On Sun, 30 Nov 2008 15:08:16 +0000, Graham Murray
wrote:

David Hansen writes:

A dangerous impression. If there was no (electrical) danger from the
central conductor rail then it would not be mounted on insulators.

Insulators are a give-away that something is energised.

Does that necessarily follow? If the reason for using a 4-rail system
rather than a 3-rail with return via the running rails were to avoid the
problems such as electrolysis and interaction with signalling, would it
not be possible to do it by having the centre insulated rail at a
nominal ground potential but only bonding it to ground at the
substations?

There will always be leaks due to build up of dirt.

In article ,
(Paul Scott) wrote:

wrote in message

On hybrid sections (e.g. East Putney to Wimbledon) the 4th rail is
at +630v.

That would be the third (positive) rail. Otherwise the 'third rail'
stock wouldn't work too well...

Yes, I meant the outside rail. I was counting across with the centre as
third.

--
Colin Rosenstiel

"Christopher A. Lee" wrote

Of course it made sense to use the existing 4 rail system because
apart from the LBSCR's overhead AC that was what the other London area
lines used. The LNWR electrification was planned in 1907 and opened in
1914, with the Bakerloo linking up a year later.

The original plan was to extend the New Lines from South Hampstead in
deep-level tube to a terminus below Euston. In 1911, before the New Lines
opened, this plan had been abandoned in favour of linking with the Bakerloo.

The LSWR 3 rail system was planned later with the first section
opening in 1915.

Did the LSWR ever consider using the 4 rail system? The first LSWR line to
be electrified (apart from the isolated Waterloo & City) was the route
between Waterloo and Wimbledon, via East Putney, including the section
between East Putney and Wimbledon which had already been electrified on the
4-rail system for District trains. So this was the first use of a line
adapted to take both 3rd rail and 4th rail trains.

Peter

On Sun, 30 Nov 2008 18:00:27 -0000, "Peter Masson"
wrote:


"Christopher A. Lee" wrote

Of course it made sense to use the existing 4 rail system because
apart from the LBSCR's overhead AC that was what the other London area
lines used. The LNWR electrification was planned in 1907 and opened in
1914, with the Bakerloo linking up a year later.

The original plan was to extend the New Lines from South Hampstead in
deep-level tube to a terminus below Euston. In 1911, before the New Lines
opened, this plan had been abandoned in favour of linking with the Bakerloo.

OK.

Even what was done was a major effort, quadrupling the track out to
Watford with other major engineering works.

The LSWR 3 rail system was planned later with the first section
opening in 1915.

Did the LSWR ever consider using the 4 rail system? The first LSWR line to
be electrified (apart from the isolated Waterloo & City) was the route
between Waterloo and Wimbledon, via East Putney, including the section
between East Putney and Wimbledon which had already been electrified on the
4-rail system for District trains. So this was the first use of a line
adapted to take both 3rd rail and 4th rail trains.

I don't know.

By the time the LSWR electrified there were other systems for
comparison. I believe they had looked at the Liverpool-Southport
electrification before they made up their mind.

I do know that the New York Subway has major electrolytic corrosion
problems on their elevated sections, which are like continuous girder
bridges.

I've never read of the third rail system having the running rails at a
negative potential on either side of the Atlantic.

Tram and streetcar track did this so the problem has been known for a
very long time.

Perhaps it is because pipes etc were laid under streets and surface
trains had their own right of way. The original Met and Metropolitan
District lines ran cut-and-cover under the streets, as did the tubes
because of easement issues. And of course the latter tunnels were
lined with cast iron segments.

Peter

On Sun, 30 Nov 2008 15:08:16 +0000 someone who may be Graham Murray
wrote this:-

Insulators are a give-away that something is energised.

Does that necessarily follow?

Pretty much.

If the reason for using a 4-rail system
rather than a 3-rail with return via the running rails were to avoid the
problems such as electrolysis and interaction with signalling, would it
not be possible to do it by having the centre insulated rail at a
nominal ground potential but only bonding it to ground at the
substations?

That would mean, for the same voltage difference between the
conductor rails, increasing the voltage on the other conductor rail
and thus needing larger insulators for that. One would also have
greater leakages, as the higher the voltage the greater the leakage
through something like damp ballast against the conductor rail.

However, one would still be able to use heated conductor rails,
which is not AFAIAA done (at least in the UK) as that would also
involve heating the running rails (amongst other undesirable
things).


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Sun, 30 Nov 2008 16:50:43 +0000 someone who may be Steve
Fitzgerald ] wrote this:-

http://www.tubelines.com/whatwedo/tr...guidance/LU_sh
ort_circuiting_device.pdf

Which sadly in this case, the SCD was the cause of the problem.

I guessed that it was one of a series of problems which caused the
voltage from a still energised positive rail to be transferred to
the negative rail. Presumably there was some sort of broken
connection or open circuit breaker/fuse in the feed to the negative
rail.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Sun, 30 Nov 2008 08:04:16 -0800 (PST) someone who may be Mr Thant
wrote this:-
Crocodile clips or something, and how to use them, in glossy brochure
form:
http://www.tubelines.com/whatwedo/tr...ing_device.pdf

Figure 3 of
http://www.raib.gov.uk/cms_resources/2008-02-28_R052008_Merstham.pdf
is a photograph showing a third rail version of the same thing. The
design with the large wooden arm is partly to make it unlikely it
will be thrown off if the conductor rail is re-energised. It also
helps push the metal through the crud on the underneath of the
conductor rail.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Sun, 30 Nov 2008 18:00:27 -0000 someone who may be "Peter Masson"
wrote this:-

The original plan was to extend the New Lines from South Hampstead in
deep-level tube to a terminus below Euston.

Was the plan not for a terminal loop, presumably with a few
platforms?

In 1911, before the New Lines
opened, this plan had been abandoned in favour of linking with the Bakerloo.

In addition more trains were to be sent to Broad Street. In effect
the services took people to several places, rather than just Euston.
Much the same was true at Kings Cross, where trains were sent to
Broad Street and Moorgate (via the Widened Lines) rather than all
going to Kings Cross. Some even went to Ludgate Hill and further
south, though this ceased during the 1914-18 war IIRC.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Sun, 30 Nov 2008, David Hansen wrote:

On Sun, 30 Nov 2008 16:50:43 +0000 someone who may be Steve
Fitzgerald ] wrote this:-

http://www.tubelines.com/whatwedo/tr...guidance/LU_sh
ort_circuiting_device.pdf

Which sadly in this case, the SCD was the cause of the problem.

I guessed that it was one of a series of problems which caused the
voltage from a still energised positive rail to be transferred to the
negative rail. Presumably there was some sort of broken connection or
open circuit breaker/fuse in the feed to the negative rail.

Ah, so although there was no potential between the two power rails,
there was a potential between them and the ground?

Really, you need to connect the two rails to each other and also to the
ground. I was thinking the running rails would make a good ground
substitute here.

tom

--
buy plastic owl

"David Hansen" wrote

Much the same was true at Kings Cross, where trains were sent to
Broad Street and Moorgate (via the Widened Lines) rather than all
going to Kings Cross. Some even went to Ludgate Hill and further
south, though this ceased during the 1914-18 war IIRC.

Kings Cross was always remote from the City destinations of commuters, and
the link to the Met was put in in 1863, and the Widened Lines were opened
for passengers in 1868. However, despite additional Coenhagen and Gas Works
Tunnels, the approaches to Kings Cross were hiopelessly congested, with
trains taking half an hour for the 1.5 miles from Holloway to the
Metropolitan. The GNR sought running powers over the Canonbury Curve and
into Broad Street, but the LNWR prevented the North London granting these.
Accordingly the GNR invited the NLR to run trains from Broad Street out to
its suburban stations. This pattern - trains to Moorgate via the Widened
Lines and to Broad Street via the Canonbury Curve lasted until the Great
Northern Suburban electrification of 1976 - though it had its origins in
relief of congestion rather than offering passengers a choice of terminus
(Moorgate and Broad Street being very close to each other).

Around the turn of the 20th century the GNR planned a third route, the Great
Northern & City Railway, originally intended for through running from north
of Finsbury Park. However, the GNR and GN&CR fell out over through running,
so the Finsbury Park to Moorgate line had an isolated service (and was cut
back to start from Drayton Park when its Finsbury Park platforms were handed
over to enable the Victoria Line to be built). The through running
eventually started with the GN Suburban electrification.

Among the routes served by the GNR were Alexandra Palace via Highgate,
Edgware via Mill Hill, and High Barnet. The 1930s idea was to hand all these
over to London Transport, running both vvia Archway and via Finsbury Parkkk
and the GN&CR. In the event, LT did not take over Edgware to Mill Hill East,
or Alexandra Palace, and through running to the GN&C from these routes never
happened.

Peter