Running Historic 4th rail stock on 3rd rail Question

[43021HST]

This is mostly for a railway modelling scenario really, but was it theoretically possible to run stock like Metropolitan Line Met Vickers locos and and subsurface stock like F stock, Q and R Stock on the old 660v third rail without extensive modification, such as removal of 4th rail shoes, at line speed or would the 30v increase from the standard LU voltage of 630v present serious problems?

Also would it be possible to run the IOW 38 stock on the 4th rail again without any modification.

I'm unfortunately a bit of an ignoramus when it comes to even slightly technical matters of electrification.

Lastly apologies to the mods if this is the wrong place, wasn't sure whether to bung it in here or on the LU section.

 

[krus_aragon]

I think it would be practical to do so, with some modification. It seems that something similar was actually done on the Mersey Railway, where stock had to deal with both 4th and 3rd rail electrification.

See this extract from citytransport.info:

At one time the city of Liverpool was served by three independent railway companies which operated electric trains. Although they all used conductor rails (mostly energised at 600V/650V DC) the systems were incompatible because these were in different positions (relative to the running rails) and one company services (Mersey Railway) used the 4th rail system. This was for the same reason as London - its route was largely in deep level tunnels, especially the section below the River Mersey.

When the Mersey Railway's services were extended over the tracks of the Wirral Railway the Mersey Railway relocated its outer conductor rail so that instead of being 22" (56cm) from the running rail it matched that of the Wirral Railway, which was at what had become the 'standard' position for Britain, ie: 16" (41cm) from the running rail. However it retained its 4th rail, instead during the station stop at Birkenhead Park (I think!) the guard manually switched the electrical return to suit the section of line about to be served (ie: via the wheels or via the 4th rail).

With regards to which forum, I think the topic fits perfectly fine here.

 

[edwin_m]

Saw recently on another forum that Sarah Siddons did run railtours on the Southern. I'm not sure what the voltage was on the sections concerned at the time. However the central shoes would have to be bonded to the running wheels and un-bonded before returning to LU infrastructure, otherwise the fourth rail would be shorted to the running rails. Hence why anywhere LU stock regularly runs on Network Rail has a fourth rail, but bonded to the running rails unlike LU infrastructure where the running rails are isolated from both traction rails.

 

[Taunton]

The actual voltage does not matter a great deal, within limits, as it does vary quite significantly depending on distance from the substation, what other trains are in section and whether they are accelerating, etc. There is also substantial overvoltage protection in the insulation anyway, to cater for eg lightning strikes on the third rail (much more of an issue with overhead electrification). I believe that when the SR electrified west of Woking in the 1960s, at 850v instead of their normal 750v, it now allowed older suburban trains to run under their own power to Eastleigh works, the only condition being they had to have their lights turned off as it was beyond the ratings of the bulbs.

The Underground is nominally +420v in the positive outside rail and -210v in the centre negative rail, potential difference 630v, but on the shared sections with national system electrics to Harrow, Wimbledon and Richmond it is +630v in the outside and 0 in the centre, same potential difference and the train works the same. The centre is frequently bonded to the running rails, the Underground trains return through the centre and the national trains through the running rails, both as they normally do.

The Wirral arrangement (I may hail from Somerset but spent a while living on The Wirral) I always understood was changed over automatically, rather than manually, at Birkenhead Park by magnets (North polarity in one direction, South in the other) between the tracks. Both the older Mersey units and the later LMS and BR units needed this arrangement.

 

[Bald Rick]

Saw recently on another forum that Sarah Siddons did run railtours on the Southern. I'm not sure what the voltage was on the sections concerned at the time. However the central shoes would have to be bonded to the running wheels and un-bonded before returning to LU infrastructure, otherwise the fourth rail would be shorted to the running rails. Hence why anywhere LU stock regularly runs on Network Rail has a fourth rail, but bonded to the running rails unlike LU infrastructure where the running rails are isolated from both traction rails.

I remember Sarah Siddons coming through Brookwood one day in the 80s, and that is definitely in 750v territory.

 

[Wilts Wanderer]

I recall an occasion in the 1990's when a Class 73 took a TPO via the Circle Line, possibly due to engineering work on the main line? Would that have been running on the juice or did it operate in diesel mode.

 

[Bald Rick]

I recall an occasion in the 1990's when a Class 73 took a TPO via the Circle Line, possibly due to engineering work on the main line? Would that have been running on the juice or did it operate in diesel mode.

Not sure it was a tpo, more likely the gauging train, or track recording coach. I remember seeing a picture. It would have to have been operating on diesel, 3rd rail stock can’t operate on 4th rail where both +ve and -ve rails are at their usual voltages.

 

[contrex]

I read somewhere that the 1938 stock that went to the Isle of Wight at first suffered from damage to wheel bearings caused by arcing of the return current as it passed through on its way to the wheels, and they had to fit brushes that bore on the axle ends. I don't know if anything similar needed to be done to the Standard stock, and I do not know if anything was done to Sarah Siddons when she went on the third rail. I seem to remember hearing of overvoltage relays tripping on 750v and being manually reset a number of times.