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British Railways OLE, part two, Curved Track


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Curved track

Most model railways have curves, this thread hopefully will enable those who model OLE to not only have prototypical wires above the tracks but in following prototype practice will not have any problems with contact wires and pantographs becoming entangled.

 

These guidelines apply to curved track with a radius of less than a scale 55 chains or 1106.5 meters.

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With curved track the contact wire has to be set so that it remains in touch with the pantograph. Normal stagger would take the contact wire outside the pantograph sweep so the masts are arranged so the pull off is always on the outside and the push off on the inside. Stagger is also increased on curves so that the contact wire is inside the pantograph sweep. The spacing of the mast is closer than on straight track again to prevent the pantograph from separating from the wire.

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Curved track is canted, I will allow the track experts to give you more details, this canting of the track has an effect on the position of the pantograph, and the amount of cant will alter the offset from the track centre at pantograph height.  The pantograph tilts due to the cant and on the prototype a built in sag is designed in the span so the pair remain in contact. This is not normally more than a few inches and would not show on a model.

 

Contact wire is measured from the highest rail on each track.

 

Fixed tension equipment is used on small radius curves as the pull of the pantograph on the contact wire can overcome the balance weights used in auto tensioned equipment.

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Edited by Clive Mortimore
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A fabtastic set of drawings Clive and very interesting.   My modelling is Midland 6.6KV OLE from 1907.  I'm fortunate that I've got the original Midland railway Contract drawings for the production of the masts and steelwork, which give a lot of the detailed info for the wires, registration arms etc.  My attempts at modelling these are shown in the Lancaster Green Ayre thread but if anyone is interested I could try and post cleaned up scans of some of the drawings.  As a matter of manners would you suggest doing this in a new thread.

 

Jamie

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A fabtastic set of drawings Clive and very interesting.   My modelling is Midland 6.6KV OLE from 1907.  I'm fortunate that I've got the original Midland railway Contract drawings for the production of the masts and steelwork, which give a lot of the detailed info for the wires, registration arms etc.  My attempts at modelling these are shown in the Lancaster Green Ayre thread but if anyone is interested I could try and post cleaned up scans of some of the drawings.  As a matter of manners would you suggest doing this in a new thread.

 

Jamie

Thanks Jamie

 

I am enjoying viewing the developments at Green Ayre, Midland Railway and electrics.  :locomotive:  The engine shed alone would make an excellent MPD model and be made to scale in a small space.

 

I have often considered Scale Hall Station as a potential model with the later Morecombe- Lancaster EMUs.

 

I would very much like to see some of the MR OLE structure drawings.

 

Yours

 

Clive

 

PS Be careful your layout odesn't get classed Modern Image because it has EMUs on it, but I supose most the locos would be in post 1908 liveries so yes it is modern :sungum:

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Good stuff Clive!

 

One thing I am wondering about - the tension in the wires is such (around 11Kn in Mk3 equipment) that the drag from a pantograph is insignificant by comparison, and not an issue on any track either straight or tightly curved.  I am wondering if you have read the term 'along track drag' and misinterpreted it, as this is relevant to Auto Tensioned equipment but has nothing to do with pantographs.

 

I will try and explain. When the wire expands/contracts due to temperature, there is along track movement, towards the weights when hot, away from the weights when cold. The closer you get to the weights, away from the mid point anchor, the more pronounced this is. The cantilevers can hinge at the mast and move through an arc to accommodate this. So at about 10 degrees C the cantilevers will be about perpendicular, hotter they will point a little to the balance weights, colder a little to the mid point anchor (provided it is set up correctly - it often isn't!) . This dragging of the equipment one way or the other due to temperature is what the term 'along track drag' refers to.

 

Unfortunately this has an undesirable effect, a cantilever or registration at an angle is putting a slight pull on the wire. This will either add to, or subtract from, the constant tension put in to the wires by the balance weights. Each support on the wire length makes its own contribution to the effect, so if you have a lot of supports in a wire length - as you might on a sharp curve, the cumulative effect may take the tension out of limits as you get towards the mid point.  The solution to this is to shorten the distance from the Mid-point anchor to the balance weights, and thus the number of supports between the two.

 

Of course this does not apply to Fixed Equipment, since the wire does not move along track with temperature (it just sags a bit), and thus the cantilevers don't pivot to create this effect. But you would not mix Fixed Equipment and Auto Tensioned if you can avoid it, so the normal solution to sharp curves with Auto Tensioned is to keep the wire runs short.

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Hi Ian

 

Thank you for your contribution, the information is very helpful.

 

My understanding about the effect of the pantograph on moving the contact wire came from an older BR document (1970s I think) of OLE I downloaded some time ago, and I wish I had recorded which one out the fifteen or so I have from that period becuase it is not going to be tonight's bed time reading to find it. I remember the item not only mentioned the drag of the pantograph but it could also push the contact wire along and in many cases set up a wave effect causing the pantograph and contact wire to bounce off each other. This wave effect is supposed to be most noticable by the amount of arcing between the pantograph and contact wire of the trailing locomotive when a train is being doubleheaded. 

 

Thanks again for information.

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Ah the wonderful wold of OLE dynamics!  Yes the pan pushes a wave along the wire, but it is the waves up and down movement that moves along the wire rather than the wire itself being pushed along. Each pan adds its own wave on to the wire so that if the spacing between the pans corresponds to the wavelength you can get some very large wire movements and arcing, at just the right (or wrong) speed! Class 309's with their somewhat varied formations with 3 pans up at 100mph were the worst. I remember watching one race through Witham non-stop and it was several minutes after they passed before the OLE stopped dancing around and regained its composure. Whenever there was a bad dewirement on The GE the culprit was usually a 309.

 

Indeed this led to what must have been the rarest train formation I ever saw - Mentor sandwiched between two class 309's with its pan up. Normally Mentor is diesel hauled so there are no other pans to mess with its readings, so I guess they were specifically looking at the dynamic effects the 309's were having on the wire. I wonder if Mentor was through wired/piped for that sort of thing or if they had to rig up something special?

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Class 309's with their somewhat varied formations with 3 pans up at 100mph were the worst.

Now you've done it Ian... never mention 309s in an Clive topic, he'll have to go and lie in a darkened room for a week now  :locomotive:

 

Andi

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By sheer chance I've just been re reading a paper presented to the Insitution of Civil Engineers bi Dalziel and Sayers (Who did the design and construction work at :Lancaster for Deeley).  They dwell at some length on the subject of pantograph drag.  Apparently the wire was in 1000 yard lengths with an anchor at one end and 1200lbs weight at the other end.  The ends were arranged so that the trains usually entered a section at the anchored end and exited at the weighted end to stop the wire being pushed along by the pantogrpahs.  Apaprently the early system  from hamburg to Altoona had sufferred from this so Siemens reccommended this system.  However the final design was by sayers who was an S & T man who would have known a thing or two about cable runs.  The emchanical and electrical design was by Dalziel.

 

I'll try and start a new topic with the various drawings for people to comment on.

 

Jamie

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