Aolian Vibrations, also called Karman Vibration is the
result of wind forces acting transversely on the conductor which causes
alternating excitations in the vertical direction.
Aeolian vibrations occur almost on any transmission line,
for low to moderate steady winds. They are characterised by small amplitudes of
vibration (one conductor diameter) with frequency between 5 and 100 Hz,
depending on the conductor size and tensile load.
This steady wind will create air vortices or eddies on the
lee side of the conductor. These vortices on the other hand will detach at regular
intervals from the top and bottom area if the conductor, creating a force in
the conductor that is alternately impressed from above and below.
Aeolian vibrations cause an alternate bending strain of the
conductor at the suspension clamp (where bending stiffness is no more
negligible) and, depending on the strain level, may cause fatigue failures of
the cable strands.
These effects on the conductor does not always apparent
externally; failures often occur in the internal layers first. Fatigue failures
occur in the vicinity of clamps at contact points between strands where contact
stresses are quite high, in the presence of slipping.
This vibration is generally more severe in flat open terrain
where steady winds are more
often encountered. The frequency and loop length of the
vibration can be determined using equation
Aeolian vibrations can be easily controlled by adding
damping to the cable, in the form of
dampers and spacer-dampers. This is feasible for electric
power transmission lines.
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