Hello Derek!
Friday May 23 1997 19:05, Derek Brice posted a message to Ian May:
 IM>> It's not so much the power supply, but the track alignment, and
 IM>> more importantly the signalling.
 DB> Yeah, that makes sense, but just as a matter of interest, is there
 DB> more more limitations with with 750 volts DC from the third rail than
 DB> with the 25000 volt AC over head wire?
On the South-Eastern the 750V DC has been raised (on sections at which 
Eurostar
trains run at 100mph - basically Tonbridge to the Tunnel) to 820V DC.
Standard practice on the SE is for a substation every three miles, with a 
track
paralleling hut in between these. The TP huts have all been upgraded to
Substations on the above section, giving a spacing of 1.5 miles instead. This
reduces current loss between substations, which is the main disadvantage of 
C
operation compared to high tension AC.
As for the motors themselves, it doesn't make a great deal of difference, as
Eurostar trains (in common with the majority, if not all new electric motive
power) have three phase AC motors instead of DC traction motors. These are 
much
lighter than DC motors (about 55-60% of the weight of a DC motor), and being
thyristor controlled have no moving parts in the control circuitry - only 
ans
needed to dissipate the heat generated from the field switching involved.
You can hear these fans locally on Class 365/465/466 'Networker' units,
particularly as trains start away from a stand.
 DB> I notice that our trains in the SouthEast do tend to grind to a halt
 DB> in cold weather much sooner that the other systems.
Mainly due to ice build-up on the conductor rail. In times of very heavy
snowfall (not common here in the southern UK), then the conductor rail can be
totally blocked in by snow.
However, overhead power lines can also be affected by snowfall, and
particularly by high winds.
Regards,
Ian
... Tagline Distorted!
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