What is Multiple Unit Control?

[Nearholmer]

Topic moved from a thread where it was OT and beginning to get in the way.

 

Some sketch diagrams to follow when I get time.

 

Kevin

[roythebus]

Depends what you want to know about it!

[Nearholmer]

Now, a couple of sketches.

 

Comments, please, upon whether or not these sketches are understandable.

 

Kevin

[Edwin_m]

You could maybe replace the "traction control" red box by a green box with a red switch inside, and a circle for the motor might help to distinguish it from the pickup shoe.  But most significantly no train I'm aware of has a traction bus between sets. 

[Nearholmer]

Edwin, thanks. Good ideas.

 

SR EMUs had power jumpers between sets, as did a number of other older types. They made the train very "gap tolerant", but were a perennial [ spelling corrected! see quip below! and guess original spelling!] source of trouble, leading to arcing and fires, which is why the idea was given up. There is probably now no type of train in service in the UK that has them, but I'd be fairly sure that there are still some in other places - if I was to go hunting, I'd probably look at the "Petit train jaune" in The Pyrenees first, because that still has some very retro-tech rolling stock.

 

Kevin

[eastwestdivide]

...were a perineal source of trouble, ...

a.k.a. a pain in the ####

[hobbyhorse]

Power jumpers between units only upto the Sub type units.

 

Simon

[Nearholmer]

Precisely, after that came BR(S), rather than SR, EMUs.

 

K

[keefer]

Some early EPBs had a power jumper cable.

I don't know how many had it or when they were removed but I've seen at least 5001 (1951 SR design 4 EPB) and a Tyneside 2EPB (1954/5 BR design).

Of course, only the jumper cable was removed - the socket was retained as a shed socket.

 

Edit: on the subject in general, I remembered the Railway Technical Pages:

 

http://www.railway-technical.com/muops.shtml

[roythebus]

They were used only as shed jumpers, not to my knowledge to connect units together on EP and Tyneside stock.

[Edwin_m]

If the unit can run around on its own without undue risk of getting "gapped", there's no real point in connecting the power when it is linked to another unit.  As well as the jumper cables themselves, there would probably have to be some kind of circuit breaker to prevent electrocution of the people connecting and disconnecting it, unless the whole train is powered down when this happens.  And in either case the obvious risk of somebody forgetting to open the breaker before handling the cable. 

[Nearholmer]

Edwin,

 

With the right (fairly simple) interlocks, it is possible to prevent a plug being pulled or inserted with the circuit live, but at the time the EMUs were talking about were built, nobody thought that the risks, left after proper training were big enough to bother about.

 

Whether that was because "life was cheaper" (which it certainly was) or because people to a more balanced view of risk, would be an interesting topic for debate. Over a year,there would be thousands upon thousands of connections and disconnections made live, with some risk of it being under load too (compressors etc), and although there were incidents, usually due to hesitance, it wasn't a case of "dicing with death".

 

Possibly as big a risk was that the train would bridge a gap and liven up a section that was meant to be discharged - if breakers had tripped in a section, because of a short circuit, and a train came to a stand bridging to a live section, some pretty impressive fault currents could flow through the bus-jumper, which was very poorly protected (by the shoe fuses only, IIRC). And, even if it wasn't feeding a short, it would liven up a notionally "dead" section.

 

Another problem was forgetting to secure the plug properly, so that it rattled slowly out of connection, drawing a nice fat arc as it did so. Add to that the insulation failures caused by wear and tear on the jumper cables, and people dropping the thing while uncoupling, and it becomes pretty clear why they are no longer favoured!

 

K

[roythebus]

No, there was no interlock on SUB stock power jumpers. You pulled them out with 650 volts and a lot of amps at your fingertips. Providing both units have their shoes on the juice, there's little danger of drawing any sort of arc.

 

When I worked on LT in the early 1970s we still had Q stock with bus line jumpers connecting the whole train together. Coupling on the running line was rarely done, but we had to often use the shed jumpers if bringing a train out of one of the depot roads at Ealing Common or Upminster. Always make sure one shoe on the juice before you pull the jumper out!

 

As part of our driver training on BR, we had to learn and and demonstrate that we knew how to break an arc by using a couple of shoe paddles. This was usually done at south sidings at Waterloo. We'd find a SUB unit, paddle up all shoes except one, then wait for the compressors to start then lift the last shoe with another paddle. This would draw quite an arc. So drop the shoe, get a second paddle, draw the arc again, then literally cut the arc away by drawing the second paddle through the gap to break the arc. All good fun. I don't suppose today's boil in the bag drivers are let anywhere near anything with line volts on it. 

 

Some brave souls used to use the arc in the cab switches to light their cigarettes.

 

Also at various locations on LT like Putney Bridge and Gunnersbury there were very long jump leads which sat on the juice rails and plugged into the shed jumper socket in case a train got gapped in the dead section between BR and LT power!

 

There was no such thing as "powering down" the old stock, either they took power or they didn't. There was a way to minimise any arcing by the sequence of switching off various items, left to right. Compressors, heaters, lights off. Lights, heaters, compressors on. All nice old-fashioned knife blade switches with Bakelite or wooden handles and huge shiney copper contacts.

[eastwestdivide]

Roythebus - my hair's standing on end already after that description, and I'm a long way from a 650V supply!