The attached photos and graphics
show (i) static loading vs. angle rotation of six rods, and (ii) maximum
deflection of a typical rod during test. The purpose of the tests was to
determine if the rods behave as an elastic column under load.
All tests were conducted at NEETRAC that is a part of the research
facility of Georgia Institute of Technology located near Atlanta, Georgia. The
rods were fabricated by Sediver (now Maclean Corp.) and are actual production
versions of 5/8in and 1.0in diameter rods used to manufacture phase-phase
spacers. Each end of the rod is bonded to a cast fitting having an eye for
attachment to other hardware. Both compression and tension loads were applied.
Compression testing was to establish column-buckling behavior, while testing in
tension was to establish tensile strength of the rod.
There were six rods, eleven feet between eyes. Three were 5/8in. size,
and three were 1.0in. size. Otherwise the construction was the same. The tensile
test of the 5/8in rod revealed an ultimate load of about 35,000lb. While the
tensile test of the 1.0in rod revealed an ultimate load of about 50,000lb. In
both cases the failure was at the joint between the rod and the clamp.
Angle Detections
The static load tests are seen in the first photo. Each test revealed the same features. The load increased linearly with
end-point bending angle up to a maximum value, then gradually increases over a
wide range up to 90 degrees angle rotation at the tips. Upon reduction of the
compressive load the curve follows a different path lower than the increasing
load path. This could be identified as a hysterisis loop, typical of non-linear
phenomena. For any given rod this curve is repeatable, which indicates elastic
behavior in agreement with the Euler column buckling theory.
Test
results: static
loading vs. angle rotation of six rods
The second photo shows the curvature of the rod at the point of maximum load and deflection, or at 90 degrees bending angle at the tips.
Maximum deflection
of a typical rod during test
CONCLUSIONS
1/ The load testing proves that, while the buckling loads are relatively
small the rod will continue to support increased load while rotating at its ends
through large angle deflections up to 90 degrees.
2/ Upon reversal of the load, the path followed by the curve is
different from the path of increasing load, yet upon repeating the load from
zero the characteristic curve is the same as before.
3/ Both diameters of rod seem well suited to be used in the AR PRODUCTS
device identified as AR SPACER/TWISTER, described in the catalog and in the US
patent number 6,008,453, dated December 28, 1999.
DISCUSSION
The use of spacer devices has become widespread in the electric power
delivery industry. Even though the visual appearance is not pretty the benefits
provided by preventing clashing of conductors overrides that negative feature.
Such devices have been used on voltages ranging from a low of 15kV on
distribution lines to a high of 500kV on transmission lines. One can type in
“galloping conductors” into almost any browser and the internet will pull up
60 references on the subject.
Most previous designs have not considered that buckling is desirable.
The resulting design of inter-phase spacers has been overly costly and usually
does not allow the conductor to rotate. The system designed by AR PRODUCTS, LLC
encourages the conductor to twist. In twisting, ice on the conductor rotates as
well, changing the wind angle of attack, thereby controlling the gallop. If the
conductor is not allowed to rotate the conductor will continue to gallop and
will result in heavy loads on the phase spacer, diminishing its life. The AR
PRODUCTS system benefits from the allowed twisting in both performance and
installed cost.