And Uckfield has reasonable chance being rural with some upgrades e.g. fencing, foot crossing closures, 3rd rail boards...
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Cost of electrification OHLE vs 3rd rail
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Although with the current for a given power under ac is 1/33rd of the DC value. This means that an EMU requiring 2MW of power on ac will draw about 80A from the conductor wire resulting in a corresponding 80A return current through two running rails. The same train running 3rd rail would draw 2667A from the third rail requiring the steel rails to carry that current to the next feed point(s). If we are considering the real railway where there could be 3-6 trains on the same section, they may not be pulling heavy current at the same time, but with a 3rd rail current limit of 10000A or less, 3rd rail requires very short distances between feed points.
apk55
Member
In addition there are methods in AC electrification that can reduce the return voltage drop - Booster tranformers and +-25KV systems.
Ok thanks for the figure as I couldn't find anything online. I do remeber somebody defending 3rd rail on here a few years ago saying that there was no need to convert the SWML to OLE for it to be part of the Electric Spine as it was possible to increase the maximum current draw on a DC line to something like 8000A and maybe 10000A if necessary. So maybe that was a 'convenient' exaggeration in the ongoing debate.
If this is the case, why has there never been an issue with this in over 100 years of DC running worldwide (there's a lot in the USA), sufficient to close level crossings or prevent track access by maintenance staff. And furthermore, DC third rail still seems universally preferred by urban Metro systems.
Well, this is the UK, not the US. There are plenty of things taken at risk in the US because they see safety as an unnecessary cost, until the lawyers get to work on it. What happens (or doesn't happen) there is no reason for Europe to take the same risks.
The reference to US domestic mains rather than European is a measure of the actual voltage that can occur, i.e. 120V rather than 230V.
East London Line was the last one. Fairly recent.
From a pure OLE cost, Blackpool wasn’t marginally more expensive. But when you add up all costs required to enable the electrification, E-G comes out top.
That depends on your definition of reasonable. I’d say it is extremely unlikely.
Reasonable = better than some other potential routes and just slightly better hell freezing over
GRALISTAIR
Established Member
case in point - I took this a few minutes ago in the USA. No fence no nothing. Admittedly there is no 3rd rail
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And, crucially, the 3rd rail was already there west of Dalston, so it wasn’t new electrification as such on that stretch. And between Whitechapel / Shoreditch and Dalston the route is heavily segregated (being on Viaduct or in cutting the whole way, with good security), and the stations are all manned when train services are running, therefore a much lower tresspass risk.
superkev
Established Member
Some of my thoughts:-
The latest 25kv system uses a 50kv feeder along the track which is transformed down to 25kv every so often to feed the catenary. What's so different to a similar system but having the high voltage transformed and rectified to DC 3rd rail.
This avoids having every train humping several tons of transformer rectifier around.
I wonder how the safety nannies at the ORR view the bottom pick up as used by docklands and many other countries. With an insulated cover is has a number of advantages.
K
The latest 25kv system uses a 50kv feeder along the track which is transformed down to 25kv every so often to feed the catenary. What's so different to a similar system but having the high voltage transformed and rectified to DC 3rd rail.
This avoids having every train humping several tons of transformer rectifier around.
I wonder how the safety nannies at the ORR view the bottom pick up as used by docklands and many other countries. With an insulated cover is has a number of advantages.
K
Plenty of reasons above for not doing 3rd rail, or for even converting existing 3rd rail to overhead.
But if 3rd rail was so bad, why does no-one talk of converting any of the Underground to 25kv. The outer sections of the Met, the H&C perhaps.
And why do the Germans seem quite happy with 3rd rail (Yes I know they are not top contact) for their s-bahn networks, like in Berlin?
But if 3rd rail was so bad, why does no-one talk of converting any of the Underground to 25kv. The outer sections of the Met, the H&C perhaps.
And why do the Germans seem quite happy with 3rd rail (Yes I know they are not top contact) for their s-bahn networks, like in Berlin?
That's already how third rail works.
The 'safety nannies' (also known as people who don't like to see other people get fried) will evaluate the risk the same as with any other system. Bottom contact is safer, though you still have not insignificant currents being carried at ground level.
It’s not a 50kv feeder. It’s anoher 25kv but on the opposite phase.
As NajaB says, that's how 750VDC 3rd rail is done here. The HV is 33kV which is supplied from a major connection to the national grid. That infrastructure is owned and maintained by Network Rail which is necessary because the feed points need transforming and rectifying with quite critical switching and fault monitoring kit because the peak current draw is not much less than that which might occur with a fault. That kit also requires railway land onn which to put it as well as maintenance access. With OLE, all electrical tcables are carried out of reach on the masts/portals including the autotransformer feed and earth wire, (the latter two may be put into insulated cables when the line goes under bridges and through tunnels just like the 33kV feed on 3rd rail lines does).
The on-board transformers and rectifiers are getting lighter and smaller despite the power requirements going up, and as most new 3rd rail EMUs are required to be suitable for OLE conversion, the necessary provision often includes a concrete dummy weight, to enable the suspension setup to be common for all delivered stock.
Most 3rd rail systems outside the UK are on metro or suburban routes and not expected to run long distances over 150km/h as they do in UK, (e.g. SWML). LU runs a pure metro service and with absolute infrastructure constraints on 160km of the 402km total affecting every line, with track access tightly controlled throughout, there are no plans to convert it to OLE.
GRALISTAIR
Established Member
Pi radians out of phase.
Elecman
Established Member
Is Pi radians 180 degrees?
Yes it is.
contrex
Member
Yes! You could have a 33 Kv AC three-phase feeder system, (then you could us 6- or 12-phase rectifiers) and transform and rectify the DC and feed it to the third rail. You'd need substations every 5 miles or so. I'm sure nobody's ever tried that before, have they?
GRALISTAIR
Established Member
There is a great YouTube video which I will post if I can find and explains why we have 3 phase and why not 6 phase or 12 phase. It comes down to economics.
EDIT - found it (one of others actually)
superkev
Established Member
I think what is meant is the sub stations would use 6 or 12 pulse rectification.
I think the economics of such a system (hv 3ph supply to transformer rectifiers every 5 miles or so) comes down to the cost of the additional track side transformer rectifiers versus the cost having them on the train. Depends on the number of trains I suppose.
I wonder if today's semiconductor rather than the mercury arc rectifiers of the day had been available would we be doing things now with DC rather than ac.
K
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I hadn't considered the extra weight (cost) being loaded into UK third rail EMUs to make them dual ready.
There are only a half a dozen lines in the UK which are long distance 3rd rail affairs, all in the south east, and even on these the government has gone cold on conversion.
The remainder of lines are "metro" in nature, so the arguments for leaving well alone seem applicable, including provision for 3rd rail extensions where needed.
The through-life cost of provisioning and hauling the transformers or their weight equivalents around is probably covered by the additional efficiency of being able to operate or upgrade these trains to run on OLE routes through the lower energy costs.
The non-metro lines include virtually all those outside the M25, so not exactly minimal. In addition, there are concentrations of local lines in areas such as Brighton/Lewes/Eastbourne, East Kent and Portsmouth/Southampton/Eastleigh. There would be no point leaving islands of DC there.
The UK government blows hot and cold on anything to do with railways and when they are maintaining full scale austerity as a political project, well-intentioned projects like bringing trunk routes up to date get kicked into the long grass, much to their road haulier voters delight.
bishdunster
Member
Err, how long has Weymouth been in the South East ?????
But not uniformly, which is the point. If a location (Liverpool) uses third rail as metro, work on developing that network normally, as would happen in any other major city, shouldn't be held to ransom by a blanket and ill judged policy that handicaps that city's abilities and ambitions, and burdens it with extra cost and obstacles unlike cities anywhere else in the world.
3phase supply = 6pulse rectification on simple ancient equipment or 12 pulse* on modern dual secondary star- delta windings (or the even more complex 18 or 24 pulse rectification to produce smoother DC and reduce harmonics issues)
* very asymmetric waveform with 30degree phase offset between the 2 sets of 6 pulses
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