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> raising the rail bridges
Simon Kirby
post Mar 7 2013, 04:08 PM
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Am I right in thinking that the rail bridge in Newbury is being raised to accommodate electrification like the bridge in Aldermaston was?

It's a lot of effort and expense to rebuild a bridge, so I wondered why, if the bridge is too low for the cables and pantograph, can't you just stop the overhead cables short either side of the bridge and duck the pantograph down for the 30 yards or so it would take to pass the bridge. I can't see that would take all that much engineering and it would save on an awful lot of construction. Is there a good reason that couldn't work?


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Gazzadp
post Mar 7 2013, 05:47 PM
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That is part of what is being done, but given the plans to the same on all the between Newbury & Reading were supposed to be done in a similar manner, that being the conection between the road either side being dug up and the the bridge structure jacked up to the required height... Well it has failed on each bridge east of here so far, hence the EXTRA months of delays while those bridges were completely re-built.

Personally I am not sure that the A339 bridge works will go as planned, but then I am no engineer.

What most people do not realise is that although the new electric trains will not go any further west, the over head lines due to the technical/mechanical nature of the electric circuits will have to go a couple of hundred meters west of Black Boys Bridge.


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On the edge
post Mar 7 2013, 06:21 PM
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Bring back the Southern Railway, lets have a third rail!


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Exhausted
post Mar 7 2013, 09:20 PM
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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.
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Ron
post 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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On the edge
post 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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Biker1
post 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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Andy Capp
post Mar 8 2013, 11:47 AM
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QUOTE (Biker1 @ Mar 8 2013, 08:47 AM) *

Bikers link basicly says they are repairing brickwork and raising the parapets. They are not 'lifting' the bridge up.
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Simon Kirby
post 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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Ron
post 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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John C
post 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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Biker1
post 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!! laugh.gif )
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On the edge
post Mar 8 2013, 04:32 PM
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Well done Biker, that was technically very interesting......seriously! A whole textbook of theory lucidly demonstrated in a short film.


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Simon Kirby
post 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!! laugh.gif )

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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Simon Kirby
post 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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On the edge
post Mar 8 2013, 07:43 PM
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Part of the issue is the ability of the electricity to 'jump' particularly at these voltages; the spark plug effect. However, its an interesting point to see if with today's insulating technologies if a smaller gap couldn't be used. Similarly using say photo cell technology to lower and lift the pantographs where there is a known obstruction, like a low bridge may well be possible. Might be worth suggesting to say Siemens or the like, because if a few hundred extra on the locomotive kit eliminates the several million on bridge works - you have a winner. Of course, they may well have thought of it; but no one had thought of cats eyes in the road until Percy Shaw came along!


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NWNREADER
post Mar 8 2013, 08:16 PM
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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.
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Andy Capp
post 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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Simon Kirby
post 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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Simon Kirby
post 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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