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Post by t697 on May 12, 2019 18:01:33 GMT
And it doesn't need a train length gap because LUL trains, at least those built since 1938, don't have any connections between the shoes of one car and the shoes of another. Just need the gap longer than the shoe span in one car.
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Ben
fotopic... whats that?
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Post by Ben on May 12, 2019 18:43:10 GMT
The trains length gap at District line locations remained that length until the Q stock was withdrawn in '71, possibly even later,
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Post by Dstock7080 on May 12, 2019 19:44:06 GMT
The trains length gap at District line locations remained that length until the Q stock was withdrawn in '71, possibly even later, Much later, into the mid-late 1980s. CO/CP Stock had bus-lines within the unit. Changeover switches were certainly used at Gunnersbury and Putney Bridge, where the full length train went between two rail-gaps and the traction current was switched between the two supplies, with a very short period when no supply was received, as I know roythebus is correctly remembering. |
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Post by bassmike on May 12, 2019 20:42:48 GMT
I think that the current changeover was not swithed off briefly but used resistors to stop the two supplies from shorting out. (Lineside resistors)
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roythebus
Pleased to say the restoration of BEA coach MLL738 is as complete as it can be, now restoring MLL721
Posts: 1,275
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Post by roythebus on May 14, 2019 21:38:28 GMT
Current was lost, not switched off, as the train ran onto the dead section. It was "switched on" when the leading shoes on the leading car hit the live section ahead, it really was that simple until the train stopped in the gap! Out with the jumper leads.  |
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class411
Operations: Normal
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Post by class411 on May 15, 2019 7:09:22 GMT
Current was lost, not switched off, as the train ran onto the dead section. It was "switched on" when the leading shoes on the leading car hit the live section ahead, it really was that simple until the train stopped in the gap! Out with the jumper leads. They must have been quite long leads to get to the battery of the next obliging motorist. I'll get me coat. |
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Post by John Tuthill on May 15, 2019 9:18:31 GMT
Current was lost, not switched off, as the train ran onto the dead section. It was "switched on" when the leading shoes on the leading car hit the live section ahead, it really was that simple until the train stopped in the gap! Out with the jumper leads. Not unknown when there were trams in the same situation. There are lots of photos of 'passengers' and the crew pushing a tram over a dead spot. |
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Post by d7666 on May 17, 2019 19:55:17 GMT
455 stock used 2nd (or 3rd) hand SUB motors and these were ok working at the higher voltages. They also used SUB compressors quite happily. Its extremely unlikely said motors etc. were simply transferred from the Subs to the 455s - they almost certainly were rewound / overhauled first. this would have provided the opportunity to upgrade things like the varnish / wire used in the windings to handle higher voltages and allow an increase in conductor rail voltage compared to their 'as built' state. You are correct - but the work carried out on those motors was not in a specific Sub to 455 motor rebuild. All EE507 motors of all builds from any unit were dealt with at Chart Leacon. Every motor was split into armature and carcass, a seperate overhaul path, and not mated back together except by statistical accident. All were always overhauled and where re-wound up to 750 V (nominal) even in 1970s incl.Sub units. Each re-assembled motor's actual characteristics were recorded on a test rig, and two or four closely matched *as tested* motors put in a two or four car unit. That they were versions a b c whatever as built was irrelevant and lost and the old ABC spotter books were incorrect to continue including those. The only sub-sets (pun intended) were (1) what they called "oilers" and "rollers" referring to suspension tube bearings (so applied to carcasses only) and (2) the motors on 456s (NOT 455s, just 456s) that were rebuilt by GEC with a mod (to inter poles I believe) because the DC inputs were choppers unlike all other EE507 motors production fleets. 456 motors were not new despite what the press says, but they were given a new model suffix by GEC. So the Sub units on going for scrap motors were put into a pool, in any status, some 750 some 660 V, and the 455 motors came out of the pool, not necessarily the same ones, but all at 750 V. A few Subs had run in service with 750 V motors ex Chart Leacon overhaul but to my knowledge were treated as if they were 660 V . EE507 motors treated in this way varied by power and, again despite what spotting books will tell you, all lie once ex-Chart Leacon around the 235/240 hp continuous, 260/270 hp one hour rating. There were never higher powered motors in Veps: BR and EE simply quoted a power rating against different other parametersm I do not know if any of the above applied to EE339 or MV339 motors, the latter of course common to Sarah Siddons. Mods: I know this is rolling stock, and not LU at that, but I'm simply answering where the thread had drifted to. -- Nick |
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Post by d7666 on May 18, 2019 12:33:24 GMT
Whilst Network Rail training is delivered by Skill's Development trainers (or whatever they're called this week), to be clear they are not cherry picking the information they deliver. They deliver what is contained in the RSSB working over books - the rule books that are created for Network Rail and which Network Rail nationwide work to. It is wrong to state that LU or its trainers have had any hand in the content delivered in relation to Network Rail rules & procedures to Bakerloo and District line drivers. In all honesty, I wouldn’t really expect OL to pay much attention to the finer details. It’s a quirk which isn’t particularly well known about, and doesn’t have any impact on operating staff in the course of their duties. So long as train staff appreciate that “750V DC” is the equivalent of LU’s 630V DC supply and there’s no scope for confusing 630V train equipment with other voltage circuits/equipment then there’s no real issue. In the same way that “750V DC” can actually mean something else elsewhere on NR too - IIRC the Pirbright-Bournemouth electrification scheme is or was one such area, in this case the nominal voltage being a nominal 850V DC in some areas at least, which IIRC allowed the substation spacing to be extended as an economy measure. To be fair, I’ve only heard the 660V DC referenced by two rather obscure albeit reliable sources. Once in a talk I attended some years ago delivered by a senior NR electrification design engineer at the time of the upgrades for slam-door replacement, and rather more recently in various NR and LU documentation which refers to a NR-led project to separate off LU supplies. As it doesn't affect operating staff, there's no need for it to be more widely documented. Needless to say from an electrification engineering point of view the difference will have more importance. They have perhaps learned from TBTC as the training for CBTC uses the terms halted, communicating, active and passive. Does this imply trains are always in communication with the system, even if inside an unsignalled depot? With the looped based system they lose communication as soon as the train goes off the inductive cable, which in reality is Morden, Edgware, Highgate, Golders Green, Neasden or Stratford Market depots (or during a loop failure). Ref 750 / 850 on the Bournemouth line west of Pirbright, this is also myth - but introduced by non technical media people not understanding all of the technical data presented to them. The Bomo line did indeed have greater substation spacing than preceding projects, but not because the nominal traction voltage was 850 V, but becuase it was the first DC project to utilise silicon rectifiers in those substations, and the open circuit (ie no load) voltage across those is higher than across mercury arc rectifier. As soon as you put a load ( ie a train) there, it is nominal 750 V. More recently, and perhaps more of interest to this underground forum, is the same confusion has occurred with the new traction supplies under the Thameslink project for the DC section of the core south of Farringdon have been variously stated at 800 or 900 V. Again this is the no load value, not the nominal traction supply. At night, in LU Engineering hours, if you ever can look at traction SCADA and read the busbar voltages at substations, a 630 V line can be reading as high as 700 V or higher when traction current is discharged so at no load. As a point of interest the entire SR zone uses 675 V for timetabling and performance calculations, and the power values quoted in spotting books etc are at 675 not 750 V, and likewise rolling stock powers for 25 kV stock are actually those at 22.5 kV. The key point is, these are nominal values, and, rightly as written upthread, it makes no difference from a (non engineering specific need to know) view if DC is 630 660 750 or 890 V - it should be treated all in the same way - with due care. -- Nick |
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