|
|
Post by stapler on Nov 12, 2015 15:17:40 GMT
The Tyneside electrics of 1904 were indeed 600v DC third rail. But didn't Sir Vincent Raven decide (and publish research on)1500v OHE was better as long ago as WW1 for express passenger and heavy freight?
|
|
|
|
Post by brigham on Nov 12, 2015 15:33:16 GMT
I was hoping for some debate on the Ganz system, or the 3-phase Simplon Tunnel installation. These low-frequency polyphase systems with the running rails as one of the phases are fascinating.
One of the reasons for the 16-and two-thirds c/s. frequency was to allow for physically larger motors with direct side-rod drive, still seen in Switzerland and other places which take railways seriously.
Raven adopted overhead collection for the 1500v DC Shildon-Newport electrification of 1913.
|
|
|
|
Post by norbitonflyer on Nov 12, 2015 15:47:20 GMT
The Tyneside electrics of 1904 were indeed 600v DC third rail. But didn't Sir Vincent Raven decide (and publish research on)1500v OHE was better as long ago as WW1 for express passenger and heavy freight? A rather extreme form of publication, but yes! Plans to expand the initial system to York were well in hand by the time of the Grouping, but were shelved by the new management. Ten years before even that, the NER had built a small scale ohle installation for the Newcastle Quayside line. The two locomotives were equipped for both third rail (in the tunnels) and overhead (on the quayside itself, and in the marshalling yards). The local passenger services on Tyneside were electrified on the third rail system, but evidently the advantages of higher voltages (mainly reduced transmission losses) led Raven to switch to overhead for his later, longer-distance, projects. The Southern's (Classes 70 and 71) were also fitted with pantographs , and several freight facilities on the South Eastern division such as the Angerstein Wharf branch and the sidisngs at Hither Green, fitted with basic overhead tramway-style cabling (full catenary being unnecessary at the low speeds involved) I too would be interested in the three phase systems. I guess a significant problem with them is the need for twice as much and the need to ensure the two current pickups don't contact the wrong wire, especially at junctions, making low speeds a prerequisite to reduce swaying. |
|
|
|
Post by stapler on Nov 12, 2015 16:24:55 GMT
Counterfactual history, I know, but if the LNER had persisted with Raven's plans, would we still be on a 1500v DC standard today?
|
|
|
|
Post by norbitonflyer on Nov 12, 2015 17:12:01 GMT
Counterfactual history, I know, but if the LNER had persisted with Raven's plans, would we still be on a 1500v DC standard today? The LNER did eventually continue with 1500V electrification, but it didn't help in the long run, as all the routes were either closed or converted to ac by 1984 The Manchester-Altrincham line (jointly run with the LMS, and electrified on the LNER system albeit with rolling stock strongly reminiscent of LNWR London area units) was electrified on 1500V, and work on the LNER's Shenfield line and Manchester- Sheffield-Wath route was well advanced when work was once again suspended by war. These schemes were all completed by BR by 1954. The Altrincham line was converted to ac in 1971, and converted back to dc (at 750V) in 1992. |
|
|
|
Post by spsmiler on Nov 13, 2015 0:36:15 GMT
Some photos I took many years ago, showing Jungfraubahn trains which are powered at 1125V AC 50Hz three phase. The Italians used to have an extensive three phase mainline railway network. All now converted to single phase. Simon   |
|
|
|
Post by stapler on Nov 13, 2015 8:17:06 GMT
Yes - why make something more complicated than it needs be, unless there are real, crunchy-cost, advantages? In the end, surely that will apply to most non-standard systems, like SR third rail, and DLR side contact?
|
|
|
|
Post by brigham on Nov 13, 2015 17:49:29 GMT
Aesthetics is important too, not just cost. The DLR could have had Sprague-era DC overhead very easily (and probably cheaply) by buying in existing tramway-style components, rather than designing an all-new third-rail system. I presume the eyesore of overhead conductors in such a 'prestige' development scuppered it.
Cheapness isn't everything.
|
|
|
|
Post by stapler on Nov 14, 2015 8:31:20 GMT
Much of the DLR is parallel or near other OHE structures anyway! And as for the Isle of Dogs, some of the buildings erected there would win any prize for ugliness, compared with tramway-style masts!
|
|
Chris M
Global Moderator
Forum Quizmaster
Always happy to receive quiz ideas and pictures by email or PM
Posts: 19,772
|
Post by Chris M on Nov 14, 2015 10:56:27 GMT
The only issue (other than cost) of converting the DLR to OHLE now might be some of the clearances in tunnels and flyunders. However the bottom-contact third rail has proven to be the more reliable I think, certainly in winter weather, than either OHLE (very susceptible to high wind) or top-contact third rail (prone to icing).
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Nov 20, 2015 10:52:16 GMT
Hi Everybody I am a new contributor.
I was interested to read this thread as I feel I can offer something to the discussion.
The LBSCR system of 1909 was quite forward thinking and it was installed at the very early stages of development of single phase railways in this country. The equipment was similar to a systems operating in Hamburg and the Lancaster Morecombe area. In some ways the UK systems could be seen as experimental. The low supply frequency of 25 Hz made series ac commutator motors viable, but at reduced voltage, so were a bit flaky in their commutation. The LBSC 1909 units used 'Winter Eichberg' compensated repulsion motors which had no such voltage limitations and could run on 750v ac albeit with some more complicated circuitry.
The second generation of single phase 'power' in the form of the milk vans equipped by GEC (Witton) were a much more developed design that was produced with longer distance electrification in mind to Brighton. I think maybe then the policies of the Southern Railway influenced the balance of ac versus dc systems.
The ac system as it is now is essentially a main line railway system with dc suited to suburban lower distance routes. The use of 25kV enables a much more cost effective way of delivering the current to the collection system. The high voltage thus suited to long distances through minimal need for feeding points unfortunately cannot be used with a ground based current collection system. The 660v dc system was ok with shorter distance as the cost of substations could be limited by the shorter distances involved in a suburban system. The 660v system was deemed operable with ground based collection .The LSWR had probably seen their need for electrification on a suburban basis. They spent a bit more on substations, less on current collection and a lot less on vehicle based transformers and the associated control system. They didn't need a 5 ton transformer on every motored vehicle and the units were lighter as a result. The LSWR did not seem too concerned about the wastage of energy in starting resistors that the LBSC didn't suffer as a result of voltage tapping transformers. They did not suffer clearance limitations like the LBSC had in their tunnels which necessitated long neutral zones. What the LSWR didn't get was a more viable way of electrifying longer distances in a cost effective way for future more extensive schemes. It could be said that the Bournemouth electrification contradicted the thinking on long distance dc suitability. However, that's what the Southern Region did and it seems that LSWR thinking had played a part, insomuch as to limit the choice, given the already existing commitment to dc on the many other schemes of later companies.
It could be said that 25kV ac has had it's day as there would seem no technical reason why 25kV dc could be used instead. Obviously this would involve massive expense with perhaps limited economic viability. Technically with the advent of inverter drives and high power converting technology 25kv dc could feed the 3 phase induction motors very much in vogue at present. If this system could be engineered with modern switched mode techniques, even the need for a transformer could be eliminated. The cost balance may then be favourable, but this is speculation and I have no knowledge of any such work.
Hope you all don't mind this long post, but I offer it as potentially helpful to my fellow posters. |
|
|
|
Post by nickf on Nov 20, 2015 11:39:51 GMT
A very interesting post, wintereichberg. Thank you and welcome to the forum.
|
|
|
|
Post by norbitonflyer on Nov 20, 2015 13:54:56 GMT
25kV all the way to the traction motors? Surely from a safety perspective you would need some hefty insulation to make that safe? Not to mention the inter-car connections.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Nov 20, 2015 20:43:51 GMT
Hi Norbitonflyer Consider a mobile phone charger or something like that where 240v ac goes in and for arguments sake 6v dc comes out. It would be dc to 3 phase ac but essentially if electronic switching was used theoretically 25kV dc in could be converted to 750v 3 phase ac without wound components. This is theoretical and may be far fetched by present standards. You remind me that isolation may be an issue as potentially the 750 volt circuits could be energised at 25kV under some fault conditions. Clearly design and safety issues exist and would need robust solutions before a design could be approved.
|
|
|
|
Post by brigham on Nov 23, 2015 13:03:13 GMT
I'm not sure how the voltage drop could be obtained without wound components or resistance. You would have to make 25kV AC on-board, then transform it down for the motors. It would save having on-board line-rectification, though.
Would you be generating at 25kV dc, or rectifying AC from the grid in one huge central station?
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Nov 23, 2015 15:47:01 GMT
I would envisage a system based on converter substations where ac at industrial frequency would be converted to 25kV dc and fed to the catenary. The rational for this is based on the relative superiority of HV dc transmission over HV ac transmission regarding ac specific losses and induced voltages of surrounding structures. HV dc transmission over the National Grid has been thought about and there are HV dc feeds to this country from the continent using converter substations.
On the train the dc would be fed into a chopper and reduced from 25kV to a suitable dc voltage, say 1kV to feed a 3 phase inverter for the traction motors. The inverter would be variable voltage and frequency just like now. It would be roughly equivalent to how a 3kV dc scheme could operate with 3 phase traction motors. I.e: Chopper, dc link and inverter.
I realise that this is just a concept and huge engineering challenges would need to be tackled. Some wound components would probably be needed to 'process' the current and prepare it for further manipulation. It may be a bit radical, but who knows what may be possible in the years to come. Other developments may happen to make this sort of idea redundant and if looked into in depth it may not be economical either. I found it interesting to imagine what could be possible. hope you do too. |
|
|
|
Post by spsmiler on Nov 24, 2015 0:37:39 GMT
regarding the class 455 with SWT: Are there any in service with the new traction package, and if not when will they start entering service? Does the new traction package make the trains sound different? Simon |
|
|
|
Post by phil on Nov 24, 2015 0:46:30 GMT
.... and there are HV dc feeds to this country from the continent using converter substations.
This is done for frequency reasons rather than anything else. If you tried to connect the French AC grid to the British AC grid both would have to be EXACTLY in phase with each other - in other words if you took the 50Hz waveform for each grids and overlayed them they MUST be in phase, or chaos would ensue. (Its notable that at times of heavy demand in the Uk, the grid is allowed to drop the voltage quite significantly - but they must NEVER let the frequency change by a single Hz, so the former is sacrificed to keep the latter stable. This matters because there is an awful lot of vital equipment that relies on that magic 50Hz being maintained - most of which is invisible to us incidentally, i.e. we are not talking about your flat screen TVs here.) By using a HV DC link the grids are never connected directly and the issue of one countries phase being slightly different never causes an issue. |
|
|
|
Post by domh245 on Nov 24, 2015 8:10:54 GMT
regarding the class 455 with SWT: Are there any in service with the new traction package, and if not when will they start entering service? Does the new traction package make the trains sound different? Simon They won't have the old camshaft noises (so no random air as it accelerates out of the platform) which will be replaced by inverter whine, which will most likely sound like that on Electrostar units. The motors may have a slightly different sound as well |
|
|
|
Post by nickf on Nov 24, 2015 9:02:07 GMT
.... and there are HV dc feeds to this country from the continent using converter substations.
This is done for frequency reasons rather than anything else. If you tried to connect the French AC grid to the British AC grid both would have to be EXACTLY in phase with each other - in other words if you took the 50Hz waveform for each grids and overlayed them they MUST be in phase, or chaos would ensue. (Its notable that at times of heavy demand in the Uk, the grid is allowed to drop the voltage quite significantly - but they must NEVER let the frequency change by a single Hz, so the former is sacrificed to keep the latter stable. This matters because there is an awful lot of vital equipment that relies on that magic 50Hz being maintained - most of which is invisible to us incidentally, i.e. we are not talking about your flat screen TVs here.) By using a HV DC link the grids are never connected directly and the issue of one countries phase being slightly different never causes an issue. If you want to check up of the frequency of the UK power supply, this site provides loads of fascinating detail. UK Power Supply |
|
|
|
Post by brigham on Nov 24, 2015 12:10:00 GMT
Interesting site. Look at the 'Judas' scales on the wattmeters! Wind and coal appear about equal, with nuclear and gas also equal but far higher!
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Nov 24, 2015 15:26:04 GMT
There is a nice german technical term called "Gleichstromzwischenkreisumrichter", which first rectifies the AC input to DC and then inverts the DC back to the desired kind of AC (voltage, number of phases and frequency).
The components can be split between lineside equipment and vehicle-based equipment.
If e.g. there is no space on the vehicle for a main transformer and a rectifier (like on tube trains), the lineside equipment suppplies DC to the vehicle.
Obviously, every substation would need a rectifier.
If the vehicle has space for a main transformer and a rectifier, the lineside equipment can be basically just a transformer.
The french even went as far as having a 25kV AC locomotive with a 3000V main DC circuit, thus creating a dual voltage locomotive.
|
|
