Evaluation of the effect of salt water and a counterpoise on the voltage profile of a HV power transmission line grounding system in a two layer with high resistivity soil

Soil resistivity plays a key role in designing grounding systems of high voltage transmission lines and substations. This paper deals with an already in service HV utility, it is a 69 kV transmission line with a power generation plant at one end and a transformation substation at the other. What makes this case very interesting is that this installation is located in a high soil resistivity area, at the same time as being in the vicinity of sea water with very low resistivity. It belongs to Hydro-Quebec and does not have a shield wire nor counterpoise. This research highlights the impact of the salt water in reducing the potential rise during an electrical fault and the effectiveness of the counterpoise when the resistivity of the soil is very high. The method of images from electromagnetics is applied to calculate the potential rise. All results are validated by experimental measurements performed by a specialized field test group from Hydro-Quebec