Train collectors - arching in winter

Hi Folks,
It is now below zero in the mornings. While I wait for my train, a number of "high speed" trains come past. The light show, as well as
noise, emitting from the collectors is rather spectacular.
My question is why does this only happen when it is cold and frost is about? The connection, I would imagine, is fairly good and you generally don't see sparks any other time. It cannot be a buildup of frost as it happens to two trains on the same line about 5 minutes apart. I would imagine that both train's collectors have pretty much the same track so it would not be about it running over a new frosty section.
TIA for any answers...
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My guess is the lines and their tension springs grow a bit stiff at lower temps, which can cause an increase in bounce or vibration in the lines. The struts holding the collectors against the lines may be a little sluggish in the cold, so that the bounce is amplified.
CS
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I suppose this does make some sense. But still seems weird that it only happens when there is frost. When it is cold, but no or not much frost, it's does not happen. it also stops as the collector goes under the bridge. Although, your theory would still work because the cables are lower which pushes the collectors down, tensions the spring which reduces bounce...
Does seem possible... Thanks.
Cheers, Crispin
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Something else I just thought of which is why it might not be the spring stiffness idea: it happens as the train starts to pull away. i.e. As soon as there is a high current draw as a well as movement. The moment in the first few seconds is so slow that there would now be any bounce in the collector.
Just thinking out loud...
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On 12 Dec, 15:03, snipped-for-privacy@gmail.com wrote:

A few points...
The "collector" is called a pantograph.
The commonest cause of arcing is icing of contact wire and/or the renewable carbon (or copper) collector strip on the pantograph.
The contact wire does not exactly parallel the rails, it is zigzagged, so that it does not touch the same part of the collector strip all the time. Thus frost can build up on the parts of the strip not recently in contact.
The pantograph is held against the contact wire by air pressure.
5 minutes is plenty of time for a new frost build up on the wire, but it sounds as if the pantographs are implicated here.
Arcing is outside design parameters and can cause damage to equipment and interfere with electronic traction equipment and signalling.
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