Validating GIC Modeling in the Spanish Power Grid by Differential Magnetometry

Abstract

Disturbed conditions in the Sun are potential sources of events of strongly enhanced dissipation of solar wind energy in the near-Earth space environment, also known as Space Weather events, which manifest themselves as varying electric currents flowing in the coupled magnetosphere -ionosphere system. These events trigger numerous and diverse phenomena both in the surface and in the space environment of our planet. One of the consequences of such variable currents is a varying electromagnetic field on the ground that, in the presence of the conductive earth, induces an electric current in the subsurface. This, in turn, produces a secondary electromagnetic field that is superposed to the incident one, giving rise to the observed geoelectric and geomagnetic fields. Geomagnetically induced currents (GIC) are electrical currents induced in earthed conductors in response to geoelectric fields ultimately resulting from space weather events. Electric-power transmission grids and pipelines are commonly affected negatively by GIC, potentially causing problems such as damaged power transformers and

Expected Geomagnetically Induced Currents in the Spanish Islands Power Transmission Grids

“…Indeed, the validity of the assumptions made in the modeling could be checked if we could compare their results with actual GIC observations. Given the expected small signal‐to‐noise ratio of the recorded GIC, this is not envisaged for Canary Islands, especially if indirect measurements are involved (e.g., Marsal et al., 2021), as we should proceed to install almost permanent instrumentation and wait until we can record significant signals that exceed the noise threshold. However, the relatively higher GIC values expected in Majorca encourage us to plan the establishment of temporary differential magnetometer measurements there before reaching the maximum of the present solar cycle.…”

“…For the construction of the network models, we had to start from high levels of uncertainty, especially regarding the number of transformers operating in each substation, as well as the values of their winding and grounding resistances, so it would be too risky to predict the actual GIC values expected in each of these transformers, from so many nominal values. There was another reason to focus on GIC values across transmission lines and that is that our current measuring facilities serve to measure GIC in power lines and not in transformers (Marsal et al., 2021). Indeed, the validity of the assumptions made in the modeling could be checked if we could compare their results with actual GIC observations.…”

“…On the other hand, GICs are split between the different windings in case of multiple transformers, which tends to reduce the hazard. In other cases, however, the GIC can be measured as it flows along a power transmission line, either directly (e.g., Rosenqvist et al., 2022) or indirectly (e.g., Marsal et al., 2021), so that vulnerability assessment could also be given for GIC flow in power lines (note that these can also be multiple between substations). As shown by Torta et al.…”

“…GIC signals of small to medium amplitudes (units to tens of amps according to the above mentioned categorization) have been directly or indirectly measured (e.g., Albert et al., 2022; Mac Manus et al., 2017; Marsal et al., 2021; Torta et al., 2012), and signals of medium to large amplitudes (50–100 A to more than 100 A) have been predicted for scenarios for a return period of 100 or 200 years (Torta et al., 2014), or for worst‐case scenarios in mid latitudinal power grids (Ingham et al., 2017; Liu et al., 2013). In addition to the system‐wide operational impacts caused by severe GMDs that can occur at high latitudes, power transformers elsewhere can experience considerable loss of life because of cumulative stress from successive exposures to GIC, a fact that has been actually reported in transformers at latitudes as low as South Africa (Gaunt, 2014; Gaunt & Coetzee, 2007).…”

“…On the other hand, GICs are split between the different windings in case of multiple transformers, which tends to reduce the hazard. In other cases, however, the GIC can be measured as it flows along a power transmission line, either directly (e.g., Rosenqvist et al, 2022) or indirectly (e.g., Marsal et al, 2021), so that vulnerability assessment could also be given for GIC flow in power lines (note that these can also be multiple between substations). As shown by Torta et al (2021), with examples for a simple case or for a substation with numerous power transmission lines converging on it with different orientations, the amplitudes of GICs in the power lines may be smaller or larger than those at the earthing point of the substation where they converge, because the former and their sign depend on their orientation with respect to that of the geoelectric field.…”