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Post by superteacher on Apr 6, 2021 14:26:30 GMT
I am thinking about the Bakerloo / LO north of Harrow and Wealdstone, and the Northern City line, both of which had the 4th rail dropped to track level after ceasing to be operated by London Underground trains.
I understand that completely removing the 4th rail would be difficult and expensive, but why not just leave it as it was (at the same height as the 3rd rail)?
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Post by Dstock7080 on Apr 6, 2021 14:32:34 GMT
I am thinking about the Bakerloo / LO north of Harrow and Wealdstone, and the Northern City line, both of which had the 4th rail dropped to track level after ceasing to be operated by London Underground trains. I understand that completely removing the 4th rail would be difficult and expensive, but why not just leave it as it was (at the same height as the 3rd rail)? rail on sleepers would be relatively low, clear of train borne obstructions, require less maintenance (pots etc) ps. negative rail is not same height as positive rail. |
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Post by superteacher on Apr 6, 2021 14:34:54 GMT
I am thinking about the Bakerloo / LO north of Harrow and Wealdstone, and the Northern City line, both of which had the 4th rail dropped to track level after ceasing to be operated by London Underground trains. I understand that completely removing the 4th rail would be difficult and expensive, but why not just leave it as it was (at the same height as the 3rd rail)? rail on sleepers would be relatively low, clear of train borne obstructions, require less maintenance (pots etc) ps. negative rail is not same height as positive rail. Thanks - forgot that 3rd / 4th were different heights! |
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Post by selbiehouse on Apr 6, 2021 17:32:27 GMT
For information I have a note that the Euston - Watford DC line was converted from 4th rail to 3rd rail operation on 2nd August 1970. Shortly after a Southern Region 4COR unit ran to Watford Junction as a special.
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Post by taylor on Apr 6, 2021 17:36:07 GMT
Apart from Stonebridge Park Depot, "DC Electric Lines" NW of the the NR/LU property boundary at Queens Park are electrified at 750V dc according to the Bakerloo Line Infrastructure Line Overview (ILO) (1) The bonding of the running rails could date back to when the "DC Electric Lines" or LNWR "Watford New Line" were resignalled in 1932 see here: www.railsigns.uk/info/watnew1/watnew1.htmland here: www.davros.org/rail/signalling/lmsr/newlines.htmlI've found no reference when it was resignalled with conventional colour lights in 1988 (now controlled I believe from Wembley Main Line Signalling Centre) how AC track circuits were installed (help!!). Without nearer inspection, I cannot be sure how such circuits were installed north of Harrow along the stretches, where you note, the 4th rail is "dropped". My hunch is that the bonding between some stretches of running rail pre-dates the 1980s when the line was being converted to conventional colour lights and could have been inadequate to carry heavy return currents. (Bakerloo trains continued to Watford until 1982). So to ensure an efficient current return, the running rails were, and remain in part, bonded to the 4th Rail. No doubt their removal is on someone's "to-do-list" As an aside, do classes 387/2 and 710/2 have trip-cocks? Must check that out! (1) LUL sold copies of the Infrastructure Line Overviews to the general public at the LT Museum Depot during 2019. I have them (dated 1/102013 for the Bakeroo) for all lines. |
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Post by superteacher on Apr 6, 2021 17:41:08 GMT
I think the 4th rail was retained (in working condition) between Harrow and Watford until at least 1984, because after Bakerloo services were cut north of Stonebridge Park in 1982, there was an ongoing discussion about reintroducing the service. In the end, it was decided that the Bakerloo would not go beyond Harrow and Wealdstone.
There is a rumour that a 1959 stock made it to Watford Junction (after the Bakerloo service had ceased) - no idea how true it is, but it's been mentioned in various places.
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Post by Dstock7080 on Apr 6, 2021 18:46:15 GMT
As an aside, do classes 387/2 and 710/2 have trip-cocks? Must check that out! 710/2 are only TPWS and 378/2 are having the tripcocks isolated/removed |
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Post by taylor on Apr 6, 2021 19:09:31 GMT
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Post by Dstock7080 on Apr 6, 2021 20:34:17 GMT
Dstock 7080, when was the GUN to RMD TPWS completed? 2019 as noted in the the project plan above? My photographs show new installation at Gunnersbury June 2019 and Richmond May 2020. |
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Post by trog on Apr 26, 2021 10:33:09 GMT
The fourth rail was kept north of Harrow as the electrical engineers said that it was needed as part of the electrical return path. When the PW maintenance removed about a mile of it north of Carpenders Park in the late 1980's, the electrical engineers insisted that it was replaced which it was with scrap quality CWR removed from Kilsby tunnel. However the electrical engineers did not install any bonds on this rail for over ten years, so how much it was/is needed must be open to question.
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metman
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Post by metman on May 4, 2021 20:50:26 GMT
From memory (and this was a few years ago) the middle conductor rail is still on pots in places which led me to believe it partly collapsed due to disrepair. I’m sure the pots were removed in places too.
When the BR class 501 were converted to 3 rail operation the traction return was bonded to the axels (not that successfully I believe). I assume, perhaps wrongly, that it was in 1970 that the 4th was then bonded to the running rails as it is today?
The Northern City tunnels also have the former 4th rail placed on the sleepers but this was deliberate to assist in current return in the tunnels (I note that the bottom half of the Northern City tunnels were replaced with brick?
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Post by ertowerty1 on Feb 11, 2022 10:28:28 GMT
Are there any impedence bonds on the DC lines North of Queens Park?
I suspect that using the 4th (negative) rail in parallel provides sufficient traction conductivity so that single rail track circuits can be used. The loss of bonding would not be immediatly apparent as the trains themselves are fairly tolerant of a wide range of DC voltage. (I suspect that if the volts at the train shoes fell below 400V there would be issues).
The last time I visited Watford High Street, the 4th rail was heavily corroded in places, to the point of being perforated.
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