Hello Ian!
Saturday May 24 1997 22:53, Ian May posted a message to Derek Brice:
 IM> Standard practice on the SE is for a substation every three miles,
 IM> with a track paralleling hut in between these. The TP huts have all
 IM> been upgraded to Substations on the above section, giving a spacing of
 IM> 1.5 miles instead. This reduces current loss between substations,
 IM> which is the main disadvantage of DC operation compared to high
 IM> tension AC.
How often do they have substations on the overhead?
From what I understand, the National Grid operates at 400,000 volts,
so where is it dropped to 25,000 ?
 IM> As for the motors themselves, it doesn't make a great deal of
 IM> difference, as Eurostar trains (in common with the majority, if not
 IM> all new electric motive power) have three phase AC motors instead of
 IM> DC traction motors. These are much lighter than DC motors (about
 IM> 55-60% of the weight of a DC motor), and being thyristor controlled
 IM> have no moving parts in the control circuitry - only fans needed to
 IM> dissipate the heat generated from the field switching involved.
So where does that weird siren noise come from when they move off?
 IM> You can hear these fans locally on Class 365/465/466 'Networker'
 IM> units, particularly as trains start away from a stand.
Yeah, I've heard them, and you should see the way they tend to blow
the dust up in some locations.
 DB>> I notice that our trains in the SouthEast do tend to grind to a
 DB>> halt in cold weather much sooner that the other systems.
 IM> Mainly due to ice build-up on the conductor rail. In times of very
 IM> heavy snowfall (not common here in the southern UK),
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Now you've said that, we're bound to have some of that WRONG KINDA SNOW
next winter.....   I wonder if the Eurostar and Networkers will like
some of that.  :-)).....  It'll kill the DC stock for sure.
 IM> then the conductor rail can be totally blocked in by snow.
Even a thin layer of unexpected ice can cause problems, can't it?
 IM> However, overhead power lines can also be affected by snowfall, and
 IM> particularly by high winds.
I can only go by past travel broadcasts, that the Third Rail trains
get effected much easier than the others.
Bye For Now,
Derek
                 FidoNet: 2:440/7.58       +       2:257/145.1
                 INTERNET:  derek.brice@plightning.coracle.com
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