At 06:32 AM 9/29/2005, donovanf@starpower.net wrote:
>Mark,
>
>I've used Garolite (a tradename for Type LE phenolic) on my
>antennas for 35 years and I've never had mechanical or
>electrical degradations of any kind.
>
>There are two types of Garolite rod: machined and formed
>
>Machined rod is cut from flat plate stock. As a result, all of the
>grain is exposed to the weather. Formed rod is wound as a rod,
>so the grain is nearly concentric (like the rings in a tree). This
>would be an ideal choice where significant voltages could be
>developed across the insulator such as when it bridges a
>loading coil.
There's also pultruded forms.. the fibers run lengthwise. You see this a
lot in structural composites.
breakdown voltages are more a function of the surface treatment than the
bulk properties. Creeping discharges over the surface will go about 3
times the distance of a free air discharge, and both are lower breakdown
voltage than even crummy composites.
Figure, for conservatism, 1 inch per 10 kV.
Jim.
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