, so why is this
> > happening now?
> I think maybe it's not that simple. News I saw said it was a matter
> of snow blowing into the engine's works, and then when the train moved
> down into the tunnel, the snow melted there and made trouble. Old
> story but larger scale.
It can happen on a smaller scale too. My brother-in-law was a
maintenance foreman for the MBTA (Boston transit) before he retired.
At one point, he got a commendation and award for working out that he
could prevent similar problems on the trains by putting mesh hairnets
over the air intakes when snow was expected.
pt
Martha Adams
=======================
Well, I was thinking about this. Suppose the maximum power of the electric
engine is about 1000 hp. Suppose that works out to 1,000 watts per hp,
which I think is in reality 640 watts, but let's try 1,000. Then the
1000 hp engine wants a megawatt at full power, as in accelerating or
going up a grade. Now I'm an engineer and I want to get that megawatt
down to the train. Transmission loss depends upon amperage, so I want
low amps which wants high volts. I arrive at 10,000 volts at 100 amps,
and I'm not sure how large conductors I'd want to carry this at adequate
efficiency for say 20 miles; but I imagine conductors dia is about 4 to
5 inches. So there's your system that powers the train, key point, if
you've ever worked with systems at 10,000 volts you know that's fairly
hot stuff. Snow is distilled water but when it melts in a dirty place,
as I expect you have down in the interiors of those electric engines,
it's a good bet to make trouble. The designers would allow margin for
some of this; but I can well imagine what happened here, might have been
simply *much more* snow in the engine's motor systems than anyone thought
would ever happen in service. I think the mesh hairnets is a good sensible
idea, if the air intakes are large enough for not too much air velocity
through them.
Titeotwawki -- mha [2009 Dec 24]
Keith F. Lynch
> I arrive at 10,000 volts at 100 amps, and I'm not sure how large
> conductors I'd want to carry this at adequate efficiency for say
I don't know about Chunnel trains, but the DC Metro's third rails are
600 volts. On the other hand, Metro's substations are much closer
together than 20 miles. On the gripping hand, Metro trains do a lot
of accelerating and decelerating. Chunnel trains can presumably
maintain their speed except at the endpoints. And they don't have to
undergo high acceleration -- so what if it take ten minutes to get up
to full speed? They're probably going downhill while accelerating,
anyway, which helps.
I strongly doubt any trains anywhere use anything close to 10,000
volts. At that voltage, insulators have to be impracticably thick.
--
Keith F. Lynch - http://keithlynch.net/
Please see http://keithlynch.net/email.html before emailing me.
Alan Woodford
<k...@KeithLynch.net> wrote:
>Martha Adams <mh...@verizon.net> wrote:
>> I arrive at 10,000 volts at 100 amps, and I'm not sure how large
>> conductors I'd want to carry this at adequate efficiency for say
>> 20 miles; ...
>
>I don't know about Chunnel trains, but the DC Metro's third rails are
>600 volts. On the other hand, Metro's substations are much closer
>together than 20 miles. On the gripping hand, Metro trains do a lot
>of accelerating and decelerating. Chunnel trains can presumably
>maintain their speed except at the endpoints. And they don't have to
>undergo high acceleration -- so what if it take ten minutes to get up
>to full speed? They're probably going downhill while accelerating,
>anyway, which helps.
>
>I strongly doubt any trains anywhere use anything close to 10,000
>volts. At that voltage, insulators have to be impracticably thick.
A quick, if somewhat disorganised search seems to show two sets of
voltages in common use around the world.
Third rail systems tend to run at 750 volts dc (the rails are large
section conductors), while overhead systems typically run at 25,000
volts ac, presumably to keep the resistance losses down.
Alan Woodford
The Greying Lensman!
Paul Dormer
mh...@verizon.net (Martha Adams) wrote:
>
> I think maybe it's not that simple. News I saw said it was a matter
> of snow blowing into the engine's works, and then when the train moved
> down into the tunnel, the snow melted there and made trouble. Old
> story but larger scale.
That was said in later news reports, after I made my original post.