----- Original Message -----
From: "Jim Lux" <jimlux@earthlink.net>
To: "jeremy-ca" <km1h@jeremy.mv.com>
Cc: "David Gilbert" <xdavid@cis-broadband.com>; "N7DF" <n7df@yahoo.com>;
<towertalk@contesting.com>; <Greenacres113@aol.com>
Sent: Saturday, September 15, 2007 8:16 PM
Subject: Re: [TowerTalk] re; exploding concrete
>
> Oh yeah, and the other thing that could lead to certain destruction
> would be if you coil the cable. Run a current through a coil, and it
> tries to expand, and if the current is high enough, the forces will
> exceed the tension strength of the wire and it will come apart. A
> transient current in a coil can also cause things in or near the coil to
> be squashed and deformed and destroyed.
TT:
I was exposed to this phenomenon as an engineer with my local electric
utility company years ago. My group was responsible for purchasing and
inspecting all the medium and large three-phase power transformers (5 MVA
through 350 MVA+) that were installed at the substations around the system.
These are the brutes that can be as large as a small house. Besides
insulation of the various windings (which was paper, BTW), the main thing I
looked for when I inspected the transformers' cores before they were sealed
inside the steel tanks was the bracing used to keep the phase windings in
place under short-circuit currents. ( For photos of the guts of a medium
power transformer, see page 6 of
http://www.geindustrial.com/products/brochures/sst_brochure.pdf . For a
view of the bottom of a transformer tank see page 7 ibid.) As Jim said, 60+
kA of SS current could tear the windings apart as the magnetic fields in
each phase repelled each other in the close space of the transformer tanks.
73 de Gene Smar AD3F
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