Increasing Overhead Line Power Rating By Optimising Conductor Electro-Mechanical Perfomance

Abstract

The electricity generation and demand have increased rapidly in recent years due to the improved quality of life, developed renewable energy strategies (RES), and electrification of traditional heat and transport energy sectors to replace fossil fuels. To accommodate this trend, electric utilities try to avoid the expensive traditional solution of building new overhead lines (OHLs) and reinforce existing networks through re-tensioning old conductors or re-conductoring with HighTemperature Low-Sag (HTLS) conductor technologies. The effect of conductor structure and material properties of its individual components (core and aluminium) on the vibrations response have not yet been captured thoroughly in the literature. This thesis investigates the possibility of increasing the electrical network power capacity by constraining the OHL-Conductor system design to aeolian vibrations and therefore evaluates the appropriateness of existing conductor vibrations methods for the various conventional conductor sizes and new conductor technologies. In this respect, a vibrations model is developed based on the standard method known as the Energy Balance Method (EBM) which permits evaluating conductor vibration response in terms of vibration amplitudes and bending stresses for all expected wind-excitation frequencies and mitigating their performance with vibration dampers. An effort towards improving the existing models within the EBM to predict the vibrations response of HTLS conductors has been achieved by incorporating the tension-temperature characteristics within the damping system formulation to form the so-called STARcol-EBM. To validate the developed model, the obtained analytical solutions are compared with field recorded measurements available in CIGRE and collated by ESB. The analytical solutions showed that CIGRE-EBM does not account for the structure and material properties, while STARcol-EBM provides more accurate predictions of conductor vibrations response. However, there are inaccuracies in low frequencies which requires further investigation. Moreover, a Finite Element Model (FEM) has been established in COMSOL to study the free and forced wind-induced vibrations and the resultant fatigue on single multi-layer conductors considering their complex round and trapezoidal stranding patterns. The FEM analysis is based on Multiphysics accounting for the conductor’s thermal and mechanical aspects as well as material and geometry properties. Consequently, the fatigue is quantified for both inter-layer and inter-wire interactions. The simulations show that free conductor vibrations are dictated by the conductor materials and tension distribution between the core and aluminium strands. Forced vibration simulations identified non-linear fatigue stresses for round and trapezoidal designs, which is more pronounced in larger conductor sizes. Furthermore, CFD simulations developed for wind flow around single OHL conductors with different outer layer stranding shape and sizes utilising COMSOL. Thus, an equation was established numerically to quantify the induced forces into the conductor, permitting the feasibility of using FEM solutions to develop the wind-induced forces into the OHL conductor span. The proposed FEM is limited to the efficiency of used computers and consumed time.