Quote:
Originally Posted by Deathbyteacup
Just out of curiosity, what causes a train to bring down overhead power lines? General wear and tear?
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The contact wire of the catenary bounces around quite dramatically as the top surface of a train's pantograph (actually carbon strips) pushes up against it. The catenary is stressed at many points by having heavy weights hung from it, and the whole lot is actually quite fragile. If the pantograph causes the contact wire to move further than it's supposed to...then sometimes it all comes down like a house of cards. Don't forget that in addition to vertical excursions there is also "swagger" - IE, the contact wire continuously moves from side to side in relation to the pantograph head, to ensure even wear for the carbons.
Also all pantographs have an Automatic Dropping Device (ADD) which senses when things aren't right. Unfortunately if the pantograph is misplaced and the ADD puts the pan down, this can have the effect of tearing the whole catenary down at the same time.
If you're travelling at 100 mph, you've dragged the best part of 1000 yards of OHLE with you by the time you come to a stand. It's a real guilt trip when you look back and see the chaos which your train has just caused !!
Our Driving Policy is to immediately "Drop & Stop" if you're an 8 car and the line light goes out for an unexpected reason, because at high speed having 2 pantographs at a distance of 4 cars apart can occasionally provoke oscillation in the catenary. It's cheaper in the long run to stop and have a look, rather than stop the job entirely.
HTH,
Foggy