Vibration in Overhead Conductors

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CONTENT
> Vibrations in Overhead Conductors
> Types of Vibrations
>  Precautions

Vibrations in Overhead Conductors

Vibration is one of the serious cause of conductor failure (i.e. having cracks , breaking of conductor , or flash over ) in overhead conductors of transmission lines. So, vibration should be kept within limits for safe operation of the transmission lines. 

Types of Vibrations 

Vibration in Power Lines can be categorized into three types caused under the influence of wind : 

i) Resonant or Aeolian Vibration 
ii) Galloping 
iii) Simple swinging

i) Aeolian Vibration 
1) These vibrations are caused by aerodynamic forces generated as the wind blows across the conductor.
      fig : Damage due to Aeolian vibration

2) The frequency of the vibration may receive a positive feedback from the conductor's natural vibration frequency. 

3) This self- exciting vibration can cause cracks on the conductors due to fatigue and can cause damage particularly where the conductors is fastened to the insulators by means of clamps.

Prevention : 
1) This kind of vibration can be minimized by the use of Dampers.  

2) Stock bridge damper - It is the most widely used damper having two weights, which are fitted on either side of a cable. The shape is called " dog bone"  ( observe it in fig 1 and fig 2 )
                               fig :1

                              fig : 2

3) When the conductor vibrates the weights fitted in either side of the damper vibrate too and dissipate it into the vibrational energy. 

ii) Galloping
1) These vibrations are caused by the wind blowing over conductors which are not circular.

2) These vibrations are of low frequency and high amplitudes.

3) These vibration can result in breaking of conductor or flashover when conductors come too close while oscillation.
 
Prevention : These vibrations can be avoided by using conductors of circular design. 

iii) Simple Swinging 
1) This kind of vibration occurs in the horizontal direction as the conductors swings under the influence of wind.

2) Such swinging vibrations does not have any major impact.

Prevention : To avoid flash over keep ensure that conductors does not come to close.   

 


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