Found this on you tube

http://www.youtube.com/watch?v=LzCEF1CUqqk

must have been a wet day!

Thanks Dave, quite a fascinating view.

The 2½ minutes shown illustrates a couple of things very well.  First is the seldom-noticed zig-zag effect of the contact wire which is purposely done to even the wear on the pan; if this were not the case it would soon cut a notch or groove in the head which I believe still uses carbon strips as they make the best self-lubricated contact with the overheads.

The second is the continual and variable arcing caused, as noted by the poster, due to the current being drawn through icy contacts.  Ice and frost on the overhead will create a barrier to power transmission and cause the power to "jump" a slight gap of even a few molecules of water lining the contact wire.  This effect can also be seen on a frosty day in third-rail electrified areas and even on outer sections of the London Underground.

Such arcing can cause very significant wear to the pan (or pick-up shoes on live-rail systems) and creates uneven power supply to the motors.  On modern electronically-controlled stock this can be "smoothed" to provide the required "clean" current but on older trains this facility is not present.  That can result in power gaps and surges leading to erratic performance and in extreme cases to a blown fuse causing the train to stop.

On DC systems arcing can very occasionally cause currents to short to earth and / or cause severe damage to the train as they create an unstable arc whereas AC current only generates stable arcs.  That is one reason why the lower voltage DC systems require far greater structure clearances than do modern high voltage AC systems.

The video looks to have been specially shot to examine the effects in those conditions and for research purposes into how best to overcome them.  The former BR research department at Derby also commissioned occasional filming of a similar nature particularly before the higher speeds above 100mph for WCML (upgraded to 110mph pre-rebuild, now 125mph) and ECML (140mph design speed, 125mph maximum service speed) were authorised.

Quite an interesting piece of video and a good explaination by Rick.
Rick you sound quite versed in electrical knowledge, I wonder if you have an electrical engineering background?

After watching the above clip I looked at a few of the other suggested clips and as an electrical technician myself I found the clips quite interesting.
I did note though that most of the shots were of USA origin and looking at the way they do things electrically over there I'm not surprised at the results!
Why they insist on overhead supplies to homes in known hurricane areas is beyond me!

Frankly Frank (I've been waiting years to be able to say that in context! ;-)) the last thing I would say I have is any electrical engineering knowledge.

I have always professed myself to be electrically-ignorant whether it be 12v model wiring or high-tension transmission lines.

But with many years knowledge of and enthusiasm for railways and with a significant proportion of those having electric propulsion at one point or another I have at least acquired some sort of useful understanding of how they work and the factors which affect that operation.

Having worked for Melbourne tramways, one of the largest systems in the World, for some years has also provided me with some first-hand operational experience of the quirks and vagaries of traction current supply.

I am always happy to share and pass on what ever I have gained over the years and thank you for your comments as well.

Hi Rick

The third thing to notice is that the pantograph doesnt 'bounce' Something I have tried to ensure with my model OLE.  Nothing more unrealistic on a model than seign the pan rise between masts.

That amount of arcing is not good!

Cheers

Jim

Did you also notice the way that the wires were strung. If you watch the wires you can see how one wire comes in from the side then two run side by side before going back to one again. This will be the overlap between lengths of wire. There are some other good clips there too the Russian one looks amazing although I recomend that you dont watch the one of the bloke walking along the coach roof before touching the 25kv twice then falling down and catching fire!

I have seen that video Dave and it is very similar to what happened to a chap at Luton who decided that rather than pay the Â£2 fare to Leagrave he would climb down to the platforms from the overbridge instead.  Presumably he thought the wires would be handy to swing from.  Amazingly he survived, but suffered something like 90% burns and was in hospital for months afterwards.

We were always taught never to look at an arcing pantograph or third rail shoe as it can be as bright as a welder.