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Old August 9th 03, 07:06 PM posted to uk.transport.london
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Default Shielding 750 volt 3rd rail ?

On Fri, 8 Aug 2003 23:43:59 +0100, Michael Bell

wrote in :

* The danger of electrocution means that voltages cannot be
raised to increase power delivery. Italian state railways (FS =
Ferrovia della Stato) started with 3000 volt overhead wires, but
everything has now been done so that they can increase the voltage to
6000 volts, so doubling the power that can be delivered.


Redo your maths; V*2 = P*4, modulo foibles of inductive loads.

--
Ivan Reid, Electronic & Computer Engineering, ___ CMS Collaboration,
Brunel University. Room 40-1-B12, CERN
KotPT -- "for stupidity above and beyond the call of duty".
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Old August 9th 03, 09:40 PM posted to uk.transport.london
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Default Shielding 750 volt 3rd rail ?

Michael Bell wrote:
In article , Richard
J. wrote:
Michael Bell wrote:
It has always seemed to me that the 750 volt 3rd rail is a bad
idea. snip So I have been thinking of the possibilities
of shielding the 3rd rail. snip


Other people have designed such systems too. There is one already in
operation in London - the DLR.

To complete this would obviously be a 10 or 20 year project,
(even longer to replace some of the longer-lived stock with higher
voltage stock) but some of the benefits, such as no icing in winter,
would come immediately.


Your design includes a plastic cover over the top of the rail.
Doesn't this prevent existing stock from using rails fitted with
your plastic covers? I don't understand how you intend to operate
during the 10-20 year conversion period.


Obviously the fleet has to be modified first. That's the smallest part
of the job!


Ah, so the fleet is modified in such a way that it can use both the old and
the new design of rail. Not exactly a trivial task.

Also, have you done any sort of cost-benefit analysis for this
project?


No, I have done no cost-benefit analyis.


So you have proposed an expensive project for safety reasons which HSE don't
consider mandatory, with no analysis of whether it's worth spending the
money. I think you need to justify it better than that.

But if DLR (which I should have thought of) have done it, and foreign
systems have done it, then they must have made some sort of calculation.


DLR did it AFAIK because by then it was mandatory for new systems. The fact
that HSE did not mandate changing existing networks suggests that this would
not produce a reasonable cost-benefit.
--
Richard J.
(to e-mail me, swap uk and yon in address)

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Old August 9th 03, 10:28 PM posted to uk.transport.london
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Default Shielding 750 volt 3rd rail ?

In article , Dr Ivan D. Reid
wrote:
On Fri, 8 Aug 2003 23:43:59 +0100, Michael Bell

wrote in :

* The danger of electrocution means that voltages cannot be
raised to increase power delivery. Italian state railways (FS =
Ferrovia della Stato) started with 3000 volt overhead wires, but
everything has now been done so that they can increase the voltage to
6000 volts, so doubling the power that can be delivered.


Redo your maths; V*2 = P*4, modulo foibles of inductive loads.


I don't see that. Current can't be increased because it is
limited by the crosssection of the overhead wire, at least not
without it overheating, sagging and other undesireable behaviour. But
if you double the voltage at the same current, you double the power.
At least that's my thinking.


--
Michael Bell


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Old August 10th 03, 12:06 AM posted to uk.transport.london
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Default Shielding 750 volt 3rd rail ?

Dave wrote in message ...

The live rail is always furthest from the platform. It would have to be
a spectacular fall in order to land on the live rail.


Usually, but not always. Where there is a platform on both sides of
the track one of them has to be on the same side as the conductor
rail. Norwood Junction sprigs to mind, and I think this situation
also existed at Ryde Pier Head when it was first electrified.

I can also think of a case where there was, until recently, a
conductor rail on the platform side when there was a platform on only
one Side. This was at London Bridge, where the conductor rail had to
be on the platform side for a short distance because of a crossover
which I believe was used to allow the locomotive of a mail train to
run around. It was disused for some years before removal. I suspect
that the same situation also existed in other places. Generally, I
think the third rail system is acceptably safe, but I don't like
conductor rails below platform edges.


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Old August 10th 03, 12:17 AM posted to uk.transport.london
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Default Shielding 750 volt 3rd rail ?

Stephen Furley writes
The live rail is always furthest from the platform. It would have to be
a spectacular fall in order to land on the live rail.


Usually, but not always. Where there is a platform on both sides of
the track one of them has to be on the same side as the conductor rail.


And in the few places where this is the case, you'll usually find the
live rail is protected with wooden boards.

--
Dave
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