Fahad
In memoriam
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Post by Fahad on Jul 7, 2012 21:52:39 GMT
What will the arrangement of rails be when the SSR voltage is bumped up to 750V?
Will the current ratio of voltages be retained, with the posirail giving 500V and the negarail 250V? Will the third rail give all 750V, BR-style, with no need for the fourth rail? Will any rails need replacement?
Will running rail electrification ever be investigated in the future for new lines, now that there are no track circuits to worry about?
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Post by revupminster on Jul 8, 2012 7:15:09 GMT
Traction current has always been a mystery to me. I was taught it was 630v in the positive rail and the negative rail depended on how close a train was as to what was being discharged into the negative rail. Then later that it was 430v positive and 210v negative. And even more mysterious properties of the negative rail in earthing situations that I have forgotton about.
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Post by tubeprune on Jul 8, 2012 8:23:03 GMT
The simple explanation is that lifting the voltage to 750 has nothing to do with the current rail layout. The present 4-rail system will be retained. Some new current rails will be provided to reduce the resistance in the circuit so that getting up to 750 will be easier. Also some substations will be upgraded and, I think one or two new ones will be built.
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Post by tubeprune on Jul 8, 2012 8:28:16 GMT
Will running rail electrification ever be investigated in the future for new lines, now that there are no track circuits to worry about? I assume you mean 3-rail traction where the return of the circuit uses one of the running rails. I doubt LU will consider it at this stage. It was looked at many years ago and again during the PPP phase. It didn't stack up financially. As for track circuits, they will be with us for the foreseeable future. |
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Post by crusty54 on Jul 8, 2012 8:39:24 GMT
The simple explanation is that lifting the voltage to 750 has nothing to do with the current rail layout. The present 4-rail system will be retained. Some new current rails will be provided to reduce the resistance in the circuit so that getting up to 750 will be easier. Also some substations will be upgraded and, I think one or two new ones will be built. Large new substation nearly finished at Edgware Road |
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Fahad
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Post by Fahad on Jul 8, 2012 8:45:20 GMT
The simple explanation is that lifting the voltage to 750 has nothing to do with the current rail layout. The present 4-rail system will be retained. Some new current rails will be provided to reduce the resistance in the circuit so that getting up to 750 will be easier. Also some substations will be upgraded and, I think one or two new ones will be built. Does this mean 500V->ground->250V? Will running rail electrification ever be investigated in the future for new lines, now that there are no track circuits to worry about? I assume you mean 3-rail traction where the return of the circuit uses one of the running rails. I doubt LU will consider it at this stage. It was looked at many years ago and again during the PPP phase. It didn't stack up financially. As for track circuits, they will be with us for the foreseeable future. I could also be talking about 2-rail traction with (at least) one rail isolated, to save on metal What does the Cityflo 650 system use track circuits for? |
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Post by revupminster on Jul 8, 2012 13:59:23 GMT
How will the voltage rise affect the Picc trains where it runs with the District and Met
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Post by 100andthirty on Jul 8, 2012 16:26:00 GMT
Just to be clear, the system is floating and although there's a nominal reference to earth, it's not 500V - ground - -250V. Either rail could be at 750V relative to earth.
I don't understand what you mean by "I could also be talking about 2-rail traction with (at least) one rail isolated, to save on metal".
Cityflo is likely to use track circuits in sidings to ensure train detection even when there are interruptions to power or signalling during engineering hours.
In areas operated by Piccadilly trains, the voltage won't be increased.
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Post by 1018509 on Jul 8, 2012 18:32:22 GMT
If the traction current is to be increased in areas where the S stock run how does this bode for future rail tours with Sarah Siddons and the preserved 38 stock for example?
What about battery locos, will they need to be always on battery power when in these areas?
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Fahad
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Post by Fahad on Jul 8, 2012 19:04:53 GMT
Just to be clear, the system is floating and although there's a nominal reference to earth, it's not 500V - ground - -250V. Either rail could be at 750V relative to earth. Does traction voltage presently float, then? I don't understand what you mean by "I could also be talking about 2-rail traction with (at least) one rail isolated, to save on metal". I was thinking that if there was a new installation that didn't have any track circuits, the running rails could be mounted on insulator pots, with 750V between them. I've since read an article reganorak recently linked to on how trains steer, and realise how difficult it would be to make axle-less trains: I now see why what I suggested is impossible Cityflo is likely to use track circuits in sidings to ensure train detection even when there are interruptions to power or signalling during engineering hours. I see In areas operated by Piccadilly trains, the voltage won't be increased. Do these not have any tolerance when it comes to voltage, as it's been implied that most LUL trains do? If the traction current is to be increased in areas where the S stock run how does this bode for future rail tours with Sarah Siddons and the preserved 38 stock for example? What about battery locos, will they need to be always on battery power when in these areas? How will the voltage rise affect the Picc trains where it runs with the District and Met I would be surprised if all of the above stocks don't have a voltage tolerance, but if it is the case that they don't, battery locos, and heritage trains, are already being modified to fit CBTC equipment - adjustment to the traction packages could surely occur then? |
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Deleted
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Post by Deleted on Jul 8, 2012 19:11:49 GMT
Traction voltage is set by a potential divider with the centre tied to earth at the substation.
Sarah Siddons has worked on 3rd rail 750v before.
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Colin
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Post by Colin on Jul 8, 2012 19:14:26 GMT
C and D stocks have run on both LU and NR metals all their lives, with the associated varying voltages - so why would the Picc's 73ts suddenly have an issue?!!
I'm certain Sarah and the batteries have nothing to fear either.
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mrfs42
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Post by mrfs42 on Jul 8, 2012 20:48:12 GMT
A little voice in the back of my head is saying 'inverters' but I can't remember any more than that, I'm afraid.
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Post by 100andthirty on Jul 8, 2012 21:06:12 GMT
'73ts is a 630 volt train; 750V trains can generate up to 900V in regenerative braking. I've no doubt '73ts can be made to work on the higher voltage. However that's not the current plan.
The positive conductor rail and the negative rails are supplied from the sub-stations - currently at nominal 600V, later to be 750V. Resistors are used to provide a nominal bias to earth (eg +450V, -150V). One running rail is "continuous" and is earthed at the substation. However, in the event of an earth fault, say a tin can between the positive rail and a running rail, the other rail will float upt to line voltage - in the example it would be at -600V.
In all areas where LU and TOC electric trains run on the same tracks, the negative rail is bonded to the continuous running rail.
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Post by d7666 on Jul 9, 2012 17:24:22 GMT
C and D stocks have run on both LU and NR metals all their lives, with the associated varying voltages - so why would the Picc's 73ts suddenly have an issue?!! In those areas where C and D operate the NR supply voltage is dropped from the nominal 750 V to (I think) 630 V. On NR adjacent sections to where 630 V is necessary there are voltage step sections of another voltage between 750 V and 630 V either to ensure smooth transitions. In the RT/NR SR zone power reinforcement project of the early 2000s to cater for AC motor units like Desiros and Electrostars there is provision to step up those section to 750 V once the older LU stock types have gone. BTW, SR zone third rail main line train performance calculation and all continuous electrical ratings are all at 675 V not 750 V - the latter is actually the one hour rating. (and 25 kV OLE is really 22.5 kV for equivalent discussions). "spotting" books like the old IA ABC and present day P5 books ignore this fact - the power and so on figures given are not 750/25000 V but 675/22500 V ... tis is easily proved by looking at was used to be called the "BR Diagram Book". Not sure how true that is. SS had the same generic 339 traction motor type as 4Sub units did. At the time 4Subs were in traffic, they themselves as 660 V units had restrictions on where they could go in "country" 750 V areas. Now all thats 30 years ago, it is possible SS has had rewound motors, it is normal practice these days to wind motors to the highest insulation standards which easily handle something like 630 to 750 V. AIUI this also applies to C and D stock, they are all old enough that their motors at some point in their lives will have had a major overhaul and possibly a rewind ... I don't know what LU does in this respect, but certainly BR SR did this. The question will be, has SS had such work on it ? The motors on batteries are even older. yes they did work to Streatham Hill etc, but that was still a lower voltage suburban area at the time they did that. Bet we won't ever see that again. -- Nick |
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Fahad
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Post by Fahad on Jul 9, 2012 18:43:48 GMT
I would assume Sarah was rewound prior to her jaunt to Portsmouth - it's certainly stated that modifications were required |
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Post by norbitonflyer on Jul 9, 2012 18:54:58 GMT
At the time 4Subs were in traffic, they themselves as 660 V units had restrictions on where they could go in "country" 750 V areas. I did read (can't find the book at the moment) that test runs to Basingstoke when that was first electrified were done with 2BILs. The only modification mentioned was to isolate the heating circuits. |
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Post by d7666 on Jul 9, 2012 19:37:56 GMT
I would assume Sarah was rewound prior to her jaunt to Portsmouth - it's certainly stated that modifications were required As I was one of the organisers on the SEG side of things, I can definitely say SS was not specifically rewound for that or any other of the BR SR runs. If SS was rewound before then, maybe that action that allowed it to happen i.e. cause (rewind) and effect (it went on BR SR) , but certainly not the other way around. -- Nick |
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Deleted
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Post by Deleted on Jul 9, 2012 21:16:28 GMT
IIRC the original LSWR/Southern Railway electrification (pre war) was all done at (nominal) 660V dc, to match the Underground (Metropolitan District Railway). For the Kent Coast electrification (1959-62) the nominal voltage was raised to 750V; and for the Bournemouth electrification even higher (825V?) and those areas electrified earlier have at least in part had the voltage increased to match: but one of the restrictions on doing this was that the old 'suburban' units (SUB, BIL, etc.) had heating and/or lighting circuits which couldn't cope with the higher voltages, so it had to wait till they had gone (although they could work 'out of area' with the relevant circuits disconnected).
But all these voltages are nominal, at the substation bus bars - the trains would normally have something less. Quite what the actual figures are I don't know. (Reading about Italian electrics, a nominal 3kV means anything between 2kV and 4kV should be expected (and coped with) by the train)
My understanding is that the recent electrification improvement works did not not involve an increase in Volts; rather provision to provide more Amps.
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Post by d7666 on Jul 9, 2012 22:16:21 GMT
IIRC the original LSWR/Southern Railway electrification (pre war) was all done at (nominal) 660V dc, Correct More or less correct ... it was being raised anyway, it happened that Kent Coast was the first major project newly electrified at 750 V. Urban mythical legend misunderstanding of a technical fact ... publicity at the time seemed to imply this ... and the media picked it up, but the 1967 Bomo line is nominally 750 V DC just like the rest of the third rail network. I forget the exact reason higher voltages were quoted but it is something to do with a different voltage drop across mercury arc rectifiers and silicon rectifiers, the Bomo line being the first major scheme to deploy them. Likewise 4Vep which were newly introduced with the Bomo line scheme are oft quoted as 275 hp motors compared with other EE507 motor units; in fact it is rubbish if the values were quoted against a standard reference, the 275 hp value is simply one of the short term ratings, the motors are the same - indeed interchangeable - which are /around/ 235 hp (not 250 hp) continuous rating, depending on which version it is. Exactly. 675 V is the value used for calculating performance, and the value at which continuous ratings are supposed to be quoted at. Thus, from above, and EE507 motor is ~235 hp continuous at 675 V full field. Yes, because a DC series wound motor is /oversimplifying/ constant voltage variable current machine while a AC asynchronous motor is a variable voltage constant current machine ... ... hence new substations e.g. EdgwARE rOAD Phew .. got the subject back on LU topic again before a moderator noticed the drift  -- Nick |
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Post by revupminster on Jul 9, 2012 22:35:55 GMT
I still want to know if I put a volt meter on the positive rail, will it read at the momemt 630v and in future 750v
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rincew1nd
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Post by rincew1nd on Jul 9, 2012 22:56:51 GMT
Depending on the meter, it might just go bang...  |
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Post by norbitonflyer on Jul 10, 2012 5:43:45 GMT
I still want to know if I put a volt meter on the positive rail, will it read at the momemt 630v and in future 750v Depends where you put the other terminal...........! |
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Post by 100andthirty on Jul 10, 2012 17:52:11 GMT
I still want to know if I put a volt meter on the positive rail, will it read at the momemt 630v and in future 750v If you put the positive terminal on the positive rail and the negative terminal on the negative rail, depending on the location and or the time of day, you'll get 600V to 700V. Later you'll get something around 750V to 800V. The voltage with no load around is always higher than when trains are running and you wouldn't get to attach your meter to the current tails if there were any trains moving in the section!!! |
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Post by bassmike on Jul 11, 2012 1:12:38 GMT
This whole topic has been discussed before about nine months ago. Nothing needs re-winding or re-building, motors can stand higher voltages within reason as their back EMF limits the current. The only mod : needed is to remove the negative shoes and connect their leads to bogie frames/ motor cases, and dont use the heaters or lights unless absolutely necessary.
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Post by d7666 on Jul 11, 2012 9:49:00 GMT
This whole topic has been discussed before about nine months ago. Nothing needs re-winding or re-building, motors can stand higher voltages Please explain then why the arrangements at main line NR locations to drop 750 V to 660 V are in place. They are there, at 660 V, exactly *because* of lower voltage ratings on board older - where older includes C and D stock - LU stock. -- Nick |
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Ben
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Post by Ben on Jul 11, 2012 11:08:28 GMT
So no special measures other than the obvious would have been needed for the proposed R stock excursion to the south coast?
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Deleted
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Post by Deleted on Jul 11, 2012 12:00:42 GMT
This whole topic has been discussed before about nine months ago. Nothing needs re-winding or re-building, motors can stand higher voltages within reason as their back EMF limits the current. The only mod : needed is to remove the negative shoes and connect their leads to bogie frames/ motor cases, and dont use the heaters or lights unless absolutely necessary. If I recall correctly, Sarah Siddons was fitted with 4 sub compressors, replacing the CP30s, when it went onto the SR metals and retained those compressors afterwards. |
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Post by bassmike on Jul 11, 2012 12:49:44 GMT
Answer 1. The 660/750 volt changeover is where newer work on extensions meet older work which will be raised as the older part of the system is refurbished. The voltage on both levels is probably jiggering up and down between 550--800 volts depending on current draw etc: at the time. Answer 2. The fitting of different compressors was nothing to do with the voltage,but general maintainence.( SS also has the same motors as did the 4subs )
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Deleted
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Post by Deleted on Jul 11, 2012 21:26:01 GMT
If I recall correctly, Sarah Siddons was fitted with 4 sub compressors, replacing the CP30s, when it went onto the SR metals and retained those compressors afterwards. And just to keep her upto date, she will be getting Cityflo fitted too! |
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