[BC] Ground system

[Bobby Cox]

I certainly agree that the single wire "cylinder" model is just as good
as the stick-built lattice tower model when it dealing with guyed towers
that are series fed.  However, when it comes to self supporting towers
with a significant base width, and most skirted towers, I find the
stick-built model a necessity to get reasonably accurate modeling
results.   The self supporting towers yield wire segments that are far
too "fat" vs. their length to yield accurate numerical results.  NEC
likes long thin elements,  not ones proportioned like coke cans, and
certainly not hockey pucks.  For skirted towers, the problem comes from
closely spaced parallel wires that are of greatly different diameter.
If the tower is modeled as a big fat wire and it's got several much
thinner wires running very close to it (the skirt),  this is a bad
numerical scenario as well.  Using very long skirt standoff insulators
helps this situation, but most skirts aren't built this way.  Only the
lattice tower model gets around this problem for most skirt models.

This is something that I was fortunately able to discuss with Cebik in
early 2008 before he passed.  I was glad to hear his input, which agreed
for the most part with what I've mentioned above.  

By the way, the lattice models don't have to include very many cross
members to give good results.  The tower legs are the key current
carrying elements.  I use far fewer and less detailed cross member
geometry than the actual tower would have.

Best Regards,
 
Bobby Cox , Ph.D.
Senior Staff Engineer
Kintronic Laboratories, Inc.
Phone:  423-878-3141