"Cast_Iron" wrote in message
...
The Equalizer wrote:
"Acrosticus" wrote in message
...
From: Michael Bell
Date: 08/08/2003 23:43 GMT Daylight Time

It has always seemed to me that the 750 volt 3rd rail is
a bad
idea.

Too right! Massive amperages, high resistances, huge
numbers of substations in relation to the length of a
line. It's an idea that's really past its sell by date. If
you want to electrify, do it properly with 25Kv at 50
Hertz in a wire up on some sticks. Tinkering about with
750v DC is about as much good as rearranging the
deckchairs on the deck of the "Titanic".



And as soon as we get some windy weather all the overhead
lines come down and the entire rail network is screwed.

Not all, just that which was put up on the cheap.



Network Rail = Cheap

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".

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)

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

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.

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

From: Michael Bell
Date: 09/08/2003 22:28 GMT Daylight Time

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.

Unless you install wire with a greater cross sectional area of course, which is
more difficult to keep up in the air because it'll be heavier, so I think
you're right there.

But
if you double the voltage at the same current, you double the power.
At least that's my thinking.

And you seem to be right here two. Since volts x amps = watts, double the
voltage whilst keeping the amperage the same and you've doubled the power too.

"Acrosticus" wrote in message
...
From: Michael Bell
Date: 09/08/2003 22:28 GMT Daylight Time

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.

Unless you install wire with a greater cross sectional area of course,
which is
more difficult to keep up in the air because it'll be heavier, so I think
you're right there.

But
if you double the voltage at the same current, you double the power.
At least that's my thinking.

And you seem to be right here two. Since volts x amps = watts, double the
voltage whilst keeping the amperage the same and you've doubled the power
too.


Don't forget loaded voltage drop - that is often a major limitation in the
design length of a power feeder, not the absolute current carrying capacity
of cable or rail. When the train is drawing power at the far end of a
section, with higher voltage but with the same old feeder spacing, more
current might be passed by the same conductor without voltage dropping by so
much as a proportion of the feed.

--
Mark

"The Equalizer" wrote in message
...

"Cast_Iron" wrote in message
...
The Equalizer wrote:
"Acrosticus" wrote in message
...
From: Michael Bell
Date: 08/08/2003 23:43 GMT Daylight Time

It has always seemed to me that the 750 volt 3rd rail is
a bad
idea.

Too right! Massive amperages, high resistances, huge
numbers of substations in relation to the length of a
line. It's an idea that's really past its sell by date. If
you want to electrify, do it properly with 25Kv at 50
Hertz in a wire up on some sticks. Tinkering about with
750v DC is about as much good as rearranging the
deckchairs on the deck of the "Titanic".



And as soon as we get some windy weather all the overhead
lines come down and the entire rail network is screwed.

Not all, just that which was put up on the cheap.



Network Rail = Cheap

Network Rail = Expensive
Railtrack = Less Expensive
British Rail = Cheap

are (Acrosticus) wrote in message ...
From: Michael Bell
Date: 08/08/2003 23:43 GMT Daylight Time

It has always seemed to me that the 750 volt 3rd rail is a bad
idea.

Too right! Massive amperages, high resistances, huge numbers of substations in
relation to the length of a line. It's an idea that's really past its sell by
date. If you want to electrify, do it properly with 25Kv at 50 Hertz in a wire
up on some sticks. Tinkering about with 750v DC is about as much good as
rearranging the deckchairs on the deck of the "Titanic".

OTOH hand , when was the last time that you heard of trains being stuck or
cancelled because the 3rd rail fell over? There doesn't seem to be a winter
that goes by without some AC line being screwed by snapped overhead wires.
Catenary is fragile and flakey and is a terrible design plus it looks bloody
awful too. The only place its really needed is street based tramways.

What is needed is some sort of mid voltage (maybe 3000-6000V) sturdy ground
based 3rd rail system which isn't as fragile as overhead wires but doesn't
have the power losses of standard 750V 3rd rail. I'm sure isn't beyond the wit
of man to devise it.

B2003