Evaluation de l'effet de la mer et du contrepoids sur le profil de la tension d'un systeme de mise a la terre d'une ligne de transport d'energie a haute tension dans un sol resistif (French text)

Soil resistivity plays an important role in the design of grounding systems. When the soil resistivity is very high, the potential raise generated by a fault ground current can be problematic in the absence of an efficient grounding system.; This research treats a practical case, it consists of evaluating the impact of salt water and the eventual installation of a counterpoise connected through an electrode line to salt water on the potential raise profile of a 69 kV power transmission line which is already in service and located in the Labrador region in the province of Quebec at the vicinity of the Atlantic Ocean.; The power transmission line making the object of this research is of 21 km length between a distribution sub-station (Latabatière) and a power generating station (Lac-Robertson). It has been built without a shield wire neither counterpoise but a line electrode connecting the grids of the distribution and power stations to salt water. Some measurements of the grounding resistance of some towers carried out by a special test group of Hydro-Quebec reveal that their values vary between 10 and 500 Ω which can be problematic when a lightning strike occurs on the line.; The electromagnetic image method is applied in order to compute the potential raise generated by a current injected into the ground. The soil is modeled by two horizontal layers in a side and other from a vertical fault, which separates the ground from the salt water. The simulations shows that the installation of a counterpoise connected to salt water can reduce significantly the potential raise and make the grounding system very efficient in case of a short circuit or lightning strike occurring on the power line.