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Havard Engineering Inc. - Bundle Vibration and Oscillation Control
Havard Engineering Inc.
Bundle Vibration and Oscillation Control
Bundle conductor lines vibrate due to aeolian vibration when
light steady winds blow across the conductors. When the bundle is separated by rigid, hinged or
flexible spacers the aeolian motions can require added damping to avoid fatigue damage, and so
Stockbridge dampers are often attached at the span end points. Alternatively spacer-dampers, which
include elastomeric damping elements at the hinge points, are used to suppress this aeolian vibration.
An example of a spacer damper on a 500 kV quad bundle line is shown on the left above.
When the winds are moderate to high, and steady, a more violent oscillation mode can occur.
This is wake induced oscillation and can take one of several forms. At the right is a drawing of the
subspan mode of wake induced oscillation, which is the form of motion most commonly causing conductor
damage in bundle conductors.
In this type of motion the individual subconductors oscillate in synchronism in balanced elliptical
orbits, with the motion amplitude approaching half the subconductor spacing. Clashing of subconductors
can occur under some conditions. The effect is greatest with long subspans, and can be controlled by
use of unequal subspans limited to a maximum length according to the prevailing wind intensity and
The subspan mode of wake induced oscillation causes high bending stresses at the spacer or spacer-damper
clamps. If the clamps do not retain sufficient slip strength throughout the life of the line, these
high stresses can lead to loosening of the grip on the conductor, wear of the outer strands and even
to complete failure. The photo at the left shows a spacer-damper clamp where wear of the outer
strands has occurred due to reduced clamp grip strength.
If you have concerns regarding wake induced oscillation on your bundle conductors, let us help you
assess the situation and offer a spacer or spacer-damper design to suit your line. Just send us an
E-mail and we will contact you promptly to discuss your problem.
Updated January 20, 2010
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