AOLIAN VIBRATION OF TRANSMISSION LINES

 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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