ECML/MML major power problems (09/08)

Discussion in 'UK Railway Discussion' started by yorkie, 9 Aug 2019.

  1. cactustwirly

    cactustwirly Established Member

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    That's because Siemens put forward a better product, power cuts aside, the 700s are far superior to the 710s
     
  2. Saperstein

    Saperstein Member

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    Not in the area under discussion no (ECML/MML), but the Wirral line lost power for a time (Merseyrail) and that’s 750V DC.

    Saperstein.
     
  3. roadie

    roadie Member

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    Bombardier is not necessarily a bed of rose petals, a Canadian company that has supplied its own citizens in Toronto with a trams that 80% have gone back for structural repairs before they had all entered service.
     
  4. hwl

    hwl Established Member

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    The quality of everything coming out of their Mexican factory is appalling, including several thousand the EMD SD70s over 2+ decades
     
  5. DerekC

    DerekC Member

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    My guess is that this is a problem with the kit which detects the harmonics generated by the train drive system and shuts everything down if they exceed the limits set for safety of the signalling system. There have been troubles with this before - as I recall, on Electrostars (before anyone orders bouquets for Bombardier). It seems plausible to me that a big excursion of the AC mains frequency somehow caused this kit to trip, although the AC input is transformed down and rectified to DC on board so you might have thought this would provide some isolation. The fact that it affected all the 700s at once points to this sort of issue.
     
  6. Jimini

    Jimini Member

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    I read somewhere else that it was an issue with the reboot sequence taking place before the OHLE was re-energised. If they don't detect any power after 90 seconds then the pans drop again. Do that three times and the on board systems lock themselves out, thus requiring the presence of a of a technician with laptop to physically attend each unit.
     
  7. AM9

    AM9 Established Member

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    Much of your post is just wrong. The trains like any new trains, would have been procured against a published requirement including performance, safety and other parameters. Apart from the obvious performance requirements, (speed, capacity, passenger environment etc.), there would be a whole plethora of legal/safety issues defined such as operating with defined signal systems, power supplies, failure detection and recovery, etc.. Many of these requirements conflict with each other to the extent that one can be achieved at the expense of the other, e.g., power efficiency in contemporary EMU designs tends to require an ac conversion to a DC bus from which a three-phase inverter feeds power efficient ac induction motors. This involves a lot of high-frequency high-power switching electronics that unless carefully designed, would seriously interfere with other systems both on the train and trackside. Sometimes, the careful design techniques required not only increase weight and physical servicing accessibility but also energy efficiency of the traction system. However, interoperability of equipment (including equipment not under the control of the railway is mandated under Electro-Magnetic Compatibility legislation which uniformly applies across the EU specifically and in some form or another all of the developed world.
    As has been mentioned in other posts in this thread, this power supply problem was different to any of the previous major failures in that the 50Hz frequency varied outside established norms and varied at greater rates. If as I believe, the relaxation in the supply specification was not included in the specification for the trains, it wouldn't have been tested for during design qualification. If so, then the reviews that have been kicked-off will identify that, and presumably a) recommend a suitable design update to deal with it and b) revise the process of creating technical requirements to prevent a repeat of something similar.

    As far as ac traction being synchronised with the grid, no, that is not the case. As I said above contemporary EMU designs tend to have a DC bus, conveniently at or around 750VDC. The 3 phase power to the traction motors is variable with the speed at which they rotate. This has been true since the need for all new EMU designs to be potentially suitable for either OLE and/or 3rd rail networks. Thus (I believe), all Electrostars, all Desiros, all Aventras, the class 395s and probably the new stock currently on order, (e.g. CAF 331s, Stadler etc.), have a DC to 3 phase ac traction inverter fed from a 750VDC bus. During manufacture, they can be fitted with pantographs, transformers and rectifiers for OLE operation and/or pick-up shoes for 3rd rail operation. Some types have both, e.g. class 377/2, /5, /7; class 387, class 350/1, class 700 and class 717.
    It's also worth mentioning that 1980's designed class 319s also have a 750VDC bus, because of the Thameslink route's dual power systems although they have DC motors.
     
  8. AM9

    AM9 Established Member

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    Yes the ac from the OLE is transformed and then rectified to DC but that DC would have a 2 x ac frequency ripple. This nominal 100Hz ripple, owing to it's high current, and non-siusoidal waveform create a harmonic spectrum that would be managed on the train by EMC design measures. Those measures would include monitors and protection circuits that would guard against other systems being affected, (signal/comms etc.). As the class 700s have a 'space ship' warble when under power from 3rd rail, I imagine that this is to spread the spectrum of these harmonics to reduce the potential for interference. They do not have the same modulation whilst running under OLE, so I assume that the ripple provides sufficient spreading of the harmonic spectrum without delibarate modulation. As the 750VDC is derived from a three phase National Grid feed, it would have a mjuch lower level of ripple (at 6 x 50Hz i.e. 300Hz, which would considerably reduce the harmonics issues).
     
  9. paul1609

    paul1609 Established Member

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    and 375/6s
     
  10. QueensCurve

    QueensCurve Established Member

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    Just after #NoDealBrexit.
     
  11. hwl

    hwl Established Member

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    Most DC supplies for 3rd rail are now 12 pulse rectifiers to further reduce lower order harmonics - the 12 pulse rectifier consists of 2x 6 pulse rectifiers (you describe above a nominal 6 pulse design above) in parallel but connected to different secondary windings with one star and one delta configuration producing a 30 degree phase shift (i.e. 1/12th) between the 2 sets of 6 pulses so a more complex 300/600/1200Hz picture with much lower harmonics and EMC issues.
     
  12. hwl

    hwl Established Member

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    There are 2 sets of harmonic generation / interference / EMC to worry about:
    a) rectification of AC in the 4 quadrant converter (where Friday's fun and games seemingly partly originated)
    b) DC link to variable frequency AC conversion which is where the late 1990s electrostar issues were (or rather weren't) as the issues mostly lay with new IGBT switching tech at much higher frequencies than Railtrack was used to so the issues were largely to do with it being new and needing a through investigation by the inquisition rather than real problems.
     
    Last edited: 11 Aug 2019
  13. AlexNL

    AlexNL Established Member

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    Isn't it the case that the 700s are paid for on a per-diagram basis (like the 800s) which means that if a train is not available, XLT don't get paid for it?

    This could be why Siemens having built-in overly strict protections and lockout mechanisms, which was then inherited by the 707s and 717s as they're based on the same platform.
     
  14. Nicholas Lewis

    Nicholas Lewis Member

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  15. fkofilee

    fkofilee Member

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    QQ for the forum - Before Friday (Which i was affected badly by) - When was the last time CSL2 Black was triggered for GTR?

    It was triggered half hour after this incident occurred... But ive checked out the CSL Guide and its quite significant to need to be triggered...
     
  16. edwin_m

    edwin_m Veteran Member

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    I wonder if the problem was that at the same time as the drivers were re-booting the trains, the National Grid was still trying to resolve the problem so the mains frequency might still have been out of spec, causing the reboot to fail. I read somewhere (maybe further back on here) that after a certain number of reboots by the driver the system locks out and has to be attended to by the technician. It sounds like nobody really foresaw that the mains might go that far off its expected frequency, so didn't think through the consequences of the response to that condition.
     
  17. jon0844

    jon0844 Veteran Member

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    If that turns out to be the case I'm sure it will be quite easy to avoid should we have a repeat incident. Allowing more reboot attempts and waiting longer between reboots.

    Also perhaps allowing the cab screens to show more diagnostic information, so if the train knows the power source is incorrect it displays that.

    Having a train that relies almost exclusively on computers does at least make it easier to fix certain things without mechanical changes.
     
  18. DerekC

    DerekC Member

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    I wonder if German designers expect the mains supply to stay within spec? That's not entirely a facetious comment, by the way.
     
  19. ashkeba

    ashkeba Member

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    I will not be entirely surprised if any investigation concludes that only the Siemens stock reacted to the problem as required in the train specifications while the Bombardier, Hitachi and BREL/ABB units ignored a potentially dangerous problem!
     
  20. AM9

    AM9 Established Member

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    Could you please explain what QQ, CSL2 Black and CSL mean?
     
  21. tsr

    tsr Established Member

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    I believe it was last done by GTR at least some months ago; perhaps more than a year ago. However, Code Black is declared almost every week by some TOCs, particularly LNER and their predecessors, and GTR used it more often at one point - indeed, I remember one day with two GTR Code Black events about 3 years ago.

    The CSL/PIDD guidance is nice to have, but in reality instinct takes over. It varies as to whose instinct is relevant. Code Black is generally authorised at a higher level than Red and Yellow, and implies that people really shouldn’t even consider travelling on the affected network, as nothing will be moving for some time. As well as the impact on travel, this does have fairly far-reaching commercial and PR implications as well.

    Some TOCs, such as Virgin, tend to have more nuanced colour bands reflecting grades of severity for PIDD messages, and the associated levels of advice have almost superseded the whole “it’s all fallen over... don’t go anywhere” thing.
     
  22. AM9

    AM9 Established Member

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    Ah yes I'd forgotten that they would have a star and delta transformer/rectifier configurationgiving a 600Hz component. That would be high enough to be almost smooth. In addition, the presence of trains with regen feeding back DC from the 3 phase motors asychronously, would further remove any 50Hz related components.
     
  23. AM9

    AM9 Established Member

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    Most electric trains in Germany are 15kV 16.7Hz fed by a DB-only distribution system. They are not dependant on the exact 50Hz grid frequency.
     
  24. Bayum

    Bayum Established Member

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    Were the 800s not stopped BY the problem, or were they stopped as a result of the congestion?
     
  25. yorkie

    yorkie Administrator Staff Member Administrator

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    A member of GTR staff on my train told me that Azumas were affected by the problem. However, if that was the case, it was presumably straightforward to reset them; my next train was an Azuma and it was pretty much on time.
     
  26. HSTEd

    HSTEd Established Member

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    Its also likely that the grid frequency spec is tighter on the modern trains because they have fewer tolerances to optimise the weight and size of the transformer.
    If its a static substation you can use equipment with far bigger margins than anything you have to be able to move.
     
  27. Fred26

    Fred26 Member

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    QQ - Quick Question.

    CSL2 - It's the level of disruption. I'm not entirely sure what it stands for though. Customer Service Level 2, anyone?! (Tongue in cheek).

    Black Status - Service is so bad you shouldn't even consider travelling. For frontline staff it usually means all hands on deck. Indeed, there were several 'call-to-arms' made on Friday for any staff available to attend their local station. It wasn't compulsory, but many staff did go in.
     
  28. Gerald Fiennes

    Gerald Fiennes Member

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    So we should certainly thank all staff that turned out to help resolve what proved in practice a most difficult situation, even by GTR standards.

    Separately, it seems that the 2nd grid failure (Hornsea) was at a bank of inverters converting wind power-derived DC to AC and there is some discussion that this also was due to underfrequency (specifically, the rate of drop of frequency) following the first fault (what is the chance of two separate large-scale faults happening within 5 mins of each other...). (Underfrequency protection at Hornsea is not something that National Grid directly controls because this power source is connected to the local network (Northern Powergrid) rather than the NGC network.) In other words, Hornsea potentially experienced a similar problem to the C700s...
     
  29. pdeaves

    pdeaves Established Member

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    Yes, the letters CSL stand for Customer Service Level.
     
  30. youngpete

    youngpete Member

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    When the generation at Little Barford was lost the network frequency fell and at a number of major bulk supply points between National Grid and the Regional Electricity companies (RECs) the Low Frequency protection correctly kicked in and disconnected supplies to preserve the stability of the National Grid. In the former SEEBOARD area it was the practice that the traction supplies to the former Southern Region were NOT disconnected in such circumstances. Unfortunately what has not become clear is if supplies were actually lost to the ECML and MML catenary systems and if so why. Or was it a case that the trains could just not deal with the frequency blip and shut down.
     

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