Dynamic characteristics of bare conductors.

Abstract

The dynamic characteristic of transmission line conductors is very important in designing and constructing a new line or upgrading an existing one. This concept is an impediment to line design and construction because it normally determines the tension at which the line is strung and this in respect affects the tower height and the span length. Investigations into the phenomenon of mechanical oscillation of power line conductors have been extensively looked into by many researchers using concepts from mechanics and aerodynamics to try and predict the conductor dynamic behaviour. Findings have shown that precise prediction of conductor windinduced vibration is very difficult i.e. non-linearity. Over the years, various analytical models have been developed by researchers to try and predict the mechanical vibration of transmission line conductors. The first part of this dissertation considers the analysis of the model describing the transverse vibration of a conductor as a long, slender, simply supported beam, isotropic in nature and subjected to a concentrated force. The solution of this beam equation was used to obtain the conductor natural frequencies and mode shapes. Conductor self-damping was obtained by the introduction of both external and internal damping models into the equation of motion for the beam. Next, also using the same beam concept was the application of the finite element method (FEM) for the dynamic analysis of transmission line conductors. A finite element formulation was done to present a weak form of the problem; Galerkin‟s method was then applied to derive the governing equations for the finite element. Assembly of these finite element equations, the equation of motion for the transverse vibration of the conductor is obtained. A one dimensional finite element simulation was done using ABAQUS software to simulate its transverse displacement. The eigenvalues and natural frequencies for the conductors were calculated at three different tensions for two different conductors. The damping behaviour of the conductors was evaluated using the proportional damping (Rayleigh damping) model. The results obtained were then compared with the results from the analytical model and the comparison showed a very good agreement. An electrical equivalent for the conductor was developed based on the concept of mechanicalelectrical analogy, using the discrete simply supported beam model. The developed electrical equivalent circuit was then used to formulate the transfer function for the conductor. Matlab software was used to simulate the free response of the developed transfer function. Finally, the experimental study was conducted to validate both the analytical model and the FEM. Tests were done on a single span conductor using two testing methods i.e. free and force vibration. The test results are valid only for Aeolian vibration. From the test results the conductor‟s natural frequencies and damping were determined. The experimental results, as compared with the analytical results were used to validate the finite element simulation results obtained from the ABAQUS simulation.