They do on insulators. Where I used to work we tested insulators in
accelerated aging environments, breakdown voltage, and mechanical stress.
Most insulators are supposed to have an expansion material, usually like a
heavy tar, between the metal pin and porcelain. In some cases the assembly
is defective and the metal is in direct contact with the porcelain which can
contribute to failures. In other cases an air gap between the pin and
filler allows corona and discharge internal to the insulator which is also
bad. Non-ceramic insulators have other types of problems and are easily
damaged by rough handling or incorrect installation.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: rfi-bounces@contesting.com [mailto:rfi-bounces@contesting.com] On
> Behalf Of kd4e
> Sent: Thursday, September 15, 2005 01:50
> To: rfi@contesting.com
> Subject: Re: [RFI] A `Time Bomb' Sits Atop Utility Poles
>
> mike@rfiservices.com wrote:
> > The porcelain problem is caused by the expansion and contraction of the
> steel inside the porcelain. When it contracts their is a void between the
> steel and porcelain. When it expands the porcelain is forced by the steel
> to expand and can't.
> > This type of situation has exsisted for years when using
> aluminum/porcelain insulators. The problem is enhanced by the aluminum
> because aluminum is more suseptable to expansion and contraction.
> > Also, the polymer insulators are actually fiberglass inside. The polymer
> is the outer shell and is formed to increase the surface area and distance
> from end to end.
>
> Why did they not put a flexible liner between the two?
>
> We have a similar problem n our new steel-shell home.
> I am sitting here listening listening to creaking, cracking,
> and grinding.
>
> The problem is that the builders failed to consider that
> drywall expands and contracts at a different rate than
> the steel roof panels -- so when the sun comes out the
> two separate as much as 1/8" !
>
> Doesn't anyone think about the real-world environmental
> operating conditions prior to designing insulators or
> building houses? Sigh.
>
>
> --
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Can we all just help the hurting and save the criticism?
> List of Organizations who are HELPING Katrina's Victims:
> http://www.bibleseven.com/em.html
>
> Thanks! & 73, doc kd4e
>
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> KD4E =========================================
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>
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