EMU Pantograph Positioning

Discussion in 'Traction & Rolling Stock' started by MK Tom, 23 Dec 2018.

  1. MK Tom

    MK Tom Established Member

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    I noticed looking at this photo that the pantograph cas on the Class 710s are arranged so the pantograph end is adjacent to the driving car:

    https://mkrail.smugmug.com/MiltonKeynesRailways/2018/Milton-Keynes-Area-November-2018/i-CpRV45n/A

    Typically 4-car EMUs have the pantograph in the centre, adjacent to the other trailer. The 710s are reminding me of the Class 304/305 in this respect, which also had the pantograph carriage the other way round.

    Is there any significance to the placement of pantographs on EMUs? It seems very rare in this country to have pantographs on driving cars - 506s and the 2-car 309s are the only examples I can think of. But that does happen a lot overseas.

    This might also be a good time to ask why some high speed units like 390s and 395s have two pantographs but usually only one in use, and also why that tends to be the rear one?
     
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  3. Elecman

    Elecman Established Member

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    On 390s The pans are the opposite way round so the rear one is always the aerodynamically the best way round for the direction of travel. I assume the 395s are the same
     
  4. 61653 HTAFC

    61653 HTAFC Established Member

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    307s had the pantograph over one of the cabs, at least as built. Can't recall if it was moved when they were converted from DC to AC.

    I think one issue these days when EMUs work in multiple is how close together the pans are.
     
  5. AM9

    AM9 Established Member

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    Those EMUSs built in the days of 1500VDC electrification, owing to the high currents drawn at that voltage had diamond type pantographs and much heavier conductor wires. Added to the lower maximum speeds run (by modern 25kV ac standards), standing waves and other interactions between the OLE and multiple pantographs were much less on an issue. The GE EMUs' conversion to ac (classes 306 and 307) involved leaving their DC traction equipment largely unchanged and installing a 25kV to 1500VDC pantograph-transformer-rectifier set in adjacent cars. In the case of the class 306 which was originally virtually identical to the class506s, the new equipment was located in the centre open trailer along with the guards compartment. Thus the pantograph was also moved from over the driving cab. The original configuration of the class 307s was more in keeping with other MKI and MKIII ac EMUs where all the equipment wa contained in one of the centre cars. On conversion, there was insufficient spce to accomodate the extra kit for ac so it was located on the inner end of the driving car (also along with the guards compartment).
    The class 309s, apart from being the only MKI full corridor EMUs, are also the only ac type to include a 2-car version. This was to give flexibility in train make-up allowing 10 car trains for normal use and even giving a high-powered 12-car train allowing a fast peak train on a very busy mainline.
    It has been reported on this forum that drivers would sometimes have visibility issues at high speed at night when the pantograph was directly over the cab because of frequent arcing on the OLE causing reflection from the track immediately in front of the train.
    Some modern high-speed EMUs (classes 390, 395 and 80x) have a 25kV bus running through the train allowing the motor cars to be powered by pantographs at either end. It also means that the pantograph furthest from the cab can also be used to avoid the arcing issues mentioned above.
    Even more recently, the introduction of outer suburban EMUs like the class 700s and 345, has brought in trains where there are two separate functional traction systems where each has sufficient power to haul the whole train when one part fails. This is important where very high density services make external recovery of failed trains too disruptive, e.g. in the Thameslink and Crossrail core tunnels respectively. As these trains are at least 8-cars long, the two pantographs will always be far enough apart to prevent severe standing wave issues.
     
    Last edited: 23 Dec 2018
  6. 43096

    43096 Established Member

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    I assume there is an ‘AC’ missing from that as the SR REPs, CIGs, VEPs, CEPs etc had gangways throughout.
     
  7. edwin_m

    edwin_m Veteran Member

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    Just to be clear, when there is a 25kV bus through the whole train then only one pantograph can be used at a time because of the risk of bridging neutral sections. The 700 and 345 don't have this bus, so need both pantographs raising to power the two halves of the traction system.

    What happens with 5-car 80x? Does each unit have two pantographs, and if so which ones are raised when running as a pair?
     
  8. Bald Rick

    Bald Rick Established Member

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    Yes they have 2. And which one is up tends to vary (in my very small sample of observations).
     
  9. TRAX

    TRAX Member

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    Having the rear pantograph raised can also help in preventing too much OHLE dust from spraying the train.

    In icing conditions, having two pantographs raised can help in scraping ice off the wire (with the first pan) with the second pan being able to better draw current.
     
  10. Bald Rick

    Bald Rick Established Member

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    Never heard of either of these before. Indeed never heard of pantograph dust spraying a train!

    As mentioned upthread, trains with multiple pantographs and a 25kv bus MUST only have one pan up to avoid bridging neutral sections.
     
  11. TRAX

    TRAX Member

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    You just have to see the dust, no need to hear of it. ;)

    As for pantograph ice scraping, maybe it’s not a procedure in the UK.
     
  12. AM9

    AM9 Established Member

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    Yes you are correct, typo.. :)
    My mind was on them being the sole 2-car EMU for (ac) OLE
     
  13. AM9

    AM9 Established Member

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    Hence my use of the word 'either' as opposed to 'both'.
     
  14. MK Tom

    MK Tom Established Member

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    Thanks everyone, particularly AM9, for the replies.

    So does having multiple pantographs up at once have nothing to do with the power needed? I always assumed that the Pendolinos would need both pantographs up to operate at the 140mph design speed but clearly that's not the reason for the second pantograph (and likewise on the 395s, which also have the pantograph at the rear of the driving car).

    I'm now trying to find pictures of the 307s in their original DC mode. I was aware the 306s were originally DC but not the 307s.

    The only question that hasn't really been answered yet is the first one - why is the pantograph trailer on the 710s, 304s etc. reversed with the pantograph next to the driving car?
     
  15. TractiveEffort

    TractiveEffort Member

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    When running as 2x5 coupled, the front and rearmost panrographs are used. If there is an issue with one of those and another is raised, then there are speed restrictions.

    100 mph if leading or trailing pantograph of both sets raised and 80 mph if the middle two are raised.
     
  16. MrPIC

    MrPIC Member

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    I always thought on stock with 2 pans the rearmost one was used in order to give max distance and time if an object is spotted on the OLE for the driver to press pan down
     
  17. a_c_skinner

    a_c_skinner Member

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    I've a vague recollection of Virgin changing from front to rear pan on the 390s about 8 years ago and someone saying it actually gave an alert drive just enough extra time to drop the pan and coast if there was a visible OHLE fault. No one mentioned the aerodynamics of the pan for direction of travel. OTOH I may have been dreaming.
     
  18. CNBRail

    CNBRail New Member

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    In 5 car config an extra MS car is inserted between the PMS and DMS2 so the pantograph is near enough central. I guess it was done to save having two different PMS car variants.
     
  19. physics34

    physics34 Established Member

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    Cant find pics of 2 car AM9s anywhere
     
  20. AM9

    AM9 Established Member

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    I think that the aerodynamics of the pantograph itself are by design as direction-independent as possible. It's the turbulence created by the leading vehicle that creates the problem. The rear pantograph is far enough downstream of this to encounter a much more laminar flow. That would also account for the class 700 style of set having the pantographs on the second car in from each end.
     
  21. talltim

    talltim Established Member

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    I’ve not come across using multiple patographs on units for ice scraping in the UK, but certainly in the recent past NR have hired in various preserved mainline electrics for ice scraping duties
     
  22. DarloRich

    DarloRich Veteran Member

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    Is this a non uk approach?
     
  23. 73001

    73001 Member

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    https://goo.gl/images/wH5MxY
    It was very unusual to see them about and they were converted to 4 car in the 70s. The photo is part way down the Railscot page.
     
  24. TRAX

    TRAX Member

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    I can’t say. Ice scraping is standard practice in France - even with two different pantographs (one 1500 V, one 25000 V, works only one way though).
     
  25. DarloRich

    DarloRich Veteran Member

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    Ok.not sure it is standard here
     
  26. TRAX

    TRAX Member

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    I’ve certainly never heard nor read of it.
     
  27. ComUtoR

    ComUtoR Established Member

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    Some quick research into ice scraping with a pantograph led me to discover that some units appear to have an ice scraper that can be raised when required. Sounds like a decent approach.
     
  28. TRAX

    TRAX Member

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    I think in France the pantograph itself is the scraper; nothing is added to help scraping.
     
  29. AM9

    AM9 Established Member

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    Here is another picture that shows the power car quite clearly:
    https://www.flickr.com/photos/86020500@N06/7943638074
    To qualify that, there were a total of eight built. They spent most of their service life attached to a four-car buffet set and a vanilla four-car set. usually at the London end of the train, the trains travelled as 10-cars to Thorpe-le-Soken, then the front four-car unit detached and departed to serve Frinton and Walton (on-the-Naze) and the 4-car buffet set and the two-car units went on to Clacton. So unless there was an ECS or other special move, they might not be easily noticed. In their later years, very quiet trains were sometimes run a 2 + 4-car and split at Thorpe.
    The 2-car units had over 1100 hp available to draw about 85 tons. Their most impressive usage was to boot the busiest train in the evening rush hour, - 1F78 or 1F80 istr, the 17:40 ex Liverpool St. It had two two-car and two four-car sets giving the train a total of over 4500 hp to keep a tight (by GE standards) schedule.
     
  30. WatcherZero

    WatcherZero Established Member

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    Yes you absolutely don't want two neighbouring carriages to have pantographs raised at the same time and generally the bigger the gap the better. Its because of the oscillation introduced into the wire by the first pantograph meaning another pantograph immediately behind wouldn't be able to maintain a consistent contact and possibly even risks becoming entangled.
     
  31. matchmaker

    matchmaker Member

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    I noticed a lot of sparking from a 365 this morning (Stirling). Below freezing (-4C)
     

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