Post by ReclinerPost by M***@dastardlyhq.comOn Thu, 09 Nov 2023 16:28:25 +0000
Post by ReclinerPost by M***@dastardlyhq.comOn Thu, 09 Nov 2023 11:28:55 GMT
Post by ReclinerPost by M***@dastardlyhq.comDunno, thats why I'm asking.
I can't find any reports of 'consequences'. It's a very small, simple
line, with no more than two short trains accelerating at any one time, so
return currents would be small, probably not enough to cause any problems.
Maybe, though AFAIK it used 750V, not 630, so making current leakage more
likely.
The only reason I can think of for 3rd rail given it was a self contained
line
Post by M***@dastardlyhq.combuilt from scratch with one off stock is to drive the trains under their own
power to a maintenance depot on the surface one they'd been lifted out.
Yes, that was one reason. But, simply, the LSWR just wanted to use the same
electrification kit as it did on the main
line. It seems not to have been a problem.
Which perhaps begs the question of whether the tube really needed 4th rail or
it was just an over abundance of caution especially on the sub surface lines
where corrosion isn't an issue anyway.
With many more, much heavier, faster accelerating trains in a section,
there are much greater return currents to deal with on the Tube. The SSL
share tracks with Tube trains, so they need to use the same system.
Mutleys question is one I have wondered about myself The W&C line
electric wasn’t quite the same as that later used on the LSWR the
conductor rail was central between the running lines and IIRC the original
voltage was 500.
The W&C is a self contained line but the same question could be applied to
the Central London Railway which also used a central third rail until LT
standardised it in 1940 and that was a much bigger operation.
The 4th Rail std started on the District and Metropolitan after the latter
gave up ideas of using 3 phase AC and as the District was part of the
Yerkes group it made sense to standardise across that organisations lines.
I wonder if one of the reasons for the District Railway choosing 4th rail
was because it was pioneering the use of track circuits and automatic
signals and keeping those and returning traction current separate. The
reduced leakage was an added benefit .
The LSWR main suburban electrification actually started quite late , it
wasn’t practical to use the system of the W&C as central third rail has
more gaps at point work whereas side mounted can change sides, also by 1915
the District had already commenced electric running on LSWR territory.
By adopting the same conductor rail position as the Districts Positive
conductor rail
it was relatively straight forward to have 3 and 4 rail trains share a
route , though you need a gap between true 4th rail with its + and -
voltages relative to earth and the shared route with the positive
at full voltage and the middle rail at ground.
GH
