Third rail systems return path
 

On Fri, 24 Jan 2020 19:55:18 +0000
Charles Ellson wrote:
On Fri, 24 Jan 2020 17:10:13 +0000 (UTC), wrote:

On 24 Jan 2020 15:25:11 GMT
Marland wrote:
Once it was done they had to be towed from Acton to Wimbledon by battery
locomotives with the positive shoe fuses removed as any current going into
LTs running rail track circuits would have caused problems , once at
Wimbledon on the Southern the fuses were put back and the units driven
away on the third rail. That’s what happened for the stock converted in
the mid sixties, I don’t know the movements of the 1938 stock when it got
converted.

There must have been more to it than that because I can't imagine putting
750V through equipment thats expecting 630V for a couple of hours as it
slowly makes its way to the coast could end all that well.

Don't use full parallel ?
AFAIAA the main consideration for running LU stock on BR/NR was the
insulation not the motors. Older tube stock was only insulated to cope
with ~+420v to earth on LU thus any running over LMS/BR shared tracks
required to be rewired; ISTR there were restrictions on which surface
stock was allowed on SR (I am going back to the days of Q stock or
older). Current stock is insulated for 750v, allowing for working over
shared NR or any part of LU that might get converted to third rail.

Not sure an LU train would be much use on 3rd rail tbh :) The ELL got converted
to 3rd rail to become part of the Overground (unfortunately - **** poor slow
service and subject to SR delays, would have been much better left as a self
contained tube line running to highbury) but I can't see that happening anywhere
else on the tube anytime soon.

Third rail systems return path
 

wrote:


Not sure an LU train would be much use on 3rd rail tbh :)

Some of the battery Locos would be fine even when running on power being
drawn , I don’t know which particular ones but because LT/LUL or whoever it
was at the time of ordering was hoping to hire them out for use on
Infrastructure work on 3rd rail equipped National rail lines they were
constructed with the ability to be switched between the two systems.
I don’t know if it has ever taken place though they did at least one rail
tour on ‘Southern’ tracks.

Readers may remember that the Met Loco Sarah Siddons at one time was also
modified to run on third rail and did some tours to the South Coast, at the
time though the traction motors and circuits could cope with the higher
voltage IIRC the braking compressors could not so they were isolated and
braking air came from the older Southern Multiple unit that was coupled to
it.
With the withdrawal of that old stock it was no longer possible.
Sarah Siddons has been overhauled since then but I don’t know if it could
be worked on the third rail,
the recentish moves to Eastleigh Works for various things have seen it
hauled .

GH

Third rail systems return path
 

In article , Marland
writes
Readers may remember that the Met Loco Sarah Siddons at one time was also
modified to run on third rail and did some tours to the South Coast, at the
time though the traction motors and circuits could cope with the higher
voltage IIRC the braking compressors could not so they were isolated and
braking air came from the older Southern Multiple unit that was coupled to
it.

I remember one such tour to Portsmouth Harbour. At both photo stops I
went forward to look at the loco. On one of them I spoke to the BR pilot
or inspector, who was complaining that the driver had a very light hand
on the controller. At the other I was talking to the LU driver who said
every time he put the controller too far round all the breakers went
because of the higher voltage.

So the impression I got was that the wiring could handle 750V (that's
just insulation) but the motors couldn't and so you had to keep some
resistance in the circuit.

IIRC, at the time South Western and South Central divisions were 650 V
near London, rising to 750 V once past the M25-to-be and 850V after
Southampton. While South Eastern division was 750 V throughout.

--
Clive D.W. Feather

Third rail systems return path
 

Clive D.W. Feather wrote:
In article , Marland
writes
Readers may remember that the Met Loco Sarah Siddons at one time was also
modified to run on third rail and did some tours to the South Coast, at the
time though the traction motors and circuits could cope with the higher
voltage IIRC the braking compressors could not so they were isolated and
braking air came from the older Southern Multiple unit that was coupled to
it.

I remember one such tour to Portsmouth Harbour. At both photo stops I
went forward to look at the loco. On one of them I spoke to the BR pilot
or inspector, who was complaining that the driver had a very light hand
on the controller. At the other I was talking to the LU driver who said
every time he put the controller too far round all the breakers went
because of the higher voltage.

So the impression I got was that the wiring could handle 750V (that's
just insulation) but the motors couldn't and so you had to keep some
resistance in the circuit.

IIRC, at the time South Western and South Central divisions were 650 V
near London, rising to 750 V once past the M25-to-be and 850V after
Southampton. While South Eastern division was 750 V throughout.


Surely the breakers went because the current was too high, not the voltage?
Of course, the current could become excessive because of the higher
voltage.

Third rail systems return path
 

In article , Recliner
writes
So the impression I got was that the wiring could handle 750V (that's
just insulation) but the motors couldn't and so you had to keep some
resistance in the circuit.

Surely the breakers went because the current was too high, not the voltage?
Of course, the current could become excessive because of the higher
voltage.

Indeed: Ohm's Law applies.

(Though what I learned at school is Ohm's actual law was that resistance
is constant for most materials and therefore V is proportional to I.)

--
Clive D.W. Feather

Third rail systems return path
 

In message , at 22:34:04 on Mon, 27 Jan
2020, Clive D.W. Feather remarked:
So the impression I got was that the wiring could handle 750V (that's
just insulation) but the motors couldn't and so you had to keep some
resistance in the circuit.

Surely the breakers went because the current was too high, not the voltage?
Of course, the current could become excessive because of the higher
voltage.

Indeed: Ohm's Law applies.

(Though what I learned at school is Ohm's actual law was that resistance
is constant for most materials and therefore V is proportional to I.)

Ironically, today's trains (diesel as well as electric) rely heavily on
materials where the resistance is *not* constant.
--
Roland Perry