Calculation Of Geomagnetically Induced Currents Research Articles

Modeling GIC in the Southern South Island of Aotearoa New Zealand Using Magnetotelluric Data

AbstractMagnetotelluric (MT) impedances from 62 sites in southern South Island of Aotearoa New Zealand have been used to model geomagnetically induced currents (GIC) in four transformers during two solar storms. Induced electric fields during the storms are calculated from the MT impedances using the magnetic fields measured at the Eyrewell (EYR) geomagnetic observatory, approximately 200 km north of the study area. Calculated GIC during the sudden storm commencements (SSC) give a generally good match to GIC measured by the network operator, Transpower New Zealand. Long period GIC (periods longer than about 10,000 s) are less well modeled. Calculations based on thin‐sheet modeling, which has restrictions on the shortest period of variation which can be modeled, perform less well for the GIC associated with SSC, but are equally good, if not better, at modeling longer period GIC. Consistent underestimation of large GIC at one transformer (HWBT4) near Dunedin are likely to be the result of uncertainty in the assumed values of line, transformer, and earthing resistances. The assumption of a spatially uniform magnetic field across the study area, which is implied by use of the magnetic field measured at EYR as a basis for calculation, may also lead to incorrect calculation of GIC. For one storm use of magnetic field data from a magnetometer within the study area leads to much improved modeling of the observed GIC. This study compares modeled and measured GIC using specifically measured MT impedance data.

Modeling GIC in the Southern South Island of Aotearoa New Zealand Using Magnetotelluric Data

AbstractMagnetotelluric (MT) impedances from 62 sites in southern South Island of Aotearoa New Zealand have been used to model geomagnetically induced currents (GIC) in four transformers during two solar storms. Induced electric fields during the storms are calculated from the MT impedances using the magnetic fields measured at the Eyrewell (EYR) geomagnetic observatory, approximately 200 km north of the study area. Calculated GIC during the sudden storm commencements (SSC) give a generally good match to GIC measured by the network operator, Transpower New Zealand. Long period GIC (periods longer than about 10,000 s) are less well modeled. Calculations based on thin‐sheet modeling, which has restrictions on the shortest period of variation which can be modeled, perform less well for the GIC associated with SSC, but are equally good, if not better, at modeling longer period GIC. Consistent underestimation of large GIC at one transformer (HWBT4) near Dunedin are likely to be the result of uncertainty in the assumed values of line, transformer, and earthing resistances. The assumption of a spatially uniform magnetic field across the study area, which is implied by use of the magnetic field measured at EYR as a basis for calculation, may also lead to incorrect calculation of GIC. For one storm use of magnetic field data from a magnetometer within the study area leads to much improved modeling of the observed GIC. This study compares modeled and measured GIC using specifically measured MT impedance data.

Improved Model for GIC Calculation in the Mexican Power Grid

AbstractWe present the first observations of geomagnetically induced currents (GIC) in the Mexican power grid and an improved model to calculate them. The new model comprises ca. 250 substations working at various voltage levels, a methodology to estimate geomagnetic disturbances (δB) at different points throughout the Mexican territory, and a 1D piecewise model that considers lateral variations in the ground conductivity. This is an improvement of a former uniform conductivity model presented previously to calculate our first GIC estimates (Caraballo et al., 2020). We compared the observed and calculated GIC between August and November 2021 at a coastal 400 kV substation. During this interval, five geomagnetic storms occurred (G1 and G2). The observed GIC exceeded 10 A during the most strong event; this shows a clear grid response even under weak geomagnetic perturbations that occurred during the solar minimum. Further comparison with the results of the former model suggests that the new 1D piecewise model yields better GIC estimates for the Mexican power grid.

A New Standalone Tool for DC‐Equivalent Network Generation and GIC Calculation in Power Grids With Multiple Voltage Levels

AbstractSpace Weather phenomena pose a major socio‐economic threat due, in part, to the vulnerability of power network transformers to geomagnetically induced currents (GIC). In 1985, Lehtinen and Pirjola (LP) provided a method to calculate GICs in a single‐voltage‐level network. The need to account for lower voltages has caused the proliferation of GIC risk assessments applied to power grids with multiple voltages. We hereby present a tool to systematically generate the direct currents (DC)‐equivalent of a multiple‐voltage‐level network. The LP and Nodal Admittance Matrix methods are the most popular schemes to compute the GIC from the resulting equivalent network by solving the circuit laws for the earthing current or the voltage at each node, respectively. A new scheme is presented here that solves the circuit laws for the current flowing between the bus nodes and the neutral point which, unlike LP, requires no (infinite‐resistance) earth connections for the buses. The number of equations/unknowns of the resulting GIC matrix equation is reduced compared to the traditional methods, thus optimizing the computational cost ‐an advantage that becomes important for large networks‐, while keeping a good condition of the design matrix associated with the inversion. Examples are shown for different test cases and a standalone computationally efficient code is provided.

A Mitigation Method Based on the Principle of GIC-Even Distribution in Whole Power Grids

The geomagnetically induced currents (GIC) caused by geomagnetic storms can inflict the anomalous operation of power systems, damaging electrical equipment, or even resulting in a large-area blackout of power systems. Therefore, to reduce the impact of GIC and avoid severe disasters has been a major challenge for the development of large-scale power grids. Considering the fact that geoelectric field may have random orientation in mid-low-latitude areas, this paper employs GIC-Benchmark model, to calculate the GIC of East-China 1000kV ultra-high voltage (UHV) and 500kV extra-high voltage (EHV) power grids under a uniform geoelectric-field of 1V/km. We further analyze the characteristics and the pattern of GIC in UHV power grid and identify high-risk nodes which can be vulnerable to GIC encroachment. Then we propose installing additional resistors in the transformer neutral points of high-risk nodes to even the GIC distribution in whole networks, and make the theoretical calculation of GIC in East-China 1000kV power grid after installation. The results show that the principle of GIC-even distribution can reduce edge effect remarkably, which works well in mid-to-low- latitude areas at least, thus we expect to avoid space weather disaster in power grids with power operation scheduling and other mitigation methods.

Comparison Between 1-D and 3-D Geoelectric Field Methods to Calculate Geomagnetically Induced Currents: A Case Study

Severe Geomagnetic Disturbances (GMD) pose a threat to the reliability of the United States bulk electrical power system. The NERC reliability standard TPL-007 requires transmission planners to assess potential problems in their service territories due to Geomagnetically Induced Currents (GIC) including transformer thermal assessment. If the assessment indicates a vulnerability, the standard requires the development of a corrective action plan to resolve potential issues. GIC calculation accuracy is critical to the assessment. In this paper, the impact of various geoelectric field calculation methods on the accuracy of calculated GIC is evaluated by comparing with observations for a geomagnetic storm that occurred on 07–08 September, 2017. The GIC calculation is carried out for a fairly large-scale power system model and the comparison with observation indicates that better results are achieved using magnetotelluric transfer functions that incorporate the effects of 3-D earth conductivity. The results also indicate an improvement in the comparisons when the transfer-function derived E-fields are interpolated between the original survey site locations.

Sensitivity of geomagnetically induced currents to varying auroral electrojet and conductivity models

Geomagnetically induced currents (GIC) are created by the interaction of rapid changes in the magnitude of the magnetic field with the conductive subsurface of the Earth. The changing magnetic field induces electric currents, which are particularly strong along boundaries between regions of contrasting conductivity structure such as the land and sea. A technique known as the ‘thin-sheet approximation’ can be used to determine the electric field at the Earth’s surface, which in turn allows the calculation of GIC in the earthing connections of high-voltage nodes within a power grid. The thin-sheet approximation uses a spatially varying conductance over the region of interest on a 2D surface, combined with a 1D layered model of upper lithosphere conductance. We produce synthetic models of the auroral electrojet in different locations over the United Kingdom (UK) and investigate the effects of varying the 2D thin-sheet model. We assess different two-dimensional surface conductance models and vary the underlying 1D conductivity models to simulate the effects of resistant through to conductive lithosphere. With an advanced network model of high-voltage electrical distribution grid, we compute the expected GIC at each node in the system given the input surface electric fields from the various synthetic electrojets and conductivity models. We find that the electrojet location is the primary control on the size of GIC, with conductivity being a second-order effect in general, though it can be locally important.

Analysis of geomagnetically induced currents at a low-latitude region over the solar cycles 23 and 24: comparison between measurements and calculations

Geomagnetically Induced Currents (GIC) are a space weather effect, which affects ground-based technological structures at all latitudes on the Earth’s surface. GIC occurrence and amplitudes have been monitored in power grids located at high and middle latitudes since 1970s and 1980s, respectively. This monitoring provides information about the GIC intensity and the frequency of occurrence during geomagnetic storms. In this paper, we investigate GIC occurrence in a power network at low latitudes (in the central Brazilian region) during the solar cycles 23 and 24. Calculated and measured GIC data are compared for the most intense geomagnetic storms (i.e. −50 < Dst < −50 nT) of the solar cycle 24. The results obtained from this comparison show a good agreement. The success of the model employed for the calculation of GIC leads to the possibility of determining GIC for events during the solar cycle 23 as well. Calculated GIC in one transformer reached ca. 30 A during the “Halloween storm” in 2003 whilst most frequent intensities lie below 10 A. The normalized inverse cumulative frequency for GIC data was calculated for the solar cycle 23 in order to perform a statistical analysis. It was found that a q-exponential Tsallis distribution fits the calculated GIC frequency distribution for more than 99% of the data. This analysis provides an overview of the long-term GIC monitoring at low latitudes and suggests new insight into critical phenomena involved in the GIC generation.

Comparison of methods for modelling geomagnetically induced currents

Abstract. Assessing the geomagnetic hazard to power systems requires reliable modelling of the geomagnetically induced currents (GIC) produced in the power network. This paper compares the Nodal Admittance Matrix method with the Lehtinen–Pirjola method and shows them to be mathematically equivalent. GIC calculation using the Nodal Admittance Matrix method involves three steps: (1) using the voltage sources in the lines representing the induced geoelectric field to calculate equivalent current sources and summing these to obtain the nodal current sources, (2) performing the inversion of the admittance matrix and multiplying by the nodal current sources to obtain the nodal voltages, (3) using the nodal voltages to determine the currents in the lines and in the ground connections. In the Lehtinen–Pirjola method, steps 2 and 3 of the Nodal Admittance Matrix calculation are combined into one matrix expression. This involves inversion of a more complicated matrix but yields the currents to ground directly from the nodal current sources. To calculate GIC in multiple voltage levels of a power system, it is necessary to model the connections between voltage levels, not just the transmission lines and ground connections considered in traditional GIC modelling. Where GIC flow to ground through both the high-voltage and low-voltage windings of a transformer, they share a common path through the substation grounding resistance. This has been modelled previously by including non-zero, off-diagonal elements in the earthing impedance matrix of the Lehtinen–Pirjola method. However, this situation is more easily handled in both the Nodal Admittance Matrix method and the Lehtinen–Pirjola method by introducing a node at the neutral point.

Geomagnetically induced currents in the Uruguayan high-voltage power grid

We estimate the influence of the geomagnetically induced currents (GIC) on the Uruguayan electrical distribution grid. The GIC are related to time variations in the geomagnetic field caused by the interaction of the solar wind with the Earth's magnetosphere. These currents may cause several problems in power grids, pipelines, among others. South America is close to the South Atlantic Magnetic Anomaly (SAA). Particle precipitation in the anomaly region could lead to pulsations in the horizontal component of the geomagnetic field, that may contribute to the GIC production. Scarce research has been done to assess the space weather impact on this area. Due to the lack of magnetic field data at the Uruguayan territory, spherical elementary currents system (SECS) was used to interpolate field values with data available from three magnetic observatories located at Vassouras, Trelew and São Martinho da Serra. The simple topology of the Uruguayan power grid provides some advantages in the calculation of GIC. To calculate these currents, a plane wave method combined with a ground conductivity model was used. Estimated GIC suggest peak currents ca. 15 A, at the earthing points of some substations in a 770 km power line during the Halloween Magnetic Storm on 2003 October 29.

Prediction of extreme geomagnetically induced currents in the UK high‐voltage network

Geomagnetically Induced Currents (GIC) can be damaging to high‐voltage power transmission systems. GIC are driven by rapid changes in the strength of the magnetic field external to the Earth's surface. Electric fields are produced in the ground by the interaction between this changing magnetic field, the sea and the conductivity structure of the Earth. Using a technique known as the “thin‐sheet approximation,” we can determine the electric field at the Earth's surface, which in turn allows the calculation of GIC in the earthing connections of high‐voltage transformers within a power grid. We describe two new developments in the modeling of GIC in the UK, though the results are applicable to GIC‐related research in other regions. Firstly, we have created an updated model of the UK surface conductivity by combining a spatial database of the UK geological properties (i.e., rock type) with an estimate of the conductivity for specific formations. Secondly, we have developed and implemented a sophisticated and up‐to‐date model for the 400 kV and 275 kV electrical networks across the whole of Great Britain and, in addition, the 132 kV network in Scotland. We can thus deduce the expected GIC at each transformer node in the system based on the network topology from an input surface electric field. We apply these developments to study the theoretical response of the UK high‐voltage power grid to modeled extreme 100 year and 200 year space weather scenarios and to a scaled version of the October 2003 geomagnetic storm, approximating a 1 in 200 year event.

European Project to Improve Models of Geomagnetically Induced Currents

Geomagnetically induced currents (GICs) from solar storms pose a risk to the operation of power transmission grids in Europe and across the globe. The European Risk from Geomagnetically Induced Currents (EURISGIC) project, which began in March 2011 and is supported by the Seventh Framework Programme of the European Union, seeks to mitigate this natural hazard by developing European capabilities for GIC forecasting and warning. Recent well-recognized GIC events were the province-wide blackout in Quebec, Canada, in March 1989 and the blackout in the city of Malmö, in southern Sweden, during the Halloween storm of October 2003. The progressive integration of interconnected and geographically wide power transmission grids is obviously increasing the GIC risk. Hence, there is a need for greater scientific understanding of phenomena in the solar-terrestrial environment that lead to GICs and for the development of systems that facilitate GIC modeling, forecasting, and mitigation. Within the EURISGIC project the flow of GICs throughout the European grid for hypothetical and real events will be simulated using improved grid network models and conductivity models for the continent. The project will produce the first Europe-wide real-time prototype forecast service of GICs in high-voltage power systems, based on in situ solar wind observations by the Advanced Composition Explorer (ACE) spacecraft, empirical modeling, and comprehensive simulations of Earth's magnetosphere. Moreover, on the basis of long-term geomagnetic recordings, EURISGIC will derive the first map of the statistical risk of large GICs throughout Europe. Of special interest is a search for untapped data sources for the solar storm of September 1859, famously observed by British astronomer Richard Carrington, which is often referred to as the most intense geomagnetic storm ever recorded. The project aims to assist European scientists as they strive for 30- to 60-minute lead time forecasts of GIC events. There is presently only one European magnetohydrodynamic code for global simulations of the solar wind-magnetosphere interaction, namely, Grand Unified Magnetosphere-Ionosphere Coupling Simulation (GUMICS-4), developed at the Finnish Meteorological Institute. During EURISGIC, GUMICS-4 will be upgraded to be able to produce real-time GIC forecasts. For this development, EURISGIC will obtain valuable contributions from the U.S. expertise gained from NASA's Solar Shield project (http://ccmc.gsfc.nasa.gov/Solar_Shield/). The U.S. and European codes will run in parallel to produce GIC forecasts in Europe, and they will also stimulate further improvements in simulations. Calculation of GICs in a given power grid is a straightforward problem, which has been considered in several previous national studies, for example, in Finland, Sweden, and the United Kingdom. The key problem is to determine the geoelectric field that drives GICs in power grids. This electric field can be calculated from the measured magnetic field using models of the Earth's conductivity. A special challenge for EURISGIC is to compile a simplified conductivity map of Europe that enables efficient computation of Europe's electric field. When the geoelectric field is known, calculation of GICs in a power grid is reduced to a simple direct current (DC) mathematical problem. In combination, early warning forecasts, risk maps, and worst-case-scenario assessments provided by EURISGIC will contribute to mitigating the risks that GICs represent, thereby avoiding destruction of transformers and enhancing the protection of critical infrastructure in Europe and elsewhere in the world. The project began in March 2011 and will last until February 2014. The Finnish Meteorological Institute is the coordinator, with Ari Viljanen as the coordinating person. Other European Union partners come from Hungary, Sweden, and the United Kingdom. In addition, Russia and the United States belong to the consortium, ensuring the best global GIC expertise within the team. An external group of advisors representing power engineering, education, and space weather services will provide independent reviewing and suggestions to help the consortium reach its ambitious goals. EURISGIC is funded by the Seventh Framework Programme of the European Union (Project 260330). The EURISGIC Web site is http://www.eurisgic.eu. The following are members of the consortium, with their representatives given in parentheses: Finnish Meteorological Institute, Finland (Ari Viljanen); British Geological Survey/Natural Environment Research Council, United Kingdom (Alan Thomson); NeuroSpace, Sweden (Magnus Wik); Swedish Institute of Space Physics, Sweden (Peter Wintoft); Geodetic and Geophysical Research Institute, Hungary (Viktor Wesztergom); Polar Geophysical Institute, Russia (Yaroslav Sakharov); and Catholic University of America, United States (Antti Pulkkinen). Ari Viljanen is a senior scientist at the Finnish Meteorological Institute, in Helsinki, Finland. E-mail: [email protected]

On the flow of geomagnetically induced currents in an electric power transmission network

Geomagnetically induced currents (GICs) in conductor networks are among the ground-level effects of space weather. GICs are a possible source of problems to the system. Today, electric power transmission grids are the most important concern regarding GICs, which may in the worst cases lead to blackouts in large areas and permanent damage to transformers. The evaluation of GIC risks and the design of possible countermeasures require estimation of expected GIC magnitudes in transformers. This can be achieved by model calculations supplemented by GIC recordings at some sites. Although in principle GICs can flow all over a large galvanically-connected power grid, which should thus be included as a whole in a GIC calculation, the network must usually be restricted somehow in practical computations of GICs. By using a power grid test model, this paper provides a systematic numerical investigation showing that GICs do not flow over very long distances in a power grid, which is a good result and justifies the neglect of the parts of the network that lie far away from the area of primary interest. Besides practical significance in electric power engineering, studies of GICs can be used for space physics and geophysical research as well. It is also important to understand the features of the flow pattern of GICs in a network.

Calculation of geomagnetically induced currents (GIC) in a high-voltage electric power transmission system and estimation of effects of overhead shield wires on GIC modelling

Geomagnetically induced currents (GIC) flowing in ground-based technological networks, such as electric power transmission grids, are the ground end of the space weather chain originating from the Sun. GIC constitute a possible source of problems to the system. Matrix formulas enabling the calculation of GIC in a power grid have been presented before. In this paper, we summarise the formulas and also express them in an alternative form that includes the (geo)voltages driving GIC during a space weather event more explicitly. An issue usually ignored in GIC modelling is the effect of overhead shield wires protecting a power grid and generally earthed at the towers. By numerical examples, it is shown in this paper that such neglect causes an insignificant error in comparison with other inaccuracies involved in GIC modelling and is thus really acceptable in practice.

Effects of space weather on high-latitude ground systems

Geomagnetically induced currents (GIC) in technological systems, such as power grids, pipelines, cables and railways, are a ground manifestation of space weather. The first GIC observations were already made in early telegraph equipment more than 150 years ago. In power networks, GIC may saturate transformers with possible harmful consequences extending even to a collapse of the whole system or to permanent damage of transformers. In pipelines, GIC and the associated pipe-to-soil voltages may enhance corrosion or disturb surveys associated with corrosion control. GIC are driven by the geoelectric field induced by a geomagnetic variation at the Earth’s surface. The electric and magnetic fields are primarily produced by ionospheric currents and secondarily affected by the ground conductivity. Of great importance is the auroral electrojet with other rapidly varying currents indicating that GIC are a particular high-latitude problem. In this paper, we summarize the GIC research done in Finland during about 25 years, and discuss the calculation of GIC in a given network. Special attention is paid to modelling a power system. It is shown that, when considering GIC at a site, it is usually sufficient to take account for a smaller grid in the vicinity of the particular site. Modelling GIC also provides a basis for developing forecasting and warning methods of GIC.

On the possibility of performing studies on the geoelectric field and ionospheric currents using induction in power systems

Geomagnetically induced currents (GICs) flowing in man-made conductors, such as power systems, depend on the integrated geoelectric field induced by a geomagnetic variation. Thus, in addition to the practical significance of GIC investigations, GICs also provide a means to make large-scale electromagnetic induction studies of the Earth and of ionospheric-magnetospheric current systems. This paper deals with the calculation of GICs in the Finnish 400 kV power grid, although the conclusions obtained are obviously not restricted to the particular grid studied. The treatment is based on a general computer program permitting the horizontal geoelectric field to be arbitrary. It is demonstrated that GICs induced in Sweden have practically no influence in Finland, i.e. GICs do not flow very long distances in the power system. On the other hand, GICs are not sensitive to small-scale spatial details of the geoelectric field, which supports their large-scale nature mentioned. Using the present knowledge, a preliminary large-scale conductivity model of Finland is also applied here for the estimation of GICs. As an example of nonhomogeneous primary sources describing auroral currents, a sheet current is considered. GICs are recorded at four Finnish transformers and at one transmission line for 1 year beginning in June, 1991. Data collected then will be used also in induction studies according to the guidelines given in this paper.

Statistics on geomagnetically-induced currents in the Finnish 400kV power system based on recordings of geomagnetic variations.

A method to estimate geomagnetically-induced currents (GICs) in a power grid based directly on magnetic recordings is presented. To determine the electric field on the earth's surface for the calculation of GICs based on available magnetic data, a model is used in which the geomagnetic variation field propagates as a vertical plane wave in the earth and the earth is a half-space with a constant conductivity. To get statistically reliable results, the earth's conductivity is allowed to be a function of the geomagnetic K-index. The reason for this unphysical behaviour, which means that the conductivity is, of course, not real but some kind of an effective conductivity, is explained.