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Bakerloo Line beyond Harrow & Wealdstone
On Sat, 29 Nov 2008, Steve Fitzgerald wrote:
In message , Christopher A. Lee writes No. Current leaking to ground and causing electrolytic corrosion. Remember, there were already pipes etc under London before the tubes were built, and the tubes were lined with cast iron segments.. Tram and streetcar track had the running rails at minus 10 volts so that stray current leaked from ground to the rails instead of vice versa. LU's centre rail is I believe at minus 200 volts. Traction current is fed at +420v (positive) on the outside rails and -210v on the centre rail (negative) the sum of these giving a traction feed of 630v dc. They are 'loosely' tied to earth through resistances in the sub stations that feed the supply. Despite being an electrician in a previous life and now a driver, I struggle to get my head round 'loosely tied to earth' and what it means in real life. I recollect an incident a few years ago when the traction current had been discharged (turned off) due to person under a train. For complicated reasons, the centre rail had become live at +420v. This must be some new meaning of the term 'turned off' of which i was not previously aware! As you say, complicated reasons - but this sounds like the kind of thing that really, really shouldn't happen. Crumbs. tom -- This is your life and it's ending one minute at a time. |
Bakerloo Line beyond Harrow & Wealdstone
On Sat, 29 Nov 2008 18:33:29 -0000, wrote:
"MIG" wrote in message ... : That's interesting, because I was under the impression that there was : no danger from the middle track, but 200 V could presumably give a : whack if there was any current. Doesn't the live rai change back and forth between third and fourth position? I remember hearing that the live rail is always in the third position when in a station, because there is less of a risk of somebody getting fried, should they fall onto the tracks. But the positive can be in fourth position just before and after the station. No. The outside rail goes outside the opposite running rail from the platform in stations. |
Bakerloo Line beyond Harrow & Wealdstone
In message , Tom
Anderson writes I recollect an incident a few years ago when the traction current had been discharged (turned off) due to person under a train. For complicated reasons, the centre rail had become live at +420v. This must be some new meaning of the term 'turned off' of which i was not previously aware! As you say, complicated reasons - but this sounds like the kind of thing that really, really shouldn't happen. Crumbs. It had been correctly discharged but been re-fed in error from elsewhere. You will note that what should normally have been -210v had now become +420v. -- Steve Fitzgerald has now left the building. You will find him in London's Docklands, E16, UK (please use the reply to address for email) |
Bakerloo Line beyond Harrow & Wealdstone
On Sat, 29 Nov 2008 12:52:12 -0500, Christopher A. Lee
wrote: On Sat, 29 Nov 2008 09:26:38 -0800 (PST), MIG wrote: On Nov 29, 2:52*pm, Christopher A. Lee wrote: On Sat, 29 Nov 2008 14:06:54 -0000, wrote: "Charles Ellson" wrote in message .. . On Mon, 24 Nov 2008 20:32:20 -0000, wrote: Is a fourth rail really necessary out that way, however? It is if you want the same train to work both there and on the Underground. Was the 38 stock on Island Line modified to work only on third rail? What did that require, if that was the case? Modification to the same general standard as other SR 3rd-rail stock, returning current via the wheels and chassis instead of via a central pickup to a conductor rail. Older LU stock might also have required upgrading of cables if the insulation was not suitable for 660v (or 750v?) use; under normal conditions an LU train running on LU 4-rail track doesn't have any parts at more than 440v to earth but when running on sections of "hybrid" 3or4-rail the highest normal voltage to earth is 440V to earth. Under fault conditions (centre conductor rail earthed) on LU the 3rd rail voltage can rise to the full supply voltage and current stock has cable insulation already rated to cope. I always understood that they were really needed only for the tub sections of the tube, to help power flow into the motors. No the LU 4-rail power supply is intended to keep the traction current within the two conductor rails and not find its way back via other bits of metal with consequent damage. In case of flooding, perhaps? No. Current leaking to ground and causing electrolytic corrosion. Remember, there were already pipes etc under London before the tubes were built, and the tubes were lined with cast iron segments.. Tram and streetcar track had the running rails at minus 10 volts so that stray current leaked from ground to the rails instead of vice versa. LU's centre rail is I believe at minus 200 volts. That's interesting, because I was under the impression that there was no danger from the middle track, but 200 V could presumably give a whack if there was any current. There isn't much current if there's nothing in section. You used to see track workers hopping on and off the centre rail and walking along it. |
Bakerloo Line beyond Harrow & Wealdstone
On Sat, 29 Nov 2008 18:53:49 +0000, Tom Anderson
wrote: On Sat, 29 Nov 2008, Steve Fitzgerald wrote: In message , Christopher A. Lee writes No. Current leaking to ground and causing electrolytic corrosion. Remember, there were already pipes etc under London before the tubes were built, and the tubes were lined with cast iron segments.. Tram and streetcar track had the running rails at minus 10 volts so that stray current leaked from ground to the rails instead of vice versa. LU's centre rail is I believe at minus 200 volts. Traction current is fed at +420v (positive) on the outside rails and -210v on the centre rail (negative) the sum of these giving a traction feed of 630v dc. They are 'loosely' tied to earth through resistances in the sub stations that feed the supply. Despite being an electrician in a previous life and now a driver, I struggle to get my head round 'loosely tied to earth' and what it means in real life. Doing it by memory from an old issue of "Underground" the resistor network is thus :- POS RAIL - ~400ohms - EARTH - ~200ohms - NEG RAIL Each resistor has a relay across it. If the power supply fails both relays drop out causing an alarm; if either conductor rail is earthed then one of the relays will drop out and bring up an alarm to indicate an earth fault (if both rails are earthed then you have a short circuit anyway). Transient earth faults can be caused by windblown metallic debris so IIRC the alarms will be reset up to three times in succession before someone is sent out to investigate. The "loose tie" to earth is an electrical consequence of the detection system and a design method of limiting the maximum conductor rail voltage under non-fault conditions. Purely "floating" (nothing connected to earth) systems can lead to such things as fault voltages which are the sum of two or more supplies if the wrong wires come into contact. I recollect an incident a few years ago when the traction current had been discharged (turned off) due to person under a train. For complicated reasons, the centre rail had become live at +420v. This must be some new meaning of the term 'turned off' of which i was not previously aware! As you say, complicated reasons - but this sounds like the kind of thing that really, really shouldn't happen. Crumbs. One train (or two?) bridging two sections ? It doesn't need to be a "good" connection to make a conductor rail lethally live. If it isn't the same incident ISTR there was also at least one incident involving incorrect closure of the switches (or failure to re-open one/them) between two adjacent sections. |
Bakerloo Line beyond Harrow & Wealdstone
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Bakerloo Line beyond Harrow & Wealdstone
On Sat, 29 Nov 2008 14:06:54 -0000 someone who may be
wrote this:- Was the 38 stock on Island Line modified to work only on third rail? Undoubtedly. What did that require, if that was the case? Leaving aside the incidentals, in a four rail system the traction electricity flows from one conductor shoe via a cable to the motor and then via another cable to the other conductor shoe. The traction current is thus confined to its own separate circuit and will not interfere too much with other circuits. In a three rail system the traction electricity flows from the conductor shoe via a cable to the motor and then via another cable to a rotating contact on the axle, from where it flows to the wheel and to the running rail. Thus the traction electricity is sharing the running rails with any other circuits and arrangements have to be made to stop it swamping these. In a nutshell, to convert the train from one system to the other the central conductor shoes are removed and the cable connected to newly installed rotating contacts instead. These contacts are very much like the commutator of a "traditional" electric motor but there is only one segment. Then what is the problem with Bakerloo line trains continuing further north, assuming that they don't require any modifications? They don't require any modifications (other than in the past those already mentioned by others to do with insulation if they are older trains). In these sections the central conductor rail is not energised but is rather connected to the running rail which is used for traction return. A "BR" train will "see" the traction voltage between the (outside) conductor rail and running rail and work. A "LT" train will "see" the same traction voltage between the outside and central conductor rail and also work. The difference is that on these sections the voltage difference is between +600 odd volts and zero, while on "LT" lines the voltage difference is between +400 odd volts and - 200 odd volts. The voltage difference used to drive the motors is the same, but the potential to the earth is different on the two systems. I have deliberately used round numbers for the voltages, rather than the nominal ones. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
Bakerloo Line beyond Harrow & Wealdstone
On Sat, 29 Nov 2008 09:26:38 -0800 (PST) someone who may be MIG
wrote this:- LU's centre rail is I believe at minus 200 volts. That's interesting, because I was under the impression that there was no danger from the middle track, A dangerous impression. If there was no (electrical) danger from the central conductor rail then it would not be mounted on insulators. Insulators are a give-away that something is energised. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
Bakerloo Line beyond Harrow & Wealdstone
wrote in message On hybrid sections (e.g. East Putney to Wimbledon) the 4th rail is at +630v. That would be the third (positive) rail. Otherwise the 'third rail' stock wouldn't work too well... Paul S |
Bakerloo Line beyond Harrow & Wealdstone
On Nov 30, 11:14*am, David Hansen
wrote: On Sat, 29 Nov 2008 09:26:38 -0800 (PST) someone who may be MIG wrote this:- LU's centre rail is I believe at minus 200 volts. That's interesting, because I was under the impression that there was no danger from the middle track, A dangerous impression. If there was no (electrical) danger from the central conductor rail then it would not be mounted on insulators. Insulators are a give-away that something is energised. Piecing it all together, I suppose it adds up, in that if a neutral rail was to be used, it might as well the the running rails or something earthed. So the fact that there's a special rail on insulators means it can't be neutral. Never really thought it through though. |
Bakerloo Line beyond Harrow & Wealdstone
MIG wrote:
On Nov 30, 11:14 am, David Hansen wrote: On Sat, 29 Nov 2008 09:26:38 -0800 (PST) someone who may be MIG wrote this:- LU's centre rail is I believe at minus 200 volts. That's interesting, because I was under the impression that there was no danger from the middle track, A dangerous impression. If there was no (electrical) danger from the central conductor rail then it would not be mounted on insulators. Insulators are a give-away that something is energised. Piecing it all together, I suppose it adds up, in that if a neutral rail was to be used, it might as well the the running rails or something earthed. So the fact that there's a special rail on insulators means it can't be neutral. Never really thought it through though. No, the fourth rail was used because allowing the current to return though earthed running rails causes corrosion to any metal utility pipes in the area, so the fourth rail and insulators are there to protect water mains. |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008 03:46:02 -0800 (PST) someone who may be MIG
wrote this:- Piecing it all together, I suppose it adds up, in that if a neutral rail was to be used, it might as well the the running rails or something earthed. So the fact that there's a special rail on insulators means it can't be neutral. Never really thought it through though. The reasons for adopting the four rail system remain sound. As well as corrosion it allows a simpler arrangement for the traction and other electrical systems, like signalling. With a three rail system one needs gadgets like impedance bonds to keep the electrical systems separate enough to avoid interference, but there is one less rail to install and maintain. Roughly speaking, in a small but complicated system the reduction in the number of gadgets outweighs the extra rail, but in a less complicated system over longer distances not having an extra rail is the important factor. That assumes starting from scratch, but that is not entirely accurate in a number of ways. Unprotected conductor rails would not be allowed in a new system anyway and a protected central conductor rail could probably not be devised, but protected conductor rails could be fitted either side of the running rails. None of that outweighs the fact that low voltage conductor rails, especially unprotected ones, are not ideal and were things being done from scratch a high voltage overhead system, with the larger tunnels this implies, would be chosen. In fact an overhead system wouldn't in fact involve any larger tunnels. As any new system would be fitted with emergency walkways and so the tunnels would be larger anyway. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008 13:57:11 +0000, David Hansen
wrote: None of that outweighs the fact that low voltage conductor rails, especially unprotected ones, are not ideal and were things being done from scratch a high voltage overhead system, with the larger tunnels this implies, would be chosen. In fact an overhead system wouldn't in fact involve any larger tunnels. As any new system would be fitted with emergency walkways and so the tunnels would be larger anyway. And would be better off larger so that more capacity can be provided in a given platform length. Neil -- Neil Williams Put my first name before the at to reply. |
Bakerloo Line beyond Harrow & Wealdstone
David Hansen writes:
A dangerous impression. If there was no (electrical) danger from the central conductor rail then it would not be mounted on insulators. Insulators are a give-away that something is energised. Does that necessarily follow? If the reason for using a 4-rail system rather than a 3-rail with return via the running rails were to avoid the problems such as electrolysis and interaction with signalling, would it not be possible to do it by having the centre insulated rail at a nominal ground potential but only bonding it to ground at the substations? |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008, Steve Fitzgerald wrote:
In message , Tom Anderson writes I recollect an incident a few years ago when the traction current had been discharged (turned off) due to person under a train. For complicated reasons, the centre rail had become live at +420v. This must be some new meaning of the term 'turned off' of which i was not previously aware! As you say, complicated reasons - but this sounds like the kind of thing that really, really shouldn't happen. Crumbs. It had been correctly discharged but been re-fed in error from elsewhere. You will note that what should normally have been -210v had now become +420v. Aha. Would it be sensible to electrically connect all four rails, with a set of crocodile clips or something, when working on the track in situations like this? Then, if there was a mistake which fed voltage to one or more rails, it would short out, and circuit breakers located wherever the feed-in was happening would break and cut it off. It would be something you could do at the site which would absolutely guarantee that there was no dangerous voltage there. The problem might be the effect it had on other parts of the system, though. tom -- Scheme is simple and elegant *if you're a computer*. |
Bakerloo Line beyond Harrow & Wealdstone
In message
David Hansen wrote: [snip] Roughly speaking, in a small but complicated system the reduction in the number of gadgets outweighs the extra rail, but in a less complicated system over longer distances not having an extra rail is the important factor. That assumes starting from scratch, but that is not entirely accurate in a number of ways. Unprotected conductor rails would not be allowed in a new system anyway and a protected central conductor rail could probably not be devised, You could do it providing you never turned the stock, so the Circle line would be out for a start. -- Graeme Wall This address is not read, substitute trains for rail. Transport Miscellany at http://www.greywall.demon.co.uk/rail/index.html |
Bakerloo Line beyond Harrow & Wealdstone
On 30 Nov, 15:43, Tom Anderson wrote:
Would it be sensible to electrically connect all four rails, with a set of crocodile clips or something Crocodile clips or something, and how to use them, in glossy brochure form: http://www.tubelines.com/whatwedo/tr...ing_device.pdf U |
Bakerloo Line beyond Harrow & Wealdstone
On 30 Nov, 13:57, David Hansen
wrote: Unprotected conductor rails would not be allowed in a new system anyway and a protected central conductor rail could probably not be devised, but protected conductor rails could be fitted either side of the running rails. Or you put the conductor rails above each other: http://upload.wikimedia.org/wikipedi...amome-7280.jpg U |
Bakerloo Line beyond Harrow & Wealdstone
In message
, Mr Thant writes Would it be sensible to electrically connect all four rails, with a set of crocodile clips or something Crocodile clips or something, and how to use them, in glossy brochure form: http://www.tubelines.com/whatwedo/tr...guidance/LU_sh ort_circuiting_device.pdf Which sadly in this case, the SCD was the cause of the problem. -- Steve Fitzgerald has now left the building. You will find him in London's Docklands, E16, UK (please use the reply to address for email) |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008 12:38:22 -0000, "John Rowland"
wrote: MIG wrote: On Nov 30, 11:14 am, David Hansen wrote: On Sat, 29 Nov 2008 09:26:38 -0800 (PST) someone who may be MIG wrote this:- LU's centre rail is I believe at minus 200 volts. That's interesting, because I was under the impression that there was no danger from the middle track, A dangerous impression. If there was no (electrical) danger from the central conductor rail then it would not be mounted on insulators. Insulators are a give-away that something is energised. Piecing it all together, I suppose it adds up, in that if a neutral rail was to be used, it might as well the the running rails or something earthed. So the fact that there's a special rail on insulators means it can't be neutral. Never really thought it through though. No, the fourth rail was used because allowing the current to return though earthed running rails causes corrosion to any metal utility pipes in the area, so the fourth rail and insulators are there to protect water mains. On a related note, the original LNWR/LMS electrification was 4th rail. It was converted to three with the return and running rails bonded, in 1970. Of course it made sense to use the existing 4 rail system because apart from the LBSCR's overhead AC that was what the other London area lines used. The LNWR electrification was planned in 1907 and opened in 1914, with the Bakerloo linking up a year later. The LSWR 3 rail system was planned later with the first section opening in 1915. |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008 15:08:16 +0000, Graham Murray
wrote: David Hansen writes: A dangerous impression. If there was no (electrical) danger from the central conductor rail then it would not be mounted on insulators. Insulators are a give-away that something is energised. Does that necessarily follow? If the reason for using a 4-rail system rather than a 3-rail with return via the running rails were to avoid the problems such as electrolysis and interaction with signalling, would it not be possible to do it by having the centre insulated rail at a nominal ground potential but only bonding it to ground at the substations? There will always be leaks due to build up of dirt. |
Bakerloo Line beyond Harrow & Wealdstone
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Bakerloo Line beyond Harrow & Wealdstone
"Christopher A. Lee" wrote Of course it made sense to use the existing 4 rail system because apart from the LBSCR's overhead AC that was what the other London area lines used. The LNWR electrification was planned in 1907 and opened in 1914, with the Bakerloo linking up a year later. The original plan was to extend the New Lines from South Hampstead in deep-level tube to a terminus below Euston. In 1911, before the New Lines opened, this plan had been abandoned in favour of linking with the Bakerloo. The LSWR 3 rail system was planned later with the first section opening in 1915. Did the LSWR ever consider using the 4 rail system? The first LSWR line to be electrified (apart from the isolated Waterloo & City) was the route between Waterloo and Wimbledon, via East Putney, including the section between East Putney and Wimbledon which had already been electrified on the 4-rail system for District trains. So this was the first use of a line adapted to take both 3rd rail and 4th rail trains. Peter |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008 18:00:27 -0000, "Peter Masson"
wrote: "Christopher A. Lee" wrote Of course it made sense to use the existing 4 rail system because apart from the LBSCR's overhead AC that was what the other London area lines used. The LNWR electrification was planned in 1907 and opened in 1914, with the Bakerloo linking up a year later. The original plan was to extend the New Lines from South Hampstead in deep-level tube to a terminus below Euston. In 1911, before the New Lines opened, this plan had been abandoned in favour of linking with the Bakerloo. OK. Even what was done was a major effort, quadrupling the track out to Watford with other major engineering works. The LSWR 3 rail system was planned later with the first section opening in 1915. Did the LSWR ever consider using the 4 rail system? The first LSWR line to be electrified (apart from the isolated Waterloo & City) was the route between Waterloo and Wimbledon, via East Putney, including the section between East Putney and Wimbledon which had already been electrified on the 4-rail system for District trains. So this was the first use of a line adapted to take both 3rd rail and 4th rail trains. I don't know. By the time the LSWR electrified there were other systems for comparison. I believe they had looked at the Liverpool-Southport electrification before they made up their mind. I do know that the New York Subway has major electrolytic corrosion problems on their elevated sections, which are like continuous girder bridges. I've never read of the third rail system having the running rails at a negative potential on either side of the Atlantic. Tram and streetcar track did this so the problem has been known for a very long time. Perhaps it is because pipes etc were laid under streets and surface trains had their own right of way. The original Met and Metropolitan District lines ran cut-and-cover under the streets, as did the tubes because of easement issues. And of course the latter tunnels were lined with cast iron segments. Peter |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008 15:08:16 +0000 someone who may be Graham Murray
wrote this:- Insulators are a give-away that something is energised. Does that necessarily follow? Pretty much. If the reason for using a 4-rail system rather than a 3-rail with return via the running rails were to avoid the problems such as electrolysis and interaction with signalling, would it not be possible to do it by having the centre insulated rail at a nominal ground potential but only bonding it to ground at the substations? That would mean, for the same voltage difference between the conductor rails, increasing the voltage on the other conductor rail and thus needing larger insulators for that. One would also have greater leakages, as the higher the voltage the greater the leakage through something like damp ballast against the conductor rail. However, one would still be able to use heated conductor rails, which is not AFAIAA done (at least in the UK) as that would also involve heating the running rails (amongst other undesirable things). -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008 16:50:43 +0000 someone who may be Steve
Fitzgerald ] wrote this:- http://www.tubelines.com/whatwedo/tr...guidance/LU_sh ort_circuiting_device.pdf Which sadly in this case, the SCD was the cause of the problem. I guessed that it was one of a series of problems which caused the voltage from a still energised positive rail to be transferred to the negative rail. Presumably there was some sort of broken connection or open circuit breaker/fuse in the feed to the negative rail. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008 08:04:16 -0800 (PST) someone who may be Mr Thant
wrote this:- Crocodile clips or something, and how to use them, in glossy brochure form: http://www.tubelines.com/whatwedo/tr...ing_device.pdf Figure 3 of http://www.raib.gov.uk/cms_resources/2008-02-28_R052008_Merstham.pdf is a photograph showing a third rail version of the same thing. The design with the large wooden arm is partly to make it unlikely it will be thrown off if the conductor rail is re-energised. It also helps push the metal through the crud on the underneath of the conductor rail. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008 18:00:27 -0000 someone who may be "Peter Masson"
wrote this:- The original plan was to extend the New Lines from South Hampstead in deep-level tube to a terminus below Euston. Was the plan not for a terminal loop, presumably with a few platforms? In 1911, before the New Lines opened, this plan had been abandoned in favour of linking with the Bakerloo. In addition more trains were to be sent to Broad Street. In effect the services took people to several places, rather than just Euston. Much the same was true at Kings Cross, where trains were sent to Broad Street and Moorgate (via the Widened Lines) rather than all going to Kings Cross. Some even went to Ludgate Hill and further south, though this ceased during the 1914-18 war IIRC. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008, David Hansen wrote:
On Sun, 30 Nov 2008 16:50:43 +0000 someone who may be Steve Fitzgerald ] wrote this:- http://www.tubelines.com/whatwedo/tr...guidance/LU_sh ort_circuiting_device.pdf Which sadly in this case, the SCD was the cause of the problem. I guessed that it was one of a series of problems which caused the voltage from a still energised positive rail to be transferred to the negative rail. Presumably there was some sort of broken connection or open circuit breaker/fuse in the feed to the negative rail. Ah, so although there was no potential between the two power rails, there was a potential between them and the ground? Really, you need to connect the two rails to each other and also to the ground. I was thinking the running rails would make a good ground substitute here. tom -- buy plastic owl |
Bakerloo Line beyond Harrow & Wealdstone
"David Hansen" wrote Much the same was true at Kings Cross, where trains were sent to Broad Street and Moorgate (via the Widened Lines) rather than all going to Kings Cross. Some even went to Ludgate Hill and further south, though this ceased during the 1914-18 war IIRC. Kings Cross was always remote from the City destinations of commuters, and the link to the Met was put in in 1863, and the Widened Lines were opened for passengers in 1868. However, despite additional Coenhagen and Gas Works Tunnels, the approaches to Kings Cross were hiopelessly congested, with trains taking half an hour for the 1.5 miles from Holloway to the Metropolitan. The GNR sought running powers over the Canonbury Curve and into Broad Street, but the LNWR prevented the North London granting these. Accordingly the GNR invited the NLR to run trains from Broad Street out to its suburban stations. This pattern - trains to Moorgate via the Widened Lines and to Broad Street via the Canonbury Curve lasted until the Great Northern Suburban electrification of 1976 - though it had its origins in relief of congestion rather than offering passengers a choice of terminus (Moorgate and Broad Street being very close to each other). Around the turn of the 20th century the GNR planned a third route, the Great Northern & City Railway, originally intended for through running from north of Finsbury Park. However, the GNR and GN&CR fell out over through running, so the Finsbury Park to Moorgate line had an isolated service (and was cut back to start from Drayton Park when its Finsbury Park platforms were handed over to enable the Victoria Line to be built). The through running eventually started with the GN Suburban electrification. Among the routes served by the GNR were Alexandra Palace via Highgate, Edgware via Mill Hill, and High Barnet. The 1930s idea was to hand all these over to London Transport, running both vvia Archway and via Finsbury Parkkk and the GN&CR. In the event, LT did not take over Edgware to Mill Hill East, or Alexandra Palace, and through running to the GN&C from these routes never happened. Peter |
Bakerloo Line beyond Harrow & Wealdstone
In message , Tom
Anderson writes Would it be sensible to electrically connect all four rails, with a set of crocodile clips or something, when working on the track in situations like this? Then, if there was a mistake which fed voltage to one or more rails, it would short out, and circuit breakers located wherever the feed-in was happening would break and cut it off. It would be something you could do at the site which would absolutely guarantee that there was no dangerous voltage there. The problem might be the effect it had on other parts of the system, though. Don't tube trains still carry Short Circuiting Devices (SCDs) anymore? It used to be that when traction current had been discharged a driver would clip the device over the outside (live) rail, look away incase of arcing, then smartly smack the other end down onto the centre negative rail. It would then be left there in situ for safety until it was required to restore traction current. -- Clive |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008 20:03:37 -0000 someone who may be "Peter Masson"
wrote this:- The GNR sought running powers over the Canonbury Curve and into Broad Street, but the LNWR prevented the North London granting these. Accordingly the GNR invited the NLR to run trains from Broad Street out to its suburban stations. I have seen photographs of LMS locomotives operating trains amongst LNER trains. The coaches were presumably LMS coaches too, possibly former NLR coaches. IIRC this lasted until the early 1930s, when the LNER took over at least the locomotives. I could be wrong about the date though and it may have lasted into the 1950s. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
Bakerloo Line beyond Harrow & Wealdstone
In message , Clive
writes Would it be sensible to electrically connect all four rails, with a set of crocodile clips or something, when working on the track in situations like this? Then, if there was a mistake which fed voltage to one or more rails, it would short out, and circuit breakers located wherever the feed-in was happening would break and cut it off. It would be something you could do at the site which would absolutely guarantee that there was no dangerous voltage there. The problem might be the effect it had on other parts of the system, though. Don't tube trains still carry Short Circuiting Devices (SCDs) anymore? It used to be that when traction current had been discharged a driver would clip the device over the outside (live) rail, look away incase of arcing, then smartly smack the other end down onto the centre negative rail. It would then be left there in situ for safety until it was required to restore traction current. Yes, one at each end of the train with the emergency equipment. -- Steve Fitzgerald has now left the building. You will find him in London's Docklands, E16, UK (please use the reply to address for email) |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008 19:11:56 +0000 someone who may be Tom Anderson
wrote this:- Ah, so although there was no potential between the two power rails, there was a potential between them and the ground? Sounds like it. However, I wouldn't like to go much further without knowing the complicated reasons why it occurred. There are a few ways this could happen. Really, you need to connect the two rails to each other and also to the ground. I was thinking the running rails would make a good ground substitute here. It should be enough to connect the conductor rails to each other. However, there are failure modes where one pole of the circuit fails (broken cable and non-interlinked fuses/circuit breaker are the obvious ones) and if this happens unexpected voltages can be present. Although AC circuits can suffer these problems they tend to be minimised by various means. Two, three and five wire DC circuits can suffer a number of maladies which those who work on them would be wise to be aware of. There is a lot to be said for treating all equipment as energised at all times except when working on it under a safe system of work. I recall one fairly well known evacuation of a tube train, probably 2-3 decades ago, when the conductor rails remained energised for a short distance, but were discharged for most of the way along the tunnel on either side of this short section. The fire brigade, police, ambulance and passengers walked alongside these energised conductor rails, fortunately without incident. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
Bakerloo Line beyond Harrow & Wealdstone
In article , (Peter
Beale) wrote: wrote: In article , (Paul Scott) wrote: wrote in message On hybrid sections (e.g. East Putney to Wimbledon) the 4th rail is at +630v. That would be the third (positive) rail. Otherwise the 'third rail' stock wouldn't work too well... Yes, I meant the outside rail. I was counting across with the centre as third. If you count in such a way that the outside ("live") rail is the fourth, then the centre is the second. If you do it the other way so that the centre is third, then the live rail is first! I was assuming, whatever else, that the running rails were first and second! Bear in mind that the first third rail systems were the City and South London and Central London Railway's and theirs were between the running rails. -- Colin Rosenstiel |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008 16:00:14 +0000, Graeme Wall
wrote: In message David Hansen wrote: [snip] Roughly speaking, in a small but complicated system the reduction in the number of gadgets outweighs the extra rail, but in a less complicated system over longer distances not having an extra rail is the important factor. That assumes starting from scratch, but that is not entirely accurate in a number of ways. Unprotected conductor rails would not be allowed in a new system anyway and a protected central conductor rail could probably not be devised, You could do it providing you never turned the stock, so the Circle line would be out for a start. You provide appropriate changeover switches as on the original Great Northern and City line system which IIRC used two outer conductor rails until later changed to conventional four-rail working. |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008 12:34:42 -0500, Christopher A. Lee
wrote: On Sun, 30 Nov 2008 15:08:16 +0000, Graham Murray wrote: David Hansen writes: A dangerous impression. If there was no (electrical) danger from the central conductor rail then it would not be mounted on insulators. Insulators are a give-away that something is energised. Does that necessarily follow? If the reason for using a 4-rail system rather than a 3-rail with return via the running rails were to avoid the problems such as electrolysis and interaction with signalling, would it not be possible to do it by having the centre insulated rail at a nominal ground potential but only bonding it to ground at the substations? There will always be leaks due to build up of dirt. And it would assist the occurence of faults where the return path breaks and the conductor on the load side achieves a good connection via the wrong path (think RCD). |
Bakerloo Line beyond Harrow & Wealdstone
On Sun, 30 Nov 2008 19:11:56 +0000, Tom Anderson
wrote: On Sun, 30 Nov 2008, David Hansen wrote: On Sun, 30 Nov 2008 16:50:43 +0000 someone who may be Steve Fitzgerald ] wrote this:- http://www.tubelines.com/whatwedo/tr...guidance/LU_sh ort_circuiting_device.pdf Which sadly in this case, the SCD was the cause of the problem. I guessed that it was one of a series of problems which caused the voltage from a still energised positive rail to be transferred to the negative rail. Presumably there was some sort of broken connection or open circuit breaker/fuse in the feed to the negative rail. Ah, so although there was no potential between the two power rails, there was a potential between them and the ground? Really, you need to connect the two rails to each other and also to the ground. I was thinking the running rails would make a good ground substitute here. Only on one running rail of a 3-rail system where there is intentional permanent bonding suitable for traction currents (and even then it isn't necessarily at the same PD as the local earth). On a LU 4-rail system the running rails are not "earthed" WRT traction supplies and have no certain/permanent low-resistance path to earth even if they did when a 3-rail SCD (positive-to-running rail) was first applied. Think of the earth wire in a domestic system - this normally carries no current but still has a minimum current rating and maximum permitted impedance to the supply earth as it is an intentional path, albeit with a limited expectation of actual use. |
Bakerloo Line beyond Harrow & Wealdstone
"Tom Anderson" wrote in message .li... On Sun, 30 Nov 2008, David Hansen wrote: On Sun, 30 Nov 2008 16:50:43 +0000 someone who may be Steve Fitzgerald ] wrote this:- http://www.tubelines.com/whatwedo/tr...guidance/LU_sh ort_circuiting_device.pdf Which sadly in this case, the SCD was the cause of the problem. I guessed that it was one of a series of problems which caused the voltage from a still energised positive rail to be transferred to the negative rail. Presumably there was some sort of broken connection or open circuit breaker/fuse in the feed to the negative rail. Ah, so although there was no potential between the two power rails, there was a potential between them and the ground? Really, you need to connect the two rails to each other and also to the ground. I was thinking the running rails would make a good ground substitute here. Unfortunately, in the incident Steve is referring to, the "ground substitute" turned out to be a para-medic... (She survived). -- Cheers, Steve. Change jealous to sad to reply. |
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