Geophysical and geological pre-investigations for HVDC-electrodes

The potential differences caused by the current injected in the ground by a HVDC-electrode can cause corrosion of e.g. pipelines and operational problems in transformer stations. Also, hazardous electric fields can arise in the vicinity of HVDC- electrodes. High potentials and strong fields from electrodes are, in principle, related to high-resistivity rock in the ground. The presence of such potentially problematic rock volumes is not routinely checked before the construction of an electrode site. However, geophysical methods are available that can estimate the electrical properties of the bedrock down to considerable depths. Such surveys, in combination with geological knowledge and modeling can be used to predict the environmental impact of an electrode. In this paper we present modeling results that shows the relevance of geo-electrical surveys in a HVDC-electrode project. Some methods that can be used to estimate the electrical properties of the ground around an electrode site are also presented. Good electrode sites can thus be selected at an early stage of a power transmission project.