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

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