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New geomagnetically induced current (GIC) computations for mainland Portugal include the entire power network, with network parameters and topology provided by the transmission grid operator for all the high voltage lines (150, 220, and 400 kV). The first 3D conductivity model for the west region of the Iberian Peninsula, based on 31 broadband magnetotelluric soundings, is used in calculations, revealing the effect of different crustal domains in GIC distribution. Geomagnetic field variations are taken from Coimbra or San Fernando magnetic observatories, according to the Nearest Neighbor method, and used together with surface impedance values predicted from the new conductivity model to calculate the induced electric field on a regular grid. The global distribution of GICs over the power network is characterized based on results derived for the eight most significant storms registered in the Iberia during solar cycle 24. Substations susceptible to the highest GICs are found near the transition between the granitic geotectonic unit of Central Iberian Zone and the Lusitanian Basin. A prototype of a Hall effect sensor has been installed at a substation and is active since the end of August 2021. In order to validate our GIC model, recent measurements are compared with simulations. GIC computation is prone to uncertainties from various sources, possibly contributing with different weights to the final error in computed values. Here, we evaluate the contribution of substation earthing resistance and nonuniqueness of the conductivity model to the final GIC uncertainties.

<p>Geomagnetically Induced Currents (GICs) are one of the main hazards of Space Weather for modern society since they may lead to electricity blackouts over large regions. The awareness and comprehension of GICs on power systems are the keys to dipping into a more resilient and robust energy system.</p> <p>This study aims to understand the real contribution of shield wires (ShW) in GIC simulations. ShW are protective cables against atmospheric discharges for transmission lines and are commonly connected to the ground at substations and, often, at each supporting pylon. Although ShW represent an additional path for GICs, they are in general not considered in simulations. Possible reasons might be the need for more information on ShW parameters from the transmission system operators, as well as the increase in computational time. But another reason has possibly been the conclusions drawn in preliminary studies, showing that the ShW effect on GICs should be small.</p> <p>By applying the equivalent circuit derived in [1], GIC simulations were obtained for the entire Portuguese power grid using realistic parameters for the grid and a 3D conductivity model. Simulations were carried out using an adaptation of GEOMAGICA [2] by calculating a realistic induced electric field and determining GIC magnitudes in each transformer. Also, more tests were done using the analogue circuit simulator software LTSpice to calculate GIC in the power grid using the induced electric field calculated through GEOMAGICA.</p> <p>Results for different geomagnetic storms are presented and compared with GIC measurements at the transformer neutral in a particular substation of the Portuguese power network.</p> <p> </p> <p>[1] Santos, R., Pais, M. A., Ribeiro, J. A., Cardoso, J., Perro, L., & Santos, A. (2022). Effect of shield wires on GICs: Equivalent resistance and induced voltage sources. International Journal of Electrical Power & Energy Systems, 143, 108487.</p> <p>[2] Bailey, R. L., Halbedl, T. S., Schattauer, I., Römer, A., Achleitner, G., Beggan, C. D., ... & Leonhardt, R. (2017, June). Modelling geomagnetically induced currents in midlatitude Central Europe using a thin-sheet approach. In Annales Geophysicae (Vol. 35, No. 3, pp. 751-761). Copernicus GmbH.</p>

<p>Geomagnetically Induced Currents (GICs) are the result of rapid variations in the Earth's geomagnetic field and of the finite conductivity of the Earth. Along grounded conducting structures such as the power grids, the induced electric field drives electric currents in closed circuits. Extreme values of GICs can be a threat to the normal operation of the power system. So, there is an increasing interest in the study of the GICs’ risk and the first step to take is the numerical modelling. In order to model GICs, different factors/parameters must be considered, as the distribution of conductivity, laterally and in depth and characteristics of the different components of the network. These include the values of the different resistances in the power network, the types of transformers and also the transmission path for the GICs. Shield wires represent possible paths for GIC currents. In this study the influence of shield wires on GICs in power systems is modelled. Tests were done using realistic values for the circuit parameters provided by the Portuguese high voltage power network company (REN).</p><p>The MAG-GIC (Geomagnetically induced currents in Portugal mainland) project has already produced GIC simulations for the South of Portugal. However, there are still no direct records of GICs in the electrical transmission network to validate that model. This study also encompasses the task of producing a measuring instrument to monitor GICs in the neutral of a given transformer. Such an instrument can provide for the measurement and recording of quasi-DC currents with Hall current sensors, with high resolution. It is targeted to operate remotely over a time interval of several months while being minimally invasive to the power transformer (PT). The system relies on LEM high sensitivity closed loop Hall effect current sensors and it is built over a Raspberry Pi 4 Model B platform with a high resolution digitizer (24 bits) expansion board (Waveshare AD/DA). The system also includes temperature monitoring for offset correction. Recorded data are locally stored on a database (InfluxDB) and a wifi interface allows rapid long term trend visualization through a customized dashboard (Grafana).</p>

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