Yes. 25322 is talking nonsense.
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Pantographs on Pendolinos
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Yes. 25322 is talking nonsense.
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25322
Member
Apologies accepted from all those that put what I said down as nonsense.
Sensibility prevails and a dictate from Network Rail insist that rear most Pans are used. Saving virgin and Network rail a fortune in repairs
starrymarkb
Established Member
It was a Dictate from Railtrack/NR to use the front pan. They wanted the knuckle to be trailing (something to to with the damping fitted for 140mph operation)
That is because it has changed since the thread was started. The thread was dragged up today after being dormant since August.
royaloak
Established Member
At the time he was wrong, but as NR have changed the rules he is now right, he just wants to tell everyone as if he was right all along, which of course he wasnt!
O L Leigh
Established Member
33056
Established Member
FYI the change from Pendos using the front pantograph to using the rear one was in December 2009.
The original intention and design was for them to operate using the rear pan but, until recently, this was not possible due to various issues. Using the rear pan is kinder to the infrastructure as the uplift forces on the rear pan with the knuckle leading is around half that of the front pan with the knuckle trailing and there are also other advantages.
The original intention and design was for them to operate using the rear pan but, until recently, this was not possible due to various issues. Using the rear pan is kinder to the infrastructure as the uplift forces on the rear pan with the knuckle leading is around half that of the front pan with the knuckle trailing and there are also other advantages.
ChrisCooper
Established Member
I suppose if uplift force difference for knuckle trailing or leading is that different, the idea is that with just one pan it evens out as it will travel half the time leading, half the time trailing, wheras with 2 pans it will either do all the time leading or all the time trailing. Oviously even if the difference is fairly slight, it does make sence to always run in the best configuration instead of the worst. Considering the amount of research BR did with pantographs at high speeds, going back to the 60s, it is surpsising that this issue has only just come up, and does add weight to the idea that the desision to run front pan up was for looks not anything technical. To be honest, in these cash short times it's these sort of areas which really need to be looked at urgantly. If you can save a bit of money by making something not look as nice, it's better than saving the same money by making something not work as well. Save the pennies they say.
starrymarkb
Established Member
As I said it was nothing to do with looks, Alstom/NR wanted the knuckle trailing for 140mph running under UK spec knitting. Presumably some mods have been done since and it is now better to have the knuckle leading..
O L Leigh
Established Member
I'm still quite some distance away from being even remotely convinced that there are any differences in uplift on a BRBW high-speed pan relative to it's direction of travel.
While this was certainly the case with the original prototype, the problem was quickly addressed by aerodymanicallly balancing the head with modified carbon carriers, adjustable aerofoils and "tabs" on the horns and successfully tested in June 1976 long before they went into production and use. During the testing phase these pans were successfully trailled in the UK at speeds in excess of 150mph with the APT-P, at speeds in excess of 125mph using a specially formed HST set to test the performance of two pans raised, and at speeds of up to 164mph by the Pennsylvania Railroad (who also briefly ran them in service on Metroliner trains at up to 150mph). In all of these tests the pans performed successfully irrespective of the direction of travel. (More info here.)
Consequently I am extremely dubious of any claims over the difference in uplift as a consequence of the direction of travel for a train travelling at what is actually a fairly modest 125mph. However, if someone would like to cite some source or give a technical explanation as to why the uplift might be different then I am all ears. However, I would still be inclined to give more credence to the man actually involved in the pan's design and testing.
O L Leigh
While this was certainly the case with the original prototype, the problem was quickly addressed by aerodymanicallly balancing the head with modified carbon carriers, adjustable aerofoils and "tabs" on the horns and successfully tested in June 1976 long before they went into production and use. During the testing phase these pans were successfully trailled in the UK at speeds in excess of 150mph with the APT-P, at speeds in excess of 125mph using a specially formed HST set to test the performance of two pans raised, and at speeds of up to 164mph by the Pennsylvania Railroad (who also briefly ran them in service on Metroliner trains at up to 150mph). In all of these tests the pans performed successfully irrespective of the direction of travel. (More info here.)
Consequently I am extremely dubious of any claims over the difference in uplift as a consequence of the direction of travel for a train travelling at what is actually a fairly modest 125mph. However, if someone would like to cite some source or give a technical explanation as to why the uplift might be different then I am all ears. However, I would still be inclined to give more credence to the man actually involved in the pan's design and testing.
O L Leigh
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Wyvern
Established Member
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Are these Brecknell Willis pantographs, out of interest?
O L Leigh
Established Member
Which?
O L Leigh
O L Leigh
Wyvern
Established Member
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Sorry. The ones on the Class 390
O L Leigh
Established Member
Yes. In fact no new train has been produced with any other type of pan since the Cl319/0's were rolling out of York in 1987/88.
O L Leigh
O L Leigh
Wyvern
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Presumably then it is Brecknell Willis that should have the answer.
Their early design was produced in cooperation with BR Research for APT-P including during tilting.
POSTSCRIPT:
I've just had a look at their website. Their FAQ page is interesting but doesn't answer our question.
http://brecknell-willis.co.uk/faq_panto.htm
Thinking about it, one would expect travelling knuckle first would tend to throw the contact surface away from the catenary, while knuckle trailing would cause the contact to "dig in" to the cable increasing the pressure.
As for having two pantographs raised, it will be remembered that the APT-P had a single (central) motor coach simply because of the problems discovered with using two pantographs. And loco hauled electrics use a DVT at the opposite end.
It tool a change in the law to allow Virgin's Pendolinos to be introduced.
Their early design was produced in cooperation with BR Research for APT-P including during tilting.
POSTSCRIPT:
I've just had a look at their website. Their FAQ page is interesting but doesn't answer our question.
http://brecknell-willis.co.uk/faq_panto.htm
Thinking about it, one would expect travelling knuckle first would tend to throw the contact surface away from the catenary, while knuckle trailing would cause the contact to "dig in" to the cable increasing the pressure.
As for having two pantographs raised, it will be remembered that the APT-P had a single (central) motor coach simply because of the problems discovered with using two pantographs. And loco hauled electrics use a DVT at the opposite end.
It tool a change in the law to allow Virgin's Pendolinos to be introduced.
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Old Timer
Established Member
Originally the intention was that the locomotives would operate with the pan knuckle leading, so that in the event of an incident anything striking the pan would cause it to fold down. Travelling knuckle trailing would have the opposite effect that the pan could be ripped from the roof and or would cause considerably more damage. The original electrics were built with two pans for that reason but interlocking them became an issue and they wer removed.
The pan is held against the contact wire with a vertical force about that of a 2lb bag of sugar. You can actually move the pan up and down with your little finger. Too much upwards pressure causes wear on both the carbons as well as the contact wire and causes the catenary system to "bounce", this being a key factor in operation with two pans, and the reason why double electrically headed trains were limited to 80 mph.
One of the issues when DVTs were introduced was the potential of the OHL to "flutter" through the aerodynamic effect of the train passing underath, and the effect on current collection.
As OL Leigh states pantograph contact is controlled by the use of aerofoils coupled with the aerodynamic design of the pantograph.
Bounce in both the pan and the catenary system leads to a loss of physical contact and the generation of a short arc, the effect of which over time is to cause localised heating of the droppers, which subsequently leads to a failure of the dropper wire. One of the reasons why the UK1 system uses flexible AF copper droppers.
The pan is held against the contact wire with a vertical force about that of a 2lb bag of sugar. You can actually move the pan up and down with your little finger. Too much upwards pressure causes wear on both the carbons as well as the contact wire and causes the catenary system to "bounce", this being a key factor in operation with two pans, and the reason why double electrically headed trains were limited to 80 mph.
One of the issues when DVTs were introduced was the potential of the OHL to "flutter" through the aerodynamic effect of the train passing underath, and the effect on current collection.
As OL Leigh states pantograph contact is controlled by the use of aerofoils coupled with the aerodynamic design of the pantograph.
Bounce in both the pan and the catenary system leads to a loss of physical contact and the generation of a short arc, the effect of which over time is to cause localised heating of the droppers, which subsequently leads to a failure of the dropper wire. One of the reasons why the UK1 system uses flexible AF copper droppers.
Is there that much change in the dynamics from 100mph (the likes of Networkers can go that fast with three pans up) to 125mph? They obviously go that quick with the knuckle in either direction.
Also, are the potnetial problems more to do with the british wiring than with the fundamentals of pantograph current collection, given the use of multiple pantographs atmuch higher speeds elsewhere?
Also, are the potnetial problems more to do with the british wiring than with the fundamentals of pantograph current collection, given the use of multiple pantographs atmuch higher speeds elsewhere?
O L Leigh
Established Member
We're getting a few things mixed up, so lets break this down into it's constituent parts.
The mechanical thrust or uplift of a pan is vertical. All the different movements and actions of the various parts, such as the upper and lower parts of the arm and the head, all resolve to remove any horizontal forces.
Put the train in motion and aerodynamic forces start to have an affect, but not really as much as some folk would imagine. No matter which way the pan is travelling, whether the knuckle is leading or trailing, the drag on the upper and lower parts of the arm are forcing one part up and the other part down. Just to illustrate this point, where the knuckle is leading the drag on the lower part of the arm will be attempting to force it up while the drag on the upper part will be attempting to force it down. Reverse the direction so that the knuckle is trailing and the forces are also reversed. However, the important point to consider here is that no matter which way round the pan is these forces acting on the pan as a consequence of drag will be the same.
In fact, in this particular area the BRBW high-speed pan performs better than the old Faiveley AMBR "bicycle frame" pan because the drag on each part of the arm is broadly balanced due to the broadly similar cross-section of each part. The old Faiveley pan almost certainly creates more drag with it's more complex upper section compared to the single arm used for the lower part.
So far so good. But where the BRBW pan caused problems at prototype stage was because of the design of the pan head with it's additional suspension unit. The aerodynamic drag on the carbon carriers and horns themselves was causing the pan head to lose contact with the wire with the knuckle trailing because the drag on the pan head itself was forcing it down and away from the contact wire. It was this problem that required the aerodynamic redesign of the head and the addition of aerofoils and tabs. As the speed increased and the aerodynamic drag on the head grew, so these modifications generated lift to counteract the effect and keep the pan head in contact with the wire.
As Old Timer suggests, the key is getting the amount of uplift right. Just as having too much uplift can cause bounce so can too little uplift, especially where the geometry of the OLE is perhaps a wee bit marginal. We have a couple of sections around Broxbourne where the pan loses contact because the contact wire changes height suddenly to accommodate a couple of bridges. Quite simply, when travelling at the full linespeed the pan cannot react to the height changes quickly enough and as a result loses contact.
Also, if I may be permitted to clear up a couple of other associated points.
The proposed APT-S production train required two motor coaches in order to achieve the high speeds required. However, these were required to be in the centre of the train primarily because of the reluctance to have a 25kV "bus" running the length of the train. The use of two pans was tested at speeds exceeding 125mph using a temporary HST formation, as described in the webpage I linked to earlier, and the performance was found to be acceptable. In addition, the original testing of the BRBW pan was done by hooking Lab 6 "Prometheus" onto the back on an electric train and running it up and down the WCML between London and Carlisle. Even then "...the pantograph's performance at the rear of the train as the second pantograph was remarkable. It was as good as the Faiveley when leading and our pan was running on an already moving contact wire."
I would usually defer to Old Timer's greater experience and depth of knowledge, but I'm not sure that the theory that a snagged pan would be likely to incur less damage travelling one way compared to the other holds up in practice. Clearly operational experience must have demonstrated that any advantage was small as the practice of fitting two pans to locos was short-lived and not applied to EMU's.
Now it may just be the customary practice of Virgin to run a particular way around or the pans on the Cl390's may have been specifically tuned to alter the amount of uplift, but that is nothing to do with any shortcomings of the pan design itself. One or two minor operating advantages have been pointed out to me by another member by PM, but those alone still don't really convince me that there is any significant advantage to running the pan in one direction or the other.
Nor, for that matter, why it should be generating quite so much interest or discussion.
O L Leigh
The mechanical thrust or uplift of a pan is vertical. All the different movements and actions of the various parts, such as the upper and lower parts of the arm and the head, all resolve to remove any horizontal forces.
Put the train in motion and aerodynamic forces start to have an affect, but not really as much as some folk would imagine. No matter which way the pan is travelling, whether the knuckle is leading or trailing, the drag on the upper and lower parts of the arm are forcing one part up and the other part down. Just to illustrate this point, where the knuckle is leading the drag on the lower part of the arm will be attempting to force it up while the drag on the upper part will be attempting to force it down. Reverse the direction so that the knuckle is trailing and the forces are also reversed. However, the important point to consider here is that no matter which way round the pan is these forces acting on the pan as a consequence of drag will be the same.
In fact, in this particular area the BRBW high-speed pan performs better than the old Faiveley AMBR "bicycle frame" pan because the drag on each part of the arm is broadly balanced due to the broadly similar cross-section of each part. The old Faiveley pan almost certainly creates more drag with it's more complex upper section compared to the single arm used for the lower part.
So far so good. But where the BRBW pan caused problems at prototype stage was because of the design of the pan head with it's additional suspension unit. The aerodynamic drag on the carbon carriers and horns themselves was causing the pan head to lose contact with the wire with the knuckle trailing because the drag on the pan head itself was forcing it down and away from the contact wire. It was this problem that required the aerodynamic redesign of the head and the addition of aerofoils and tabs. As the speed increased and the aerodynamic drag on the head grew, so these modifications generated lift to counteract the effect and keep the pan head in contact with the wire.
As Old Timer suggests, the key is getting the amount of uplift right. Just as having too much uplift can cause bounce so can too little uplift, especially where the geometry of the OLE is perhaps a wee bit marginal. We have a couple of sections around Broxbourne where the pan loses contact because the contact wire changes height suddenly to accommodate a couple of bridges. Quite simply, when travelling at the full linespeed the pan cannot react to the height changes quickly enough and as a result loses contact.
Also, if I may be permitted to clear up a couple of other associated points.
The proposed APT-S production train required two motor coaches in order to achieve the high speeds required. However, these were required to be in the centre of the train primarily because of the reluctance to have a 25kV "bus" running the length of the train. The use of two pans was tested at speeds exceeding 125mph using a temporary HST formation, as described in the webpage I linked to earlier, and the performance was found to be acceptable. In addition, the original testing of the BRBW pan was done by hooking Lab 6 "Prometheus" onto the back on an electric train and running it up and down the WCML between London and Carlisle. Even then "...the pantograph's performance at the rear of the train as the second pantograph was remarkable. It was as good as the Faiveley when leading and our pan was running on an already moving contact wire."
I would usually defer to Old Timer's greater experience and depth of knowledge, but I'm not sure that the theory that a snagged pan would be likely to incur less damage travelling one way compared to the other holds up in practice. Clearly operational experience must have demonstrated that any advantage was small as the practice of fitting two pans to locos was short-lived and not applied to EMU's.
Now it may just be the customary practice of Virgin to run a particular way around or the pans on the Cl390's may have been specifically tuned to alter the amount of uplift, but that is nothing to do with any shortcomings of the pan design itself. One or two minor operating advantages have been pointed out to me by another member by PM, but those alone still don't really convince me that there is any significant advantage to running the pan in one direction or the other.
Nor, for that matter, why it should be generating quite so much interest or discussion.
O L Leigh
Old Timer
Established Member
OL
The idea of running knuckle first was that the pan would be forced downwards and pass underneath bridges and OHL structures rather than opening up and snagging if it ran knuckle trailing. Of course ADD removed the need for this.
The idea of running knuckle first was that the pan would be forced downwards and pass underneath bridges and OHL structures rather than opening up and snagging if it ran knuckle trailing. Of course ADD removed the need for this.
captainbigun
Member
- Joined
- 3 May 2009
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- 977
That's if the ADD activates, which on occasions it doesn't. The carbon has to crack sufficiently, detach from the holder or the pipework has to split sufficiently to activate the ADD. A number of incidents have occurred where the ADD has remained sufficiently intact not to drop the pan. EC pan heads have a modification which increases the likelihood of the pipework becoming disturbed therefore the ADD becoming activated.
A pendo has a different ADD arrangement whereby it is fed from either end of the carbons.
TGV
Member
Apologies for dragging this up, but as somone already did a couple of weeks ago, I don't feel so bad...
I used to be Eurostar's pantograph technical engineer, so I'm probably well enough qualified to answer this one!
Mr O L Leigh is making some sense and many others would do well to understand his points. I'll not bore you (unless you want boring), but here are some bullet points to what I've skimmed in this thread:
- Dynamically it doesn't matter AT ALL which way round the pan is travelling with modern designs. The uplift force is set within some fairly loose tolerances (around 20 lb force roughly), but they are that way to take account of the varying tensions in different sections of line and any height changes - also remember the line tension IS affected by temperature, even though the system takes much of that into account with the weights, there is always lag, discrepancy and difference between areas.
- Eurostars ALWAYS ran and still do with BOTH pans raised in normal service - both on CTRL (High speed 1) and ECML use with GNER. They also ran at 125mph with both pans raised on the southern section of the ECML. The rear one always had a harder time because of the wave set up in the line by the leading pan leaving the rear pan head trying to make good contact with a rapidly moving line. However it wasn't catastrophic - in fact, look at any EMU running in multiple - there will be 2 or more pans raised and the rear always has this problem to a more or lesser extent. It's not a game ender - it just shortens the life of the carbon contact strips. 373 power cars have 2 pans each - a Brecknell Willis (DC) and Faiveley (AC). The DC one can be used as an AC pan in an emergency but at limited speed.
- Some people think of 373's as 2 EMUs back to back. Kind of. Only in terms of how the set is split and numbered. When in service, it's more accurate to think of it as an electric HST - 2 separate power cars that are CONTROLLED together, but work independantly.
- ADD is one of those things that is a god-send when it works and when it doesn't, it's line-closed time.
That's my 2 cents worth.
I used to be Eurostar's pantograph technical engineer, so I'm probably well enough qualified to answer this one!
Mr O L Leigh is making some sense and many others would do well to understand his points. I'll not bore you (unless you want boring), but here are some bullet points to what I've skimmed in this thread:
- Dynamically it doesn't matter AT ALL which way round the pan is travelling with modern designs. The uplift force is set within some fairly loose tolerances (around 20 lb force roughly), but they are that way to take account of the varying tensions in different sections of line and any height changes - also remember the line tension IS affected by temperature, even though the system takes much of that into account with the weights, there is always lag, discrepancy and difference between areas.
- Eurostars ALWAYS ran and still do with BOTH pans raised in normal service - both on CTRL (High speed 1) and ECML use with GNER. They also ran at 125mph with both pans raised on the southern section of the ECML. The rear one always had a harder time because of the wave set up in the line by the leading pan leaving the rear pan head trying to make good contact with a rapidly moving line. However it wasn't catastrophic - in fact, look at any EMU running in multiple - there will be 2 or more pans raised and the rear always has this problem to a more or lesser extent. It's not a game ender - it just shortens the life of the carbon contact strips. 373 power cars have 2 pans each - a Brecknell Willis (DC) and Faiveley (AC). The DC one can be used as an AC pan in an emergency but at limited speed.
- Some people think of 373's as 2 EMUs back to back. Kind of. Only in terms of how the set is split and numbered. When in service, it's more accurate to think of it as an electric HST - 2 separate power cars that are CONTROLLED together, but work independantly.
- ADD is one of those things that is a god-send when it works and when it doesn't, it's line-closed time.
That's my 2 cents worth.
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