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Post by trt on Apr 9, 2018 14:24:37 GMT
Gents. This thread is the reason i do not understand Electricity. It's basically witchcraft - no-one has ever seen an electron after all, or can even say how big it is (quantum probability functions mean it can be considered to be infinite). So we draw pictures to try to describe the phenomena we experience. Some of those pictures are better at predicting what will happen than others, but in whether they are real is an interesting philosophical question. Nah, we've got a tunnel full of 'em in the basement here.  I seem to recall there did used to be a long wooden paddle in the emergency equipment locker. Is that still in there? |
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Post by Deleted on Apr 9, 2018 16:28:24 GMT
To lift the train shoes and or on some stocks a nice coffee table
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Post by principlesdesigner on Apr 10, 2018 0:12:16 GMT
15v through the running rails if memory serves Until you take the relay connection off, when it goes to 100v! |
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Post by Deleted on Apr 10, 2018 16:55:28 GMT
33 1/3hz tracks were always bad especially with 40uf in the circuit you certainly knew about it
uf = microfarad
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Post by class411 on Apr 10, 2018 17:51:20 GMT
33 1/3hz tracks were always bad especially with 40uf in the circuit you certainly knew about it uf = microfarad You talkin abart yer gramaphone, grandad? Seriously, the 33 1/3 sort of implies a vinyl record and whilst most record players would certainly include caps, I can't quite make the connection between the rotation speed and an electric shock. ETA, Pot here - after complaining about kettle a couple of minutes ago, I've just done it myself: 'caps' = capacitors. High voltage ones can give you a nasty belt and really big low voltage ones (as used in mainframe computer power supplies could literally (and, yes, I do mean literally) melt a screwdriver shank. |
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Post by Deleted on Apr 10, 2018 19:07:49 GMT
LU has 125hz and 33 1/3hz and 50hz track circuits
I always found 33 1/3hz tracks gave the biggest shock
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Post by zbang on Apr 11, 2018 3:12:17 GMT
That makes some sense, the skin effect at 33.33 Hz about 13mm whilst at 125 Hz it's only 7mm (approximate). There's probably also some bio-electrical effects that I'm not aware of, too.
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Post by principlesdesigner on Apr 11, 2018 5:55:10 GMT
LU has 125hz and 33 1/3hz and 50hz track circuits I always found 33 1/3hz tracks gave the biggest shock That makes some sense, the skin effect at 33.33 Hz about 13mm whilst at 125 Hz it's only 7mm (approximate). There's probably also some bio-electrical effects that I'm not aware of, too. I've always found the 33 1/3Hz tracks the most evil! |
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Post by trt on Apr 11, 2018 6:52:38 GMT
Muscle provides no conduction attenuation to electrical signals up to around 50Hz. At 125Hz, it's around 40% dampened. It's all to do with the speed of ion channels in cell membranes.
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Post by superteacher on Apr 14, 2018 8:42:17 GMT
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Post by will on Apr 14, 2018 10:45:05 GMT
How many amps are on LU I've heard in the past from one of the Tube documentaries that its 3000?.
Also which lines have 750v is it just the SSL and Victoria with all others running on 630V? thanks
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Post by zbang on Apr 15, 2018 3:05:35 GMT
(I hope I'm not further splitting the subject) 15v through the running rails if memory serves Until you take the relay connection off, when it goes to 100v! It's been a long time since I thought about the minutia of track circuits, but do you mean the open-circuit voltage is 100v and the relay drags that down to 15v (and an occupied block would be down close to zero). That must be a fairly high ballast in the feed circuit. I'd expect a feed supply of maybe 10-15v and an relay which doesn't load that down much. OTOH, I'm more thinking of main-line practice than the short blocks of urban transit. Still, 100v will get your attention! |
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Post by class411 on Apr 15, 2018 8:21:25 GMT
How many amps are on LU I've heard in the past from one of the Tube documentaries that its 3000?. I'm afraid the question doesn't really make much sense, unless you mean very specifically: 'How many amps are available in on one section of track', and even there, the answer will be 'it varies'. I'll wait for an LU expert to give you a more detailed answer as I could only talk in generalities which might confuse the issue. |
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Post by Deleted on Apr 15, 2018 8:53:59 GMT
SSL is higher then 630v except on a couple of sections Barons Court through to Ealing Broadway due to dual running with the Picc and also west of West Harrow again due to dual running of the Picc from Rayners Lne through to Uxbridge
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Post by Deleted on Apr 15, 2018 9:06:07 GMT
(I hope I'm not further splitting the subject) Until you take the relay connection off, when it goes to 100v! It's been a long time since I thought about the minutia of track circuits, but do you mean the open-circuit voltage is 100v and the relay drags that down to 15v (and an occupied block would be down close to zero). That must be a fairly high ballast in the feed circuit. I'd expect a feed supply of maybe 10-15v and an relay which doesn't load that down much. OTOH, I'm more thinking of main-line practice than the short blocks of urban transit. Still, 100v will get your attention! Initially the signal supply is 600v AC then it’s transformed down locally to 100v it will then go through a variable capacitor which then will go through the rails and at the other end will be the relay. Once the relay is in circuit the R coil on the relay will work between approx 5 to 15v. The relay requires 2 feeds to energise a Q coil which depending on its location requires 100v be it straight fed or through a train stop, and the R coil which always come from the track. If you take the R coil out of circuit then the open circuit voltage is 100v as the r coil on the relay is the load for the circuit. When a train or device shunts / shorts the track circuit then the voltage is around 0.2v thus removing the feed to the r coil and thus the relay will not energise as it requires 2 feeds. |
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Post by Dstock7080 on Apr 15, 2018 9:06:22 GMT
Finchley Road-Harrow also remains 630v.
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Post by Deleted on Apr 15, 2018 9:07:35 GMT
I thought that was also boosted as the jubilee can take the higher voltages oh well I stand corrected
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Post by croxleyn on Apr 15, 2018 10:58:54 GMT
For a system using regenerative braking, the voltage can rise significantly, depending on the balance of trains slowing versus those accelerating. There will be a "feed" working voltage, defined by the substation, say 630V. At the train, this can of course drop due to a heavy load versus the conductor rail resistance.
There will also a "maximum" voltage, to which the system can rise when trains are braking, say 750V. I presume that the train will have a limit detection circuit, causing the mechanical brakes to operate (and therefore waste the kinetic energy) if the voltage rises too high.
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Post by domh245 on Apr 15, 2018 11:02:22 GMT
There will also a "maximum" voltage, to which the system can rise when trains are braking, say 750V. I presume that the train will have a limit detection circuit, causing the mechanical brakes to operate (and therefore waste the kinetic energy) if the voltage rises too high. I would think that they'd switch it to rheostatic rather mechanical braking if the supply voltage went to high as a result of too many trains feeding the system simultaneously. It'd be quicker to swap to than trying to bleed the mechanical brakes in, and would avoid wear and tear on them. |
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Post by will on Apr 15, 2018 11:41:23 GMT
There will also a "maximum" voltage, to which the system can rise when trains are braking, say 750V. I presume that the train will have a limit detection circuit, causing the mechanical brakes to operate (and therefore waste the kinetic energy) if the voltage rises too high. I would think that they'd switch it to rheostatic rather mechanical braking if the supply voltage went to high as a result of too many trains feeding the system simultaneously. It'd be quicker to swap to than trying to bleed the mechanical brakes in, and would avoid wear and tear on them. The maximum voltage under regenerative breaking is 890v. This was increased as the traction current was increased to 750v to be useful and to provide a headroom to be useful the regenerative rate had to increase too.
I know they were working on a solution to feed back the regenerative voltage back into the grid through the sub stations any one know any details?
Thanks
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Post by norbitonflyer on Apr 15, 2018 14:06:23 GMT
How many amps are on LU I've heard in the past from one of the Tube documentaries that its 3000?. The current drawn by a train depends on what it is doing - it will draw the most current when on full power, for example on starting. I can't find any figures for installed power on Tube trains, but assuming the figure is the current drawn when on full power, 3000amps on a 750 Volt supply equates to only 2250kW or about 3000hp. Unless we are talking about the 4-car trains on the Waterloo & City Line, that seems a bit on the low side - an 8-car class 700 unit has 3300 kW installed. |
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Post by croxleyn on Apr 15, 2018 19:29:57 GMT
How many amps are on LU I've heard in the past from one of the Tube documentaries that its 3000?. The current drawn by a train depends on what it is doing - it will draw the most current when on full power, for example on starting. I can't find any figures for installed power on Tube trains, but assuming the figure is the current drawn when on full power, 3000amps on a 750 Volt supply equates to only 2250kW or about 3000hp. Unless we are talking about the 4-car trains on the Waterloo & City Line, that seems a bit on the low side - an 8-car class 700 unit has 3300 kW installed. Does anyone know if there are restrictions applied with regard to trains pulling away?
When people say "Electrify our (diesel) trains", they don't realise that with each train taking several MegaWatts, the generating capacity into the UK Grid is finite, at typically 40,000 MegaWatts for every possible electric load in the country, so gets ever closer to being overloaded = blackouts. At the end of major sporting or concert events, like The Last Night of the Proms, Grid Control have to turn up the Power Stations + Dinorwig Hydro (North Wales) to compensate for all the kettles being turned on, but they can see when this will happen with a bank of TV screens.
If chance happened that every underground train was to pull off at the same instant, that could cause major problems.
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