View single post by Huw Griffiths
 Posted: Wed Nov 17th, 2010 01:44 pm
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Huw Griffiths



Joined: Wed Oct 21st, 2009
Location: Cwmbran, Wales, United Kingdom
Posts: 268
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Thanks for your kind comments.

Here's a link to the Faiveley website (with a number of PDF brochures - some more interesting than others - and most not related to current collection) - http://www.faiveley.com/uk/plandusite.php - and here's a direct link to the section about pantographs - http://www.faiveley.com/uk/categorie.php?ID=23#cat19.


Another major manufacturer of electrification equipment is the Chard (Somerset, UK) based Brecknell, Willis. A few years ago, David Hartland wrote a very interesting book, Collectors for Trains, Trams and Trolleys (ISBN 1-984474-292), which details the company history. The book also includes a number of photos of prototype OHLE and current collectors.

The Brecknell, Willis company website also includes some interesting literature - http://brecknell-willis.co.uk/bwdocs.htm. I particularly enjoyed the technical papers "good looking overhead wires" and "developments towards an active pantograph". (There's also some interesting stuff on their product specific pages.)


In case anyone is wondering, I believe the reason why pantographs are normally used with "stiff wire", catenary systems under tension is to prevent damage when the car reaches a wire support pole, or a junction. Without the tension, the pantograph would push the wire up - probably jumping, or causing a kink in the wire, the moment a support is reached. Apart from possible damage to wire and support, this could cause the pantograph head to break. In an extreme case, the pantograph could be ripped off the car.

To prevent this, the wire is always kept under tension. Also, the pantograph head doesn't actually contact the wire directly. Instead, contact is via a shaped carbon block, which slides along the wire. To stop the wire wearing a groove in the contact block, the wire also zigzags between supports, over a short range either side of the track centre line. This also allows the pantograph to continue collecting current on curves.

By the way, I'm aware that a lot of research has been done into working out the correct contact force between pantographs and wire on full size railways and tramways - it seems to vary according to the speed of trains (etc) using the lines and how much current they draw. There's also been a lot of research into how to achieve this ideal force.


Perhaps not strictly relevant here, I also enjoyed reading some of this material: http://www.old-dalby.com/Brecknell.htm

(Also of limited relevance, your comment about the high resistance of thin cross section wire reminds me of some gear I installed for a living, when I worked as a "university "labrat" - specifically, strain gauges. These work on the basis that, as a wire gets longer and narrower, its resistance goes up - and this change in resistance can be used to measure strain. I know there's also a lot of very OTT maths relating to this stuff - thankfully, I never needed to understand it!)


Anyway, I think I've said enough for now.


Regards,

Huw.

Last edited on Wed Nov 17th, 2010 01:55 pm by Huw Griffiths

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