Power Line conductors self damping : a new approach.

Up to now, self damping data generally comes from dynamic tests performed on test spans which length is of the order of some tens of meters. Those tests rely on the assumption that the conductor self damping changes the amplitude of incident and reflected travelling wave. In other words, there are no standing wave within a vibrating conductor and in practice, the amount of self damping is deduced from measurements of vibration amplitudes at adjacent “false vibration nodes”. The corresponding measurements require lots of dexterity and accuracy.
This paper investigates the possibility of deducing the self damping properties of power line conductors from a series of tests performed quasi statically on a short prestressed conductor sample.
Data recorded by Godinas [1] on 4 m long prestressed conductor samples has been used as an input (the conductors used are made of aluminium alloy, type AMS). This data was obtained by applying a cyclic quasi-static bending moment in the middle of the conductor sample and recording the corresponding strains. The experiment was reproduced at several prestress levels.
A mining and analysis of this data has been performed so that in a first time the relationship between moment and curvature can be adequately defined. Then the corresponding internal work has been computed analytically (per integration). Finally a formulation for the self damping per unit length is proposed as a function of the antinode amplitude of vibration, frequency, conductor tension, bending stiffness, mass per unit length plus a special parameter called “b”. The latter parameter has the dimension of energy [J]. The corresponding results are found to be consistent with those deduced from the widely used “power law”, using Noiseux’s exponents [2, 3]. Also, a simplified version of the formula shows that the sensitivity of the self damping to the vibration amplitude, frequency and tension is comparable to that found by others authors using another self damping measurement technique [1], but with the difference that in this case, the exponents for frequency, amplitude and tension are integers, fully justified by the physics behind the phenomenon of damping.