Exploitation optimale des lignes électriques aériennes à haute tension par évaluation en temps réel de la flèche des conducteurs et du vent agissant sur la portée

The primary concern with the electrical loading of high-voltage overhead lines is ground clearance, which depends on several factors, including constantly varying weather parameters. Sagging of the conductor, the main safety criteria, is due to (thermal) expansion of the line, a complex function of air temperature, solar radiation, local wind and actual current. A patented (patent US 8184015B2) method (based on a smart sensor named AmpacimonTM attached directly to an overhead line conductor) to directly measure the sag of overhead transmission line conductors is described. The main advantage of the concept is the real time direct measurement of the sag needed for the operation of the transmission or distribution system without the need for any additional and intermediate data, such as for example load, topological data, conductor tension, conductor temperature, and ambient weather conditions. The sag is determined by analyzing the conductor's vibrations, detecting the span's frequencies of vibrations. The fundamental frequencies form the exact signature of the span. Exterior conditions such as load, weather, topology, suspension movement, creep and the presence of snow and ice affect the sag, and, therefore, are automatically incorporated into the frequency of vibrations. Thus, this method is a direct sag evaluator compared to other methods that determine the sag based on conductor temperature or conductor tension measurements and inferences about other parameters (mass of conductor, span length,…). Moreover, sensor and method does not need to be calibrated, as the sag is deduced from the detected frequencies and not from signal amplitude. Completed field tests have confirmed that the method (and sensor) gives appropriate and highly accurate sag measurements (less than a 20 [cm] margin of error). The wind speed has a dramatic impact on power line ampacity as it is the main variable responsible for cooling down the conductor, and hence for the sag value. However, a single-spot measurement does not allow knowing the global effect of the wind over the whole span, in particular for low wind speeds (typically for wind speeds whose component perpendicularly to the conductor axis lower than 2-3 [m/s]) which are dramatic for ampacity (ampere capacity) determination. A patented (patent WO 2014090416 A1) direct method (based on a smart sensor named AmpacimonTM attached directly to an overhead line conductor) for measuring a perpendicular wind speed component with respect to a suspended cable span is presented. Appropriate data analysis coupling conductor's motion frequency detection, Strouhal equation and swing angle measurement gives a full picture of any wind speed. As the cable moves as a whole, the presented method provides a value which is representative of the mean perpendicular wind speed effect along the entire suspended cable span. In the past, the difficulty of predicting weather parameters and sag has resulted in conservative assumptions to ensure public safety and power-system security. If transmission system operators are to increase the use of the overhead line circuits' load-transfer capacity while ensuring the regulatory clearances above ground are maintained, they need a system that determines the available real-time load-transfer capacity, conductor sag (and perpendicular wind speed) by direct measurement, without the need to factor in unreliable parameters. The methods and system presented in this work will open new insights to power system network management in many aspects, from congestion management to preventive maintenance.