Toward More Accurate GIC Estimations in the Portuguese Power Network

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. Plain Language Summary Magnetic storms on the Sun can trigger geomagnetic disturbances (GMD) on Earth, affecting technological infrastructures and gadgets we depend upon. As an example, they can interfere with the normal operation of power networks transporting electricity by inducing spurious currents along the conducting lines, which are called geomagnetically induced currents (GICs). We computed GICs at all substations of the transmission power network in Portugal mainland, gathering information on the electric circuit parameters, the most intense GMD events registered at the magnetic observatories of Coimbra (Portugal) and San Fernando (Spain), and measuring the Earth response to electromagnetic waves of different frequencies to obtain a conductivity model. Our results show the influence of local geotectonic structures on the geographic distribution of GICs during a given GMD. GICs tend to be stronger close to sharp discontinuities of the ground resistivity, which occur at the transition between different geotectonic units. Among different possible sources of errors in GICs, we compute error estimates due to uncertainties in the ground conductivity model and in the grounding resistances at certain substations. Finally, we give account of a first GIC sensor installed in the power network, and use its data to test different conductivity models.