Great Western Coffee Shop

Guy filming in the right place at the right time.

http://www.youtube.com/watch?v=0YqLB-TMvhg&feature=youtu.be

That'll be two new pantographs please, some filler and roof paint.  Oh, and send the invoice to Network Rail  :) Note how the damaged insulator and registration arm dings nearly the entire roof of the train and takes out the rear pantograph.

I guess that a dewirement like this could happen anywhere, but it does show the weakness of using headspans in OHLE. Those complaining about the "industrial-scale" robustness of the OHLE  being installed on the GWML take note.  This is why headspans are no longer installed on 125mph lines.

Very good catch by the person filming.

Could you explain what a headpan is please? I did try a Google search but could not find much.

You may have had trouble because it is headspan.

Headspan refers to there being a headspan wire running between the stanchions on each side of the track, which holds up all of the other wiring. It is these installations which usually are the ones falling down.

On the GWML we are going to have a mostly portal style OHLE, which is a solid beam between the stanchions on each side of the track.

A headspan (with an 's') refers to the type of overhead line construction where (usually on plain line sections away from junctions and such like) the catenary is supported on a system of wires and insulators perpendicular to the track between vertical girders.  So invariably if a de-wirement occurs it will damage the OHLE on both (or more) tracks.   It is the usual style of OHLE used on much of the ECML and the southern parts of the MML.

The method of construction is obsolete, what they install now are either cantilevers or portals, the difference being that all the support devices above the track are substantial members in their own right.

Found a decent picture on wiki:  http://upload.wikimedia.org/wikipedia/commons/0/05/Otterington_railway_station_MMB_01.jpg
All that stuff is under tension, so a break anywhere and it all goes badly wrong...

Paul

Agree with all that has been said above about Headspan construction, it was adopted by BR as a cost effective way to get electrification done through the 1970's and 80's  While it has its venerability's there is a lot of Headspan OLE in the UK that has served the network well over the last 30 to 40 years.

Looking at the video it seems to be a section insulator that was involved. Section insulators are a device that allows a pantograph to travel over it but keeps 2 electrical sections separate.  Adjustment of this is important and the alignment with the track is crucial, also a pantograph failure must not be ruled out either.

As others have said current NR practice on mainline is independent mechanical registration basically portals or separate masts that support the registration arms and insulators, there is also a change of equipment that is going through the acceptance process which is lighter which improves the dynamics.

I've read that headspan (tensioned cross wire) support halved the cost of fixed OHLE compared to portal (steel frame) support. I also imagine that wire height dipped to pass under the bridge in the video clip.

However, if you halve the capital cost you usually increase the maintenance cost and skill required.

Recent OHLE episodes don't support the view that this is suitable for contracting out.

I could say more but won't frighten the horses.

OTC