Rail Mail in London.

[45669]

Evening All,

 

I had a trip on the new Mail Rail in London this week and can thoroughly recommend it to anyone in, near or visiting London.  For anyone unfamiliar with Rail Mail, it's the old 2ft gauge underground Post Office Railway that until 2003 carried millions of letters between Paddington and Liverpool Street Stations and the Mount Pleasant sorting office.  It ran in deep level tube tunnels and had driverless trains operated from control panels.

 

Completely unknown to the majority of Londoners it was called London's secret railway, but a short section of it has now been re-opened in conjunction with the Post Office Museum near Mount Pleasant sorting office and the public can take a short ride on trains deep below Mount Pleasant.  

 

I took a few pictures whilst there and these are now on Flickr.  This is the link:

 

https://www.flickr.com/photos/train-pix/albums/72157661375104808

 

Hope they're of interest.  

[KeithHC]

Great set of photos. Do I notice that the third rail has gone now. So are the passeneger trains now battery powered.

 

Keith

[45669]

Great set of photos. Do I notice that the third rail has gone now. So are the passeneger trains now battery powered.

 

Keith

 

Correct; there's a compartment in the middle of the train full of batteries.

[PhilJ W]

Great set of photos. Do I notice that the third rail has gone now. So are the passeneger trains now battery powered.

 

Keith

 

 

Correct; there's a compartment in the middle of the train full of batteries.

IIRC there never was a third rail, power was supplied through the running rails exactly the same as a model railway DC system. Undoubtedly as they operated at a greater voltage than a model railways 12 volts battery operation is a necessity for health and safety.

[Vanders]

IIRC there never was a third rail, power was supplied through the running rails exactly the same as a model railway DC system. Undoubtedly as they operated at a greater voltage than a model railways 12 volts battery operation is a necessity for health and safety.

There was a 3rd central power rail, with the return via. the running rails. You can see it in the various pictures in http://www.placehacking.co.uk/2011/04/24/security-breach-london-mail-rail/

 

For obvious reasons it's not a great idea to run a live 3rd rail at ground level were members of the public will be, so they had to remove it and rely on battery power.

Edited October 14, 2017 by Vanders

[Claude_Dreyfus]

This is certainly on my list of places to visit. Thank you for posting the pictures.

[Davexoc]

For obvious reasons it's not a great idea to run a live 3rd rail at ground level were members of the public will be, so they had to remove it and rely on battery power.

Are you sure? What about the entire LU and most of the lines south of the Thames?

 

Dave

[Pete the Elaner]

Are you sure? What about the entire LU and most of the lines south of the Thames?

 

Dave

Maybe platform height makes a difference? RailMail's platforms look at most 6"-9". BR & LU have platforms 18"-3' higher than rail level.

BR's 3rd rail stops each side of any sort of public crossing.

Would they allow such 3rd rail systems to be created today? I doubt it because DLR's 3rd rail is upside down, presumably for safety reasons.

[melmerby]

There was a 3rd central power rail, with the return via. the running rails. You can see it in the various pictures in http://www.placehacking.co.uk/2011/04/24/security-breach-london-mail-rail/

 

For obvious reasons it's not a great idea to run a live 3rd rail at ground level were members of the public will be, so they had to remove it and rely on battery power.

 

The traction voltage was 440DC and overhead was used in depots, instead of third rail, for safety reasons

 

Keith

[stewartingram]

Maybe platform height makes a difference? RailMail's platforms look at most 6"-9". BR & LU have platforms 18"-3' higher than rail level.

BR's 3rd rail stops each side of any sort of public crossing.

Would they allow such 3rd rail systems to be created today? I doubt it because DLR's 3rd rail is upside down, presumably for safety reasons.

Doesn't stop passengers stepping off the platform, crossing the track and stepping onto the opposite side platform. I've witnessed this a number of times on LU platforms.

 

Stewart

[Suzie]

All the fun of the Post Office railway was the automatic control of trains via the traction supply. The sounds of the contactors connecting and disconnecting the supply was just magic as the trains braked and accelerated.

[Edwin_m]

Would they allow such 3rd rail systems to be created today? I doubt it because DLR's 3rd rail is upside down, presumably for safety reasons.

 

No.  Office of Road and Rail has a strong presumption against even extensions of existing top contact third rail systems.  You couldn't really argue that Mail Rail has "grandfather rights" because previously it was accessible only to trained employees and now it is accessible to the general public so the electrocution risk would increase vastly. 

 

DLR and other third rail networks that have started up in the last few decades do indeed use a bottom contact third rail for safety reasons.  But if the trains have shoegear on both sides then that on the opposite side from the third rail would still be live - notice that DLR has shields on the platform wall where the shoegear normally stops, to prevent contact by dropped umbrellas etc.  On Mail Rail the shoegear would be close to the legs of people standing on the low platform. 

[melmerby]

 

 

  On Mail Rail the shoegear would be close to the legs of people standing on the low platform. 

No it wouldn't

It was a centre third rail not a side third rail. and the shoe gear was just under the "front" of the motor units.

https://cdn.arstechnica.net/wp-content/uploads/sites/3/2017/07/Detail-of-1980s-Greenbat-Train-in-Tunnel-5-1440x960.jpg

 

http://assets.atlasobscura.com/media/W1siZiIsInVwbG9hZHMvYXNzZXRzLzZlOWRkOWI0OGVjMzI1YzVkZF9Qb3N0MTE4XzM4Ni5qcGciXSxbInAiLCJjb252ZXJ0IiwiLXF1YWxpdHkgODEgLWF1dG8tb3JpZW50Il0sWyJwIiwidGh1bWIiLCIxMjgweD4iXV0/Post118_386.jpg

There is no reason why a third rail supply couldn't be used with a non hazardous voltage. The power required for the people movers now used wouldn't be particularly high.

 

Keith

Edited October 15, 2017 by melmerby

[Edwin_m]

No it wouldn't

It was a centre third rail not a side third rail. and the shoe gear was just under the "front" of the motor units.

https://cdn.arstechnica.net/wp-content/uploads/sites/3/2017/07/Detail-of-1980s-Greenbat-Train-in-Tunnel-5-1440x960.jpg

 

http://assets.atlasobscura.com/media/W1siZiIsInVwbG9hZHMvYXNzZXRzLzZlOWRkOWI0OGVjMzI1YzVkZF9Qb3N0MTE4XzM4Ni5qcGciXSxbInAiLCJjb252ZXJ0IiwiLXF1YWxpdHkgODEgLWF1dG8tb3JpZW50Il0sWyJwIiwidGh1bWIiLCIxMjgweD4iXV0/Post118_386.jpg

There is no reason why a third rail supply couldn't be used with a non hazardous voltage. The power required for the people movers now used wouldn't be particularly high.

 

Keith

 

Sorry didn't make that clear, I was referring to a bottom contact third rail to meet modern safety standards, which would have to be at the side. 

 

I recall a voltage has to be as down to about 50 volts to be considered non-hazardous.  One of the Parry People Movers charged from a third rail at about 70V but they were advised it wouldn't be acceptable in public areas.   At 50V a fairly modest 10kW motor would be drawing 200 amps. 

[Talltim]

Was there an 80's box-shifter called Mail Rail? Or was it Rail Mail?

[melmerby]

Sorry didn't make that clear, I was referring to a bottom contact third rail to meet modern safety standards, which would have to be at the side. 

 

I recall a voltage has to be as down to about 50 volts to be considered non-hazardous.  One of the Parry People Movers charged from a third rail at about 70V but they were advised it wouldn't be acceptable in public areas.   At 50V a fairly modest 10kW motor would be drawing 200 amps. 

Electrical equipment intended for external use are normally 110v but they are fed from an isolating transformer which is arranged 55v-0-55v with the zero connected to ground, so that no part is more than 55v above any conducting object.

 

Keith

[PhilJ W]

With modern batteries such as those used in hybrid and electric cars an external power source will not be neccessary. Something to be considered for other preserved electric stock.

[EddieB]

Is there a reason why a.c. has seldom (if ever?) been used on contact third/four rail electrification schemes?

[Edwin_m]

Is there a reason why a.c. has seldom (if ever?) been used on contact third/four rail electrification schemes?

Firstly it isn't necessary - the main reason to use AC is so a higher voltage can be used for the supply and reduced by a transformer in the train.  The sorts of voltage that are useable on third rail systems can be applied directly to traction motors (or perhaps to pairs of motors in series) so no transformer is needed. 

 

Secondly there is something called the Skin Effect which means that AC current only flows near the outer edge of the conductor.  It depends on frequency but at 50Hz the conducting layer is a few millimetres thick, and not by coincidence this is half the diameter of an AC overhead line.  Putting 50Hz through a third rail, most of the cross-section would be contributing nothing to the conductivity so the resistance losses would be far higher than on a DC system of the same voltage (which in turn are already far higher than for a high voltage AC overhead system). 

[Nearholmer]

And, for the first hundred or so years of railway electrification, the direct current series motor was the 'machine of choice', both because of its torque/speed characteristic and the ease with which it could be controlled, so, unless the distances over which the railway spanned were great, it made sense to transform down to a low voltage, and rectify to d.c., at the substation, allowing for a very simple, light, and compact installation on the train.

 

It's only since the advent of power-electronics that it has made sense to use a.c. motors on the train on urban and suburban railways.

 

A.c. traction motors, of several different kinds, were used in the pre-power-electronic period, but either the supply configuration and control circuitry was horribly complicated, or the electrification had to be at a low frequency, which is why 16.67Hz was used widely in Europe, and why the LBSCR and Midland systems operated at 25Hz. Incidentally, the LBSCR and MR systems were both intended to spread over long distances, in the MR case for hauling goods through the Peak District and coal trains into London, which is why both companies chose an arrangement that wasn't a natural fit for the short distances over which they were actually applied.

 

Kevin

Edited October 15, 2017 by Nearholmer

[EddieB]

Firstly it isn't necessary - the main reason to use AC is so a higher voltage can be used for the supply and reduced by a transformer in the train.  The sorts of voltage that are useable on third rail systems can be applied directly to traction motors (or perhaps to pairs of motors in series) so no transformer is needed. 

 

Secondly there is something called the Skin Effect which means that AC current only flows near the outer edge of the conductor.  It depends on frequency but at 50Hz the conducting layer is a few millimetres thick, and not by coincidence this is half the diameter of an AC overhead line.  Putting 50Hz through a third rail, most of the cross-section would be contributing nothing to the conductivity so the resistance losses would be far higher than on a DC system of the same voltage (which in turn are already far higher than for a high voltage AC overhead system). 

Thank you, Edwin.  I get the bit about using higher voltages to minimise losses between supply stations, but wasn't aware of the Skin Effect.

 

The thinking behind my original question is that d.c. is more dangerous in that if touched, it causes muscles to contract involuntarily and the person (or creature) cannot pull themselves away from the live rail - they remain a hazard until the current is switched off.  On the other hand, a.c. tends to throw those touching away from the danger.  Consequences in both cases are pretty serious - but perhaps (other things being equal) a greater chance of survival on a.c.  Or have I got it wrong?

[luckymucklebackit]

Was there an 80's box-shifter called Mail Rail? Or was it Rail Mail?

 

RailMail of Sheffield, also had a shop in Glasgow, specialized in cheap Lima models, put PHONE instead of the price in its RM listings if the bargains were spectacular

 

Jim

[Edwin_m]

There was a Railmail of Watford, is this the same one? 

[Nearholmer]

Eddie

 

There is a great, big, detailed CEN document setting out the affects of electric currents on the human body, and the upshot is that it is the voltage (and hence the current flowing through the body) that is important, along with the route through the body (across the heart is particularly bad, even at surprisingly low voltage/current).

 

In short(!) ac or dc is not to be messed with at voltages above a few tens, and even if it doesn't get you by electric shock, it can get you by burns ....... think of a 12V car battery, and the electrical burns that can cause, for instance.

 

Kevin

[melmerby]

Eddie

....... think of a 12V car battery, and the electrical burns that can cause, for instance.

 

Kevin

How do you get electrical burns from a 12v battery?

I can hold both terminals and measure the current through my body with an ammeter and it is miniscule!

(and I have moist skin)

 

Keith