The WCML modernisation scheme uses (mostly!) 400 V three-phase, but
this has not been a great success owing to the higher currents (and
therefore greater number of sources of supply, known as Principal
Supply Points or PSPs) required.

Ummm.. Rather interesting this but this 400 volt 3 phase supply was
"difficult" in quite what way for signalling purposes?..
--
Tony Sayer

On Tue, 13 Apr 2010 08:37:22 +0000 (UTC), d
wrote:

On Tue, 13 Apr 2010 09:08:00 +0100
"Peter Masson" wrote:
"Mortimer" wrote

Would signalling or GSM use such high voltages? I'd expect low voltages
for anything that didn't require large amounts of power and would
therefore incur I-squared-R losses. I thought that the proposed GW
electrification would be OHLE, so why would it need 650V supplies?
What voltage do point motors run at?

I can't imagine them running at 650V would be very healthy for the track
maintenance staff!

OH routes used to run 240v to locations remote from a public supply on
the topmost/outermost wires which were indicated by red insulators.

On Tue, 13 Apr 2010 22:00:22 +0100, tony sayer
wrote:

The WCML modernisation scheme uses (mostly!) 400 V three-phase, but
this has not been a great success owing to the higher currents (and
therefore greater number of sources of supply, known as Principal
Supply Points or PSPs) required.

Ummm.. Rather interesting this but this 400 volt 3 phase supply was
"difficult" in quite what way for signalling purposes?..

As implied above, it requires more transformation points and/or more
copper in the ground. If it replaces a single-phase supply, it also
(assuming 3P+N) doubles the number of wires to be played with (or
stolen) and enables the various "interesting" effects caused by breaks
in the neutral or one phase wire without other conductors being
interrupted.

In article , Charles Ellson
scribeth thus
On Tue, 13 Apr 2010 22:00:22 +0100, tony sayer
wrote:

The WCML modernisation scheme uses (mostly!) 400 V three-phase, but
this has not been a great success owing to the higher currents (and
therefore greater number of sources of supply, known as Principal
Supply Points or PSPs) required.

Ummm.. Rather interesting this but this 400 volt 3 phase supply was
"difficult" in quite what way for signalling purposes?..

As implied above, it requires more transformation points and/or more
copper in the ground. If it replaces a single-phase supply, it also
(assuming 3P+N) doubles the number of wires to be played with (or
stolen) and enables the various "interesting" effects caused by breaks
in the neutral or one phase wire without other conductors being
interrupted.

OK what sort of current draw does a typical signal post, gantry frame,
need then?...

Suppose in that you could include points motors etc...

And that much difference in overall power supplied 650 V single phase
rather then I presume 415 or 440 or was it actually 400 three phase?.

Take your point re more cable required seem the price of copper is on
the up again. Bit on the news of some scrota almost frying himself in a
sub station...
--
Tony Sayer

On Wed, 14 Apr 2010 10:28:42 +0100, tony sayer
wrote:

In article , Charles Ellson
scribeth thus
On Tue, 13 Apr 2010 22:00:22 +0100, tony sayer
wrote:

The WCML modernisation scheme uses (mostly!) 400 V three-phase, but
this has not been a great success owing to the higher currents (and
therefore greater number of sources of supply, known as Principal
Supply Points or PSPs) required.

Ummm.. Rather interesting this but this 400 volt 3 phase supply was
"difficult" in quite what way for signalling purposes?..

As implied above, it requires more transformation points and/or more
copper in the ground. If it replaces a single-phase supply, it also
(assuming 3P+N) doubles the number of wires to be played with (or
stolen) and enables the various "interesting" effects caused by breaks
in the neutral or one phase wire without other conductors being
interrupted.

OK what sort of current draw does a typical signal post, gantry frame,
need then?...

The relevant figure is probably something more like how much average
current is drawn overall by the various equipment in the general area
x miles away at the end of the cable, remembering that other than
signal lamps and track circuits ...

Suppose in that you could include points motors etc...

.... a lot of it is transient.

And that much difference in overall power supplied 650 V single phase
rather then I presume 415 or 440 or was it actually 400 three phase?.

It's years since I played with 3-phase calculations (and in 20 years I
only ever had one 3-phase device to deal with) but IIRC the
(theoretical) "trick" is that with a balanced load your neutral
conductor can be almost non-existent (as occasionally occurs on LU
when it gets stolen) thus significantly cutting down on the amount of
copper compared with a single-phase circuit delivering the same amount
of power over two wires. Someone who has covered the subject rather
more recently might be able to do a quick back-of-a-Niquitin-patch
calculation but assuming ideal conditions my quick calculation is that
the CSA reduction of 3-phase (sans neutral) over 1-phase for the same
total current delivered is around 50% although I have a nagging doubt
that root-2 comes into it somewhere and pushes the reduction down to
25-33%.

Take your point re more cable required seem the price of copper is on
the up again. Bit on the news of some scrota almost frying himself in a
sub station...

As implied above, it requires more transformation points and/or more
copper in the ground. If it replaces a single-phase supply, it also
(assuming 3P+N) doubles the number of wires to be played with (or
stolen) and enables the various "interesting" effects caused by breaks
in the neutral or one phase wire without other conductors being
interrupted.

OK what sort of current draw does a typical signal post, gantry frame,
need then?...

The relevant figure is probably something more like how much average
current is drawn overall by the various equipment in the general area
x miles away at the end of the cable, remembering that other than
signal lamps and track circuits ...

Yes.. Just wondered if that had now fallen due to LED lighting etc?..

--
Tony Sayer

In uk.transport.london message , Wed, 14
Apr 2010 10:28:42, tony sayer posted:

And that much difference in overall power supplied 650 V single phase
rather then I presume 415 or 440 or was it actually 400 three phase?.

Take your point re more cable required seem the price of copper is on
the up again.

For the same power, three-phase requires little over half of the amount
of conductor in comparison with single-phase. Consider three single-
phase supplies driven at 120 degrees to each other : obviously the live
wires deliver the same AC current as the live wires in a three-phase
supply, but three neutral wires are required. Now join the three
neutrals into one; the three return currents, being of different phases,
add to nothing, with balanced loads; therefore the neutral, carrying
only off-balance currents, can be comparatively thin. See sig.

--
(c) John Stockton, near London.
Web URL:http://www.merlyn.demon.co.uk/ - FAQish topics, acronyms, & links.
Correct = 4-line sig. separator as above, a line precisely "-- " (RFC5536/7)
Do not Mail News to me. Before a reply, quote with "" or " " (RFC5536/7)

On Tue, 13 Apr 2010 10:48:59 -0700 (PDT) someone who may be The
Gardener wrote this:-

Like a lot of things on the railway, its origins are historical. 650 V
was the highest value of "medium" voltage under the old Factories Act,
which meant that (at that time) a permit-to-work system was not
required for "live" work. Such a system of work would these days be
illegal under the Electricity at Work Regs, of course.

That is rather amusing on a railway line equipped with unprotected
conductor rails energised at a nominal 750 V d.c. (For those who
don't know unprotected conductor rails are one of the very few
exemptions under the Electricity At Work Regulations 1989).

The policy for main lines now is that the distribution systems have
either a PSP at each end (WCML practice) or a PSP at one end and an
auxiliary PSP (APSP) at the other (Western practice), to enable
resupply in the event of a failure. In particular, a dual-fed system
will allow a faulted cable section to be isolated and the two sections
to be fed from each end.

Do you know if switching is automatic, remote,or manual? Perhaps the
answer is, it depends:-)

Thanks for taking the time to produce a comprehensive posting. I
found it very interesting.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000...#pt3-pb3-l1g54

On Apr 13, 6:48*pm, The Gardener wrote:

650 V
was the highest value of "medium" voltage under the old Factories Act,

aha ... cue sound of things falling into place ... I did not know
that ... a useful fact when trying to understand these things.


--
Nick

On Apr 15, 8:28*pm, David Hansen
wrote:
On Tue, 13 Apr 2010 10:48:59 -0700 (PDT) someone who may be The
Gardener wrote this:-

Like a lot of things on the railway, its origins are historical. 650 V
was the highest value of "medium" voltage under the old Factories Act,
which meant that (at that time) a permit-to-work system was not
required for "live" work. Such a system of work would these days be
illegal under the Electricity at Work Regs, of course.

That is rather amusing on a railway line equipped with unprotected
conductor rails energised at a nominal 750 V d.c. (For those who
don't know unprotected conductor rails are one of the very few
exemptions under the Electricity At Work Regulations 1989).

The policy for main lines now is that the distribution systems have
either a PSP at each end (WCML practice) or a PSP at one end and an
auxiliary PSP (APSP) at the other (Western practice), to enable
resupply in the event of a failure. In particular, a dual-fed system
will allow a faulted cable section to be isolated and the two sections
to be fed from each end.

Do you know if switching is automatic, remote,or manual? Perhaps the
answer is, it depends:-)

Thanks for taking the time to produce a comprehensive posting. I
found it very interesting.

--
* David Hansen, Edinburgh
*I will *always* explain revoked encryption keys, unless RIP prevents me
*http://www.opsi.gov.uk/acts/acts2000...#pt3-pb3-l1g54

In response to your query about switching, the WCML system has
automatic switching, whereas the (significantly cheaper) Western
system has manual switching. At the moment, these are the only routes
where reconfigurable supplies have been provided. In the case of the
Western, this is slowly being rolled out across the system's main
lines and is in use of the lines south from Gloucester towards Swindon
(the first significant application and primarily as a testbed) and
Bristol, for example.

Present policy is that if the average cost of delay minutes on a route
exceeds a certain amount, then at resignalling, a reconfigurable
system is to be provided. This is a fairly recent change of policy,
which is why it has only been applied extensively on the WCML. The
Western schemes are not, generally, associated with resignallings
(except for the new scheme in the Newport area) but are the result of
a policy to improve the availability and reliability of sigpower
schemes.

In response to some other queries raised:

The 650 V system supplies all signalling and telecoms loads,
interlockings and point machines. In addition, a certain level of
emergency lighting at relay rooms is also supplied off the 650 V
system. The power supply arrangements at level crossings varies; at
some sites all the equipment is supplied from the 650 V system and at
others, only the signalling interlockings, with the barriers and
lights supplied directly from the mains. Owing to the risk of wrong-
side failures caused by a loss of supply, level crossings apart from
AOCL and ABCL are fitted with battery back-up and the equipment is
supplied directly from the battery, in the manner of a UPS. Telecoms
loads are also usually fitted with battery back-up.

One of the problems with a three-phase system is that all UK approved
signalling equipment is single-phase, and given that point machines
tend to have much higher loads than any other equipment (typically 2-3
kVA, whereas most other equipment has demands in the tens of VA), load
balancing is difficult. In the case of level crossings, three-phase
battery chargers are used. As to why we don't use three-phase point
machines, the answer is I don't know, apart from that there are no
product-approved examples. They are used elsewhere, so they do exist.

I have, somewhere in my possession, a table of typical signalling
equipment loads, which I will try to find and summarise on this group
next week. As far as LED signals are concerned, I believe that they
have a higher demand than bulb signals, owing to the large number of
individual LEDs as opposed to a single bulb.

Hope this is of further use.