Improving the modeling of geomagnetically induced currents in Spain

Abstract

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 improved in this study by resorting to different strategies to progress in the three aspects identified above. First, although at midlatitude regions the source fields are rather uniform, we have investigated the effect of their spatial changes by interpolating the field from the records of several close observatories with different techniques. Second, we have performed a magnetotelluric (MT) sounding in the vicinity of one of the transformers where GICs are measured to determine the geoelectrical structure of the Earth, and we have identified the importance of estimating the MT impedance tensor when predicting GIC, especially where the effect of lateral heterogeneities is important. Finally, a sensitivity analysis to network changes has allowed us to assess the reliability of both the information about the network topology and resistances, and the assumptions made when all the details or the network status are not available. 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.

Assessment of GIC Based On Transfer Function Analysis

“…Objective assessments of how well the predicted GIC match the measurements are given by the correlation coefficient ( ρ ) and the performance parameter P defined by Torta et al (, ) and Marsal et al (). The calculated correlation coefficient between the predicted and measured GIC for the example shown in Figure is 0.813.…”

“…By way of comparison, Torta et al () found values of between 0.45 and 0.68 for predictions of low‐amplitude GIC in a transformer at Vandellòs in Spain, based on the magnetotelluric impedance tensor. However, calculations of P for 256 min subsections of the time series shown in Figure yield higher values, comparable with that found by Torta et al (), of between 0.40 and 0.60, for the first 1,280 min of the time series when GIC variations are more significant. Lower values of P are found for the much quieter period between about 1,200 and 1,800 min.…”

Geoelectric hazard assessment: the differences of geoelectric responses during magnetic storms within common physiographic zones

“…Some of these variables include the latitude of the site with respect to the auroral oval and the development of the magnetic storm itself with time. Future study will need to examine the geoelectric response associated with sharp lateral conductivity gradients, such as those at the ocean-land interface (Torta et al 2017). Such factors will require further study to determine how each specifically influences estimates of the behavior of the geoelectric field at a given location.…”

“…Love et al (2016a) used these impedances to produce a hazard map of half of the USA by convolving these impedances against latitudedependent maps of extreme geomagnetic activity. Torta et al (2017) improved the estimate of the phase and magnitude of measured geomagnetically induced currents (GICs) in power transmission systems by modeling local 2-and 3-dimensional conductivity structures with their impedances.…”

Quantifying the Performance of Geomagnetically Induced Current Models

“…It can also be useful in assessing the model when it is applied to different test fields, for example, to different storm events in our example (plotted as black dots). They correspond to the events of Table 1 in Torta et al ().…”