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The mechanical behavior at contact points in high-voltage electrical cable conductors is simulated to find where damage may occur. The presented approach is based on a numerical model that is referred to as the wire model. The critical zones are detected by simulating the mechanical behavior of a cable conductor section with a large number of contacts. For the wire model, a relevant regularized contact law that improves convergence of the contact algorithm compared to the standard contact law is implemented. This model is validated by making comparisons with experimental results available in the literature for various conductors. However, this approach employs a costly finite element method. In order to reduce the evaluation cost and allow sensitivity analysis of the input parameters, a surrogate model is proposed to replace the initial wire model. The surrogate model approximates the input–output relationship of the costly wire model. The choice of the sampling method that allows selection of the best fitting surrogate model for this application is discussed, but comparisons show little influence on the obtained scores. The robustness of the obtained result depends mostly on the chosen surrogate model, where the scores obtained with random forest and neural network are better than the scores obtained with linear and polynomial regression. The application is the French high-voltage network, but the work is relevant for any other network.

This work focuses on the study of the phenomenon of vortex-induced vibrations in overhead lines under the effect of weak winds. Full three-dimensional simulation is not feasible because of the high length to width aspect ratios of the overhead lines. Thus a quasi-3D method based on strip theory is adopted in this work. This method decouples the system of interactions between the overhead line and the wind into a series of sub-systems. The fluid flow in each sub-system is represented as a series of independent rigid oscillating cylinder flows that are only coupled through the transmission line model. To avoid the use of a moving mesh for the fluid domain, a moving reference frame approach is employed. In this approach, the coordinate axes of the flow simulation are attached to the oscillating cylinder and an acceleration term in the flow equations accounts for the cable motion. Moreover, in order to take into account the turbulent effect in the flow, turbulence models, including RANS, LES and DES, are evaluated for the present application involving flows in the sub-critical regime. Finally, numerical test cases are performed in order to validate the turbulence models and the moving reference frame approach, then cable dynamics test cases are conducted to validate the quasi-3D method.

International audience

A methodology is developed for the prediction of fretting fatigue phenomenon that results in crack initiation in strands of overhead power line conductors. A numerical approach based on finite element analysis is used to obtain the local stress and strain fields for application of crack initiation criteria in the high cycle fatigue regime. Solutions for the stress field in the stabilised state, where further loading cycles no longer introduce changes to the plastic deformation, are obtained using the stationary incremental method. Cases where convergence does not occur due to significant ratcheting are disregarded as low cycle fatigue. Post-treatment analysis that includes localised averaging is used to implement a fatigue criteria that estimates the crack initiation risk. Validation of this approach is made by comparing with results obtained from experimental measurements made on a simplified clamp wire configuration. Analyses of a simplified three-dimensional configuration with fretting is presented for a range of loading parameters and qualitative trends are established, which will prove invaluable for lifespan assessment of overhead power lines.

International audience

Les travaux présentés dans cet article s’inscrivent dans un projet de R&D mis en place par RTE (Réseau de Transport d’Electricité) et visant à évaluer le vieillissement des conducteurs électriques de lignes aériennes par des outils de simulation numérique. Après avoir rappelé la géométrie de tels conducteurs et l’utilisation qui en est faite, le principal risque d’endommagement de ces derniers est présenté. Il s’agit du phénomène de fretting-fatigue intervenant à proximité des systèmes de fixation des conducteurs au niveau des pylônes, pouvant produire la rupture de brins les constituant. Ainsi, une méthodologie originale est proposée de façon à évaluer, par l’intermédiaire d’un modèle éléments finis, la durée de vie des conducteurs vis-à-vis de ce risque. Cette méthodologie est ensuite appliquée sur un cas-test dont les données proviennent de la littérature. Enfin, des perspectives sont données concernant le modèle numérique employé et l’intégration de la démarche dans le projet de R&D concerné.