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Old June 18th, 2010, 07:18 AM   #4101
lightrail
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Quote:
Originally Posted by Tubeman View Post
No real reason why not, the gauge and electrification are the same... There is a significant difference in floor height though so it's not desirable. There's plenty of platforms served by both surface and tube stocks... Although you'd expect them to generally be a compromise height halfway between the two, for some reason Ealing Common is pretty much at Tube stock height, making it a huge step up / down to District Line trains:

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I think there's 8 2009 Stock trains in operation now. The total fleet is 43 trains currently, but I think this will be more like 50 when the 2009 stock delivery is complete.



It might just be historical really... simple Traction motors need DC current, so I guess when technology was in its infancy and lines first started being electrified, DC was opted for. Generally the first overhead electrifications were also DC (1,500V), only being converted to 25,000V AC in the second half of the 20th century when rectifiers (converting AC to DC) or later AC motors began to be used.

3rd / 4th rail is only suitable for lower speeds due to the 'shoes' which collect the power, at higher speeds they'd just get knocked off or cause too much friction, but it's much cheaper to install and maintain than OHLE.

I guess DC motors are cheaper and simpler, so at low speeds (i.e. metros) DC motors and 3rd / 4th rail is more cost effective.
Isn't there more leakage to ground with AC. Given the small clearance for the third rail, DC makes sense - no point using AC if you're limited in voltage through the rail. I think DC is actually cheaper option too.

On the motor side, you can run AC motors off a DC rail - many light rail vehicles are switching to AC motors with DC pickup. An advantage to AC is faster acceleration and deceleration and regenerative braking. I also read that you can use the AC motor to hold a train on a hill, whereas DC this is not possible - so AC is better in hilly situations.

Anybody else - that's as much as I've learned on the subject.
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Old June 18th, 2010, 09:23 PM   #4102
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Isn't there more leakage to ground with AC. Given the small clearance for the third rail, DC makes sense - no point using AC if you're limited in voltage through the rail. I think DC is actually cheaper option too.

On the motor side, you can run AC motors off a DC rail - many light rail vehicles are switching to AC motors with DC pickup. An advantage to AC is faster acceleration and deceleration and regenerative braking. I also read that you can use the AC motor to hold a train on a hill, whereas DC this is not possible - so AC is better in hilly situations.

Anybody else - that's as much as I've learned on the subject.
I think the principle is, the higher the voltage, the more efficient the transmission... that's why cross-country transmission lines are very high voltage. You simply couldn't have 25kv in a 3rd rail though, as 25kv can jump up to 1.75m in an arc. That's why 3rd or 4th rail, especially running through cast-iron Tube tunnels, must be low voltage (relatively), which is much less efficient transmission-wise and wastes a lot more energy through resistance. Otherwise, it'd just arc to the tunnel lining and earth.
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Old June 18th, 2010, 09:35 PM   #4103
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Because of a discussion at the DLR/Underground thread, what safety features (i.e. track intrusion systems) are present at DLR stations? I know this isn't the Underground, but I'm sure you are the best one to ask.

Cheers!
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Old June 19th, 2010, 10:14 AM   #4104
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Because of a discussion at the DLR/Underground thread, what safety features (i.e. track intrusion systems) are present at DLR stations? I know this isn't the Underground, but I'm sure you are the best one to ask.

Cheers!
Beyond CCTV, nothing I guess... No ticket barriers, no staff... So no nothing beyond CCTV
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Old June 19th, 2010, 10:20 AM   #4105
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Having read your post in the other thread, I understand what you're asking now... No, there are no systems to detect an obstruction / person on the track on DLR to my knowledge, so they just get hit, basically.
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Old June 19th, 2010, 11:07 AM   #4106
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Having read your post in the other thread, I understand what you're asking now... No, there are no systems to detect an obstruction / person on the track on DLR to my knowledge, so they just get hit, basically.
That's just excellent.
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Old June 19th, 2010, 11:14 AM   #4107
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I can only think of one accidental 'one under' on DLR ever, and that was a poor unfortunate Portuguese fellow who ran onto the tracks to escape a couple of muggers just as a train arrived. Some things are just so rare they're not worth the expense to mitigate against... Even with some form of detection system, I presume he ran in front of the train too late for anything to have stopped it in time.
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Old June 19th, 2010, 10:13 PM   #4108
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I guess DC motors are cheaper and simpler, so at low speeds (i.e. metros) DC motors and 3rd / 4th rail is more cost effective.
Most modern traction motors are 3 phase AC even if the line current is DC. Indeed even on AC systems if the motors are 3 phase, which is the norm the AC is first converted to DC before being being changed back to AC, but in 3 phase form.
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Old June 20th, 2010, 02:47 AM   #4109
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For the whole third rail discussion, after poking around a bit on Wikipedia, it seems that DC delivers 41% more power than an equivalent AC peak voltage, which would make sense as a choice with third rail being restricted to relatively low voltages.

That along with the reasons already stated seems to answer my question.
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Old June 20th, 2010, 10:39 AM   #4110
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Most modern traction motors are 3 phase AC even if the line current is DC. Indeed even on AC systems if the motors are 3 phase, which is the norm the AC is first converted to DC before being being changed back to AC, but in 3 phase form.
Thanks... I wonder if LU stocks are a mixture then, i.e. older stocks = DC and newer = AC?
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Old June 20th, 2010, 05:31 PM   #4111
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Tubeman, Does this kind of thing happen every time someone falls under a train?

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Old June 20th, 2010, 06:07 PM   #4112
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Thanks... I wonder if LU stocks are a mixture then, i.e. older stocks = DC and newer = AC?
Yep, you will find the stock on the Northern and Jubilee lines have 3 phase AC traction motors, as does the new Victoria line and S stock. In this day and age 3 pahse AC motors give much better performance characteristics so is considered standard practice.

All the other stock still has single phase DC traction motors.
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Old June 20th, 2010, 06:09 PM   #4113
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For the whole third rail discussion, after poking around a bit on Wikipedia, it seems that DC delivers 41% more power than an equivalent AC peak voltage, which would make sense as a choice with third rail being restricted to relatively low voltages.

That along with the reasons already stated seems to answer my question.
You will find that when the choice was made there were very few other options. When it comes to electricity you just cannot perform a simple comparison as you have done, the figures are meaningless as there are so many other issues to consider. Two major ones being ability to deliver current and capacitance with DC systems.
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Old June 20th, 2010, 06:56 PM   #4114
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Tubeman, Does this kind of thing happen every time someone falls under a train?
If they're alive then yes... The entire station is evacuated, which might seem a bit extreme for such a big station with so many platforms, but the logic is that having passengers milling around would impede the emergency services entering or exiting the station. All other lines non-stop.

If the person is alive then they're probably seriously injured, so the air ambulance is no surprise. You might think the Fire brigade are a strange emergency service to turn up, but they have specialist jacks which are often required if the person is still alive to lift part of the train.

If the person's dead, then the station still evacuates but obviously the air ambulance and LFB are a waste of time... If the person is confirmed dead, then they just drive the train back off the body and pick up the pieces.

A survivor is likely to cause a far longer delay than an obvious death due to the care that has to be taken moving them without causing further injury.
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Old June 20th, 2010, 09:22 PM   #4115
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Hi Tubeman,

Just bought your book, had it shipped all the way to Malaysia. I'd really enjoyed it, maybe you can do an atlas on all the LU rolling stocks after this. :P

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If the person's dead, then the station still evacuates but obviously the air ambulance and LFB are a waste of time... If the person is confirmed dead, then they just drive the train back off the body and pick up the pieces.
Anyhoo, don't want to sound disrespectful or anything, does TfL have a unit to clean up and 'pick up the pieces' or you really outsource it to a company that really do this sort of things.

Cheers.
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Old June 20th, 2010, 10:02 PM   #4116
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Hi Tubeman,

Just bought your book, had it shipped all the way to Malaysia. I'd really enjoyed it, maybe you can do an atlas on all the LU rolling stocks after this. :P



Anyhoo, don't want to sound disrespectful or anything, does TfL have a unit to clean up and 'pick up the pieces' or you really outsource it to a company that really do this sort of things.

Cheers.
Thanks for the purchase (and the dedication!)

Yes, London Underground have the in-house ERU (Emergency Response Unit), who are a testosterone-pumped unit of hairy-arsed men who turn up at all major incidents and do everything from picking up body parts to re-railing derailed trains. Speaking of outsourcing, our ERU have been called upon for several incidents on Network Rail, such as the Ladbroke Grove disaster, as they are recognised as being about as good as it gets when it comes to dealing with the business end of major incidents. We have provided this service for free as far as I'm aware, too.

It's usually the unenviable job of someone from the ERU to crawl under a train immediately after a 'one under' to locate the person and establish if they're alive or not... There must be few jobs less pleasant than crawling in an extremely confined space only to be confronted by a mangled body.
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Old June 21st, 2010, 01:18 PM   #4117
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Tubeman

A history question here: do you know if Sir Joseph Bazalgette was involved in the construction of the Tube? I ask because his early career was in railways, and he is of course famous for building London's sewer system; I would have thought that these two areas of expertise would have made him an obvious candidate for working on the tube, especially as it was around his time.

However I can't find any info about that, surprisingly enough. Therefore from that I assume that he had no involvment, but I find that hard to believe somehow, especially in an age where civil engineers tended to work on a variety of different projects.

Just wondering if his biggest claim to fame (the sewers) has obscured other projects he may have worked on, namely the Underground.
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Old June 21st, 2010, 07:08 PM   #4118
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Tubeman

A history question here: do you know if Sir Joseph Bazalgette was involved in the construction of the Tube? I ask because his early career was in railways, and he is of course famous for building London's sewer system; I would have thought that these two areas of expertise would have made him an obvious candidate for working on the tube, especially as it was around his time.

However I can't find any info about that, surprisingly enough. Therefore from that I assume that he had no involvment, but I find that hard to believe somehow, especially in an age where civil engineers tended to work on a variety of different projects.

Just wondering if his biggest claim to fame (the sewers) has obscured other projects he may have worked on, namely the Underground.
Interesting question.

From what I can gather, although he was initially very much a railway engineer, his involvement in the 1840's predated the development of even the Metropolitan Railway, and long predated the first 'Tubes'. It appears he was totally focused on developing London's sewers from 1849 onwards, and this was undoubtedly a big enough job on its own to preclude any further involvement in the railways. He was appointed assistant surveyor to the Metropolitan Commission of Sewers in 1849, then Engineer in 1852 (bear in mind the Metropolitan Railway was still 11 years away at this point), so sewers were basically his full-time job. When the MCS became the Metropolitan Board of Works in 1856, he was chief engineer, a post which he stayed in until 2 years before his death. It simply appears that there wasn't the time for him to be involved in railways after 1849, and possibly not the inclination either, bearing in mind they led to a nervous breakdown in 1847!
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Old June 22nd, 2010, 03:54 AM   #4119
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If they're alive then yes... The entire station is evacuated, which might seem a bit extreme for such a big station with so many platforms, but the logic is that having passengers milling around would impede the emergency services entering or exiting the station. All other lines non-stop.

If the person is alive then they're probably seriously injured, so the air ambulance is no surprise. You might think the Fire brigade are a strange emergency service to turn up, but they have specialist jacks which are often required if the person is still alive to lift part of the train.

If the person's dead, then the station still evacuates but obviously the air ambulance and LFB are a waste of time... If the person is confirmed dead, then they just drive the train back off the body and pick up the pieces.

A survivor is likely to cause a far longer delay than an obvious death due to the care that has to be taken moving them without causing further injury.
Damn... why can't all stations have platform-edge doors?
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Old June 22nd, 2010, 08:13 PM   #4120
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Damn... why can't all stations have platform-edge doors?
Many platforms are too curved (there would need to be a large gap between train and PED screen to accommodate the 'throw' of the cars, just as there are large gaps between train and platform at many LU stations), and also many platforms have different stocks of trains serving them, with differing door alignments so PEDs can't be installed to line up with both.
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