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raising the rail bridges |
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Mar 7 2013, 11:13 PM
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QUOTE (Exhausted @ Mar 7 2013, 09:20 PM) I know that the Boundary Road bridge needs replacing but surely the A339 bridge, fairly new in railway terms, hasn't been built without the apprpriate clearances.
Was there a planning application that I missed. I wouldn't have thought the idea of electrification in this area was thought of when that bridge was built.
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Mar 8 2013, 08:17 AM
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QUOTE (Ron @ Mar 7 2013, 11:13 PM) I wouldn't have thought the idea of electrification in this area was thought of when that bridge was built. Think it was replaced in the early 1960s. Its not so much electrification, more loading gauge or free hight above a train. The need to adopt continental loading gauges was well understood even then. However, short term cost expediency cuts in again. That coupled with the then UK view that frail didn't have a long term future, (Mr Marples et al) - decision made. NOTE - The political lessons from rail history provide an interesting parallel today with popular politicians who think they are above the law!
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Know your place!
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Mar 8 2013, 08:47 AM
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QUOTE (Simon Kirby @ Mar 7 2013, 05:08 PM) Am I right in thinking that the rail bridge in Newbury is being raised to accommodate electrification like the bridge in Aldermaston was? No! http://www.highways.gov.uk/roads/road-proj...tenance-scheme/
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Mar 8 2013, 12:48 PM
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QUOTE (Biker1 @ Mar 8 2013, 08:47 AM) Ah, righto. How about the more general question then about the bridges that have been raised for electrification: couldn't the pantograph have been pulled down while the train went under the low bridges?
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Right an injustice - give Simon Kirby his allotment back!
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Mar 8 2013, 02:18 PM
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QUOTE (Simon Kirby @ Mar 8 2013, 12:48 PM) Ah, righto.
How about the more general question then about the bridges that have been raised for electrification: couldn't the pantograph have been pulled down while the train went under the low bridges? Response time for a high speed train to 'dip' the pantograph?
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Mar 8 2013, 03:02 PM
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QUOTE (Ron @ Mar 8 2013, 02:18 PM) Response time for a high speed train to 'dip' the pantograph? If it was going that fast it would not be able to stop at Newbury. I think it is more to do with the Voltages involved and clearances of the roofs of the trains and the overhead wires
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Mar 8 2013, 03:46 PM
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QUOTE (Simon Kirby @ Mar 8 2013, 01:48 PM) How about the more general question then about the bridges that have been raised for electrification: couldn't the pantograph have been pulled down while the train went under the low bridges? No. Otherwise they wouldn't have gone to the great expense of raising them! The contact wire has to be continuous. Take a look at this and tell us how you think it could be done. (You don't have to watch all of it!! )
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Mar 8 2013, 04:58 PM
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QUOTE (Biker1 @ Mar 8 2013, 03:46 PM) No. Otherwise they wouldn't have gone to the great expense of raising them! The contact wire has to be continuous. Take a look at this and tell us how you think it could be done. (You don't have to watch all of it!! ) I think what's illustrated by that film is that the pantograph already has quite a bit of travel and at times is pretty much bottomed out, and I'm guessing that the bridges that needed raising actually had less clearance than the lowest structues on that film or otherwise there wouldn't have been a problem. I still wonder though whether the gubbins on the top of the train couldn't have been made low-profile and the pantograph designed to more fully retract. There is no particular need for the wire to be continuous. It currently needs to be continuous because the pantograph is designed to ride continuously on the wire and not to have to re-acquire a wire, but electrical continuity is easily achieved without the need for the actual contact wire to be continuous. If the wasn't clearance for the wire under existing bridges then the wire could be stopped short on either side if the pantograph was designed to dip and re-acquire the wire.
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Right an injustice - give Simon Kirby his allotment back!
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Mar 8 2013, 05:05 PM
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QUOTE (Ron @ Mar 8 2013, 02:18 PM) Response time for a high speed train to 'dip' the pantograph? Doing 125 mph, that's around 50m per second, it would need to dip in around 0.1 second. Say it has to dip a 50kg pantograph by 1.0m, accelerating it from rest and dropping it onto the deck without driving it through the carriage roof, then it needs accelerating/decelerating at something like 400 m/s2, so it needs an actuator with a 2 tonne kick. Hydraulics can do that no problem, but not at that power. It would be a challenge.
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Right an injustice - give Simon Kirby his allotment back!
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Mar 8 2013, 08:32 PM
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QUOTE (NWNREADER @ Mar 8 2013, 08:16 PM) If the wire or pantothingy cannot be lowered, why not raise the road a la Tower Bridge? The wire would rest against the bottom of the bridge deck and lift as the road raised. That would take trains off line while ground work took place, wouldn't it?
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Mar 8 2013, 10:09 PM
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QUOTE (NWNREADER @ Mar 8 2013, 08:16 PM) If the wire or pantothingy cannot be lowered, why not raise the road a la Tower Bridge? The wire would rest against the bottom of the bridge deck and lift as the road raised. That probably a more expensive option than simply building the bridge higher. I was thinking about an option that left the bridges as they are and still allowed the electrification.
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Right an injustice - give Simon Kirby his allotment back!
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Mar 8 2013, 10:16 PM
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QUOTE (Simon Kirby @ Mar 8 2013, 05:05 PM) Doing 125 mph, that's around 50m per second, it would need to dip in around 0.1 second. Say it has to dip a 50kg pantograph by 1.0m, accelerating it from rest and dropping it onto the deck without driving it through the carriage roof, then it needs accelerating/decelerating at something like 400 m/s2, so it needs an actuator with a 2 tonne kick. Hydraulics can do that no problem, but not at that power. It would be a challenge. Thinking about it a active dropping of the pantograph would be an engineering challenge, but all you'd really need to do is design the pantograph to fit snugly on the roof of the train and then drop the wire under the bridge so that it pushes the pantograph down and lets it ride up smoothly on the other side - and if there is a problem achieving the clearance necessary for electrical insulation then just don't electrify the bit of the cable than guides the pantograph under the bridge (it wouldn't be a contiguous bit of electrical conductor, just a free-standing bit of cable). Put tat least two pantographs on the train so the train always has voltage and the job's a good 'un.
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Right an injustice - give Simon Kirby his allotment back!
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