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Project: T153700 #33106
 

Part A

The industry’s standard practice utilizes the Energy Balance Method (EBM) to evaluate the homogeneous conductor vibration and does not consider the tension loads shared between the aluminum and core for multi-layered bi-metallic and bi-material conductors at different operating temperatures. This assumption has been proved, to some extent, adequate to predict the mechanical (vibration) performance of the common (AAAC, ACSR) conductors with the error becoming more prominent as the material properties differ significantly between the aluminum and core in HTLS conductors. Therefore, the industry’s standard EBM is improved to capture the effective self-damping that is influenced by the tensions expected on aluminum and core. The STARcol-EBM has offered an improved calculation method to model Aeolian vibrations. It has been proposed to provide better predictions for the vibration response of composite conductor types (i.e., ACSR, ACCC, and Gap) based on the validation cases examined in this report.

The derived work of STARcol-EBM is thought to complement the well-established CIGRE-EBM method by considering both material properties and conductor structural design. The STARcol-EBM model resulted in improved predictions of the field data discussed in this report (when compared to the present CIGRE practice) with the STARcol-EBM prediction lay area indicating accurately in all cases where the field data are expected to “lay”, while the STARcol-EBM prediction line indicates the most conservative values to ensure that the conductor system would be always adequately damped.

The traditional CIGRE-EBM method is accurate for predicting the homogenous types conductors and does not distinguish the properties of conductor types (e.g., HTLS conductors) since it considers only the general conductor properties. Nevertheless, it must be mentioned that the proposed hypothesis in this presented work should be carefully implemented when the aluminum tension becomes zero due to the wider predicted lay area especially at above knee-point operating conditions. Authors expect that more studies with existing laboratory data as well as additional experimentation are required to further improve the present model.

Part B.

Electricity generation and demand have increased rapidly in recent years due to improved quality of life, availability of clean energy resources, and electrification of traditional heat and transport energy sectors replacing fossil fuels. To accommodate this trend, electric utilities try to avoid the traditional expensive (and challenging) approach of building new overhead lines (OHLs) and reinforce existing networks through re-tensioning old conductors or re-conductoring with High-Temperature Low-Sag (HTLS) technologies. The effect of conductor structure and the material properties of its individual components on vibrations response have not yet been captured in literature.

The aim of this study is to investigate the ability of current conductor vibrations methods to evaluate the performance of new HTLS conductor technologies. In this respect, a vibrations assessment model is developed based on the Energy Balance Method (EBM), which calculates the conductor vibration response in terms of amplitudes and bending stresses for all expected wind-excitation frequencies, as well as when mitigating measures are implemented with vibration dampers.

To validate the developed model (and hence the EBM analytical solution), the calculated outputs are compared against field recorded measurements from CIGRE, EA Technology, ESBI and other published literature. The analytical solution, referred to this report as CIGRE-EBM, does not account for the force distribution between the core and outer aluminum components, which is significant on HTLS conductor types where the knee-point is used to highlight their superior electrical performance against common AAACs and ACSRs.

Finally, this report highlights the inaccuracies identified in the formulation of self-damping models within the CIGRE-EBM method, underscores gaps in knowledge, and offers recommendations to the industry for more accurate conductor vibration and fatigue assessments.

Keywords:

Aeolian vibration, aluminum alloy conductors (AAAC), aluminum conductor steel reinforced (ACSR), ampacity, high temperature, high-temperature low-sag (HTLS), re-conductoring, self-damping.