Vibration Dampers

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   How do we control mechanical vibrations generally, yeah by some sort of vibration absorbing techniques.Then, what about the vibrations present on transmission lines ? Well that's indeed a  question. It isn't the rocket science, just a matter of transferring and or dissipating the energy behind it. Lets see how it is engineered.

   As the wind passes some of its energy gets transferred to the overhead transmission lines and tends to oscillation(mostly).But as the weight of the conductor is high to limit the oscillation the energy try to get converted to the form of vibration.Vibrations then spread across the conductor length and its not a good thing in mechanical aspects as its causes the deterioration of strength of conductors.In engineering view of thinking it is only avoided by absorbing the energy causing it.The simple way for it is damping those vibrations mechanically from the line itself, that particular concept resulted in the designing of vibration dampers.Wind can generate three major modes of oscillation in suspended cables:
  • Gallop has an amplitude measured in metres and a frequency range of 0.08 to 3 Hz
  • Aeolian vibration (sometimes termed flutter) has an amplitude of millimetres to centimetres and a frequency of 3 to 150 Hz
  • Wake-induced vibration has an amplitude of centimetres and a frequency of 0.15 to 10 Hz
  Basically Vibration dampers are energy dissipating elements, so for that it has some end parts which are free to oscillate about some axis. Constructionally there are two types designs which are 

 1. Stockbridge Damper
      By construction it is two weights separated by a cable or metal part and attached to the transmission line through a clamp.In technical terms the cable connecting the two damper weights are called messenger cable.There is a provision for making symmetrical or asymmetrical connections with the clamp to match with the mechanical impedance of the line.
    The Stockbridge damper is effective in dealing with the Aeolin vibration, which are oscillating in the vertical plane by the shedding of vortices(the transverse wave propogation like vibration)
construction
Stockbridge Damper-Construction

A closer view
2. Spacer Dampers
   With the job of keeping the spaces between conductors these will also damp the transmission line vibrations.
Spacer Dampers

Spacer Dampers

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