Improving the Modelling and Measurement of GICs in Spain

Vulnerability assessments of the risk posed by geomagnetically induced currents (GICs) to power transmission grids benefit from accurate knowledge of the geomagnetic field variations at each node of the grid, the Earth's geoelectrical structures beneath them, and the topology and relative resistances of the grid elements in the precise instant of a storm. The results of previous analyses on the threat posed by GICs to the Spanish 400 kV grid are being improved by resorting to different strategies to progress in the three aspects identified above. Firstly, we have investigated the effect of the spatially varying fields by interpolating the data from several closest observatories with different techniques. Secondly, we have performed a magnetotelluric (MT) sounding in the vicinity of one of the transformers where GICs are measured to determine the underneath geoelectrical structure. Finally, we have improved the performance of our previous models by adding the current flow in lower voltage-level systems. In our case, the most essential issue to improve the coincidence between model predictions and actual observations came from the use of realistic geoelectric information involving local MT measurements, which is relevant when the effect of lateral heterogeneities is important. Lessons learnt from this and our previous GIC assessments are used in a new project aimed at establishing a series of local MT surveys to properly map the non-homogeneous geoelectric field, enabling the matching between the model predictions and actual GIC measurements across the entire Spanish territory. The number of GIC measurements are also being increased by indirectly obtaining them with the deployment of magnetometers under some selected power lines, in contrast with the more usual way of measuring the current in the neutrals of the transformers at substations.