Re: power line insulators

[William Beaty <billb@eskimo.com>]

On Thu, 12 Jun 1997, Michael N. Monce wrote:

> 	I've looked at many sources but can't seem to find an answer to
> this:  Why are the ceramic standoff insulators on the high voltage power
> lines shaped the way they are?  I looked up the resistivities which are on
> the order of 10^10 ohms, so I don't think the leakage currents are that
> high that the "fins" on these things are needed for cooling.  Any clues?

I visualize a smooth cylindrical insulator, and I see that rain, dirt,
etc., might allow the usual corona discharge to erupt into a "leader"
which follows the surface and triggers a high current electric arc.  To
stop this effect I would carve a slot in the path of the surface
discharge.  That way if corona started running along the surface, it would
meet the "dropoff" at the edge of the slot, and would need to leap through
air in order to continue its path.  The e-fields would drive it to try
crossing the gap, rather than moving down into the slot.  Numerous slots,
or ribs, might be an excellent way to prevent discharge. 

Don't forget that for high voltage, water is an excellent conductor, and
any water-paths on a 50,000 volt system would instantly turn to steam.


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