Electric Traction boffins, a question

[aussiesteve]

G'day electric traction boffins,
I have seen brief old BnW footage of third rail emu operation in the UK.
I don't remember the location, if detailed, and it would take a while to scan through my collection of DVDs.
There was a fourth rail, in the middle of the four-foot.
And sparks seemed to emanate occasionally when trains passed over gaps in this rail.
This infers that contact was being made with the fourth rail by the train.
I am wondering if this fourth rail was an additional traction current return rail.
OR, if this fourth rail was in fact the return current rail to separate traction current from signal rail circuits.
I assume that this fourth rail would need to be higher in profile than running rails.
To prevent fouling points, crosswalks and levelcrossings etc by the train central collector shoe.
I was told some time ago that a third rail was utilized on the smog hollow electrified network.
No contact with this rail was made by the train.
It was utilized to ensure that a positive return for DC traction voltage was maintained to substations.
But, I have not witnessed any evidence of this original third rail in Sydney.
And, don't recollect having espied any photos so depicting.
I think that I prefer the overhead supply system rather than third rail system.
OK, the atmosphere is cluttered with unsightly junk.
But, you can hoof around the track without getting zapped.
Mind you, you had better have that orange vest on these days.
AND, I remember one stringent instruction if the overhead was down and draped over the locomotive roof.
JUMP to the ground from the bottom step.
Steve.

[Beeyar Wunby]

Hi Aussiesteve

Originally Posted by aussiesteve

G'day electric traction boffins,
I have seen brief old BnW footage of third rail emu operation in the UK.
I don't remember the location, if detailed, and it would take a while to scan through my collection of DVDs.
There was a fourth rail, in the middle of the four-foot.
And sparks seemed to emanate occasionally when trains passed over gaps in this rail.

Sounds like the UK underground system (which of course runs on the surface for some of the time) and has four rails.

According to Wonkypedia the outer rail carries +420V DC and the inner -210V DC, giving 630V in all. This is to reduce corrosion in the cast iron tunnel linings.

Linky to uk traction current supply here..https://en.wikipedia.org/wiki/Railwa..._Great_Britain

We also have a Third rail system above ground for high -intensity commuter lines over much of the south eastern/south central part of the country which carries 750V DC. This can also occasionally have an apparent fourth centre rail, but is for an additional earth route in 'electrically difficult' areas. This rail does not contact the train, but is bonded to the running rails - which are the normal return route in third rail systems. One such place where this occurs is at Farringdon in the centre of London where EMUs used to be limited to 15mph whilst hauling themselves up a steep incline out of a wet tunnel.

And yes, I prefer Overhead traction current supply for two reasons.

1) There's no risk of electrocuting yourself if you put your feet down clumsily or take a tumble.

2) If your train has an electrical fire or fault, you will be told to isolate it from the traction supply. On the DC you have to go round the train and manually lift every shoe off the rail with a paddle (and it always seems to be raining or snowing at the time). A friend of mine was nastily burnt during a rain shower once when the last shoe flashed and his nylon trousers burnt away.

Whereas on the AC you just press the Pan Down button on your desk - and all the 25kV of scary electrickery goes away.

Best wishes. BW

[aussiesteve]

G'day BW,
Thanks, I will grab the Wikileaks info.
I may also grab the UK DVDs and take a gander at some stage and see if I can find the specific footage and see if any location details are given. I normally watch DVDs while reclining in bed if I can't sleep. Then, promptly forget about what I had watched.
Steve.

[aussiesteve]

G'day BW,
I didn't know that there were so many different electrified systems in the UK.
Europe seems to suffer a similar situation.
E Loks dropping pans and coasting into stations where the overhead system changes.
EMUs possessing multiple pantographs to permit separate system operation.
I am waiting until the local library reopens for business before I attempt to grab any of the specific system documents.
My limited home www access would quickly go belly-up if I scrounged any of the reference documents listed by Wikileaks.
I have also started viewing my UK DVDs, attempting to find the particular segment featuring the fourth rail.
I have not encountered that segment as yet, but have squizzed a number of brief glimpses of fourth rail.
I had not taken much notice of those previously, one being at Stanmore (?).
I was slightly aghast at the mention of the Tube utilizing asbestos padding in an attempt to reduce noise.
E GADs, I do hope that such has been removed today.
I am on the asbestos register, having worked Butter Boxes (NSWR 46 class Metro Vickers) which were full of asbestos.
Our initial uniform, other than overalls, was composed mostly of nylon.
I could well imagine it melting if exposed to intense heat.
Yes, some of the DB third rail cars seemed to possess collector shoes in close proximity to driver's cab steps.
No DB end vestibule doors or cab front doors, you are stranded in the car you jump into.
It was mandated early on here for our rat holes (underground) that all emus must have communication doors for evacuation.
Oh, and I hope that before you thump that Pan Down button, that you firstly flick the Main Switch or Reverser to Shut-down.
Otherwise, you will see sparks when the overhead lands on the roof.
25kVA as utilized in Brisbane and Perth is a good system, except for owners of pet dogs who use metal choker leads.
The dog apparently needed to lift it's hind leg as they were clambering over a foot bridge.
ZAP, fried them both.
Another facet of the Brissy 25kVA system that I am slightly unsure of, be the inability to employ regenerative brake.
Hence all E Loks only possess dynamic brake.
This supposedly due to the power grid supply for the rail network.
This might be just an old wives tale, as I envisage a waste of energy with electric traction dynamic brake.
The NSWR prehistoric 1500 vDC system permits regen, though did limit the maximum for multiple locomotives.
Exceed 1950 volts and you risked blowing up the substation.
Them old Butter Boxes were unique in that you could Motor in Regen.
With a light load train, descending and climbing light grades, you could set them up in series-parallel regen.
Then as the train got to the bottom and commenced to climb, they would go out of regen and into power.
Look Mum, NO hands.
No good if you were in a hurry or on heavy grades.
The subsequent Comeng Mitsubishi 85 and 86 class were not capable of this ability.
Them butter boxes were a pain though with the trio of metal head control jumper cables.
Plus, they were that modified that no two units were the same towards the end.
I remember an incident in 1990, working home with a trio of them butter boxes.
We relieved the train at Enfield North Box.
I had to enter the machinery room hunting for something.
Can't hear nada inside there with the Compressors, Motor Gennies and Traction Motor Blowers raging.
I returned to the cab to find me driver gone awl.
Poking me head out the cab, I heard people yelling at me from the tall grass near the signal box.
GET DOWN here, somebody is shooting at us !; my driver and the signalman bother cowering in the grass.
WHAT !
The dash was lit up like an Xmas tree with fault lamps.
HMMM.
After no more "gun" shots were heard, my driver joined me in the cab.
We discovered that the rear unit rear cab had shrapnel on the floor and black scorch marks all over the cab wall and roof.
This all seemingly emanating from near to the battery knife switch box on the wall.
HMMM.
We managed to reset the thing and away we sailed.
Upon arrival at home, I went into the electric foreman to ask questions.
For some inexplicable reason, a high voltage coil had been positioned exposed in the cab of that unit.
WHAT !!!!!!!.
That should not have been done by Enfield, gasped the foreman.
I hate to think had we or any crew been in that cab when the coil exploded.
Yes, a buzz to drive, but MOST uncomfortable, especially during winter.
Heavily modified over the years, and useless once coalies had extended to 3300 tonne.
So, I helped to get rid of them in 1996, being union cab committee, by demanding impossible cab improvements.
Steve.