mrfs42
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Post by mrfs42 on Jun 18, 2008 23:20:32 GMT
For once, not a TT question.  Are there still the two lengths of contactor connected/disconnected juice rails at Turnham Green onto the Richmond road? If so, are T/Ops still forbidden from going beyond series in these lengths? If not - what are the modern electrical arrangements - what clever stuff is done with the electrical demons; the old ones being insulated negative return/earthed negative on the appropriate LU/NR side ? |
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Colin
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Post by Colin on Jun 19, 2008 2:57:59 GMT
I've never been instructed to stay in series there, or anywhere else on the District line for that matter.......does that help?  |
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mrfs42
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Post by mrfs42 on Jun 19, 2008 7:05:38 GMT
Yes, it does. Thank-you. |
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Deleted
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Post by Deleted on Jun 19, 2008 11:32:59 GMT
First I've heard of them!
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mrfs42
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Post by mrfs42 on Jun 19, 2008 11:37:26 GMT
Supplement to Traffic Circular 15/66 refers....
I was reading it after cataloguing it - there were 1000' EB and 600' WB sections of current rails that were switched between the LU supply and the BR supply by the trains drawing juice.
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Post by chrish on Jun 19, 2008 11:51:03 GMT
As far as I know, there are no rail that draw current from either/or LU and NR sources on the district. We just have a rail gap (and a red sign telling us we are entering enemy territory.. I mean NR rails ;D) but as people have said, no need to be in series.
So to get this straight in my head though, as the train passed over these transition current rails, the train stays in series motoring and the rails then switch from getting juice from LU to NR (or vice versa)... my knowledge of electricals is rather lacking then... how did this work?
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mrfs42
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Post by mrfs42 on Jun 19, 2008 12:12:07 GMT
So to get this straight in my head though, as the train passed over these transition current rails, the train stays in series motoring and the rails then switch from getting juice from LU to NR (or vice versa)... my knowledge of electricals is rather lacking then... how did this work? Well, insofar as I understand the paperwork the train switches the feed itself. Herewith: On the Richmond Line 'contactor-fed' sections are provided which enable trains to travel over them in series only. These are fed first from the conductor rails in the rear and then, when a train is completely within the section, fed from the conductor rails in advance, i.e. at each end of the section is a contactor. When the train is completely within the section the entry contactor is opened and the exit contactor closed. There is a time delay between the opening and closing of the contactors which causes a momentary loss of traction current. When a train leaves the section the exit contactor is opened and the entry contactor closed. I guess it is all done with some form of check on how much current is being drawn from which rail. |
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Colin
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Post by Colin on Jun 19, 2008 14:17:21 GMT
My intrepretation of what you've posted there, mrfs, implies to me that the system needs a train with bus line - current stocks don't have them which is why we can now motor over a traction current section gap into a dead section (after consultation with the line controller).
Although it's not clear in my copy of the line diagram, there are section gaps between LU & NR current sections [1], so I suspect the only issue now is the running rail return needing to be isolated once we run onto LU metals [2]...
[1] - My copy of the line diagram shows a 48' gap at Putney Bridge between LU & NR, so I would assume the same exists in the Turnham Green area?
[2] - Would a couple of isolated block joints and a neutral section of running rail suffice?
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mrfs42
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Post by mrfs42 on Jun 19, 2008 14:26:35 GMT
[1] I think so, given that 48' is reasonably standard over the system. Although I have seen somewhere in the pile of paperwork a figure of 15 metres also - might even be 20.
[2] I'd have thought so, an 11' 6" with isolated insulated block joints either end and the neutral running rail should suffice as long as the stock doesn't have a bus line.
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Post by Deleted on Jun 20, 2008 14:12:26 GMT
15m is the standard length when they isolate for possessions
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Post by railtechnician on Jun 20, 2008 15:43:48 GMT
15 metres and 48 feet are both correct the former being the metric equivalent of the latter for the sake of documentation.
As for isolation my understanding has always been that there was none other than the traction current gap itself and usual separation of the line into track circuits. Having never had to maintain boundary signalling I am not sure of the exact arrangements but I would not be surprised to learn of a 10' 10" dead section between LU and NR track circuits.
LU traction is an earth free supply and earthing one leg will have little or no effect though it should show up at NOC and Line Control Room as a momentary traction earth fault on the TED unit. returning the traction supply is only via the neggy.
On the NR side the return is via a neggy rail bonded to the running rails of NR track circuits which as far as I know employ impedance bonds to separate the traction return current from track circuit currents.
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mrfs42
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Post by mrfs42 on Jun 20, 2008 15:58:24 GMT
On the NR side the return is via a neggy rail bonded to the running rails of NR track circuits which as far as I know employ impedance bonds to separate the traction return current from track circuit currents. Yes, especially if double rail AC Track circuits are in use, there are both resonated impedance bonds generally auto-coupled too from memory - though it's a long time since I've looked at NR Track circuit theory. |
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